Corrosion Studies on Stainless Steel 316 and their Prevention – A Review

Abstract

Corrosion is a process that causes a change of metal to chemically stabled form, by reacting with a solution or with the atmospheric air. There are various types of corrosions such as crevice corrosion, intergranular corrosion, stress corrosion, pitting corrosion, galvanic corrosion and uniform corrosion. These types of corrosion and the prevention methods are investigated in this review paper. Stainless steel 316 has excellence in corrosion resistance, due to the presence of molybdenum content. From the literature survey, stainless steel 316 has been tested in various experiments to improve the properties of the material. In the present review, several coating processes and additives which are added on SS 316 to improve the material properties are studied. The advantages of these improvements are reduced cost of change of material, reduced loss of material due to corrosion and increase in materials durability. Hence, stainless steel 316 is used for all corrosion applications which causes less damage and high durability compared with other austenitic steels.

Full text

INCAS BULLETIN, Volume 13, Issue 3/ 2021, pp. 245 – 251 (P) ISSN 2066-8201, (E) ISSN 2247-4528
Corrosion Studies on Stainless Steel 316
and their Prevention – A Review
S. THIRUMALAI KUMARAN*,1, K. BARANIDHARAN2,
M. UTHAYAKUMAR1, P. PARAMESWARAN3
*Corresponding author
1Faculty of Mechanical Engineering,
Kalasalingam Academy of Research and Education,
Krishnankoil–626126, Tamil Nadu, India,
thirumalaikumaran@yahoo.com*
2Department of Automobile Engineering,
Kalasalingam Academy of Research and Education,
Krishnankoil–626126, Tamil Nadu, India
3Former Scientist-H, Metallurgy and Materials Group,
Indira Gandhi Centre for Atomic Research,
Kalpakkam–603102, Tamil Nadu, India
DOI: 10.13111/2066-8201.2021.13.3.21
Received: 01 December 2020/ Accepted: 21 July 2021/ Published: September 2021
Copyright © 2021. Published by INCAS. This is an “open access” article under the CC BY-NC-ND
license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Abstract: Corrosion is a process that causes a change of metal to chemically stabled form, by reacting
with a solution or with the atmospheric air. There are various types of corrosions such as crevice
corrosion, intergranular corrosion, stress corrosion, pitting corrosion, galvanic corrosion and uniform
corrosion. These types of corrosion and the prevention methods are investigated in this review paper.
Stainless steel 316 has excellence in corrosion resistance, due to the presence of molybdenum content.
From the literature survey, stainless steel 316 has been tested in various experiments to improve the
properties of the material. In the present review, several coating processes and additives which are
added on SS 316 to improve the material properties are studied. The advantages of these
improvements are reduced cost of change of material, reduced loss of material due to corrosion
and increase in materials durability. Hence, stainless steel 316 is used for all corrosion applications
which causes less damage and high durability compared with other austenitic steels.
Key Words: electrochemical corrosion, stainless steel 316, corrosion resistance
1. INTRODUCTION
Corrosion is noticed in some material which is covered with orange or reddish-brown colored
layer. It is a process in which the refined metal is converted to more stable compound such as
metal sulfides, metal oxide or metal hydroxides.
The iron involves in rusting due to the formation of oxides through atmospheric moisture and
oxygen. This kind of rusted materials becomes brittle, and flaky. Corrosion is also described
as an electrochemical process which involves chemical reactions between the metal and certain
atmospheric agents such as moisture and oxygen. The factors that affect corrosion are:

