Weathering Steel - Design Guide for Bridges in Australia

Abstract

Weathering steel is a high strength, structural steel that, in suitable environments, develops
a tightly adherent oxide layer or ‘patina’, which significantly reduces the corrosion rate compared with conventional structural steel.

Weathering steel has been used since the 1930’s in railway coal wagons, bridges,
buildings, facades and many architectural features such as sculptures and landscaping.
It has been used extensively in North America, Europe and Japan for over 55 years; and over
the last 10 years in New Zealand. When designed and detailed correctly, taking into
account the environmental factors that governs its use, it has exhibited excellent performance.

A well designed and correctly detailed weathering steel bridge, in an appropriate
environment, can provide an attractive, very low maintenance, economic solution and extends
the scope for cost-effective steel bridges.

Accordingly, the Heavy Engineering Research Association of NZ and Opus International Consultants, NZ have prepared this document entitled ‘Weathering Steel Design Guide for Bridges in Australia’. The purpose of this publication is to provide a collation of the necessary guidance for the Australian industry
to assist with the efficient and appropriate application of weathering steels in Australian bridges. It also provides guidance to achieve the expected performance of weathering steel in Australian bridges, to realise the planned life span of the bridges.

This publication covers the designing, construction, inspection, maintenance and
even rehabilitation of weathering steel, should corrosion rates exceed those anticipated at
the design stage, as well as discussing the limitations on the use of weathering steel.
Comments and queries on the guide should be referred to HERA.

Full text

HERA Design Guide
for Bridges in Australia
Weathering Steel
Design Guide for Bridges in Australia
Commissioned by BlueScope Steel Ltd

Weathering Steel
Design Guide for Bridges in Australia
Every effort has been made and all reasonable
care taken to ensure the accuracy and reliability
of the material contained herein. However,
HERA and the authors of this report make
no warranty, guarantee or representation in
connection with this report and shall not be
responsible in any way and hereby disclaim any
liability or responsibility for any loss or damage
resulting from the use of this report.
BlueScope commissioned HERA to prepare the
report; BlueScope did not prepare the report;
and, in promoting the guide and its findings,
BlueScope makes no warranty or representation
as to the accuracy, completeness or reliability
of the contents of the report or its suitability for
any particular purpose
Some of the images included in this document
were reproduced from a research report for the
Texas Department of Transportation (TxDOT).
Permission was provided by the TxDOT to use
these images. The TxDOT was not involved in
the preparation of this document nor reviewed
the document. The TxDOT images were taken
by TxDOT as part of its TxDOT Weathering
Steel report.
NZ Heavy Engineering
Research Association
Structural Systems
HERA House,
17-19 Gladding Place, PO Box 76-134
Manukau, Auckland City, 2241, New Zealand
Tel: +64-9-262 2885
Fax: +64-9-262 2856
Web: www.hera.org.nz
Authors:
Raed El Sarraf
Opus International Consultants NZ
Willie Mandeno
Opus International Consultants NZ
Dr Stephen Hicks
Heavy Engineering Research Association NZ
Acknowledgement
This document was kindly reviewed by
the experienced bridge design engineers,
Mr Liam Edwards at AECOM NZ and
Mr Frank Rapattoni, at Parson Brinckerhoff
Australia.

1
Contents
1. Introduction 2
2. Background to Weathering Steel 3
2.1 What is Weathering Steel? 3
2.2 Benefits of Weathering Steel 3
2.3 Where to use Weathering Steel? 4
3. Design and Detailing 6
3.1 Design Codes 6
3.2 Material Specification 6
3.3 Allowance for Loss of Thickness 6
3.4 Design 7
3.5 Bolted Connections 7
3.6 Welded Connections 8
3.7 Fatigue 9
3.8 General Structural Detailing 10
3.9 Removal of Rust Stains 15
3.10 Interface Protection 15
3.11 Connection to Other Materials 16
3.12 Further Protection – Coating 16
4. Fabrication and Construction 18
4.1 Cold and Hot Forming 18
4.2 Cutting 18
4.3 Welding 18
4.4 Surface Preparation 19
4.5 Storage, Handling, and Erection 20
4.6 Final Site Cleaning 20
4.7 Protection of Piers and Abutments 20
4.8 Guardrails and Light Poles 20
5. In-service Inspection 22
5.1 Requirements for Inspection of Weathering Steel Bridges 22
5.2 Level 1 Inspections (Routine) 22
5.3 Level 2 Inspections (Condition Assessment) 22
5.4 Surface Appearance 22
5.5 Measuring the Steel Thickness 23
5.6 Detection of Fatigue Cracks 23
6. Maintenance 24
6.1 General 24
6.2 Maintenance Procedures 24
6.3 Graffiti Removal 24
7. Rehabilitation of Weathering Steel Bridges 26
7.1 General 26
7.2 Sealing of crevices 26
7.3 Use of Protective Coatings 26
7.4 Inspection and Maintenance of Coated Weathering Steel 26
8. References 27
Appendix 28
Appendix A: Determination of Site-Specific Atmospheric Corrosivity Category 28

2
1. Introduction
Weathering steel is a high strength, structural
steel that, in suitable environments, develops
a tightly adherent oxide layer or ‘patina’,
which significantly reduces the corrosion rate
compared with conventional structural steel.
Weathering steel has been used since the
1930’s in railway coal wagons, bridges,
buildings, facades and many architectural
features such as sculptures and landscaping.
It has been used extensively in North America,
Europe and Japan for over 55 years; and over
the last 10 years in New Zealand. When
designed and detailed correctly, taking into
account the environmental factors that governs
its use, it has exhibited excellent performance.
A well designed and correctly detailed
weathering steel bridge, in an appropriate
environment, can provide an attractive, very low
maintenance, economic solution and extends
the scope for cost-effective steel bridges.
Accordingly, the Heavy Engineering and
Research Association of NZ and Opus
International Consultants, NZ have prepared
this document entitled ‘Weathering Steel Design
Guide for Bridges in Australia’. The purpose of
this publication is to provide a collation of the
necessary guidance for the Australian industry
to assist with the efficient and appropriate
application of weathering steels in Australian
bridges. It also provides guidance to achieve
the expected performance of weathering steel
in Australian bridges, to realise the planned life
span of the bridges.
This publication covers the designing,
construction, inspection, maintenance and
even rehabilitation of weathering steel, should
corrosion rates exceed those anticipated at
the design stage, as well as discussing the
limitations on the use of weathering steel.
Comments and queries on the guide should be
referred to HERA.

3
2. Background to Weathering Steel
2.1 What is Weathering Steel?
Weathering steel, or to use its technical title
of “structural steel with improved atmospheric
corrosion resistance”, is a high strength
low alloy structural steel that, in suitable
environments, may be left uncoated because it
forms an adherent protective rust “patina” that
minimises further corrosion. The alloys added
to weathering steel compose only 2% of the
steel make-up with specific alloying elements
such as copper, chromium, silicon and in some
cases phosphorus. The additional alloying does
not diminish the structural capability of the
steel, with the steel offering strength, ductility,
toughness and weldability suitable for bridge
construction and covered by the Australian
Standard AS/NZS 3678.
All structural steel corrodes, at a rate which is
governed by the access of moisture and oxygen
to the metallic iron. As this process continues,
the oxide (rust) layer becomes a barrier restricting
further ingress of moisture and oxygen to the
metal, and the rate of corrosion slows down.
The rust layers formed on most conventional
carbon-manganese structural steels detaches
from the metal surface after a period of time
and the corrosion cycle commences again.
Hence, the corrosion rate progresses as a
series of incremental curves approximating to a
straight line, the slope of which depends on the
aggressiveness of the environment.
The weathering steel rust patina is initiated in
the same way but, due to the alloying elements
in the steel, it produces a stable corrosion
nano-layer (Kimura 2005) that adheres to the
base metal and is much less porous. This layer
develops under conditions of alternate wetting
and drying to produce a protective barrier
which impedes further access of oxygen and
moisture. Eventually, if this barrier is sufficiently
impervious and tightly adhering, the corrosion
rate will be greatly reduced. The resulting
reduction in corrosion rates is illustrated in
Figure 2.1.
In a suitable environment this stable condition
may be reached within 8 years, or more,
depending on the local environmental factors.
At this stage the metal is then protected from
significant future corrosion by the rust patina.
Assuming that there is no significant change in
the environment, and with regular inspection to
determine and treat any isolated problem areas if
they occur, the potential life of a weathering steel
bridge is expected to be more than 100 years.
2.2 Benefits of Weathering Steel
2.2.1 Cost Benefit
Depending on the market price of weathering
steel, it may be greater than carbon steels;
however cost savings from the elimination of
the protective coating system typically outweigh
the additional material costs. The total life
cycle cost of a weathering steel bridge could
be up to 30% lower than a conventional coated
steel alternative (El Sarraf & Mandeno 2010).
In most cases, a weathering steel solution is
cost-competitive with an optimised coated steel
alternative for most inland environments.
2.2.2 Reduced Construction Time
The total construction period is reduced as
both shop and site painting operations are
eliminated, to the advantage of the contractor
and ultimately the client.
2.2.3 Reduced Cost and Time of
Maintenance
If correctly detailed, periodic inspection and
cleaning should be the only maintenance
required to ensure the bridge continues to
perform satisfactorily. Since a protective coating
is not normally required, the cost of inspection,
cleaning and, in some cases, the occasional
remedial treatment of limited areas is usually
considerably lower than the costs of regular
maintenance and recoating of a fully coated
structure. This greatly reduces indirect costs
such as those resulting from traffic management
and traffic delay, caused by providing site access
while coating maintenance activities are carried
out.
2.2.4 Environmental Benefits
Coating application and maintenance requires
suitable health and safety protection for
the applicators and can also require special
Cyclic corrosion loss
(schematic)
Average corrision rate
Weathering steel
Actual corrosion loss
Time
Corrosion Loss
Unprotected Carbon/
Carbon-Manganese steels
Figure 2.1
Schematic comparison
between the corrosion
loss of weathering
and carbon steel

