Corrosion Resistance of 13Cr Steels

Abstract

Super 13Cr steels, which combine high strength and excellent corrosion resistance, are the optimal choice for developing and exploiting complex oil and gas wells, particularly in high-CO2 environments. In this study, we conducted a corrosion assessment of several high-strength steels of the 13Cr type with different alloying systems. We identified the primary parameters responsible for the corrosion resistance of these steels based on our research findings and suggested ways to optimize their chemical composition and select the most economically viable option. We demonstrate the importance of selecting the appropriate alloying system and the impact of non-metallic inclusions (NMIs) on the corrosion properties of the high strength 13Cr material.

Full text

Citation: Davydov, A.; Alekseeva, E.;
Kolnyshenko, V.; Strekalovskaya, D.;
Shvetsov, O.; Devyaterikova, N.;
Laev, K.; Alkhimenko, A. Corrosion
Resistance of 13Cr Steels. Metals 2023,
13, 1805. https://doi.org/10.3390/
met13111805
Academic Editor: Belén Díaz
Fernández
Received: 28 September 2023
Revised: 13 October 2023
Accepted: 20 October 2023
Published: 26 October 2023
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
metals
Article
Corrosion Resistance of 13Cr Steels
Artem Davydov 1, * , Ekaterina Alekseeva 1, Vladislav Kolnyshenko 1, Darya Strekalovskaya 1, Oleg Shvetsov 1,
Natalia Devyaterikova 2, Konstantin Laev 2and Aleksey Alkhimenko 1
1
Scientific and Technological Complex “New Technologies and Materials”, Institute of Advanced Engineering
Technologies, Peter the Great St. Petersburg Polytechnic University, 195251 St. Petersburg, Russia;
alekseeva_el@spbstu.ru (E.A.); kolnysh_vv@spbstu.ru (V.K.); strekal_da@spbstu.ru (D.S.);
shvetsov_ov@spbstu.ru (O.S.); a.alkhimenko@spbstu.ru (A.A.)
2TMK Pipeline Solutions LLC (TMK), 40/2a Pokrovka Street, 101000 Moscow, Russia;
n.devyaterikova@tmk-group.com (N.D.); konstantin.laev@tmk-group.com (K.L.)
*Correspondence: davydov_ad@spbstu.ru
Abstract:
Super 13Cr steels, which combine high strength and excellent corrosion resistance, are the
optimal choice for developing and exploiting complex oil and gas wells, particularly in high-CO
2
environments. In this study, we conducted a corrosion assessment of several high-strength steels
of the 13Cr type with different alloying systems. We identified the primary parameters responsible
for the corrosion resistance of these steels based on our research findings and suggested ways to
optimize their chemical composition and select the most economically viable option. We demonstrate
the importance of selecting the appropriate alloying system and the impact of non-metallic inclusions
(NMIs) on the corrosion properties of the high strength 13Cr material.
Keywords:
corrosion; super 13Cr; stress corrosion cracking; non-metallic inclusions; autoclaves;
electrolytic etching
1. Introduction
In most cases, pipe failures in the oil and gas industry occur due to internal corro-
sion [
1
]. With traditional oil and gas reserves depleting, the production of hard-to-recover
oil is increasing, leading to the utilization of new methods [
2
–
7
]. This development leads to
the exploitation of materials in extreme conditions [
8
–
12
], resulting in premature equipment
failure [
13
–
18
] when operating in aggressive environments containing chlorine ions (Cl
−
),
carbon dioxide (CO
2
), and hydrogen sulfide (H
2
S). Sulfide stress corrosion cracking (SSC),
which is typical for materials in a hydrogen sulfide-containing environment, causes metal
cracking under the action of corrosion and tensile stresses in the presence of moisture and
hydrogen sulfide [9,18–21].
Economic challenges have led to a new impulse for the development of new materials
for tubing which possess high mechanical characteristics and increased resistance to sulfide
stress corrosion cracking and general and local corrosion in CO
2
-saturated environments.
Consequently, the current state of development of the oil and gas complex demands
that consumers require high-quality and reliable tubular products [
22
] with constantly
increasing requirements [23].
In challenging downhole environments characterized by high temperature, high
pressure, and CO
2
saturation, along with the possibility of low H
2
S concentrations, 13Cr
corrosion-resistant steels (API 5CT) are commonly used as tubing and casing materials. In
such aggressive conditions, the use of low-alloy steels is not recommended as hydrogen
from H
2
S diffuses into the metal and significantly reduces the fracture resistance of carbon
steels [
24
]. Additionally, the resistance of steels to sulfide stress corrosion cracking is
dependent on the environmental pH. For example, at pH < 3.0, crack initiation can occur at
a chloride concentration of 600 ppm [
25
,
26
]. Therefore, careful selection of materials and
operating conditions is crucial for ensuring the reliability and safety of oil and gas wells.
Metals 2023,13, 1805. https://doi.org/10.3390/met13111805 https://www.mdpi.com/journal/metals

Metals 2023,13, 1805 2 of 14
In the pipe industry, martensitic corrosion-resistant steels are commonly used for
aggressive downhole conditions saturated with CO
2
and H
2
S at high pressure and high
temperature. Currently, two subclasses of martensitic corrosion-resistant steels are utilized
in the pipe industry. The well-known steels AISI 410S and AISI 420 have a simple alloying
system and low cost but are limited in strength (L80, R95), corrosion resistance, and impact
strength, especially at low temperatures. On the other hand, low carbon supermartensitic
steels contain several expensive alloying elements that provide high cost, increased tensile
strength (R95, P110, Q135), high impact strength, and corrosion resistance. However,
these materials are not economical solutions for end users. Alternatively, highly resistant
alloyed steel grades, such as duplex (22Cr-5Ni-3Mo) or super duplex (25Cr-7Ni-3Mo),
are considered, but they are even more expensive and could be implemented for specific
applications [27].
The properties of supermartensitic 13Cr steels are greatly improved compared to tradi-
tional martensitic-ferritic stainless steel (such as AISI 410S) due to the presence of residual
austenite in the matrix structure of low-carbon martensite without
δ
-ferrite. These steels typ-
ically contain 12–14% Cr, 4–6% Ni, 0.5–2% Mo, and less than 0.03% carbon, with additional
elements, such as titanium, vanadium, and niobium, to prevent softening during tempering
and improve impact strength, especially at low
temperatures [1,2,8,13,14,19,28]
. Tungsten
and copper are also added for further enhancement of the mechanical properties [3,4,9].
The properties of 13Cr steels are significantly influenced by the carbon content. With
a decrease in the carbon content, the ductility of the steel increases, the impact resistance
increases, and the machinability improves, while the hardness and strength decrease.
Additional alloying of steels of the supermartensitic 13Cr type with strong carbide-forming
elements in an amount of up to 0.05% contributes to a significant increase in strength
properties due to secondary hardening without a negative effect on the ductile and corrosion
properties [29–31].
The carbon content significantly affects the ductility, impact resistance, machinability,
hardness, and strength of steel [
32
]. Steels with a low carbon concentration, known as
supermartensitic 13Cr, exhibit better properties but are expensive to produce and not
suitable for tubing applications. The studied steels have a transitional composition between
conventional 13Cr and supermartensitic 13Cr, and this work aims to determine the optimal
chemical composition of 13Cr steels for corrosion resistance and mechanical properties.
The study evaluates the corrosion resistance of martensitic 13Cr P110 tubing after
operation. For studying steel options that exhibit satisfactory properties, several new
grades of martensitic 13Cr stainless steel types were developed (13Cr-4Ni-1Mo (P110),
13Cr-3Ni-1Mo (P110), 13Cr-5Ni-2Mo (P110), and 13Cr-5Ni-2Mo (Q135)) and manufactured
without the vacuum oxygen degasser (VD/VOD) processes, with [C] = 0.06–0.09%. The
entire life cycle, from melting to the final pipe, was simulated during the laboratory sample
production process. Corrosion properties of the samples during laboratory testing were
assessed under simulated operational conditions. The objectives are to evaluate corrosion
properties, electrochemical performance, resistance to sulfide cracking, and non-metallic
inclusions and their effect on corrosion resistance.
2. Materials and Methods
At the beginning, studies were conducted on samples of a production tubing made of
13Cr-2Ni steel with a strength group of P110 (Table 1) after operation. Numerous pittings
were observed on the tubing after operation (Figure 1). The tubing was used in an oil well.
The operating conditions involved a combination of approximately 1% H
2
S, 1.5% CO
2
, and
a total mineralization of produced water at 50,000 mg/L.
Table 1. The mechanical properties.
Type of Steel HRC YS, MPa TS, MPa δ5, %
13Cr-2Ni 29 804.8 917.1 17

Metals 2023,13, 1805 3 of 14
Metals 2023, 13, x FOR PEER REVIEW 3 of 14
Table 1. The mechanical properties.
Type of Steel HRC YS, MPa TS, MPa δ5, %
13Cr-2Ni 29 804.8 917.1 17
(a) (b)
Figure 1. Surface of the tubing after operation: (a) local corrosion, ×50; (b) local corrosion, ×25.