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 Experience of the metal to a gas containing like CO2, SO2, etc,
 Experience of the metal to moisture on saltwater,
 Existence of acid in the atmosphere which increases the process of corrosion,
 Increasing the corrosion rate by increasing the temperature.
 Presence of impurities (NaCl)
There are some types of corrosion which cause serious damage to the material like crevice
corrosion, intergranular corrosion, stress corrosion, pitting corrosion, galvanic corrosion and
uniform corrosion.
The crevice corrosion is the dissimilarity in ionic concentration between two local areas
of any metal which leads to corrosion. It occurs in gaskets, bolt heads, and under the surface
of washers etc. Most of the aluminum alloys and stainless steel undergoes crevice corrosion.
Stress corrosion is a metal cracking phenomenon which is the result of the corrosion
environment. It often occurs due to high temperature. A good example is the austenite stainless
steel in chloride solution in which stress corrosion cracking occurs. The impurities present in
grain boundaries separate the grain during solidification on metal which occurs in the
intergranular corrosion. It also occurs in the enrichment of alloy at boundary conditions, for
example, in case of all aluminum - based alloys which can be affected by intergranular
corrosion.
Galvanic corrosion occurs when there is an electric contact between two materials in an
electrolytic environment. The process of degrading occurs in a salt water environment or
copper in contact with steel. The Pitting corrosion occurs in the formation of corrosion cell by
the metal surface. It is unpredictable to detect. Once this ‘pit’ is formed, it grows continuously
with various shapes. The uniform corrosion is the common form of corrosion, which is formed
in the surface of the metal when interacting with the atmosphere. It causes a low impact on the
materials and it spreads over the whole material uniformly [1].
2. EXPERIMENTAL STUDIES
Stainless steel 316 weld metal with 0.07% nitrogen was subjected to manual metal arc (MMA)
welding process.
The pitting corrosion was evaluated in both welding and aging conditions. The evaluation
on microstructural studies in aged conditions was performed at 1023 and 1123 K for 0.5, 1,
10, 100h.
In these studies, electrochemical potentio-kinetic has no reaction peak due to the absence
of Cr depleted zone. Hence the pitting corrosion resists the sigma, carbide and Cr2N phases in
the weld metal which was aged for 100 h at 1123K [2].
In stainless steel 316, microstructure and corrosion performance were analyzed by laser
melting deposition (LMD). During LMD, the ring-shaped beam produces small residual stress
that avoids sintering, the heat accumulation, and improves the surface coating quality. The
performance of electrochemical corrosion of stainless steel 316 coatings with various
processing parameters was studied. The result showed that the stainless steel 316 has enhanced
corrosion resistance performance which was 30% overlap ratio comparing with stainless steel
304 substrate [3].
The intergranular cracks and grain boundary network on stainless steel 316 have been
experimented in stress corrosion cracking.
The large grain-clusters play a vital role in grain boundary engineering improvement [4].
Thioacetate hexadecyltrimethoxysilane was deposited on SiO2 coated with SS316 to form a
thioacetate-functionalized monolayer.

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TiO2 solution was covered on the surface of stainless steel 316 with a metal layer of 5-10
nm. Thus, the cyclic voltammetry and potentiostatic current demonstrated the efficiency of
corrosion protection which acts against the pitting corrosion [5].
On laser surface melted stainless steel 316, the localized corrosion studies were
performed. The stainless steel 316 which is solution annealed is cold worked (5, 10, 15 and
20%) and sensitized (923K, 20 h). Using scanning electron microscopy, X-ray diffraction and
optical microscopy, the characterization was performed on the melted layers of stainless steel
316. For the pitting corrosion studies, the solution annealed specimens were carried out by the
potentiodynamic polarization method on the melted region. The result explains that the laser
surface melted can be used as an in-situ method to enhance the durability by modifying the
surface microstructure and also enhancing localized corrosion resistance [6].
Electrochemical Noise technique is used to investigate the pitting corrosion behaviour of
the stainless steel 316. Electrochemical corrosion behaviour of SS316 in a deaerated solution
of sodium chloride and sulfate was analyzed. The result showed the enhanced pitting corrosion
resistance on the stainless steel 316 by using the electrochemical noise technique [7]. Stress
corrosion cracking growth on SS316 in solution-annealed and sensitized (at 923K for 20 h)
conditions was studied. The test was conducted in an environment of boiling 5 M NaCl + 0.15
M Na2SO4 + 2.5 ml/ HCl using the fracture mechanism approach. By stress parameters, the
crack growth rates were calculated. The high plateau crack growth rates were found on
sensitized stainless steel (solution – annealed material) [8].
The investigation of the corrosion behaviour on stainless steel 316 with Ni-Cr-Mo laser
coating and X70 steel with H2S and CO2 solutions was performed. This application was
concentrated on oil industries on coating applications, its surface morphology and corrosion
behaviour on CO2, H2S separate solutions as well as mixed gas were studied and compared
with stainless steel 316 and X70 steel. The results show that 316 SS and X70 displays
inclusions on the surface before corrosion, while Ni-Cr-Mo coating exhibits higher corrosion
resistance. From each simulated solution, this coating enhances corrosion resistance as
compared to pure SS316 and X70 steel. It also has an elevated polarization resistance as
compared to 316 SS and X70 steel [9].
The erosion in the corrosive environment has been identified in chemical and hydrocarbon
extraction industries which accelerate the material loss and the surface wear. The surface
morphology of SS316 (both erosion and erosion-corrosion environment) was analyzed using
focused ion beam and transmission electron microscopy techniques. In 1% uncrushed silica
and 7 m/s velocity, the samples were placed for 60 min and tested. The result is reducing in
work hardening behaviour and high erosion-corrosion rates were identified [10].
In material development, with high temperature fluoride salt cooled reactor, the corrosion
tests of SS316 were performed in primary coolant, molten Li2BeF4 at 700˚C for 3000h long
duration. This test was performed in both graphite capsules and stainless steel 316. From the
corrosion test, the corrosion attack depth in Li2BeF4 salt was predicted as 17.1 µm/year and
31.2 µm/year for stainless steel 316, respectively [11]. Table 1 shows the outcomes of the
experimental studies investigated by various researchers.
3. PREVENTION
To avoid the huge losses of the material, the prevention of corrosion is necessary. This involves
many applications in areas such as in automobiles, machinery, household goods, railway lines,
bridges etc. The metal is coated with a thin layer on the electrochemical process of another
metal using electrolysis. Copper or nickel is selected as anode, and cathode act as sacrificial