4
environmental considerations, such as
containment of abrasive blast cleaning residue.
Hence, the omission of a protective coating by
using weathering steel, yields both health and
environmental benefits.
2.2.5 Attractive Appearance
The protective mechanism of weathering steel
in bridges is the formation of a stable film of a
rust patina. Once fully formed and weathered,
the appearance of this film is uniform, usually
of a dark brown or purple colour. This colour can
blend nicely with the environment and improves
with age.
2.2.6 Safety Benefits
Health and safety issues relating to initial and
subsequent coatings are avoided, and safety
issues associated with maintenance access are
reduced, thus implementing Safety in Design
principles. For example the need to access the
confined space inside closed box girders is
minimised.
2.3 Where to use
Weathering Steel?
As with other forms of construction materials,
there are certain environments which can
lead to durability problems. The performance
of weathering steel in these environments
may not be satisfactory and its use in these
environments should be avoided.
2.3.1 Marine Environment
Exposure to high concentrations of de-
passivating chloride ions will greatly affect the
patina formation. These can be deposited from
airborne marine salts in aerosol originating
from breaking waves at sea or on the shoreline,
or from salt fogs, will greatly affect the patina
formation. The hygroscopic nature of salt can
prevent sheltered surfaces from fully drying
when relative humidity is elevated and thus
stop the formation of the rust patina, thereby
resulting in the weathering steel continuing to
corrode at a rate similar to mild steel.
Evidence of a higher corrosion rate and a
delayed, or even no, formation of the protective
patina has been identified for unwashed and
sheltered surfaces (i.e. microclimate effects),
as well as in crevices, on weathering steel
structures in coastal locations (Morcillo 2013).
Therefore, when determining the suitability
of using weathering steel in a given location,
the atmospheric corrosivity assessment needs
to take into account both the macroclimate, in
accordance with AS 4312 and/or the CSIRO
Corrosion Mapping and Model (Trinidad 2011);
as well as the microclimate effects, as described
in the Australian Steelwork Corrosion and
Coatings Guide (ASCCG) (Clifton et al 2013).
Details regarding humidity levels, wind
strengths and wind directions, which assist in
determining the macroclimate and microclimate
for a specific location, can be obtained from the
Australian Bureau of Meteorology site under
climate data.
Based on the findings of the Morcillo review
of weathering steel performance data, it is
recommended that weathering steel should
only be used in areas where the maximum first
year corrosion rate (taking into account both
the macroclimate and microclimate effects on
sheltered surfaces) of mild steel is less than
50 µm/yr. This is equivalent to a rain washed
surface in atmospheric corrosivity category
C3 (Medium) to ISO 9223. Therefore, if the
determined atmospheric corrosivity is C4 (High)
or C5 (Very High), weathering steel should not
be used.
Generally, weathering steel can be used in
locations that are more than 2km from the
open seacoast, where the maximum first
year corrosion rate (taking into account both
the macroclimate and microclimate effects
on sheltered surfaces) of mild steel is less
than 50 µm/yr. However, in some cases, this
minimum safe distance may increase up to
40km, depending on prevailing wind strength
and direction, ocean wave and coastal surf
conditions, topography, obstructions to wind
flow and the level of shelter near the site.
Table 2.1 Atmospheric corrosivity categories to AS 4312 and AS/NZS 2312 and description of typical environments
Corrosivity Categories Description Corrosion Rate for Steel (µm/year) Typical Exterior Environment
C1 Very Low <1.3 Alpine Areas
C2 Low 1.3 to 25 Rural/urban
C3 Medium 25 to 50 Coastal
C4 High 50 to 80 Sea-shore (calm)
C5 Very High 80 to 200 Sea-shore (surf)/offshore

5
Hence, confirmation of the site atmospheric
corrosivity category to assess the suitability of
the site is required. See Appendix A for worked
examples on determining the atmospheric
corrosivity category, using the guidance given in
the ASCCG (Clifton et al 2013).
In the case that weathering steel is being
considered for sites where the microclimate
corrosivity is borderline high C3 (Medium)/
low C4 (High), or less than 2km from the open
seacoast; then determination of the actual
site-specific corrosivity environment (including
those of unwashed and sheltered surfaces),
with a minimum of 1 year record, is required.
This assessment should be undertaken by an
experienced corrosion engineer, having the
minimum qualifications given in Section 3.12. It
is recommended that the ‘coupon weight-loss’
technique be used to determine the site-
specific corrosivity, rather than testing for salt
and sulphur dioxide levels in the atmosphere.
Guidance is available for conducting the ‘coupon
weight – loss’ test.
For marine locations near closed bays and
sheltered harbours, where C4/C5 environments
do not exist and C3 regions can be relatively
narrow (< 2km), weathering steels may be able
to be used closer than 2km from salt water;
the minimum distance being site specific. Site
testing of corrosion rates for sites where AS
4312 does not provide guidance for the corrosion
category of the location, should be conducted as
per the guidance given above.
2.3.2 Localised Adverse Conditions
Contaminated sprays from roads under wide
bridges create “tunnel-like” conditions that
should be accounted for when the headroom is
less than 5.3m.
“Tunnel-like” conditions are produced by a
combination of a narrow depressed road with
minimum shoulders between vertical retaining
walls, and a wide bridge with minimum
headroom and full height abutments. Such
situations may be encountered at urban/suburban
grade separations. The extreme geometry
prevents roadway spray from being dissipated
by air currents, and it can lead to excessive
contaminated spray on the bridge girders.
Leaking expansion joints can be caused by faulty
seals exposing bridge members to contaminated
runoff water; resulting in a higher time of
wetness and increases the risk to the continued
corrosion of the weathering steel surface.
Section 3.8 covers detailing solutions to avoid
localised durability issues.
De-icing salts used on roads both over and
under weathering steel bridges may also lead
to problems. These includes leaking expansion
joints where salt laden run-off flows directly
over the steel and salt spray from roads where
“tunnel-like” conditions are created. Both
of these cases are much less of an issue in
Australia than they are in countries, where
sodium chloride based de-icing salts are used on
roads, to make driving safer in winter months.
2.3.3 Continuously Wet / Damp Conditions
Alternate wet/dry cycles are required for an
adherent patina to form. Where this cannot
occur, due to excessively damp conditions, a
corrosion rate similar to that of conventional
carbon-manganese steel may be expected.
Such conditions are to be avoided.
This means that, in addition to the marine
environment guidance given in Section 2.3.1,
weathering steel members must not be
immersed in water, be in contact with soil or
be covered by vegetation. There must also be
a minimum headroom of 2.5m for crossing over
water not subject to significant wave action.
Overseas practice is to limit weathering steel
use to regions where the ‘time of wetness’
is < 60% of the total time. (‘Time of wetness’
for weathering steel applicability is defined
by ISO 9223 as when the relative humidity
exceeds 80% at the site). This is based on
the classification of times of wetness greater
than 60% as being “very damp for corrosion
purposes” by ISO 9223 (Category T5 to ISO
9223). Hence, the humidity level at the site
should be less than 80% for more than 40% of
the year.
Where the average time of wetness is greater
than 60% and up to 70%, the following
additional restrictions apply:
– the bridge must not be shaded from sunlight
between the hours of 9am to 3pm by
permanent obstructions such as surrounding
hills, at any time of the year.
– the bridge must be located so there is
unobstructed airflow past the steelwork.
– the surrounds must be constructed so there
is no vegetation taller than grass within 3
metres of the bridge steelwork.
2.3.4 Atmospheric Pollution
Weathering steel should not be used in
atmospheres where high concentrations
of corrosive chemicals or industrial fumes,
specifically SO2, are present. Such environments
with a pollution classification above P3 (SO2
> 250µg/m3 concentration or 200mg/m2/day
deposition rate) to ISO 9223, rule out the use of
weathering steels.
In Australia, this level of SO2 may occur within
the vicinity of large industrial sites such as at
Mt Isa in Queensland and Port Pirie in South
Australia.

6
3. Design and Detailing
3.1 Design Codes
In Australia, the design for weathering steel
bridges should be undertaken in accordance to
the relevant parts of Australian Standard AS
5100, especially Part 6.
However, there are a number of requirements,
mostly related to detailing and suitability
of environment, which relate specifically to
weathering steel. These are outlined below.
3.2 Material Specification
BlueScope supplies REDCOR™ weathering steel1
to the Australian Standard AS/NZS 3678, with
the typical material properties given in Table 3.1.
3.3 Allowance for Loss of
Thickness
Assuming that the protective rust patina is
formed, even with the reduced corrosion rate,
an allowance for the expected section loss
over the design life of the bridge should be
considered. The corrosion allowance is added to
each exposed surface and this added thickness
for the corrosion allowance cannot be used in
the calculation of the structural capacity of the
member.
Table 3.2 outlines the corresponding corrosion
allowance for a bridge design life of 100 years,
as specified in AS 5100.6.
Table 3.1 Properties of AS/NZS 3678 weathering steel
Steel Grade1Thickness of material
(t) (mm)
Minimum Yield Stress
(MPa)
Minimum Tensile
Strength (MPa)
Charpy Impact
toughness2
WR350
6 to 803340 450
–
WR350L0 27 Joules @ 0°C
WR350L20 27 Joules @ -20°C
Table 3.2 Corrosion allowance (use with Table 2.1 on page 4)
Atmospheric corrosion classification
(ISO 9223)
Weathering steel
environmental classification
Corrosion allowance
(mm/exposed face)
C1, C2 Mild 1.0
C3 Medium 1.5
C1, internal Interior (Box girders) 0.5
Notes to Table 3.1
1 The Australian steel grade designations mean:
WR: represents “weather-resistant” (i.e. improved
atmospheric corrosion resistance or weathering steel).
–350: represents the Nominal Yield Strength.
–L0: relates to the impact test temperature (0°C).
–L20: relates to the impact test temperature (-20°C).
More detail is found in the Australian Standard AS/NZ 3678.
2 Using Charpy 2mm V-notch impact test specimens.
3 Thicknesses down to 3mm are available as coil plate
to AS 1594.
Notes to Table 3.2
–No allowance required for interior faces of hermetically
hollow sections.
–Internals of box (tub) girders supporting concrete decks
should be classified as C2, unless designed to prevent
water ingress.
–Allowances to apply to all fillet and partial penetration
butt welds.
–No allowance is normally made for weathering steel HSFG
bolts. See Section 3.5.4.
–Allowances apply to all other structural elements,
including stiffeners and bracing etc.
–Weathering steel should not be used for Classifications
C4 and C5 or for certain Classification C3 sites as per the
guidance given in Section 2.3.1.
–If required, additional guidance on the corrosion
allowance can be sought by contacting HERA.
1 For any information on BlueScope REDCOR™ weathering steel visit steel.com.au or call 1800 800 799