For comparison, experimental closest analogues with additional Ni and Mo-alloyed
13Cr stainless steels were chosen. The properties of the investigated steels are presented
in Table 2. For a preliminary assessment of the corrosion resistance, we calculated the pit-
ting resistance equivalent number (PREN). Numbers, shown in Table 3, based on the ac-
tual chemical composition, according to the formula PREN = % Cr + 3.3 (% Mo + % 0.5 W)
+ % 16 N, where % is the mass fraction of the element, expressed as a percentage.
Table 2. The mechanical properties of the investigated steels.
Type of Steel PREN HRC YS, MPa TS, MPa δ5, %
13Cr-4Ni-1Mo (P110) 18.5 28 840 912 21.5
13Cr-5Ni-2Mo (P110) 21.4 33 905 965 22
13Cr-5Ni-2Mo (Q135) 19.9 33 980 1035 21
13Cr-3Ni-1Mo (P110) 16.3 27 780 870 24
The specimens were etched by Vilellas etchant, which contained 5 mL hydrochloric
+ 4 g picric acid + 100 mL ethyl alcohol. The microstructure was assessed using optical
microscopy at ×500 magnifications on a Reichert-Jung MeF3A5 (Reichert Inc., Depew, NY,
USA) microscope. Microstructures of the samples were evaluated at different distances
from the external wall of the tubing. For metallographic analysis of corrosion products,
longitudinal specimens were obtained from the piing depicted in Figure 1a. The extrac-
tion was carried out using an erosion machine with a corrosion-neutral cuing fluid to
minimize the deleterious effects of corrosion products. Studies of corrosion products on
the surface of the tubing were conducted using electron microscopy on a TESCAN VEGA
scanning electron microscope (SEM, TESCAN, Brno, Czech Republic) equipped with an
INCA X-Max-50 energy dispersive X-ray spectrometer (EDS, Oxford Instruments, Oxford,
UK).
Electrochemical studies were carried out using a Versa Princeton Applied Research
potentiostat (AMETEK Inc., Berwyn, PA, USA) equipped with specialized software
(AMETEK Inc., Berwyn, PA, USA) on three-electrode cells according to ASTM G3, G59,
and G102. A 3% NaCl solution was used as the working electrolyte under conditions of
natural electrolyte deaeration and at room temperature (~23 °C) with a pH of 3, 6.5, and
11. When the cell was saturated with CO2 or H2S, the solution was deaerated. Based on the
results of these tests, the most aggressive environment was chosen for subsequent critical-
condition tests. Thus, evaluation of the electrochemical characteristics presented in Table
2 was carried out in a 3% NaCl solution saturated with CO2 with a pH value of 2.8–3.0 at
a temperature of 60 °C on samples in the form of plates. The analyzed surface area of all
Figure 1. Surface of the tubing after operation: (a) local corrosion, ×50; (b) local corrosion, ×25.
For comparison, experimental closest analogues with additional Ni and Mo-alloyed
13Cr stainless steels were chosen. The properties of the investigated steels are presented in
Table 2. For a preliminary assessment of the corrosion resistance, we calculated the pitting
resistance equivalent number (PREN). Numbers, shown in Table 3, based on the actual
chemical composition, according to the formula PREN = % Cr + 3.3 (% Mo + % 0.5 W) + %
16 N, where % is the mass fraction of the element, expressed as a percentage.
Table 2. The mechanical properties of the investigated steels.
Type of Steel PREN HRC YS, MPa TS, MPa δ5, %
13Cr-4Ni-1Mo (P110) 18.5 28 840 912 21.5
13Cr-5Ni-2Mo (P110) 21.4 33 905 965 22
13Cr-5Ni-2Mo (Q135) 19.9 33 980 1035 21
13Cr-3Ni-1Mo (P110) 16.3 27 780 870 24
Table 3. Results of chemical analysis of corrosion products from the EDS data.
Spectrum O Si S Cl Ca Cr Mn Fe Ni
1 38.41 0.96 0.31 4.31 0.43 35.76 17.18 2.64
2 38.29 0.82 0.61 6.12 0.29 39.06 12.57 1.99
3 44.01 1.08 0.93 5.04 36.92 11.24 0.78
4 37.48 0.93 1.06 4.54 37.01 17.41 1.57
5 0.54 13.53 0.64 83.04 2.26
6 1.50 0.47 13.37 0.61 81.34 2.71
The specimens were etched by Vilella’s etchant, which contained 5 mL hydrochloric
+ 4 g picric acid + 100 mL ethyl alcohol. The microstructure was assessed using optical
microscopy at
×
500 magnifications on a Reichert-Jung MeF3A5 (Reichert Inc., Depew, NY,
USA) microscope. Microstructures of the samples were evaluated at different distances
from the external wall of the tubing. For metallographic analysis of corrosion products,
longitudinal specimens were obtained from the pitting depicted in Figure 1a. The extraction
was carried out using an erosion machine with a corrosion-neutral cutting fluid to minimize
the deleterious effects of corrosion products. Studies of corrosion products on the surface
of the tubing were conducted using electron microscopy on a TESCAN VEGA scanning
electron microscope (SEM, TESCAN, Brno, Czech Republic) equipped with an INCA
X-Max-50 energy dispersive X-ray spectrometer (EDS, Oxford Instruments, Oxford, UK).
Electrochemical studies were carried out using a Versa Princeton Applied Research po-
tentiostat (AMETEK Inc., Berwyn, PA, USA) equipped with specialized software (AMETEK
Inc., Berwyn, PA, USA) on three-electrode cells according to ASTM G3, G59, and G102. A 3%
NaCl solution was used as the working electrolyte under conditions of natural electrolyte
deaeration and at room temperature (~23
◦
C) with a pH of 3, 6.5, and 11. When the cell
was saturated with CO
2
or H
2
S, the solution was deaerated. Based on the results of these

Metals 2023,13, 1805 4 of 14
tests, the most aggressive environment was chosen for subsequent critical-condition tests.
Thus, evaluation of the electrochemical characteristics presented in Table 2was carried out
in a 3% NaCl solution saturated with CO
2
with a pH value of 2.8–3.0 at a temperature of
60
◦
C on samples in the form of plates. The analyzed surface area of all samples was 1 cm
2
.
Surface preparation was carried out by grinding and polishing. The research procedure
consisted of immersing the sample in the test environment, measuring the equilibrium
corrosion potential (Eq) for 55 min (3300 s), and carrying out subsequent linear polarization
in the potential range from
−
250 to 250 mV with a sweep rate of 0.16 mV/s to obtain a
polarization curve. The corrosion current density was determined graphically to determine
the corrosion rate using the Tafel equation.
The operating conditions were simulated using an autoclave; 50 by 30 by 5 mm plate
samples were immersed in a solution of 5% NaCl and 0.5% acetic acid with a solution pH
of 3–4. The vessel was sealed, deaerated with nitrogen, saturated with carbon dioxide up to
a total pressure of 3 MPa, and heated to a temperature of 80
◦
C. The tests were carried out
for 240 h. After exposure, the samples were removed from the autoclave and rinsed with
flowing water to remove corrosion products. Subsequently, they were dried using paper
and organic solvents (acetone). Any remaining corrosion residues were removed using
gentle abrasives (erasers). The weight loss of the samples was determined and visually
evaluated (according to ASTM G1).
The corrosion rate was calculated using the formula:
K=1.129·m0−m1
S·t,mm
year (1)
where 1.129 is the coefficient for steels of the martensitic class of type 13Cr for converting
the dimension of the rate of general corrosion in g/m
2
h into the dimension of mm/year;
m0
is the mass of the sample before testing, g;
m1
is the mass of the sample after testing, g;
Sis the surface area of the sample, m2; and t-test duration, hours.
Sulfide stress corrosion cracking resistance was evaluated according to NACE TM0177,
method A, on cylindrical samples in a solution of 5% NaCl plus 0.5% acetic acid, with pH of
3, and then saturated with 10% H
2
S. The duration of the tests was 720 h. The applied stress
on the samples was 80% of the standard minimum yield strength (SMYS). After testing, it
was assessed visually for cracks.
The influence of the type and composition of non-metallic inclusions (NMIs) on the
quality of the steel was evaluated using electrolytic etching, which involves the dissolution
of the matrix and residue analysis.
Metal samples were used for three-dimensional (3-D) investigations of non-metallic
inclusions extracted using the electrolytic extraction (EE) technique. The electrolytic ex-
tractions were carried out at the KTH Royal Institute of Technology (Stockholm, Sweden)
by using the following extraction parameters: electrolyte, 10%AA (10% acetylacetone-1%
tetramethyl-ammonium chloride-methanol); electric current, 40~60 mA; voltage, 2.9~3.8 V.