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metal which corrodes other metal instead of base metal. By this method, the electrons ejected
and get oxidized.
Thus, ions formed in the corrosion process by saving the base material. Painting and
greasing provide a layer on the material to prevent the exposure of material corrosion with the
external environment.
By choosing a material to increase the corrosion resistance, the presence of molybdenum
element should be high on the material.
This presence of molybdenum content decreases the corrosion rate comparing other alloys
or materials. By using corrosion inhibitors, the chemicals are added to the corrosion
environment which can cut down the rate of corrosion [12].
Table 1 – Corrosion behavior study on stainless steel 316
Author
Experiments
Outcomes
Data/Solution
Loto et. al.,
[13]
In the polarization test,
sulphuric acid and
phosphoric acid with
stainless steel are done.
A similar test with NaCl
(2% addition, 20g/l) is
performed in specified
acid concentration
Besides, 2% NaCl test
concentration has
increased in active
corrosion reaction. This
shows the enhance in the
corrosion resistance on SS
316
In H
2
SO
4
, medium
concentration (9.1
M; 48.5%), high
concentration (18.2
M; 97%), and
absolute passivity.
(18.2 M). It is same
in H3PO4 (7.4 M;
42.5% and 14.8 M;
85%)
Li et al.,
[14]
In SS 316, PEMFE with
dilute HCl and 80˚C
hydrogen gas is
investigated. Both
polarization curve and
EIS measurements are
done.
The corrosion behaviour
of SS316 in both dilute
HCl and SO42- are similar
and shows an inhibitive
effect. Thus coating is
necessary for enhancing
the corrosion resistance
In 0.01 M HCl
solution and
In 0.01 M HCl +
0.01 M Na2SO4
solution
Loto et. al.,
[15]
Electrochemical noise
generation technique,
testing on acidic
chloride environment
The corrosion behaviors
are related to
pitting/general corrosion
mechanism through SEM
Investigated in
3.5% NaCl solution
Yi et. al.,
[16]
Potentiometric
polarization behaviour
was investigated based
on the scan rate effect
SS316 with NaCl
solutions result showed
that the scan rate is highly
influential on critical
pitting potential. The
parameters in pitting
resistance on the material
were determined.
Polarization curves
are measured in
3.5% NaCl solution
at scan rates from
0.01 to 50 mV/s
Anwar Ul-
Hamid et.
al., [17]
Experiments were
exposed to seawater and
splash conditions were
done to find the
corrosion properties
The material was
analyzed for 15-months.
SS316 had excellent
corrosion resistance when
compared to SS 304
At splash zone
condition – SS316
has 0.86 µm/y and
stainless steel 304
has 1.13 µm/y