7
3.4 Design
3.4.1 Global Analysis
Since the global analysis for member actions
and deflections is usually not particularly
sensitive to the exact thickness of the steel
sections. The given member sectional area and
second moment of area, may be used.
3.4.2 Detailed Design
Although it is unlikely that, at any given section
and time during the life of the bridge, that the
entire exposed perimeter is uniformly corroded,
to the corrosion allowance given above; the
members net thickness and area, taking into
the account the corrosion allowance, should be
used when designing the members structural
capacity.
3.5 Bolted Connections
For bolted connections, the following topics
should be considered.
3.5.1 Material Selection
The standard bolts used in bridges, are usually
Property Class 8.8 structural bolts to AS/NZS
1252, which are supplied as hot-dip galvanized.
While, these can be used in weathering steel
bridges, the dissimilar metals in contact with
each other (i.e. zinc and weathering steel), will
result in the depletion of the zinc and corrosion
of the bolt over time. Furthermore, they will look
distinctly different, especially if the galvanized
bolts are coated a dissimilar colour to the
weathering steel. This in turn will introduce a
maintenance issue, due to the need to refurbish
the coating on the bolts over the design life of
the structure.
Another unsuitable option are unprotected
“black” bolts, with those manufactured to AS/
NZS 1111, which are of lower strength, being
Property Class 4.6-mild steel. However steel
shear studs that are embedded in concrete are
acceptable as the alkaline environment prevents
galvanic action from occurring.
Instead, weathering grade high strength friction
group (HSFG) bolts, nuts and washers should
be used. These are available from the United
States, Japan or Britain.
Two strengths are available; these are ASTM
A325, Type 3 or ASTM A490, Type 3 bolts. In
Australian terminology, the ASTM A325 bolt
is equivalent to Property Class 8.8 bolt and
the ASTM A490 has a higher strength, with
mechanical properties of a Properly Class 10.9
bolt. They must be used in conjunction with the
matching higher grade nuts and washers
They are available from Britain in metric sizes
(such as ASTM A325M) and come as M20, M24
and M30, or more commonly available from
the United States in imperial sizes with the
[following details:]
3.5.2 Coefficient of Friction
It has been found (Kulak et al, 2001) that for
tightly adherent mill scale on the surface of
weathering steel at a bolted connection, the
connection slips into bearing at a lower shear
stress than that of carbon steel with mill scale.
The coefficient of friction was µs = 0.2 for
weathering steel versus 0.35 for carbon steel.
However, for high friction grip connections,
the full removal of the mill scale is required, to
achieve a higher coefficient of friction of µs =
0.5. Therefore to use this higher friction factor,
all faying surfaces should be abrasive blast
cleaned using non-metallic grit to Commercial
Blast Cleaning as defined under the visual
cleanliness standard SSPC SP-6/NACE No 3,
which is similar to Sa 2 to AS/NZS 2312.1:2014.
See Section 4.4 for further guidance on surface
preparation.
Furthermore, the development of an adherent
rust film, such as that produced by wetting and
drying for several months by exposure to rain or
washing with potable water, does not degrade
the coefficient of friction. However loose rust
or any residual mill scale would impair the
performance of the joint, and its removal from
plies by wire brushing or scraping prior to
assembly of the connection must be specified.
Notes to Table 3.3
1 The minimum proof stress is the minimum stress in the installed bolt when installed in accordance with ASTM A325 (or Clause H2.5.2 of AS 5100.6).
Table 3.3
ASTM Designation No. Size Range inclusive, in Minimum Proof
Stress1, kpsi
Minimum Tensile
Strength, kpsi
Minimum Yield Stress,
kpsi
A325, Type 3 0.5-1.0 (12.7-25.4mm),
1.125-1.625 (28.58-41.3mm)
85 (586 MPa),
76 (524 MPa)
120 (827 MPa),
107 (738 MPa)
92 (634 MPa),
83 (572 MPa)
A490, Type 3 0.5-1.5 (12.7-38.1mm) 120 (827 MPa) 150 (1034 MPa) 130 (896 MPa)

8
3.5.3 Crevice Corrosion and Bolts Spacing
Crevice corrosion is an issue with all types of
bolted connections, but provided the surfaces
are held together in sufficiently close contact
it has been found (ECCS, 2001), that problems
such as rust staining and pack rust do not arise.
However, it must be recognised that any flexing
in service of the connected steel members
can open up the joint and lead to the ingress
of moisture and dissolved contaminants as a
result of capillary action. Hence more stringent
requirements on bolt centres and edge distances
are required in comparison to joints in a
conventional steel bridge.
– Bolt spacing in lines adjacent to plate/section
edges should not exceed fourteen (14) times
the thickness of the thinnest component, and
in any event should not exceed 175mm.
– The distance from the centre of any bolt to
the nearest free edge of a plate should not
exceed eight (8) times the thinnest component
and in any event should not exceed 125mm.
– These requirements given in (SCI 2015) are
slightly more stringent than the requirements
give in Clause 12.5.2.3 and 12.5.2.4 of AS
5100.6. If these limitations cannot for any
reason be met, either the joint must be
protected by a suitable coating or a suitable
sealant should be applied around the edge
of the joint. Also load indicating and spring
washers should not be used.
Designers should be aware of Issue 94 of
“Construction and Technology”, April 2002,
which covers an example of a bridge mounted
sign failure between the mounting plate and
the bridge beam in weathering steel bridges. It
gives recommendations for bolts and treatment
of the contact surface between the plate and
beam, for attachments to the beams, such as
for these signs. See Section 7.2 for guidance on
sealing of crevices.
3.5.4 Corrosion Allowance for Bolts
There are no specific code requirements for any
allowance to be made on the size of bolts. It is
reasonable to assume that in a properly detailed
bolted connection (see below), the bolt shank
may be treated as “not exposed” and hence
no allowance need to be made; the size of the
bolt heads and nuts are generally sufficient to
accommodate any loss that occurs. If there is
any cause for concern (for example poor fit-up
or flexible cover plates allowing water to be
attracted by capillary action under the bolt
head or the nut), local sealing and/or coating is
likely to be preferred treatment, since continued
wetness could cause corrosion far in excess of
any nominal allowance. Maximum bolt pitches
to avoid capillary action occurring are given
above.
3.5.5 Design of Bolted Connections
As previously discussed, while metric sized
weathering steel bolts are available, imperial
sized bolts are more commonly used. As such,
it is recommended that bolted connections are
designed for the M24 bolt, but with 1” bolt
spacing. This will maximise the procurement
options available to the contractor, who can
then substitute 1” bolts for M24 bolts, without
affecting the layout or design of the connection.
Alternatively, if it was confirmed from the
beginning of the design process that imperial
bolts will be used, it will more economical
to design for the larger 1” bolts, due to the
additional available capacity in comparison to
the slightly slimmer M24 bolts.
Bolts in tension friction and bearing-type
connections of weathering steel bridges should
be tightened using the part-turn method as
outlined in Clause H2.5.2 of AS 5100.6 and
spaced as detailed in Section 2.9.
As discussed, great care also has to be taken
to avoid crevices which can admit water at
the ends of lapping plates, and similar details.
While the designer can specify joints such
that this is unlikely, the fabricator still has to
ensure good fit-up with flat plates. As a last
resort, sealants are available which will perform
adequately with weathering steels to prevent
water ingress to such joints.
3.6 Welded Connections
Welding is of critical importance in the
fabrication of steel structures as welds are
usually the most critical parts of the structure.
Therefore great attention should be given to the
selection of welding consumables to achieve
the desired characteristics of resistance to
atmospheric corrosion and colouring pattern
of the welds; especially when a client has
particular expectations for the appearance of
a fabrication. Welding must comply with the
quality requirements of the applicable welding
standard and product specifications. In Australia
and New Zealand welding of weathering steels
is required to comply with AS/NZS 1554 Part
1 or 5. All joints, including fillet welds, should
be continuously welded to avoid moisture and
corrosion traps such as crevices.
Site welding should be generally avoided as
it requires local grit blasting or grinding after
welding which may lead to differences in
appearance of the welded joint from the rest of
the steelwork. If site welding is to be used, this
must be designed and detailed for from the start
of the design stage and preferably not made
as a late change in the design and detailing
process, once the general details and layout are
established.
A prerequisite for obtaining identical mechanical
properties in the weld and in the base material
is the use of suitable welding consumables and
the choice of appropriate welding conditions
accordingly to AS/NZS 1554. The Standard
however does not specify requirements for
every aspect of the welding; there are various
matters that need to be resolved between

9
the designer and the fabricator. This includes
the possible use of C-Mn unalloyed welding
consumables for single run welds and type and
amount of welding inspection. Appendix D in
AS/NZS 1554.1 provides the list of “Matters for
resolution”; a normative part of the Standard
that both designers and fabricators must
consider before the start of the job.
BlueScope also have an advisory Technical
Note on the Welding of Weathering steel
(Supplement to Technical Bulletin TB 26)
that provides guidance on the welding of
weathering steels.2
See also Section 4.3 and note to Table 3.2.
3.7 Fatigue
Concern has been expressed that weathering
steel bridges may exhibit lower fatigue
performance than those in ordinary structural
steel. This view comes from the fact that
corrosion forms pits from which fatigue cracks
might initiate easily, with the corrosion then
following the crack and hence increasing the
speed of propagation. Many tests have been
carried out worldwide to investigate this, and
whilst the results are not all in full agreement,
there seems to be a general consensus that:
(a) After the weathering process has occurred,
parent weathering steel (e.g. constructional
details 1-3 from Table 13.5.1(A) of AS
5100.6), will have lower fatigue strength
than parent non-corroded steel, because
of the greater surface roughness under the
corrosion layer.
(b) Fatigue failures in bridges are almost
always initiated at a point of geometrical
discontinuity or stress concentration such as
a weld: this gives a much greater reduction
below the parent steel fatigue strength
than does the presence of corrosion pits in
weathering steel. It appears that, provided
the detail category to Table 13.5.1(A) of AS
5100.6 of the critical detail is 100 or lower,
the use of weathering steel will not cause
any reduction of fatigue life. Even if the detail
is detail category 112, degradation would be
minimal.
(c) Tests which show worse behaviour of
joints with low fatigue detail category in
weathering steel have apparently always
been carried out in very adverse testing
environments (for example continuously
sprayed with salt water). Weathering steel
should not be used for bridges in such
environments. Therefore, provided that the
guidelines on suitable environments given in
Section 2.3 are observed, the results of such
tests will not be applicable.
Even though in practice welded weathering
steel bridges will not have a lesser fatigue
performance than those of coated steelwork,
it is necessary to design the details to be as
fatigue-resistant as practicable. As is discussed
in Section 5.6, fatigue cracks in weathering steel
bridges are much harder to detect than those in
coated carbon steel bridges.
Bad Detailing Good Detailing
Figure 3.1
Grinding flush of welds which otherwise form water traps
Bad Detailing Good Detailing
Figure 3.2
Spacing of Girders
2 Technical Note on the Welding of Weathering Steels, BlueScope