After an electrolytic dissolution of metal matrix, the non-metallic inclusions, which did not
dissolve in the given electrolyte, were collected on a surface of a membrane polycarbonate
film filter (with a 0.4
µ
m open-pore diameter) during filtration of the electrolyte after the
completed EE [
20
,
31
]. The characteristics of inclusions (such as size, morphology, and
chemical composition) were analyzed by using an SEM combined with EDS. The NMIs
were investigated on film filters and on surfaces of metal samples after EE.
The types of inclusions, their sizes, and the coefficient of dissolution of the metallic
matrix around the inclusion (KD) were determined:
KD=
Acr
Aincl
(2)
where Aincl is the areas of inclusion, and Acr is the areas of craters.

Metals 2023,13, 1805 5 of 14
3. Results
3.1. Investigations of the Pipe Sample after Operation
During the investigation of the microstructure of the samples at different distances
from the external wall of the pipe, no critical structural features were observed. The steel
structure corresponded to tempered martensite (Figure 2).
Metals 2023, 13, x FOR PEER REVIEW 5 of 14
(a) (b)
Figure 2. Microstructure in the sample, ×200: (a) in the middle; (b) on the surface.
Figure 3 shows an electronic photograph of corrosion damage, while Table 3 lists the
chemical compositions of the corrosion products.
Figure 3. SEM image of corrosion products.
Table 3. Results of chemical analysis of corrosion products from the EDS data.
Spectrum O Si S Cl Ca Cr Mn Fe Ni
1 38.41 0.96 0.31 4.31 0.43 35.76 17.18 2.64
2 38.29 0.82 0.61 6.12 0.29 39.06 12.57 1.99
3 44.01 1.08 0.93 5.04 36.92 11.24 0.78
4 37.48 0.93 1.06 4.54 37.01 17.41 1.57
5 0.54 13.53 0.64 83.04 2.26
6 1.50 0.47 13.37 0.61 81.34 2.71
The corrosion products contain the following elements: S is found in the products
resulting from the interaction of iron with H
2
S or SO
42−
; Ca replaces iron and nickel atoms
during corrosion; an increase in Cr concentration above the specified 13% is aributed to
iron dissolution; Cr, Fe, O and S are present as iron and chromium oxide oxidation prod-
ucts (Cr
2
O
3
, FeS, FeO and FeCO
3
). These components in the table indicate the existence of
two gases in the operating environment—H
2
S and CO
2
with the presence of chlorides. For
13Cr steels, these conditions can lead to premature failure. To assess the impact of the
Figure 2. Microstructure in the sample, ×200: (a) in the middle; (b) on the surface.
Figure 3shows an electronic photograph of corrosion damage, while Table 3lists the
chemical compositions of the corrosion products.
Metals 2023, 13, x FOR PEER REVIEW 5 of 14
(a) (b)
Figure 2. Microstructure in the sample, ×200: (a) in the middle; (b) on the surface.
Figure 3 shows an electronic photograph of corrosion damage, while Table 3 lists the
chemical compositions of the corrosion products.
Figure 3. SEM image of corrosion products.
Table 3. Results of chemical analysis of corrosion products from the EDS data.
Spectrum O Si S Cl Ca Cr Mn Fe Ni
1 38.41 0.96 0.31 4.31 0.43 35.76 17.18 2.64
2 38.29 0.82 0.61 6.12 0.29 39.06 12.57 1.99
3 44.01 1.08 0.93 5.04 36.92 11.24 0.78
4 37.48 0.93 1.06 4.54 37.01 17.41 1.57
5 0.54 13.53 0.64 83.04 2.26
6 1.50 0.47 13.37 0.61 81.34 2.71
The corrosion products contain the following elements: S is found in the products
resulting from the interaction of iron with H
2
S or SO
42−
; Ca replaces iron and nickel atoms
during corrosion; an increase in Cr concentration above the specified 13% is aributed to
iron dissolution; Cr, Fe, O and S are present as iron and chromium oxide oxidation prod-
ucts (Cr
2
O
3
, FeS, FeO and FeCO
3
). These components in the table indicate the existence of
two gases in the operating environment—H
2
S and CO
2
with the presence of chlorides. For
13Cr steels, these conditions can lead to premature failure. To assess the impact of the
Figure 3. SEM image of corrosion products.
The corrosion products contain the following elements: S is found in the products
resulting from the interaction of iron with H
2
S or SO
42−
; Ca replaces iron and nickel atoms
during corrosion; an increase in Cr concentration above the specified 13% is attributed to
iron dissolution; Cr, Fe, O and S are present as iron and chromium oxide oxidation products
(Cr
2
O
3
, FeS, FeO and FeCO
3
). These components in the table indicate the existence of two
gases in the operating environment—H
2
S and CO
2
with the presence of chlorides. For 13Cr
steels, these conditions can lead to premature failure. To assess the impact of the operating
environment parameters as well as the presence of hydrogen sulfide and carbon dioxide,
electrochemical tests were conducted under variable conditions.
Figure 4depicts polarization curves plotted in coordinates of potential versus cur-
rent density. The studies were conducted to assess the influence of various parameters—

Metals 2023,13, 1805 6 of 14
presence of CO
2
, H
2
S or in the open cell (without saturation and deaeration, “air”) with
different pH values—on the corrosion resistance of the samples from the investigated pipe.
Metals 2023, 13, x FOR PEER REVIEW 6 of 14
operating environment parameters as well as the presence of hydrogen sulfide and carbon
dioxide, electrochemical tests were conducted under variable conditions.
Figure 4 depicts polarization curves ploed in coordinates of potential versus current
density. The studies were conducted to assess the influence of various parameters—pres-
ence of CO2, H2S or in the open cell (without saturation and deaeration, “air”) with differ-
ent pH values—on the corrosion resistance of the samples from the investigated pipe.
The results revealed high corrosion resistance of the P110-13Cr steel in an environ-
ment with pH 11 and no gas saturation. However, when the pH is lowered to 6.5, the
corrosion rate increases to 0.04 mm/year, and corrosion exhibits a localized nature. Further
reduction of pH to 3 significantly elevates the corrosion rate to 1.5 mm/year, and corrosion
becomes more general.
In an environment with pH 11 and CO2 saturation, the metal remains passive and
corrosion-resistant. Nevertheless, when the pH is reduced to 6.5, the corrosion rate in-
creases to 0.02 mm/year, and corrosion exhibits a piing. With a pH decrease to 3, along
with CO2 saturation, the corrosion rate escalates to 2.2 mm/year, and corrosion becomes
more general.
In an environment with pH 11 and H2S saturation, the metal remains passive, and
the corrosion rate is 0.001 mm/year. However, when the pH is lowered to 7-3, the corro-
sion rate increases to 0.86–1.5 mm/year, and corrosion proceeded more through the gen-
eral mechanism rather than the local.
(a) (b) (c)
Figure 4. Polarization curves for 13Cr-2Ni sample: (a) in open cell, (b) saturated with CO2, (c) satu-
rated with H2S.
Subsequently, the theoretical corrosion rates of the investigated samples were calcu-
lated and recorded in Table 4.
Table 4. Results of electrochemical studies.
№ Sample Average Corrosion Rate,
mm/year Ecorr, mV Epit, mV
1 13Cr-pH3-air 1.5730 −460 –
2 13Cr-pH3-CO2 2.2215 −447 –
3 13Cr-pH3-H2S 1.5790 −623 –
4 13Cr-pH6.5-air 0.0353 −271 −93
5 13Cr-pH6.5-CO2 0.0284 −511 −185
6 13Cr-pH6.5-H2S 0.8690 −678 –
7 13Cr-pH11-air 0.0011 −349 364
8 13Cr-pH11-CO2 0.0015 −251 6
9 13Cr-pH11-H2S 0.0099 −435 25
From the results presented in Figure 4 and Table 4, it is evident that pH critically
influences the materials resistance in the environment. In the case of low pH, this steel
Figure 4.
Polarization curves for 13Cr-2Ni sample: (
a
) in open cell, (
b
) saturated with CO
2
, (
c
) saturated
with H2S.
The results revealed high corrosion resistance of the P110-13Cr steel in an environment
with pH 11 and no gas saturation. However, when the pH is lowered to 6.5, the corrosion
rate increases to 0.04 mm/year, and corrosion exhibits a localized nature. Further reduction
of pH to 3 significantly elevates the corrosion rate to 1.5 mm/year, and corrosion becomes
more general.
In an environment with pH 11 and CO
2
saturation, the metal remains passive and
corrosion-resistant. Nevertheless, when the pH is reduced to 6.5, the corrosion rate in-
creases to 0.02 mm/year, and corrosion exhibits a pitting. With a pH decrease to 3, along
with CO
2
saturation, the corrosion rate escalates to 2.2 mm/year, and corrosion becomes
more general.
In an environment with pH 11 and H
2
S saturation, the metal remains passive, and the
corrosion rate is 0.001 mm/year. However, when the pH is lowered to 7-3, the corrosion
rate increases to 0.86–1.5 mm/year, and corrosion proceeded more through the general
mechanism rather than the local.
Subsequently, the theoretical corrosion rates of the investigated samples were calcu-
lated and recorded in Table 4.