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Several factors cause stainless steel 316 to corrode and the following methods describe
the causes and prevention. The presence of sodium chloride (NaCl) can cause pitting corrosion.
The pitting corrosion is exposed to environments that have the presence of enormous salt
(Chloride). If stainless steel 316 is used for marine applications, it may cause pitting due to
direct contact with seawater (sea-enriched).
To avoid pitting corrosion, the specialized coating can be applied to stainless steel 316
(by avoiding direct contact with chlorides). Galvanic corrosion is formed when welding
dissimilar stainless-steel.
The less noble metal which accepts new electrons quickly will become an anode and start
to corrode (corrosion takes place rapidly). The best method to prevent bimetallic corrosion is
to avoid joining two dissimilar metals permanently. Coating the metal shall prevent the flow
of electrons from the cathode to the anode.
Transplanting of plain iron or steel onto stainless steel in some applications causes
corrosion. For example, an iron piece is transferred onto the surface of a stainless-steel part or
basket. These particles can disrupt the protective oxide layer of the stainless-steel workpiece
and rust forms.
To prevent the transplanting of plain steel or iron to stainless steel workpieces, it’s
necessary to thoroughly clean and prepare equipment when changing over to new material
[18]. The effect of low-temperature oxy-nitriding (LTON) treatment, the liquid lead-bismuth
eutectic (LBE) corrosion behaviours on stainless-steel 316 were studied under the vacuum at
823K in the stagnant liquid LBE.
The result shows that the untreated samples were severely selective leaching in liquid
LBE contact. LTON treatment produced an outer porous Fe-Cr spinel film and inner S phase
layer on the surface of the sample, which transformed into a thicker spinel film containing γ
low-N and region distribution with CrN precipitate after liquid LBE corrosion.
The main attribute is the oxidation and decomposition of the S phase in a metastable phase
and easier to be oxidized than matrix in high temperatures. It showed an improvement in the
ability to form protective oxide film for materials [19].
The investigation on the decrease in pitting corrosion resistance of extra-high purity type
stainless steel 316 with Cu 2+ in NaCl was performed.
The effect of Cu 2+ in bulk solution on pitting corrosion resistance of extra-high purity
type stainless steel 316 was done. Pitting occurred in 0.1 M NaCl-1 mM CuCl2, whereas pitting
was not initiated in 0.1 M NaCl.
The deposition of Cu 2+ on the surface occurred regardless of a potential region in 0.1 M
NaCl-1 mM CuCl2, Cu 2+ in bulk solution which did not influence passive film formation.
The decrease in pitting corrosion resistance in 0.1 M NaCl-1 mM CuCl2 resulted in Cu
compound deposited and supply of Cu 2+ on the surface [20].
Additively manufactured stainless steel receives widespread attention due to its excellent
mechanical properties, corrosion mechanism in Cl--. Researchers reported the pitting and
passivation behaviour of additively manufactured stainless steel 316 in 3.5 wt.% NaCl
solution.
The result shows that stainless steel 316 exhibits a fine sub-grain structure of 5 µm in
diameter and dislocations and Mo elements enriched at the sub-grain boundary. Compared
with the wrought 316L stainless steel, huge sub-grain boundaries and high dislocation density
promote the formation of the more compact and thicker passive film. The low hydroxide
content in the passive film and the micro-galvanic corrosion effect between Mo-rich sub-grain
boundaries and sub-grains reduce the self-repairing ability of passive film. Hence, the pitting
corrosion resistance of stainless steel 316 is higher [21].

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4. FUTURE SCOPE
The stainless steel 316 is an excellent material to reduce the corrosion rate and it is widely
used in all corrosion applications. To increase the durability of the material, the method of
additive or coating with selective materials can be further applied to increase the corrosion
resistance with experimental tests.
5. CONCLUSIONS
In this paper experimental studies were performed on 316 stainless steel and several
classifications of corrosion studies as well as corrosion prevention were investigated. The
prevention of these types of corrosion can be achieved through electroplating, cathode
protection, galvanization, painting and greasing, choosing the perfect material which has high
corrosion resistance and using corrosion inhibitor. Hence, stainless steel 316 has excellent
corrosion resistance, high durability, mechanical strength compared with other austenitic
stainless steel. The properties are further improved by adding additives and performing coating
process on the stainless steel 316.
ACKNOWLEDGEMENT
The authors thank UGC-DAE CSR for their financial support to carry out this work (CSR-
KN/CRS-115/2018-19/1053).
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