10
3.8 General Structural Detailing
The first principle to be stated when detailing a
weathering steel bridge is that good structural
detailing practice should be used. In this regard,
in the correct environment, a bridge whose
details would give no problems in coated carbon
steel bridge would behave entirely satisfactorily
if designed in weathering steel.
However, the following details are particularly
important to be aware of:
3.8.1 Drainage
A weathering steel bridge should not be
permanently wet or damp. Hence, even if
the general environment is satisfactory, it is
important to ensure by good detailing that a
high time of wetness does not occur at any point
on the bridge steelwork.
There are a number of ways in which this can be
achieved, some of which are illustrated below.
Some of these details may be expensive to
fabricate or, if in fatigue sensitive areas, may
lead to a reduced fatigue life. A designer must
carefully weigh the relative advantages and
disadvantages, taking all factors into account,
before selecting a detail.
Weathering steel bridges should be detailed to
ensure that all parts of the steelwork can dry
out, by avoiding moisture and debris retention
and by ensuring adequate ventilation and any
ponding of water.
Common practices in this regard are to:
– Grind flush weld details which may cause
water traps. (Figure 3.1)
– Provide 50mm copes where stiffeners are
attached to the bottom flange.
– Avoid closely spaced girders to aid
ventilation. (Figure 3.2). This is also a more
economical layout.
– Avoid overlaps, pockets, faying surfaces
and crevices, which can collect and retain
moisture. (Figure 3.3 to 3.6)
– Hermetically seal hollow sections, or provide
adequate access, drainage, and ventilation.
(Figure 3.7)
– Provide slopes or cross fall to ensure water
runoff. Provide drip plates to direct runoff
away from bearings or where staining could
occur.
– Where possible web plates of box girders
should extend 20mm below the bottom
flange. (Figure 3.7)
Bad Detailing
1
Good Detailing
1. Bearing Stiffener
1
Figure 3.4
Optimum choice of transverse stiffener shape
Good Detailing
30mm
Bad Detailing
Figure 3.3
Curtailing transverse web stiffeners to allow drainage below

11
3.8.2 Crevices
Crevices should be minimised and where
possible, eliminated. Crevices can attract
moisture by capillary action, and can be a
particular problem for weathering steel bridges,
as they are not coated or sealed. Crevices can
occur at any point where two surfaces are in
contact, and are particularly an issue for bolted
connections where plates lap (see further
comment on bolted connections in Section 3.5.3,
including maximum bolt spacing). If a crevice
is not adequately sealed, not only is water
attracted into the crevice without much chance
of escape, but the corrosion products formed as
a consequence have a higher volume than the
original material that may result in the distorting
or bursting of the connection. Furthermore,
the corrosion products themselves will tend to
attract further water and thus aggravate the
situation.
In cross bracing between girders, use angles
“flange upwards” (Figure 3.5; good detailing),
and select “K” bracing rather than “X” bracing
to avoid crevices at the intersections. If “X”
bracing must be used, fill out the intersections
with tightly fitting filler plates, (See Figure 3.8).
3.8.3 Expansion Joints
Minimise the number of deck joints, as leaky
deck joints are one of the most common causes
of problems in weathering steel bridges,
allowing contaminated water to drop onto the
steel below the deck, as well as increase the
time of wetness that will affect the patina
formation. Therefore, weathering steel should
be used for bridges in conjunction with the
deck being continuous over intermediate piers
(Figure 3.9) and, where possible, where the deck
is integral with the abutments, see (El Sarraf et
al 2013) for additional guidance.
Bad Detailing Good Detailing
Figure 3.5
Correct orientation of
longitudinal stiffeners
Good DetailingBad Detailing
Figure 3.6
Provision of run-off slopes
on external flanges
Good Detailing
Bad Detailing
Figure 3.7
Use of Box Sections
Note:
Use box section girders where technically and economically feasible, and ensure that lower
flanges do not project horizontally (see Figure 3.5). However internal condensation may occur
and adequate internal ventilation and drainage must be provided, especially when supporting
an unsealed concrete deck.

12
If deck joints are unavoidable at abutments,
give special attention to them to ensure
that they do not leak or, if there is any risk
of leakage, that they are provided with a
positive drainage system whose outlet pipes
are of sufficient length to ensure that the
discharge water does not spray on to the
adjacent steelwork or substructure in any wind
condition. The use of drainage items of a non-
metallic type is preferable.
3.8.4 Run-off
Run-off of water from the super-structure and
drains should not be permitted to run down the
visible external surfaces of the substructure.
Until the patina is fully formed, run-off water
is liable to contain rust from the weathering
process, and unless it is kept away from such
surfaces will cause unsightly staining. The
drainage of the deck, piers, and abutments
requires careful design and detailing to ensure
that staining is avoided.
This usually means channelling any run-off
water on the tops of piers or abutments, and
around bearings to a drain, or drains, feeding
into down-pipes which discharge away from
the pier or abutment. Particular care should
be taken to ensure (by diversion strips or
otherwise) that run-off from bottom flanges
occurs away from piers. Refer to Figure 3.10
and Figure 3.11 for appropriate drainage in
the abutment, and the correct orientation of
the drip plate. Also see Figure 3.12 and Figure
3.13 which show examples of good and bad
detailing.
Web
30˚
to 40˚ 1
5
Flange
Slope
Figure 3.11
Drip plate attached to bottom flange,
sloped to prevent debris accumulation.
Sloped abutment platform and drain
1
23
4
Figure 3.10
Sloped abutment platform and drain
1. Bearing stiffener
2. Sloping top of pier
3. Drainage gutter
4. Drainage pipe
5. Drip plate
Figure 3.12a Good detailing producing
an abutement free of staining
[Image courtesy of www.steelconstruction.info]
Figure 3.12b Bad detailing (severe staining)
[Image courtesy of TxDOT]
Filler Plate
Concrete Deck
Type “X”
Type “K”
Figure 3.8
Cross Bracing Details
Figure 3.9 Long span “jointless” bridge
[image courtesy of the Texas Department of
transportation (TxDOT)]

13
Figure 3.14 shows the design of a drip pan,
followed by Figure 3.15 which demonstrates
good and bad detailing of the drip plate and drip
pan.
Figure 3.16 shows the design of a retro drip pan,
followed by Figure 3.17 which demonstrates
good and bad detailing of the retrofitted drip
pan.
It should always be kept in mind when designing
a weathering steel bridge to make it easy to
inspect. Inspection is required to ensure that
an adherent protective patina has been formed
and is not flaking off, that moisture and detritus
are not collecting, and that the thickness of the
structural elements is as expected by the Bridge
Designer at that point in time. A programme
of monitoring (in accordance with Section
B2.2 of the Guidelines for Bridge Management
(Austroads 2004) should be specified, and the
design must make allowance for this to be done.
All parts of the bridge should be designed to be
readily accessible for an appropriate level of
inspection.
Figure 3.13 Bad detailing of drip plate. Drip plate improperly set at 90˚, creating
corner for debris accumulation (left); and Drip plate not set at proper angle (right).
[Images courtesy of TxDOT]
Sole Plate
Bearing Pad
Pier
Cap Box Girder
Drip pan – stainless steel
3mm thick (approx)
100mm to 150mm
All sides
Figure 3.14
Well designed drip pan installation
Cap Box Girder
Bearing Pad
Pier
Overlap plates
25mm min
Drip pan – stainless steel
3mm thick (approx)
Weld drip pan to bottom of girder.
Seal with silicone when cool.
5mm max.
Sole Plate
100mm to 150mm
All sides
Figure 3.16
Design of retrofitted drip pan

14
3.8.5 Hangar Plate and Pin Connection
Hanger plate and pin connections (see
Figure 3.18 for details) at cantilever expansion
joints of girders are exposed to water leaking
through open deck joints. If these details are of
weathering steel they can be severely corroded
in the gap between the girder web and the
hanger plates. Also, there can be some galvanic
corrosion of the steel girder with respect to the
bronze washer installed between the girder web
and the hanger plates. If the corrosive attack
is severe, the gap between the girder web and
hanger plates becomes tightly filled with rust,
and may lead to pack out failure as discussed
earlier. These details are bad from a corrosion
standpoint even if the joints are painted.
3.8.6 Box and Tubular Members
Box and tubular members for welded girders,
columns and trusses constructed of weathering
steel will corrode on the inside if water is
continuously present. This can be prevented by
fully sealing the member or ensuring adequate
drainage holes are provided. If a pipe carrying
water passes through a girder, drain holes
should be provided in the bottom of the girder
so as to drain water in the event of a leak.
Consideration can also be given to insulating the
water line to prevent condensation on the pipe
exterior. Drain pipes should not pass through box
members.
3.8.7 Box Girders
Composite steel-concrete box girders cannot
be hermetically sealed, because moisture
may come in through cracks in the concrete
deck slab. Therefore, provision must be made
for drainage of moisture and for adequate
ventilation to minimize corrosion of the interior.
If the interior is accessible so that periodic
corrosion inspections can be made, coating of
the interior is unnecessary. However if future
interior coating becomes necessary, it would
be helpful to inspectors if a white alkyd coating
system was used. If interior inspections to
monitor condition of unsealed boxes are not
possible, coating the interior is recommended.
Alternative steps to coating may be taken to
insure satisfactory corrosion performance for
the interior of unsealed, composite box girders.
These are:
– Waterproof and pave the bridge deck to
prevent water from leaking through the deck
and into the box girder interior.
– Provide access holes with locked covers on
screens to keep out vermin and birds but to
allow inspection.
– Ventilate the girder by drilling 50 mm dia
holes in the bottom flange at the lowest
point of each compartment. Where there is
<2 degrees slope to bottom flange provide
drainage holes at ~10m centres. Insert a small
tube fitted with an insect screen into the hole
so that the top of the tube is flush with the
top surface of the bottom flange and the tube
itself protrudes below the flange.
– Locate the inspection hatches for easy access
by the inspector.
Anchor spanSuspended span
Hanger plate
Hanger pins
Web reinforcement plate
Figure 3.18
Hanger plate and pin connection
(a) Concrete column without
protection of drip pan
(b) Insufficient drip pan overhang permits
run-off to blow onto pier
(c) Stain-free concrete due to
installation of drip plate
Figure 3.15 Good and bad detailing of a drip plate and drip pan
[Images courtesy of TxDOT]