Table 4. Results of electrochemical studies.
№Sample Average Corrosion
Rate, mm/Year Ecorr, mV Epit, mV
1 13Cr-pH3-air 1.5730 −460 –
2 13Cr-pH3-CO22.2215 −447 –
3 13Cr-pH3-H2S 1.5790 −623 –
4 13Cr-pH6.5-air 0.0353 −271 −93
5 13Cr-pH6.5-CO20.0284 −511 −185
6 13Cr-pH6.5-H2S 0.8690 −678 –
7 13Cr-pH11-air 0.0011 −349 364
8 13Cr-pH11-CO20.0015 −251 6
9 13Cr-pH11-H2S 0.0099 −435 25
From the results presented in Figure 4and Table 4, it is evident that pH critically
influences the material’s resistance in the environment. In the case of low pH, this steel
did not exhibit stainless properties and dissolved in any medium. The highest average
corrosion rate (~2.2 mm/year) was observed for the investigated steel in a CO
2
environment
at pH 3. This environment was selected for further testing.
Steel with a chromium content of 13% forms a passive protective film on its surface,
preventing the dissolution of the base metal in the electrolyte medium. However, this film
can be damaged and dissolved in the presence of chlorides. This process accelerates as

Metals 2023,13, 1805 7 of 14
the pH of the solution decreases. The authors of [
33
] demonstrated that reducing the pH
below 3.5, down to 1, leads to the deceleration and, sometimes, complete exclusion of the
repassivation process of the Cr
2
O
3
film on the material’s surface. The breakdown of the
passive film in an aerated electrolyte results in the formation of pits and an increased rate
of material dissolution.
3.2. Autoclave Tests
Corrosion rate resistance autoclave test results are provided in Table 5.
Table 5. Corrosion rate after autoclave in 5% NaCl plus 0.5% acetic acid with pH 3–4.
Type of Steel Average Corrosion Rate,
mm/Year Photo of Specimen
13Cr-4Ni-1Mo (P110) 0.0019 ±0.0010
Metals 2023, 13, x FOR PEER REVIEW 7 of 14
did not exhibit stainless properties and dissolved in any medium. The highest average
corrosion rate (~2.2 mm/year) was observed for the investigated steel in a CO2 environ-
ment at pH 3. This environment was selected for further testing.
Steel with a chromium content of 13% forms a passive protective film on its surface,
preventing the dissolution of the base metal in the electrolyte medium. However, this film
can be damaged and dissolved in the presence of chlorides. This process accelerates as the
pH of the solution decreases. The authors of [33] demonstrated that reducing the pH be-
low 3.5, down to 1, leads to the deceleration and, sometimes, complete exclusion of the
repassivation process of the Cr2O3 film on the materials surface. The breakdown of the
passive film in an aerated electrolyte results in the formation of pits and an increased rate
of material dissolution.
3.2. Autoclave Tests
Corrosion rate resistance autoclave test results are provided in Table 5.
Table 5. Corrosion rate after autoclave in 5% NaCl plus 0.5% acetic acid with pH 3–4.
Type of Steel Average Corrosion Rate, mm/Year Photo of Specimen
13Cr-4Ni-1Mo (P110) 0.0019 ± 0.0010
13Cr-5Ni-2Mo (P110) 0.0007 ± 0.0004
13Cr-5Ni-2Mo (Q135) 0.0025 ± 0.0015
13Cr-3Ni-1Mo (P110) 0.0106 ± 0.0020
The 13Cr-3Ni-1Mo specimens after autoclave testing have a dark layer of nearly uni-
form corrosion products on the surface that indicates the absence of passivation state in
the testing conditions. After cleaning, there were no visually detected corrosion damages
(pits).
All samples, except for the last one, exhibited low corrosion rates, with occasional
instances of piing corrosion. The 13Cr-5Ni-2Mo (P110) steel type performed the best
among all samples.
Based on the results of autoclave tests conducted in an acidic environment with the
presence of carbon dioxide, all variants of martensitic 13Cr alloying demonstrate re-
sistance in terms of dissolution. Pits on the samples are one of the factors for assessment
and comparison. Thus, the presence of surface defects, local structural heterogeneity, and
non-metallic inclusions can be potential causes for the formation of piing.
3.3. Electrochemical Tests
13Cr-5Ni-2Mo (P110) 0.0007 ±0.0004
Metals 2023, 13, x FOR PEER REVIEW 7 of 14
did not exhibit stainless properties and dissolved in any medium. The highest average
corrosion rate (~2.2 mm/year) was observed for the investigated steel in a CO2 environ-
ment at pH 3. This environment was selected for further testing.
Steel with a chromium content of 13% forms a passive protective film on its surface,
preventing the dissolution of the base metal in the electrolyte medium. However, this film
can be damaged and dissolved in the presence of chlorides. This process accelerates as the
pH of the solution decreases. The authors of [33] demonstrated that reducing the pH be-
low 3.5, down to 1, leads to the deceleration and, sometimes, complete exclusion of the
repassivation process of the Cr2O3 film on the materials surface. The breakdown of the
passive film in an aerated electrolyte results in the formation of pits and an increased rate
of material dissolution.
3.2. Autoclave Tests
Corrosion rate resistance autoclave test results are provided in Table 5.
Table 5. Corrosion rate after autoclave in 5% NaCl plus 0.5% acetic acid with pH 3–4.
Type of Steel Average Corrosion Rate, mm/Year Photo of Specimen
13Cr-4Ni-1Mo (P110) 0.0019 ± 0.0010
13Cr-5Ni-2Mo (P110) 0.0007 ± 0.0004
13Cr-5Ni-2Mo (Q135) 0.0025 ± 0.0015
13Cr-3Ni-1Mo (P110) 0.0106 ± 0.0020
The 13Cr-3Ni-1Mo specimens after autoclave testing have a dark layer of nearly uni-
form corrosion products on the surface that indicates the absence of passivation state in
the testing conditions. After cleaning, there were no visually detected corrosion damages
(pits).
All samples, except for the last one, exhibited low corrosion rates, with occasional
instances of piing corrosion. The 13Cr-5Ni-2Mo (P110) steel type performed the best
among all samples.
Based on the results of autoclave tests conducted in an acidic environment with the
presence of carbon dioxide, all variants of martensitic 13Cr alloying demonstrate re-
sistance in terms of dissolution. Pits on the samples are one of the factors for assessment
and comparison. Thus, the presence of surface defects, local structural heterogeneity, and
non-metallic inclusions can be potential causes for the formation of piing.
3.3. Electrochemical Tests
13Cr-5Ni-2Mo (Q135) 0.0025 ±0.0015
Metals 2023, 13, x FOR PEER REVIEW 7 of 14
did not exhibit stainless properties and dissolved in any medium. The highest average
corrosion rate (~2.2 mm/year) was observed for the investigated steel in a CO2 environ-
ment at pH 3. This environment was selected for further testing.
Steel with a chromium content of 13% forms a passive protective film on its surface,
preventing the dissolution of the base metal in the electrolyte medium. However, this film
can be damaged and dissolved in the presence of chlorides. This process accelerates as the
pH of the solution decreases. The authors of [33] demonstrated that reducing the pH be-
low 3.5, down to 1, leads to the deceleration and, sometimes, complete exclusion of the
repassivation process of the Cr2O3 film on the materials surface. The breakdown of the
passive film in an aerated electrolyte results in the formation of pits and an increased rate
of material dissolution.
3.2. Autoclave Tests
Corrosion rate resistance autoclave test results are provided in Table 5.
Table 5. Corrosion rate after autoclave in 5% NaCl plus 0.5% acetic acid with pH 3–4.
Type of Steel Average Corrosion Rate, mm/Year Photo of Specimen
13Cr-4Ni-1Mo (P110) 0.0019 ± 0.0010
13Cr-5Ni-2Mo (P110) 0.0007 ± 0.0004
13Cr-5Ni-2Mo (Q135) 0.0025 ± 0.0015
13Cr-3Ni-1Mo (P110) 0.0106 ± 0.0020
The 13Cr-3Ni-1Mo specimens after autoclave testing have a dark layer of nearly uni-
form corrosion products on the surface that indicates the absence of passivation state in
the testing conditions. After cleaning, there were no visually detected corrosion damages
(pits).
All samples, except for the last one, exhibited low corrosion rates, with occasional
instances of piing corrosion. The 13Cr-5Ni-2Mo (P110) steel type performed the best
among all samples.
Based on the results of autoclave tests conducted in an acidic environment with the
presence of carbon dioxide, all variants of martensitic 13Cr alloying demonstrate re-
sistance in terms of dissolution. Pits on the samples are one of the factors for assessment
and comparison. Thus, the presence of surface defects, local structural heterogeneity, and
non-metallic inclusions can be potential causes for the formation of piing.
3.3. Electrochemical Tests
13Cr-3Ni-1Mo (P110) 0.0106 ±0.0020
Metals 2023, 13, x FOR PEER REVIEW 7 of 14
did not exhibit stainless properties and dissolved in any medium. The highest average
corrosion rate (~2.2 mm/year) was observed for the investigated steel in a CO2 environ-
ment at pH 3. This environment was selected for further testing.