15
3.8.8 I-Girders
Corrosion of weathering steel members is most
likely to occur on horizontal surfaces, in crevices
and re-entrant comers. On I-girder bridges it
has been found that locations where corrosion
attack is most likely are the top surface of
bottom flanges, gusset plates, longitudinal
stiffeners, splices of horizontal and sloped
members and where flanged gusset plates
contact bearing and intermediate stiffeners.
Therefore, to reiterate the guidance given
above, good design and detailing practice should
involve:
– eliminating crevices and minimizing re-entrant
comers,
– providing for good drainage at low points
when girders slope away from the centre
supports and toward the end supports
– changing the flange thickness instead of the
width, where welded flange splices are used,
because changes in widths may cause uneven
water flow.
3.9 Removal of Rust Stains
Although rust staining should not occur on a
well detailed weathering steel bridge, it is worth
noting that concrete, stone, wood, galvanized
steel and unglazed brick are difficult to clean.
Hence, it is recommended that substructures
are sealed with washable organic coatings to
facilitate cleaning with commercial products,
should rust staining occur.
The following materials are subject to minimal
staining and can generally be cleaned relatively
easily:
– Ceramic tile and glazed brick
– Washable air-drying and thermosetting
organic coatings
– Stainless steels
– Aluminium, anodised and un-anodised
3.10 Interface Protection
Other issues to consider include:
– Elements buried in soil should be coated, up
to 100mm above the ground, with a minimum
of 350microns of a suitable barrier coating,
such as a high build epoxy or polyurea, to
minimise non-atmospheric corrosion and risk
of ‘ring bark’ corrosion.
– Interfaces between steel and concrete should
be separated, using a minimum of 150microns
of non-conductive barrier coating. See Section
4.13 of (Clifton et al 2013) for further details.
– Elements embedded in concrete need not be
coated, except 100mm from and 50mm above
the interface. See Section 4.13 of (Clifton et
al 2013) for further details.
– Contact between steel and treated timber
must be avoided, unless a mastic strip or
damp proof course is placed between these
components.
(a) Improperly retrofitted drip pan
on pier allows staining.
(b) Poor welding on retrofitted drip pan. (c) Properly retrofitted drip pan on pier.
Figure 3.17 Good and bad detailing of a retrofit drip pan
[Images courtesy of TxDOT]

16
3.11 Connection to Other Materials
In general, any connection to a galvanically
dissimilar material runs the risk of galvanic
corrosion of either the weathering steel or
the other material (such as galvanized bolts).
However, this will only occur in the presence
of water. Therefore for connections between
dissimilar metals inside a dry weathering steel
box girder, the risk of galvanic corrosion is
minimal.
Care should also be used if weathering steel
and stainless steel (for example in bearings)
are connected without appropriate electrical
insulation. In this case the weathering steel
would become anodic and corrode preferentially,
although experience has shown that provided
the joined area does not act as a crevice to
attract water; serious problems are unlikely to
arise. Such an application is the drip pan detail
shown in Figure 3.14. The contact surfaces and
regions around them can be coated with a 150
microns of non-conductive barrier coating, as
shown in Section 4.13 of (Clifton et al 2013).
3.12 Further Protection – Coating
There are some weathering steel bridges in
existence where the designer wished to provide
further protection from the outset. Coating the
steelwork has been specified in areas where it
was thought that the environment would prevent
the formation of the protective patina. This can
either be due to the accumulation of debris, salt,
and/or other contaminant. Such areas include;
the top surfaces of bottom flanges, perhaps
together with some of the bottom of the web,
areas below deck joints and under the ballast in
trough section railway bridges.
In such circumstances, coating these potential
problem areas should be considered. There is
some evidence that, although a barrier coat lasts
no longer than on ordinary structural steel, if the
coat is damaged or degraded the self-stifling
properties of the rust which is formed helps to
prevent under-creep. This can be beneficial since
damaged areas which require touch-up and
recoat will not spread to any extent even after a
prolonged period of time.
Implications for the appearance of the bridge
should be considered when specifying local
coating and the colour of the coating system on
exposed steel work should be selected to match
the expected colour of the steel. These should
be able to be applied on to a high pressure
water cleaned surface and should comprise a
single coat system where possible. See AS/NZS
2312.1 and (Clifton et al 2013), for guidance on
a suitable coating system such as a direct to
metal high build water based acrylic elastomer
or a high-ratio calcium sulfonate alkyd.
It is recommended that a qualified coating
specifier is used to prepare, or review, the
refurbishment specification. The required
qualification for such a specifier should be one
of the following:
– NACE Protective Coating Specialist.
– Australasian Corrosion Association (ACA)
Technician or Technologist with successful
completion of the ACA’s Coating Selection
and Specification Course and/or certified
to NACE Coating Inspection Program (CIP)
Level 2.

17
Image courtesy of www.steelconstruction.info

18
4. Fabrication and Construction
4.1 Cold and Hot Forming
As with most high strength structural steels,
cold forming is not generally recommended for
structural shapes or for plates and bars over
approximately 20 mm thick, in accordance
with AS 3678. The minimum cold bending radii
are given in AS3678 for plate thickness up to
20mm however, note the need to condition the
plate edge prior to cold bending. Also, where
fracture toughness is important, AS 4100, in the
sections on brittle fracture, provides guidance
on the effect of cold forming strain levels on
the resultant change in notch toughness of
structural steels.
Hot forming can affect both the tensile
properties and the notch toughness, particularly
in steels without sufficient grain refining
elements. Even in steels with grain refining
elements (including most weathering steels)
certain supply conditions (such as thermo-
mechanically controlled rolled) may incur a
significant loss of strength from hot forming.
Steel supplied in the normalised condition
may be able to sustain some heat treatment
or hot-forming processes, if the steel is
heated to the appropriate temperature range.
Accordingly a maximum temperature of 600°C is
recommended; see Clause G3.1 of AS 5100.6 or
contact the steel supplier for guidance.
4.2 Cutting
Flame-cutting (for example oxy-acetylene or oxy-
propane) or plasma-arc cutting of weathering
steels can be carried out using the same
procedures as would be applied to carbon steels
of similar carbon equivalent value and thickness.
Application of preheat temperatures similar
to those used for welding will avoid excessive
hardening of the flame-cut edges. If required,
grind the hardened edges, as if left, this will
affect the formation of the protective patina at
that surface.
As general guidance, for a thermally cut edge
not subsequently fully incorporated in a weld,
cracking is more likely to occur if the hardness
exceeds 350 HV (Vickers Pyramid Number).
4.3 Welding
4.3.1 Welding processes
Weathering steel can be is welded using the
same techniques used for low alloy steels.
Typical welding processes used are submerged
arc welding (SAW), flux-cored arc welding
(FCAW), gas metal-arc welding (GMAW or MIG)
and manual metal-arc welding (MMAW).
4.3.2 Preheat
The welding of structural weathering steels is
similar to that of conventional structural steels,
but weathering steels generally have higher
Carbon Equivalent (CE). Steel grades CW300,
HW350 and WR350 have a Weldability Group
Number 5 in accordance with the Table 5.3.4(A)
of AS/NZS 1554.1. It is based on the typical
maximum carbon equivalent encountered in
Australia and New Zealand weathering steels,
rather than a maximum specification limit
normally applied. The preheat temperature
should be determined in accordance with
Section 5.3 of AS/NZS 1554.1.
4.3.3 Hot cracking
As weathering steels typically contain levels of
phosphorus and/or copper significantly higher
than that found in C-Mn structural steels, in
certain joint configurations and higher heat
inputs typically associated with the SAW
process, the weld may be at risk of hot cracking;
also referred to as solidification cracking. The
solidification crack susceptibility of weld metal
is affected by both its composition and weld-run
geometry (depth/width ratio). The chemical
composition of weld metal is determined by the
composition of the filler material and the parent
metal, and the degree of dilution. The degree
of dilution, as well as weld-run geometry, both
depend on the joint geometry (angle of bevel,
root face and gap) and the welding parameters
(current and voltage). At normal heat inputs used
in manual or mechanised welding the risk of hot
cracking is considered low, however at higher
heat inputs, particularly >2.5kJ/mm, and for fillet
weld runs having a depth/width ratio greater
than 1, the risk of hot cracking is relatively
high. If in doubt, a hot cracking test should
be considered as part of the weld procedure
qualification test requirements to verify freedom
from hot cracking. Test methods are provided in
AS 2205.9.1.
4.3.4 Selection of welding consumables
Welding small-sized, single-pass welds typically
causes a high amount of base metal dilution; a
large amount of base metal is melted and mixed
with the weld metal. As a result, the weld picks
up a sizable amount of alloying elements from
the weathering steel, which can provide the
weld metal with the same atmospheric corrosion
resistant properties as the base metal itself.
C-Mn consumables may be used for single-
run fillet welds up to 6 mm leg length and
for butt welds made with a single run or a
single run each side and where the welds are
made with no weave. Refer to BlueScope’s
Technical Note on ‘The Welding of Weathering
Steels’, Supplement to BlueScope Technical
Bulletin Number 26 (TB 26), for more detailed
guidance. Weld procedure prequalification is
recommended to ensure sufficient dilution of
the base plate into the weld metal has been
achieved to provide adequate atmospheric
corrosion resistance. C-Mn welding
consumables to be selected in accordance with
Table 4.6.1(A), AS/NZS 1554.1.
Welds on weathering steels may be visible due
to the colour contrast between the base material
and the weld metal. In some applications it is
desirable to have the appearance of the weld
seamlessly blended into the base metal. In
these cases, the use of welding consumables