Steel with a chromium content of 13% forms a passive protective film on its surface,
preventing the dissolution of the base metal in the electrolyte medium. However, this film
can be damaged and dissolved in the presence of chlorides. This process accelerates as the
pH of the solution decreases. The authors of [33] demonstrated that reducing the pH be-
low 3.5, down to 1, leads to the deceleration and, sometimes, complete exclusion of the
repassivation process of the Cr2O3 film on the materials surface. The breakdown of the
passive film in an aerated electrolyte results in the formation of pits and an increased rate
of material dissolution.
3.2. Autoclave Tests
Corrosion rate resistance autoclave test results are provided in Table 5.
Table 5. Corrosion rate after autoclave in 5% NaCl plus 0.5% acetic acid with pH 3–4.
Type of Steel Average Corrosion Rate, mm/Year Photo of Specimen
13Cr-4Ni-1Mo (P110) 0.0019 ± 0.0010
13Cr-5Ni-2Mo (P110) 0.0007 ± 0.0004
13Cr-5Ni-2Mo (Q135) 0.0025 ± 0.0015
13Cr-3Ni-1Mo (P110) 0.0106 ± 0.0020
The 13Cr-3Ni-1Mo specimens after autoclave testing have a dark layer of nearly uni-
form corrosion products on the surface that indicates the absence of passivation state in
the testing conditions. After cleaning, there were no visually detected corrosion damages
(pits).
All samples, except for the last one, exhibited low corrosion rates, with occasional
instances of piing corrosion. The 13Cr-5Ni-2Mo (P110) steel type performed the best
among all samples.
Based on the results of autoclave tests conducted in an acidic environment with the
presence of carbon dioxide, all variants of martensitic 13Cr alloying demonstrate re-
sistance in terms of dissolution. Pits on the samples are one of the factors for assessment
and comparison. Thus, the presence of surface defects, local structural heterogeneity, and
non-metallic inclusions can be potential causes for the formation of piing.
3.3. Electrochemical Tests
The 13Cr-3Ni-1Mo specimens after autoclave testing have a dark layer of nearly uni-
form corrosion products on the surface that indicates the absence of passivation state in the
testing conditions. After cleaning, there were no visually detected corrosion
damages (pits)
.
All samples, except for the last one, exhibited low corrosion rates, with occasional
instances of pitting corrosion. The 13Cr-5Ni-2Mo (P110) steel type performed the best
among all samples.
Based on the results of autoclave tests conducted in an acidic environment with the
presence of carbon dioxide, all variants of martensitic 13Cr alloying demonstrate resistance
in terms of dissolution. Pits on the samples are one of the factors for assessment and
comparison. Thus, the presence of surface defects, local structural heterogeneity, and
non-metallic inclusions can be potential causes for the formation of pitting.
3.3. Electrochemical Tests
The calculated values can be used provided that the corresponding elements are in
solid solution. The results are presented in Table 6and Figure 5.

Metals 2023,13, 1805 8 of 14
Table 6. Results of electrochemical tests.
Type of Steel PREN Average Corrosion
Rate, mm/Year Ecorr, mV Epit, mV
13Cr-4Ni-1Mo (P110) 18.5 0.156 −455 −170
13Cr-5Ni-2Mo (P110) 21.4 0.100 −425 −130
13Cr-5Ni-2Mo (Q135) 19.9 0.056 −420 −85
13Cr-3Ni-1Mo (P110) 16.3 0.409 −475 −190
Metals 2023, 13, x FOR PEER REVIEW 8 of 14
The calculated values can be used provided that the corresponding elements are in
solid solution. The results are presented in Table 6 and Figure 5.
Table 6. Results of electrochemical tests.
Type of Steel PREN Average Corrosion Rate,
mm/Year Ecorr, mV Epit, mV
13Cr-4Ni-1Mo (P110) 18.5 0.156 −455 −170
13Cr-5Ni-2Mo (P110) 21.4 0.100 −425 −130
13Cr-5Ni-2Mo (Q135) 19.9 0.056 −420 −85
13Cr-3Ni-1Mo (P110) 16.3 0.409 −475 −190
Figure 5. Polarization curves.
The potential sweeps obtained during the research process are nearly constant over
time, exhibiting minimal deviations not exceeding 20 mV from the mean corrosion poten-
tial. This stability signifies the corrosion potentials resilience for the investigated materi-
als in this environment, enabling an evaluation of the materials corrosion resistance ca-
pability.
Based on the obtained corrosion potential data, it can be hypothesized that the 13Cr-
3Ni-1Mo steel samples exhibit lower corrosion resistance compared to the others in the
same environment. In this context, the corrosion resistance correlates well with the PREN.
When comparing other characteristics, such as theoretical corrosion rate and piing po-
tential, no significant observations can be made.
On the polarization curves for all the studied steels, there is a passive region (plat-
eau), typically within the potential range of −350 mV to −150 mV. This region is character-
ized by a relatively constant current as the potential increases. The presence of such a
plateau on the polarization curve indicates the onset of passivity in the examined steel.
Thus, it can be inferred that these steel grades exhibit passivity, signifying their corrosion
resistance under the study conditions.
In the case of the 13Cr-5Ni-2Mo (Q135) sample (red curve), it is noteworthy that there
are several breakdowns before reaching the passive region. This could be aributed to the
presence of non-corrosion-resistant inclusions on the surface. Initially, during the active
passivation process of the surface, a breakdown occurred involving the dissolution of the
inclusion, characterized by a sharp change in the current density direction towards an
Figure 5. Polarization curves.
The potential sweeps obtained during the research process are nearly constant over
time, exhibiting minimal deviations not exceeding 20 mV from the mean corrosion potential.
This stability signifies the corrosion potential’s resilience for the investigated materials in
this environment, enabling an evaluation of the material’s corrosion resistance capability.
Based on the obtained corrosion potential data, it can be hypothesized that the 13Cr-
3Ni-1Mo steel samples exhibit lower corrosion resistance compared to the others in the same
environment. In this context, the corrosion resistance correlates well with the PREN. When
comparing other characteristics, such as theoretical corrosion rate and pitting potential, no
significant observations can be made.
On the polarization curves for all the studied steels, there is a passive region (plateau),
typically within the potential range of
−
350 mV to
−
150 mV. This region is characterized
by a relatively constant current as the potential increases. The presence of such a plateau
on the polarization curve indicates the onset of passivity in the examined steel. Thus, it can
be inferred that these steel grades exhibit passivity, signifying their corrosion resistance
under the study conditions.
In the case of the 13Cr-5Ni-2Mo (Q135) sample (red curve), it is noteworthy that
there are several breakdowns before reaching the passive region. This could be attributed
to the presence of non-corrosion-resistant inclusions on the surface. Initially, during the
active passivation process of the surface, a breakdown occurred involving the dissolu-
tion of the inclusion, characterized by a sharp change in the current density direction
towards an increase. Subsequently, the passivation process continued until reaching the
pitting potential.
Therefore, based on the results of the conducted electrochemical investigations, it can
be concluded that the 13Cr-5Ni-2Mo (P110) steel exhibits the lowest corrosion rate in a
CO2-saturated environment.

Metals 2023,13, 1805 9 of 14
3.4. Resistance to Sulfide Stress Cracking
The test conditions were according to NACE MR0175, Section 3. Test results made on
triplicate specimens are provided in Table 7. Images of samples after testing are provided
in Figure 6.
Table 7. SSC test results.
Type of Steel YS, MPa Average Time before
Failure, Hours Comments
13Cr-4Ni-1Mo (P110) 758 720 Small pittings
13Cr-5Ni-2Mo (P110) 758 150 Many cracks
13Cr-5Ni-2Mo (Q135) 980 170 Pittings, many cracks
13Cr-3Ni-1Mo (P110) 758 250 Near to the end of the
working part
Metals 2023, 13, x FOR PEER REVIEW 9 of 14
increase. Subsequently, the passivation process continued until reaching the piing po-
tential.
Therefore, based on the results of the conducted electЫЬНrochemical investigations,
it can be concluded that the 13Cr-5Ni-2Mo (P110) steel exhibits the lowest corrosion rate
in a CO
2
-saturated environment.
3.4. Resistance to Sulfide Stress Cracking
The test conditions were according to NACE MR0175, Section 3. Test results made on
triplicate specimens are provided in Table 7. Images of samples after testing are provided
in Figure 6.
Table 7. SSC test results.
Type of Steel YS, MPa Average Time before Failure,
Hours Comments
13Cr-4Ni-1Mo (P110) 758 720 Small piings
13Cr-5Ni-2Mo (P110) 758 150 Many cracks
13Cr-5Ni-2Mo (Q135) 980 170 Piings, many cracks
13Cr-3Ni-1Mo (P110) 758 250 Near to the end of the
working part
The results of the study demonstrated the susceptibility of the examined steels—
namely, 13Cr-5Ni-2Mo of both strength grades and 13Cr-3Ni-1Mo—to sulfide stress
cracking (SSC). Visual examination of the samples revealed the presence of multiple
cracks and piings on their surfaces, as illustrated in Figure 6b–d. However, the 13Cr-4Ni-
1Mo samples exhibited a crack-free surface, although some piings were observed (Figure
6a).
It should be noted that while piings are not considered a definitive criterion for SSC
according to NACE TM0177, their presence suggests lower corrosion resistance in the
tested environment and may serve as potential stress points for further crack initiation, as
depicted in Figure 6c. Interestingly, no piings were observed on the surface of the 13Cr-
5Ni-2Mo specimen following the testing procedure.
Even though 13Cr-5Ni-2Mo specimens have the highest strength level (Q135 grade),
the time before failure was longer for 13Cr-5Ni-2Mo (P110) (170 h and 150 h, respectively).
(a) (b)
(c) (d)
Figure 6. Specimens after SSC test: (a) 13Cr-4Ni-1Mo (P110), (b) 13Cr-5Ni-2Mo (P110), (c) 13Cr-5Ni-
2Mo (Q135), (d) 13Cr-3Ni-1Mo (P110).
Figure 6.
Specimens after SSC test: (
a
) 13Cr-4Ni-1Mo (P110), (
b
) 13Cr-5Ni-2Mo (P110), (
c
) 13Cr-5Ni-
2Mo (Q135), (d) 13Cr-3Ni-1Mo (P110).
The results of the study demonstrated the susceptibility of the examined steels—
namely, 13Cr-5Ni-2Mo of both strength grades and 13Cr-3Ni-1Mo—to sulfide stress crack-
ing (SSC). Visual examination of the samples revealed the presence of multiple cracks
and pittings on their surfaces, as illustrated in Figure 6b–d. However, the 13Cr-4Ni-1Mo
samples exhibited a crack-free surface, although some pittings were observed (Figure 6a).
It should be noted that while pittings are not considered a definitive criterion for
SSC according to NACE TM0177, their presence suggests lower corrosion resistance in the
tested environment and may serve as potential stress points for further crack initiation,
as depicted in Figure 6c. Interestingly, no pittings were observed on the surface of the
13Cr-5Ni-2Mo specimen following the testing procedure.
Even though 13Cr-5Ni-2Mo specimens have the highest strength level (Q135 grade),
the time before failure was longer for 13Cr-5Ni-2Mo (P110) (170 h and 150 h, respectively).
In addition to convenient SSC cracks directed perpendicular to tensile stresses, cracks
parallel to the direction of the applied load were found for 13Cr-3Ni-1Mo, as shown
in Figure 6. This type of cracking is attributed to stress-oriented hydrogen-induced
cracking (SOHIC).

Metals 2023,13, 1805 10 of 14
As we can see from Figure 7, the dissolution of the material exhibits a selective pass.
Studies of non-metallic inclusions near the metal surface using electrolytic extraction
methods allow for determining their influence on environmental resistance. They also
enable the assessment of the degree of material dissolution under environmental exposure.
Metals 2023, 13, x FOR PEER REVIEW 10 of 14
In addition to convenient SSC cracks directed perpendicular to tensile stresses, cracks
parallel to the direction of the applied load were found for 13Cr-3Ni-1Mo, as shown in
Figure 6. This type of cracking is aributed to stress-oriented hydrogen-induced cracking
(SOHIC).
As we can see from Figure 7, the dissolution of the material exhibits a selective pass.
Studies of non-metallic inclusions near the metal surface using electrolytic extraction
methods allow for determining their influence on environmental resistance. They also en-
able the assessment of the degree of material dissolution under environmental exposure.
(a) (b)
Figure 7. Damages and pits on the sample 13Cr-3Ni-1Mo after SSC tests: (a) side #1; (b) side #2.
3.5. The Assessment of NMIs Using the Electrolytic Extraction Method
Table 8 presents the results of inclusion extraction using electrolytic extraction and
subsequent analysis using SEM. In all steels, manganese sulfide inclusions were found. In
the 13Cr-3Ni-1Mo steel, MnS inclusions have an irregular shape and reach a length of 14.6
µm, while in the 13Cr-4Ni-1Mo and 13Cr-5Ni-2Mo steels, the inclusions are rounded with
a diameter not exceeding 6.5 µm. The 13Cr-5Ni-2Mo samples are characterized by the
presence of manganese sulfides and molybdenum-containing carbides, which can reduce
piing resistance. Meanwhile, the 13Cr-4Ni-1Mo sample exhibits more characteristic tita-
nium and niobium nitride inclusions, which have a lesser effect on the reduction of corro-
sion resistance.
Inclusions in steels act as stress concentrators and deteriorate their mechanical prop-
erties. The stronger the deviation of the inclusion shape from spherical and the larger its
size, the more it reduces the mechanical properties of the steel. Additionally, some non-
metallic inclusions can act as piing nucleation sites—corrosion-active non-metallic inclu-
sions. The values of the metal matrix dissolution coefficient around the inclusions (K
D
) in
the 13Cr-3Ni-1Mo steel (K
D
(a)~4.5–5.0; K
D
(b)~2.1–5.4) on average exceed the correspond-
ing values for the steels 13Cr-4Ni-1Mo (K
D
~1.5–4.1) and 13Cr-5Ni-2Mo (K
D
~1.7–3.3), indi-
cating that the composition of these inclusions may have a greater influence on the corro-
sion process.
Table 8. Electrolytic etching: 1a, 2a—13Cr-3Ni-1Mo; 1b, 2b—13Cr-4Ni-1Mo; 3—13Cr-5Ni-2Mo.
Type NMI on Filter Surface NMI on Sample Surface Composition Size (µm) K
D
1a
MnS ~4.6–14.6 ~4.5–5
Figure 7. Damages and pits on the sample 13Cr-3Ni-1Mo after SSC tests: (a) side #1; (b) side #2.
3.5. The Assessment of NMIs Using the Electrolytic Extraction Method
Table 8presents the results of inclusion extraction using electrolytic extraction and
subsequent analysis using SEM. In all steels, manganese sulfide inclusions were found.
In the 13Cr-3Ni-1Mo steel, MnS inclusions have an irregular shape and reach a length of
14.6
µ
m, while in the 13Cr-4Ni-1Mo and 13Cr-5Ni-2Mo steels, the inclusions are rounded
with a diameter not exceeding 6.5
µ
m. The 13Cr-5Ni-2Mo samples are characterized by the
presence of manganese sulfides and molybdenum-containing carbides, which can reduce
pitting resistance. Meanwhile, the 13Cr-4Ni-1Mo sample exhibits more characteristic
titanium and niobium nitride inclusions, which have a lesser effect on the reduction of
corrosion resistance.
Inclusions in steels act as stress concentrators and deteriorate their mechanical proper-
ties. The stronger the deviation of the inclusion shape from spherical and the larger its size,
the more it reduces the mechanical properties of the steel. Additionally, some non-metallic
inclusions can act as pitting nucleation sites—corrosion-active non-metallic inclusions. The
values of the metal matrix dissolution coefficient around the inclusions (K
D
) in the 13Cr-
3Ni-1Mo steel (K
D
(a)~4.5–5.0; K
D
(b)~2.1–5.4) on average exceed the corresponding values
for the steels 13Cr-4Ni-1Mo (K
D
~1.5–4.1) and 13Cr-5Ni-2Mo (K
D
~1.7–3.3), indicating that
the composition of these inclusions may have a greater influence on the corrosion process.
The results of electrolytic etching should be carefully assessed in conjunction with
the results of electrochemical studies. For instance, in the case of the 13Cr-5Ni-2Mo (Q135)
samples, sulfides with molybdenum-containing carbo-nitride inclusions are observed. This
confirms the earlier assumptions regarding the influence of inclusions on passivation
processes. In comparison, the 13Cr-3Ni-1Mo sample exhibits less favorable inclusion
characteristics than the 13Cr-4Ni-1Mo sample, including size and dissolution coefficient.
The high values of K
D
, as well as the presence of large inclusions, explain the occur-
rence of pits on the surface of the 13Cr-3Ni-1Mo steel sample after SSC testing.

Metals 2023,13, 1805 11 of 14
Table 8. Electrolytic etching: 1a, 2a—13Cr-3Ni-1Mo; 1b, 2b—13Cr-4Ni-1Mo; 3—13Cr-5Ni-2Mo.
Type NMI on Filter Surface NMI on Sample Surface Composition Size (µm) KD
1a
Metals 2023, 13, x FOR PEER REVIEW 10 of 14
In addition to convenient SSC cracks directed perpendicular to tensile stresses, cracks
parallel to the direction of the applied load were found for 13Cr-3Ni-1Mo, as shown in
Figure 6. This type of cracking is aributed to stress-oriented hydrogen-induced cracking
(SOHIC).
As we can see from Figure 7, the dissolution of the material exhibits a selective pass.