19
with similar weather resistance properties in
accordance with Table 4.6.1(C), AS/NZS 1554.1
is recommended even for single-run welds.
Large, multi-pass welds typically do not
experience a significant amount of base metal
dilution. For this reason, carbon steel filler
metals cannot pick up enough alloying elements
from the base material to provide the necessary
atmospheric corrosion resistance. Instead, a
low alloy filler metal is recommended to ensure
that the weld will have the same corrosion
resistance as the weathering steel. For larger
single-run fillet welds and butt welds made
with a single run or a single run each side and
where weaving is used during the run, welding
consumables should be selected in accordance
with Table 4.6.1(C).
For multi-run fillet welds and butt welds, the
main body of the weld can be made using C-Mn
electrodes selected to Table 4.6.1(A), AS/NZS
1554.1, capped off with ‘matching’ electrodes.
For capping runs on multi-run fillet or butt welds,
the welding consumables are to be selected in
accordance with Table 4.6.1(C).
Commonly used low alloy filler metals for
weathering steel applications include those
with a minimum nominal nickel content of
one percent. That alloy content is sufficient
to provide atmospheric corrosion resistance
similar to the weathering steel, and the cost is
typically less than other low alloy filler metals
with acceptable properties. Filler metals with
a higher nickel content and other alloying
elements, can be used in accordance with the
Table 4.6.1(C), AS/NZS 1554.1. Weathering
steel welding consumables with a higher impact
grading are also acceptable.
The American Welding Society’s Standard
Table 3.3 of AWS D1.1 provides a broader range
of consumable options for common welding
processes where a matching patina is required
on multi-pass welds in particular. Consumables
meeting these requirements may be used to
weld WR350 and HW350 grades.
Where consumables are not selected in
accordance with the above, additional
qualification tests may be required to establish
suitability for use within the chosen application.
4.3.5 Quality requirements
All welding fabrication including quality of the
weld should comply with AS/NZS 1554 Part 1
or Part 5. The fabricator should demonstrate the
ability to produce sound welds via a documented
weld procedure and welder qualification
tests. The fabricators should ensure that all
welding and related activities are managed
under a suitable quality management system.
Such a system should generally comply with
the requirements of AS/NZS ISO 3834 part 2
or 3. All welding should be performed under
supervision of the welding supervisor as per
section 4.12, AS/NZS 1554.1:
4.4 Surface Preparation
Further quality requirements are given in
the Australian Standard for Fabrication and
Erection Standard for Structural Steelwork,
AS/NZS 5131. It is recommended this Australian
Standard be consulted for guidance on the
welding fabrication of weathering steel.
4.4.1 Mill scale removal
Commercial Blast Cleaning as defined under
SSPC SP-6/NACE No 3, which is similar to Sa
2 to AS/NZS 2312.1: remove oil, grease, dirt,
rust scale and foreign matter. It also removes
most of the mill scale, coating, and rust in
the bottom of pits except for slight streaks or
discolorations. At least two-thirds of the surface
area should be free of visible residues except
for the discolorations previously mentioned.
The resultant surface will weather relatively
uniformly. The process is considerably less
expensive than near-white blast cleaning (SSPC-
SP10/NACE No 2, similar to Sa 2 ½); however
the finished appearance is less uniform.
It is important that all contaminants are removed
from the surface of the steel to enable it to
form a uniform protective rust patina. Mill scale
will be undercut during the weathering process
and will fall off eventually, but will also delay
the formation of a uniform coloured protective
layer; hence it is recommended that mill scale
is removed from the whole surface and not just
the faying surfaces (Section 3.5.2). As such
the following clause should be included in the
bridge specification.
After fabrication and prior to erection, all
weathering steel components shall be abrasive
blast cleaned to SSPC-SP 6/NACE No 3 to
remove mill scale and other contaminants. This
shall be immediately followed by a minimum
of 3 cycles of wetting using potable water
and drying, to assist in the formation of the
protective patina and provide a uniform finish.

20
4.4.2 Grinding and Other Cleaning Methods
Prior to abrasive blast cleaning, or if the
following contamination was caused during
erection, the following surface preparation
methods should be undertaken.
– Wax-based crayons should not be used to
mark weathering steel. However, if such
marks are present, they may be removed by
solvent degreasing.
– Oil, grease, and cutting compounds may
also be removed by solvent degreasing (AS
1627.1 or SSPC-SP1). Alkaline cleaners or a
combination of detergents and steam may
also be used. When alkaline cleaners and
detergents are used, their use should be
followed with high pressure water cleaning to
remove any residue.
– Acids should not be used for cleaning
because of the possibility of acid residues
remaining on the steel surfaces and causing
corrosion.
– Localized weld spatter or other welding
residues may be removed by power tool
cleaning (SSPC-SP15).
– Loose deposits of rust, rust scale, coating
or other foreign matter may be removed by
hand tool cleaning (St2 or SSPC-SP2) such
as scraping or wire brushing. More adherent
deposits may require power tool cleaning (St2
or SSPC-SP3) or brush-off blast cleaning (Sa1
or SSPC-SP7/NACE No 4).
The above surface preparation processes are all
defined in AS/NZS 2312, and the relevant SSPC/
NACE documents.
4.5 Storage, Handling and Erection
Storage of weathering steel sections and plates
should ensure that the protective rust patina
continues to develop following preparation of
the surface, as discussed above. This means
that, in ideal conditions, the steel will be stored
such that each surface is alternately wetted
by rain; or preferably hosed down daily for one
week, and dried naturally after every wetting.
Particular care must be taken to ensure that
plates and sections are not stored so that they
become permanently wet, or entrap moisture
or dirt. This may easily occur, for example, if a
plate is supported so that it deflects upwards
and thus provides a water collecting area.
Covering with plastic or tarpaulins is not
recommended as it promotes condensation and
prevents the alternate wetting and drying.
Contamination of the surface should be avoided.
This may arise from concrete, mortar, asphalt,
coating, oil or grease. In particular, marking
the surface for reference during fabrication
with wax crayons should be avoided, since this
marking can be very difficult to remove. Consider
hard stamping for identification of members or
joints.
The use of metal slings for handling should be
carefully controlled, since they can damage the
developing surface protection layer on the steel.
While this will eventually redevelop over time,
it will give an uneven appearance until removed
by weathering.
During erection, continue to protect the sections
from contamination and damage. Site welded
joints may require special treatment, such as
grinding off excess weld on upper surfaces of
flanges to avoid potential corrosion traps, and
spot abrasive blast cleaning to ensure that all
surfaces weather to a uniform colour in a similar
period of time.
4.6 Final Site Cleaning
Where care has been taken in handling, storage
and erection, it may be possible to avoid any
final site cleaning. However, if contaminants
have been allowed to accumulate they must be
removed, either by washing, by chemical means,
or by a site blast clean. Similarly, areas where
severe physical damage has occurred may also
require blast cleaning after any repair (such as
heat straightening).
4.7 Protection of
Piers and Abutments
If there is any risk of piers and abutments
being stained by rust laden water run-off
during erection, consideration should be
given to providing temporary protection by
wrapping them with polyethylene sheeting or
its equivalent. This sheeting should remain in
place and be kept free of damage until the final
construction inspection is made. See Section 3.8
for detailing for stain prevention.
In the case that the sub-structure develops
stains, they may be removed by abrasive
blasting, or with a commercial cleaning solution
after completion of construction.
4.8 Guardrails and Light Poles
Guardrails and light poles on weathering steel
bridges should, where possible, be connected
to the concrete deck rather than directly to the
supporting steel beams. In most instances these
will be galvanized steelwork, with an additional
barrier coating or sealant to minimise the risk of
crevice corrosion, see Section 3.11.

21
Image courtesy of www.steelconstruction.info

22
5.1 Requirements for Inspection
of Weathering Steel Bridges
All bridges, in whatever material, require
periodic inspection to confirm that they are
performing satisfactorily and to identify and
mitigate defects at the first opportunity. A
weathering steel bridge, properly designed and
detailed, and in the correct environment, should
deliver trouble free performance. However,
regular inspection of the bridge structure will
assist in the early detection of potential issues,
and their prompt remediation will assist to
minimise the risk of more significant problems
in the future.
All parts of the bridge should therefore be
designed to be readily accessible for an
appropriate level of inspection.
5.2 Level 1 Inspections (Routine)
Level 1 Inspections (Routine) of weathering
steel bridges should be carried out by a suitably
trained bridge inspector, as described in Table 5
of (Austroads 2004). The surface condition of
the protective rust patina is a good indicator
of performance. An adherent fine grained rust
patina indicates that corrosion is progressing at
an acceptable rate, whereas coarse laminated
rust layers and flaking suggests unacceptable
performance. Other signs to look for and areas
to investigate during visual inspection include:
– Leaking expansion joints.
– Accumulation of dirt or debris.
– Moisture retention due to overgrown
vegetation.
– Faulty drainage systems.
– Condition of sealants at concrete / steel
interfaces.
– Excessive corrosion products at bolted joints
(“pack rust”).
If any issues are noted during these inspections,
the cause should be identified and the problem
rectified as soon as possible.
5.3 Level 2 Inspections
(Condition Assessment)
This level of inspection should be undertaken
every 3 years by an accredited inspector, as
described in Table 5 of (Austroads 2004).
Provided that provisions have been made for it
in the design, the routine inspection described
above will pose no particular difficulties.
However, the more detailed inspection of
weathering steel bridges differs in a number of
respects from, and in general is more difficult
than, the inspection of coated carbon steel
bridges.
One of the advantages of weathering steel is
that the surface can be seen directly. However,
whilst a heavily corroded surface will be
obvious, an inspector must be familiar with the
various colours (see following section), textures
and general appearance that the rust patina can
assume when exposed to different environments
in order to judge whether or not the patina is
acting in a protective manner. Furthermore,
visual appearance on its own may be unreliable
and mechanical or other tests may be necessary
to determine whether or not the film adheres to
the underlying steel base.
One problem which may arise with many such
tests (for example wire brushing, or preparation
of the surface for ultrasonic investigation) is that
the appearance of the protective film may be
changed; it will take time for this to return to a
uniform appearance.
Whilst design against fatigue should ensure
that cracking does not occur during the service
life of the bridge, detailed inspection is required
to confirm that this is so. As described below,
detection of fatigue cracks in weathering steel
bridges can be more difficult than detection of
cracks in coated steelwork.
5.4 Surface Appearance
An inspector must be able to distinguish
between a protective and a non-protective rust
coating. Normally this can only be done at close
range (within 1 metre distance). The appearance
will give the first indication of the quality of
the protective film. Whilst only experience can
make an inspector expert in such matters, some
guidelines are given below.
In colour the protective rust coating should
begin as yellow orange after the initial stage
of exposure, becoming light brown, and finally
chocolate to purple brown (ranging between AS
2700 Colour reference R65 Maroon, and Colour
reference X64 Chocolate ). See Figure 5.1 for an
example of 6 months old patina (left) and a fully
formed patina after 8 years (right). Note that in
some lighting conditions its appearance can vary
from metallic grey to purple.
In texture, the protective rust coating should
be tightly adhering, with a relatively smooth
surface, and capable of withstanding
hammering or vigorous wire brushing (although,
as noted earlier, such treatment will affect the
appearance, exposing a lighter layer which will
take some time to re-darken). A dusty texture, in
which loose particles can easily be rubbed off by
hand, is common in the early stages of exposure.
Granular or flaky appearances are danger signs
of a poorly performing surface.
The timing of the colour and texture changes can
vary with atmospheric conditions and the degree
of direct exposure to rain. A rural, unpolluted
atmosphere (typical of most rural areas of
Australia, Corrosion Category C2 regions, as
discussed in Section 2.3.1) or sheltered interior
beams, will result in a lighter colour and dusty
texture, taking significantly longer to change,
potentially up to 16 years (or longer). The steel
composition can also affect this – the greater
the extent of alloying elements, the darker the
final colour.
5. In-service Inspection

23
Figure 5.1
Example of a 6 month old patina (left)
on Papakura Railway Bridge, and a fully
formed patina, after 8 years of service,
on Mercer to Longswamp Off-Ramp
both in New Zealand.
In New Zealand, it has been identified that the
protective patina may take up to 8 years to fully
form in ideal conditions; this may increase up to
16 years (or more) in areas with higher time of
wetness.
If the condition cannot be reliably ascertained,
it may be necessary to remove part of the
protective layer to determine the extent
of pitting and to measure the section loss.
However, note the limitations with measuring
the steel thickness given below.
It should be noted, that in polluted and/or high
salinity environments, the darker colour that
implies the patina is formed, may develop
within a shorter time frame (from 2 to 8 years).
However, evidence has shown (Morcilli et al
2013) that this does not mean that the patina
has fully formed. Therefore, monitoring the
texture of the surface and measuring the steel
thickness will assist in determining when the
patina has achieved its protective properties.
5.5 Measuring the Steel Thickness
While the condition of the protective rust
patina should be regularly monitored (as
discussed above), it is recommended that the
measurements of the corrosion rate should be
undertaken every 6 years in a C3 environment
or every 12 years in C2. This is done by
measuring the remaining steel thickness at
clearly identified points of the structure. These
reference points should be defined on the
as-built drawings, or in the bridge maintenance
manual, along with the original (reference)
thickness measurements taken at the end of
the construction period, using callipers and/
or the use of an ultrasonic thickness gauge.
Measuring internal surfaces is quite difficult
using mechanical means.
If over time, it is identified that the corrosion
rate is higher than the rate the corrosion
allowance was originally based upon, then
remedial measures may need to be considered.
Note that the corrosion rate is usually higher
during the first 10 years of exposure, after which
the lower steady state corrosion is reached.
Therefore a minimum of 20 years of data is
required, unless significant unexpected section
loss during the period is identified.
Portable ultrasonic thickness gauges are
available to measure the actual steel thickness.
However it may be challenging to get an
accurate reading, if the patina is still forming
and the surface is still rough and easy to remove
by hand. Because of this, it is also recommended
that removable weathering steel coupons are
installed to more accurately monitor the patina
formation and measure the corrosion rate.
Allowance should be made for the installation
of a minimum of two sets of test coupons
on weathering steel bridges, on the primary
structural members. The coupons should be cut
from the same weathering steel plate used in
the bridge, with the same surface preparation
(as discussed in Section 4.4)
A total of 30 coupons, cut to 150 x 100 x 5mm
(or the thinnest plate available for that bridge),
to be installed per bridge, of which 15 are
installed on the outer girder, that is exposed
to the prevailing weather, and 15 on an inward
facing girder surface, that is sheltered from the
sun and rain washing. A set of three coupons
per side could then be removed and tested on
years 6, 12, 18, 24, and 36, to monitor the patina
formation and confirm the section loss (and
corrosion rate) by testing to ASTM G1-03(2011).
5.6 Detection of Fatigue Cracks
In a coated carbon steel bridge, the first
indication of a fatigue crack is often the colour
contrast between the coated surface and the
rust stain in the vicinity of the crack. Such
obvious signs will be absent in weathering
steels; indeed, observations of crack growth
in fatigue tests of weathered steel beams has
shown that fatigue cracks less than 150mm long
are very difficult to find by visual inspection. In
actual bridges, the shortest crack that can be
detected is likely to be even longer, since the
crack forms a crevice which completely fills with
rust during the service exposure.
The best course of action is to have a Welding
Inspector, qualified to Clause 7.2 of AS.NZS
1554.1, conduct a visual inspection for
cracks in potential locations, followed by a
magnetic particle inspection for confirmation
if that location contains a suspected crack.
Further detection using ultrasonic testing is
recommended on those locations, with the
removal of the rust patina for an accurate
testing, where the ultrasonic testing will
quantify the size and extent of the crack.
After the proper maintenance has been
performed, the removed protective rust patina
at the location will have to reform to regain its
corrosion resistance properties. This is purely
an aesthetic problem only, as once the layer
has reformed the weathering steel will perform
as expected.

24
6. Maintenance
6.1 General
Routine maintenance of weathering steel
bridges consists primarily in ensuring that
the bridges are performing satisfactorily, and
that they will continue to do so. It may include
routine and/or minor remedial works as listed
below; major works are described later under
rehabilitation.
Such maintenance activities are usually
undertaken based on the inspection findings, as
discussed in Section 5.
Highway bridges, by their nature and use,
accumulate debris; they become wet from
condensation, leaky joints and traffic spray, and
are exposed to salts and atmospheric pollutants.
Different combinations of these factors may
create exposure conditions under which
weathering steel may not form a protective
rust coating and, for the continued satisfactory
performance of the bridge, maintenance must
be directed to preventing or rectifying such
conditions.
6.2 Maintenance Procedures
The following examples illustrate the
maintenance procedures which may be required,
depending on the results of inspection:
– Remove loose debris with a jet of compressed
air or with vacuum cleaning equipment.
– Remove any poorly adhering layers of rust.
– Remove wet debris and aggressive agents
from the steel surfaces by high pressure
hosing. This is particularly important where
the surfaces are contaminated with salt.
– Trace leaks to their sources (on a rainy day or
by hosing the deck near expansion joints and
observing the flow of water). Repair all leaky
joints.
– Clean drains and down pipes.
– Remove vegetation from the vicinity of the
bridge.
– If necessary, install new drainage systems
to divert water from superstructure and
substructure.
– In the event of “pack-out” of crevices at
bolted joints, then the edges of the joint
should be sealed with an appropriate sealant.
6.3 Graffiti Removal
As with other forms of uncoated construction,
such as reinforced or pre-stressed concrete, the
removal of graffiti from weathering steel bridges
is difficult, so measures to discourage public
access to the girders should be considered.
However, this should be balanced with the need
to provide access for inspection, monitoring and
cleaning.
There are different methods to address the issue
related to graffiti, the following options can be
considered:
– Apply an anti-graffiti coating at problem areas
on the bridge, usually around the abutments.
However, this will prevent the patina
formation in those areas.
– Apply a citrus based cleaner to the graffiti,
with 24 hours of its application, before it is
fully cured. Then low pressure water clean at
4000 psi.
– Fully remove the graffiti and underlying
protective patina layer, with high pressure
water jetting at 10,000 psi. This option
will fully remove the patina layer as well,
resulting in a patch look until it is reformed
again.
– Use dry ice for removing graffiti, see (APT
International 2010)
– Leave the graffiti if not objectionable, as it
will eventually be absorbed into the patina as
it forms.

25
Lune West Bridge, Lancashire, England. Image courtesy of Jacobs

26
7. Rehabilitation of Weathering Steel Bridges
7.1 General
When a weathering steel bridge has corroded
to an extent that further deterioration cannot
be prevented by the simple maintenance
procedures described earlier, rehabilitation may
be required. Bridges designed, detailed and
constructed in accordance with the guidelines
given in this publication should not reach this
stage unless circumstances beyond the control
of the original design arise (for example a new
industrial complex causing severe pollution
is built close by). However, there are a few
existing weathering steel bridges, in the
Northern Hemisphere, where performance
has been less than ideal, probably because
some of the guidelines were not appreciated
at the time of design and construction. This
section is therefore also intended to assist
those responsible for the rehabilitation of such
bridges.
Rehabilitation may involve sealing of crevices,
removal of poorly formed patina, and possibly
coating of the corroded weathering steel. An
alternative which has occasionally been used is
the enclosure of the whole structure, although
this is only likely to be economically viable in
very unusual circumstances.
7.2 Sealing of crevices
Since the corrosion in crevices can be one of
the major problems related to section loss,
rehabilitation of such areas is a necessary
preliminary to other work. Crevices can be
treated as described below, depending on the
type of detail and the degree of corrosion:
– For non-critical connections, such as at bolted
restraints or bolted brackets, if practicable
disassemble the connection, prepare the
surface to a minimum of SSPC-SP10/NACE
No 2 (similar to Sa 2 ½), apply a suitable
coating, such as a non-conductive barrier
coating, and reassemble. Alternatively;
– For critical connections, such as splices at the
main girders, or other connections that cannot
be disassembled, apply a penetrating sealer
(such an low viscosity epoxy, moisture cured
urethane, or high ratio calcium sulfonate
primer) to displace any water, caulk all edges
with a moisture-cured polyurethane sealant,
then stripe and coat the connection (lapping
50mm on the surrounding steelwork) with a
compatible coating.
7.3 Use of Protective Coatings
The coating of a weathering steel bridge has the
same issues and challenges as a carbon steel
bridge. In both cases, preparing the surface for
coating is essential. The suitability of abrasive
blasting, either dry or wet, low pressure water
cleaning, or high pressure water jetting is
dependent on the environmental restraints,
accessibility and logistics for undertaking the
work.
As part of preparing the surface, the
refurbishment methodology should ensure
the removal of salt and other contaminates,
especially in deep pits. This includes choosing
the appropriate coating system, based on the
bridge condition, which should be undertaken in
accordance to AS/NZS 2312.1:2014 and (Clifton
2013).
7.4 Inspection and Maintenance
of Coated Weathering Steel
Inspection of coated weathering steel is
generally similar to that of coated carbon
steel bridge, although the exact symptoms of
breakdown may differ. It is recommended that a
NACE CIP Level 2 (or higher) coatings inspector
is employed to undertake the inspection of a
coated weathering steel bridge.