Studies of non-metallic inclusions near the metal surface using electrolytic extraction
methods allow for determining their influence on environmental resistance. They also en-
able the assessment of the degree of material dissolution under environmental exposure.
(a) (b)
Figure 7. Damages and pits on the sample 13Cr-3Ni-1Mo after SSC tests: (a) side #1; (b) side #2.
3.5. The Assessment of NMIs Using the Electrolytic Extraction Method
Table 8 presents the results of inclusion extraction using electrolytic extraction and
subsequent analysis using SEM. In all steels, manganese sulfide inclusions were found. In
the 13Cr-3Ni-1Mo steel, MnS inclusions have an irregular shape and reach a length of 14.6
µm, while in the 13Cr-4Ni-1Mo and 13Cr-5Ni-2Mo steels, the inclusions are rounded with
a diameter not exceeding 6.5 µm. The 13Cr-5Ni-2Mo samples are characterized by the
presence of manganese sulfides and molybdenum-containing carbides, which can reduce
piing resistance. Meanwhile, the 13Cr-4Ni-1Mo sample exhibits more characteristic tita-
nium and niobium nitride inclusions, which have a lesser effect on the reduction of corro-
sion resistance.
Inclusions in steels act as stress concentrators and deteriorate their mechanical prop-
erties. The stronger the deviation of the inclusion shape from spherical and the larger its
size, the more it reduces the mechanical properties of the steel. Additionally, some non-
metallic inclusions can act as piing nucleation sites—corrosion-active non-metallic inclu-
sions. The values of the metal matrix dissolution coefficient around the inclusions (K
D
) in
the 13Cr-3Ni-1Mo steel (K
D
(a)~4.5–5.0; K
D
(b)~2.1–5.4) on average exceed the correspond-
ing values for the steels 13Cr-4Ni-1Mo (K
D
~1.5–4.1) and 13Cr-5Ni-2Mo (K
D
~1.7–3.3), indi-
cating that the composition of these inclusions may have a greater influence on the corro-
sion process.
Table 8. Electrolytic etching: 1a, 2a—13Cr-3Ni-1Mo; 1b, 2b—13Cr-4Ni-1Mo; 3—13Cr-5Ni-2Mo.
Type NMI on Filter Surface NMI on Sample Surface Composition Size (µm) K
D
1a
MnS ~4.6–14.6 ~4.5–5
Metals 2023, 13, x FOR PEER REVIEW 10 of 14
In addition to convenient SSC cracks directed perpendicular to tensile stresses, cracks
parallel to the direction of the applied load were found for 13Cr-3Ni-1Mo, as shown in
Figure 6. This type of cracking is aributed to stress-oriented hydrogen-induced cracking
(SOHIC).
As we can see from Figure 7, the dissolution of the material exhibits a selective pass.
Studies of non-metallic inclusions near the metal surface using electrolytic extraction
methods allow for determining their influence on environmental resistance. They also en-
able the assessment of the degree of material dissolution under environmental exposure.
(a) (b)
Figure 7. Damages and pits on the sample 13Cr-3Ni-1Mo after SSC tests: (a) side #1; (b) side #2.
3.5. The Assessment of NMIs Using the Electrolytic Extraction Method
Table 8 presents the results of inclusion extraction using electrolytic extraction and
subsequent analysis using SEM. In all steels, manganese sulfide inclusions were found. In
the 13Cr-3Ni-1Mo steel, MnS inclusions have an irregular shape and reach a length of 14.6
µm, while in the 13Cr-4Ni-1Mo and 13Cr-5Ni-2Mo steels, the inclusions are rounded with
a diameter not exceeding 6.5 µm. The 13Cr-5Ni-2Mo samples are characterized by the
presence of manganese sulfides and molybdenum-containing carbides, which can reduce
piing resistance. Meanwhile, the 13Cr-4Ni-1Mo sample exhibits more characteristic tita-
nium and niobium nitride inclusions, which have a lesser effect on the reduction of corro-
sion resistance.
Inclusions in steels act as stress concentrators and deteriorate their mechanical prop-
erties. The stronger the deviation of the inclusion shape from spherical and the larger its
size, the more it reduces the mechanical properties of the steel. Additionally, some non-
metallic inclusions can act as piing nucleation sites—corrosion-active non-metallic inclu-
sions. The values of the metal matrix dissolution coefficient around the inclusions (K
D
) in
the 13Cr-3Ni-1Mo steel (K
D
(a)~4.5–5.0; K
D
(b)~2.1–5.4) on average exceed the correspond-
ing values for the steels 13Cr-4Ni-1Mo (K
D
~1.5–4.1) and 13Cr-5Ni-2Mo (K
D
~1.7–3.3), indi-
cating that the composition of these inclusions may have a greater influence on the corro-
sion process.
Table 8. Electrolytic etching: 1a, 2a—13Cr-3Ni-1Mo; 1b, 2b—13Cr-4Ni-1Mo; 3—13Cr-5Ni-2Mo.
Type NMI on Filter Surface NMI on Sample Surface Composition Size (µm) K
D
1a
MnS ~4.6–14.6 ~4.5–5
MnS ~4.6–14.6 ~4.5–5
1b
Metals 2023, 13, x FOR PEER REVIEW 11 of 14
1b
Not observed MnS ~0.5–2.0 -
2a
Al
2
O
3
+
Ti,Nb-N,C+
MnS
~3.2–12 2.1–5.4
2b
Al
2
O
3
+
Ti,Nb-N+
MnS
~3.2–6.2 1.5–4.1
3
Al
2
O
3
+
Ti,Nb-N,C+
MnS
~2.5–6.4 1.7–3.3
The results of electrolytic etching should be carefully assessed in conjunction with
the results of electrochemical studies. For instance, in the case of the 13Cr-5Ni-2Mo (Q135)
samples, sulfides with molybdenum-containing carbo-nitride inclusions are observed.
This confirms the earlier assumptions regarding the influence of inclusions on passivation
processes. In comparison, the 13Cr-3Ni-1Mo sample exhibits less favorable inclusion char-
acteristics than the 13Cr-4Ni-1Mo sample, including size and dissolution coefficient.
The high values of K
D
, as well as the presence of large inclusions, explain the occur-
rence of pits on the surface of the 13Cr-3Ni-1Mo steel sample after SSC testing.
4. Discussion
Electrochemical studies of the samples of P110 tubing made of 13Cr-2Ni-grade steel
after service revealed that pH critically affects the materials resistance in the corrosion-
active environment. The most aggressive environment for this material was found to be a
3% NaCl solution saturated with CO
2
, with a pH value less than 3.0 at a temperature of 60
°C. In this environment, four experimental closest analogs of 13Cr-Ni-Mo-alloyed steels
were tested for comparison: 13Cr-4Ni-1Mo (P110), 13Cr-5Ni-2Mo (P110), 13Cr-5Ni-2Mo
(Q135), and 13Cr-3Ni-1Mo (P110). Based on the results of the conducted electrochemical
investigations, it can be concluded that 5Ni-2Mo (P110/Q135) steels exhibit the lowest cor-
rosion rate in a CO
2
-saturated environment (0.056–0.100 mm/year), while 13Cr-3Ni-1Mo
steel shows the highest corrosion rate (0.409 mm/year). The corrosion rate of 13Cr-4Ni-
1Mo steel was the median—0.156 mm/year.
Not observed MnS ~0.5–2.0 -
2a
Metals 2023, 13, x FOR PEER REVIEW 11 of 14
1b
Not observed MnS ~0.5–2.0 -
2a
Al
2
O
3
+
Ti,Nb-N,C+
MnS
~3.2–12 2.1–5.4
2b
Al
2
O
3
+
Ti,Nb-N+
MnS
~3.2–6.2 1.5–4.1
3
Al
2
O
3
+
Ti,Nb-N,C+
MnS
~2.5–6.4 1.7–3.3
The results of electrolytic etching should be carefully assessed in conjunction with
the results of electrochemical studies. For instance, in the case of the 13Cr-5Ni-2Mo (Q135)
samples, sulfides with molybdenum-containing carbo-nitride inclusions are observed.
This confirms the earlier assumptions regarding the influence of inclusions on passivation
processes. In comparison, the 13Cr-3Ni-1Mo sample exhibits less favorable inclusion char-
acteristics than the 13Cr-4Ni-1Mo sample, including size and dissolution coefficient.
The high values of K
D
, as well as the presence of large inclusions, explain the occur-
rence of pits on the surface of the 13Cr-3Ni-1Mo steel sample after SSC testing.