27
8. References
AS/NZS 1111:2000, ISO metric hexagon bolts
and screws – Product grade C. Standards
Australia, Sydney, Australia, 2000
AS 1627.1:2003, Metal finishing – Preparation
and pretreatment of surfaces – Removal of oil,
grease and related contamination, Standards
Australia, Sydney, Australia, 2003
AS 2700: 2011, Colour Standards for General
Purposes Standards Australia, Sydney, Australia,
2011
AS 2205.9.1:1997, Methods for destructive
testing of welds in metal – Hot cracking test,
Standards Australia, Sydney, Australia, 1997
AS 4312:2008, Atmospheric corrosivity zones in
Australia. Standards Australia, Sydney, 2008
AS/NZS 5100.6: 2017 Part 6: Steel and
Composite Bridge, Standards Australia,
Sydney, Australia, 2017
AS/NZS 1252.1: 2016 High-strength steel
fastener assemblies for structural engineering
– Bolts, nuts and washers – Part 1: Technical
requirements, Standards Australia, Sydney,
Australia, 2016
AS/NZS 1554.1:2014, Structural steel welding
– Welding of steel structures, Standards New
Zealand, Wellington, 2014
AS/NZS 2312.1:2014, Guide to the protection of
structural steel against atmospheric corrosion
by the use of protective coatings, Standards
Australia, Sydney, Australia, 2014
AS/NZS 3678:2011, Structural steel – Hot-
rolled plates, floor plates and slabs, Standards
Australia, Sydney, Australia, 2011
AS/NZS ISO 3834:2008, Quality requirements for
fusion welding of metallic materials, Standards
Australia, Sydney, Australia, 2008
ASTM G1-03(2011), Standard Practice for
Preparing, Cleaning, and Evaluating Corrosion
Test Specimens, American Society for Testing
and Materials, 2011
ASTM A325-14, Standard Specification for
Structural Bolts, Steel, Heat Treated, 120/105
ksi Minimum Tensile Strength, American Society
for Testing and Materials, 2014
ASTM A325M-14, Standard Specification for
Structural Bolts, Steel, Heat Treated, 830 MPa
Minimum Tensile Strength [Metric], American
Society for Testing and Materials, 2014
ASTM A490-10, Standard Specification for
Structural Bolts, Alloy Steel, Heat Treated, 150
ksi Minimum Tensile Strength, American Society
for Testing and Materials, 2010
Austroads, Guidelines for Bridge Management –
Structure Information, Publication No AP-R252.
Austroads, Sydney, Australia. 11 June 2004
AWS D1.1, Structural Welding Code – Steel.
American Welding Society. 2015
APT International, Using Dry Ice for Spray-
Paint Removal on Weathering Steel. APT
International, Practice Points No 8, Springfield,
Illinois. 2010
DMRB, Highway Structures: Design
(substructures and special structures) materials.
Materials and Components. Weathering Steel
for highway structures. The Design Manual for
Roads and Bridges. Vol 2 Section 3 part 8 (BD
7/-). London, UK. 1981 and Nov 2001
Bridges in Steel – The Use of Weathering Steel
in Bridges, ECCS (No.81), 2001
Technical Note on the welding of weathering
steels, Supplement to BlueScope Technical
Bulletin Number 26.
Clifton, G.C., El Sarraf, R., Mandeno, W.,
Golding, P., Sheehan, A.; Australian Steelwork
Corrosion and Coatings Guide. Australian Steel
Institute, Sydney, 2013
Construction and Technology; Pack Rust on
A-588 Weathering Steel Bridges Causes Safety
Concerns, Issue 94, April 2002
AS/NZS 5131:2016 Structural steelwork –
Fabrication and erection, Standards Australia,
Sydney, Australia, 2016
El Sarraf, R., Iles, D., Momtahan, A., Easey,
D., Hicks, S., Steel-Concrete Composite Bridge
Design Guide, NZ Transport Agency, Research
Report 525. September 2013
El Sarraf, R. and Mandeno, W.L.; Design for
durable structural steelwork in New Zealand,
The Structural Engineer Magazine, The Institute
of Structural Engineers. Issue 88(19), October 2010
Kimura, M. and Kihira, H., Nanoscopic
Mechanism of Protective Rust Formation
on Weathering Steel Surface, Nippon Steel
Technical Report No. 91, January 2005
Morcillo, M., Chico, B., Dias, I., Cano, H., de
la Fuente, D., Atmospheric Corrosion Data of
Weathering Steels. A Review. Spanish National
Research Council. Madrid, Spain. 2013
ISO 9223:2012, Corrosion of metals and alloys
– Corrosivity of atmospheres – Classification,
International Organization for Standardization,
2012
ISO 9226:2012, Corrosion of metals and alloys
– Corrosivity of atmospheres – Determination
of corrosion rate of standard specimens for
the evaluation of corrosivity, International
Organization for Standardization, 2012
SCI, Guidance Notes on Best Practice in Steel
Bridge Construction, SCI-P-185, The Steel
Bridge Group, The Steel Construction Institute,
November 2015 (GN1.07, Use of weather
resistant steel)
SSPC Painting Manual: Systems and
Specifications, SSPC: The Society for Protective
Coatings, Volume 2, 2008.
Texas Department of Transportation research
report 0-1818, ‘Performance of Weathering
Steel in TxDOT Bridges’, 2nd June 2000,
by B McDad et al.

28
Appendix A:
Determination of Site-Specific Atmospheric Corrosivity Category
The guidance given in Section 3.2 of the
Australian Steelwork Corrosion and Coatings
Guide (ASCCG) (Clifton et al 2013) should
be used when determining the atmospheric
corrosivity category of the nominated site, by
determining the first year corrosion rate of mild
steel taking into account both the macro- and
microclimate. The main governing factor in this
case, is the corrosivity category of unwashed
surfaces.
The following examples outline the steps
required to determine the atmospheric
corrosivity category.
Example A.1: Bridge located at
Parramatta, NSW.
A bridge is to be built in Parramatta, within
10km from Sydney Harbour, and the prevailing
wind is a North Westerly, i.e. blowing from the
site toward sea.
Step 1: Determine the Macroclimate
Atmospheric Corrosivity Category:
The site macroclimate atmospheric corrosivity
category is taken as 25µm/annum, from Figure
A4 of AS 4312.
Step 2: Determine the Microclimate effects:
– For shaded area, + 5µm/annum (Section
3.2.3.1 of ASCCG) = 30 µm/annum.
– For unwashed surfaces, take the unwashed
factor as, Cuw = x1.2 (Section 3.2.3.2(d) of
ASCCG) = 36 µm/annum.
The microclimate atmospheric corrosivity
category for this site is taken as 36 µm/annum,
which is equivalent to C3 (Medium).
Hence weathering steel can be used in this site,
with the corrosion allowance taken as 1.5 mm,
as discussed in Section 3.3.
Example A.2: Bridge located at
Whyalla, SA.
A bridge is to be built in Whyalla, within 1 km
from the Spencer Gulf, and the prevailing wind
is a South Easterly, i.e. blowing from the sea
toward the site; but the site is sheltered by the
surrounding buildings.
Step 1: Determine the Macroclimate
Atmospheric Corrosivity Category:
The site macroclimate atmospheric corrosivity
category is taken as 15µm/annum (rounded up),
as given in Table A1 of AS 4312.
Step 2: Determine the Microclimate effects:
– For shaded area, + 5µm/annum (Section
3.2.3.1 of ASCCG) = 20 µm/annum.
– For unwashed surfaces, take the unwashed
factor as, Cuw = x2.0 (Section 3.2.3.2(b) of
ASCCG) = 40 µm/annum.
The microclimate atmospheric corrosivity
category for this site is taken as 40 µm/annum,
which is equivalent to C3 (Medium).
Hence weathering steel can be used in this site,
with the corrosion allowance taken as 1.5 mm,
as discussed in Section 3.3.
Example A.3: Bridge located at
Yorke Peninsula South, SA.
A bridge is to be built in Yorke Peninsula South,
within 3 km from the Spencer Gulf, and the
prevailing wind is a South Westerly, i.e. blowing
from the sea toward the site.
Step 1: Determine the Macroclimate
Atmospheric Corrosivity Category:
The site macroclimate atmospheric corrosivity
category is taken as 35µm/annum (rounded up),
as given in Table A1 of AS 4312.
Step 2: Determine the Microclimate effects:
– For shaded area, + 5µm/annum (Section
3.2.3.1 of ASCCG) = 40 µm/annum.
– For unwashed surfaces, take the unwashed
factor as, Cuw = x2.2 (Section 3.2.3.2(b) of
ASCCG) = 88 µm/annum.
The microclimate atmospheric corrosivity
category for this site is taken as 88 µm/annum,
which is equivalent to C4(High).
Hence weathering steel cannot be used in this
site.
Example A.4: Bridge located at
Learmonth, WA.
A bridge is to be built in Learmonth, within 3 km
from the Exmouth Gulf, and the prevailing wind
is a South-south Westerly, i.e. blowing from the
site toward the sea.
Step 1: Determine the Macroclimate
Atmospheric Corrosivity Category:
The site macroclimate atmospheric corrosivity
category is taken as 10 µm/annum (rounded up),
as given in Table A1 of AS 4312.
Step 2: Determine the Microclimate effects:
– For shaded area, + 5µm/annum (Section
3.2.3.1 of ASCCG) = 15 µm/annum.
– For unwashed surfaces, take the unwashed
factor as, Cuw = x1.2 (Section 3.2.3.2(a.ii) of
ASCCG) = 18 µm/annum.
The microclimate atmospheric corrosivity
category for this site is taken as 18 µm/annum,
which is equivalent to C2 (Low).
Hence weathering steel can be used in this site,
with the corrosion allowance taken as 1.0 mm,
as discussed in Section 3.3.

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