4. Discussion
Electrochemical studies of the samples of P110 tubing made of 13Cr-2Ni-grade steel
after service revealed that pH critically affects the materials resistance in the corrosion-
active environment. The most aggressive environment for this material was found to be a
3% NaCl solution saturated with CO
2
, with a pH value less than 3.0 at a temperature of 60
°C. In this environment, four experimental closest analogs of 13Cr-Ni-Mo-alloyed steels
were tested for comparison: 13Cr-4Ni-1Mo (P110), 13Cr-5Ni-2Mo (P110), 13Cr-5Ni-2Mo
(Q135), and 13Cr-3Ni-1Mo (P110). Based on the results of the conducted electrochemical
investigations, it can be concluded that 5Ni-2Mo (P110/Q135) steels exhibit the lowest cor-
rosion rate in a CO
2
-saturated environment (0.056–0.100 mm/year), while 13Cr-3Ni-1Mo
steel shows the highest corrosion rate (0.409 mm/year). The corrosion rate of 13Cr-4Ni-
1Mo steel was the median—0.156 mm/year.
Metals 2023, 13, x FOR PEER REVIEW 11 of 14
1b
Not observed MnS ~0.5–2.0 -
2a
Al
2
O
3
+
Ti,Nb-N,C+
MnS
~3.2–12 2.1–5.4
2b
Al
2
O
3
+
Ti,Nb-N+
MnS
~3.2–6.2 1.5–4.1
3
Al
2
O
3
+
Ti,Nb-N,C+
MnS
~2.5–6.4 1.7–3.3
The results of electrolytic etching should be carefully assessed in conjunction with
the results of electrochemical studies. For instance, in the case of the 13Cr-5Ni-2Mo (Q135)
samples, sulfides with molybdenum-containing carbo-nitride inclusions are observed.
This confirms the earlier assumptions regarding the influence of inclusions on passivation
processes. In comparison, the 13Cr-3Ni-1Mo sample exhibits less favorable inclusion char-
acteristics than the 13Cr-4Ni-1Mo sample, including size and dissolution coefficient.
The high values of K
D
, as well as the presence of large inclusions, explain the occur-
rence of pits on the surface of the 13Cr-3Ni-1Mo steel sample after SSC testing.
4. Discussion
Electrochemical studies of the samples of P110 tubing made of 13Cr-2Ni-grade steel
after service revealed that pH critically affects the materials resistance in the corrosion-
active environment. The most aggressive environment for this material was found to be a
3% NaCl solution saturated with CO
2
, with a pH value less than 3.0 at a temperature of 60
°C. In this environment, four experimental closest analogs of 13Cr-Ni-Mo-alloyed steels
were tested for comparison: 13Cr-4Ni-1Mo (P110), 13Cr-5Ni-2Mo (P110), 13Cr-5Ni-2Mo
(Q135), and 13Cr-3Ni-1Mo (P110). Based on the results of the conducted electrochemical
investigations, it can be concluded that 5Ni-2Mo (P110/Q135) steels exhibit the lowest cor-
rosion rate in a CO
2
-saturated environment (0.056–0.100 mm/year), while 13Cr-3Ni-1Mo
steel shows the highest corrosion rate (0.409 mm/year). The corrosion rate of 13Cr-4Ni-
1Mo steel was the median—0.156 mm/year.
Al2O3+
Ti,Nb-N,C+
MnS
~3.2–12 2.1–5.4
2b
Metals 2023, 13, x FOR PEER REVIEW 11 of 14
1b
Not observed MnS ~0.5–2.0 -
2a
Al
2
O
3
+
Ti,Nb-N,C+
MnS
~3.2–12 2.1–5.4
2b
Al
2
O
3
+
Ti,Nb-N+
MnS
~3.2–6.2 1.5–4.1
3
Al
2
O
3
+
Ti,Nb-N,C+
MnS
~2.5–6.4 1.7–3.3
The results of electrolytic etching should be carefully assessed in conjunction with
the results of electrochemical studies. For instance, in the case of the 13Cr-5Ni-2Mo (Q135)
samples, sulfides with molybdenum-containing carbo-nitride inclusions are observed.
This confirms the earlier assumptions regarding the influence of inclusions on passivation
processes. In comparison, the 13Cr-3Ni-1Mo sample exhibits less favorable inclusion char-
acteristics than the 13Cr-4Ni-1Mo sample, including size and dissolution coefficient.
The high values of K
D
, as well as the presence of large inclusions, explain the occur-
rence of pits on the surface of the 13Cr-3Ni-1Mo steel sample after SSC testing.
4. Discussion
Electrochemical studies of the samples of P110 tubing made of 13Cr-2Ni-grade steel
after service revealed that pH critically affects the materials resistance in the corrosion-
active environment. The most aggressive environment for this material was found to be a
3% NaCl solution saturated with CO
2
, with a pH value less than 3.0 at a temperature of 60
°C. In this environment, four experimental closest analogs of 13Cr-Ni-Mo-alloyed steels
were tested for comparison: 13Cr-4Ni-1Mo (P110), 13Cr-5Ni-2Mo (P110), 13Cr-5Ni-2Mo
(Q135), and 13Cr-3Ni-1Mo (P110). Based on the results of the conducted electrochemical
investigations, it can be concluded that 5Ni-2Mo (P110/Q135) steels exhibit the lowest cor-
rosion rate in a CO
2
-saturated environment (0.056–0.100 mm/year), while 13Cr-3Ni-1Mo
steel shows the highest corrosion rate (0.409 mm/year). The corrosion rate of 13Cr-4Ni-
1Mo steel was the median—0.156 mm/year.
Metals 2023, 13, x FOR PEER REVIEW 11 of 14
1b
Not observed MnS ~0.5–2.0 -
2a
Al
2
O
3
+
Ti,Nb-N,C+
MnS
~3.2–12 2.1–5.4
2b
Al
2
O
3
+
Ti,Nb-N+
MnS
~3.2–6.2 1.5–4.1
3
Al
2
O
3
+
Ti,Nb-N,C+
MnS
~2.5–6.4 1.7–3.3
The results of electrolytic etching should be carefully assessed in conjunction with
the results of electrochemical studies. For instance, in the case of the 13Cr-5Ni-2Mo (Q135)
samples, sulfides with molybdenum-containing carbo-nitride inclusions are observed.
This confirms the earlier assumptions regarding the influence of inclusions on passivation
processes. In comparison, the 13Cr-3Ni-1Mo sample exhibits less favorable inclusion char-
acteristics than the 13Cr-4Ni-1Mo sample, including size and dissolution coefficient.
The high values of K
D
, as well as the presence of large inclusions, explain the occur-
rence of pits on the surface of the 13Cr-3Ni-1Mo steel sample after SSC testing.
4. Discussion
Electrochemical studies of the samples of P110 tubing made of 13Cr-2Ni-grade steel
after service revealed that pH critically affects the materials resistance in the corrosion-
active environment. The most aggressive environment for this material was found to be a
3% NaCl solution saturated with CO
2
, with a pH value less than 3.0 at a temperature of 60
°C. In this environment, four experimental closest analogs of 13Cr-Ni-Mo-alloyed steels
were tested for comparison: 13Cr-4Ni-1Mo (P110), 13Cr-5Ni-2Mo (P110), 13Cr-5Ni-2Mo
(Q135), and 13Cr-3Ni-1Mo (P110). Based on the results of the conducted electrochemical
investigations, it can be concluded that 5Ni-2Mo (P110/Q135) steels exhibit the lowest cor-
rosion rate in a CO
2
-saturated environment (0.056–0.100 mm/year), while 13Cr-3Ni-1Mo
steel shows the highest corrosion rate (0.409 mm/year). The corrosion rate of 13Cr-4Ni-
1Mo steel was the median—0.156 mm/year.
Al2O3+
Ti,Nb-N+
MnS
~3.2–6.2 1.5–4.1
3
Metals 2023, 13, x FOR PEER REVIEW 11 of 14
1b
Not observed MnS ~0.5–2.0 -
2a
Al
2
O
3
+
Ti,Nb-N,C+
MnS
~3.2–12 2.1–5.4
2b
Al
2
O
3
+
Ti,Nb-N+
MnS
~3.2–6.2 1.5–4.1
3
Al
2
O
3
+
Ti,Nb-N,C+
MnS
~2.5–6.4 1.7–3.3
The results of electrolytic etching should be carefully assessed in conjunction with
the results of electrochemical studies. For instance, in the case of the 13Cr-5Ni-2Mo (Q135)
samples, sulfides with molybdenum-containing carbo-nitride inclusions are observed.
This confirms the earlier assumptions regarding the influence of inclusions on passivation
processes. In comparison, the 13Cr-3Ni-1Mo sample exhibits less favorable inclusion char-
acteristics than the 13Cr-4Ni-1Mo sample, including size and dissolution coefficient.
The high values of K
D
, as well as the presence of large inclusions, explain the occur-
rence of pits on the surface of the 13Cr-3Ni-1Mo steel sample after SSC testing.
4. Discussion
Electrochemical studies of the samples of P110 tubing made of 13Cr-2Ni-grade steel
after service revealed that pH critically affects the materials resistance in the corrosion-
active environment. The most aggressive environment for this material was found to be a
3% NaCl solution saturated with CO
2
, with a pH value less than 3.0 at a temperature of 60
°C. In this environment, four experimental closest analogs of 13Cr-Ni-Mo-alloyed steels
were tested for comparison: 13Cr-4Ni-1Mo (P110), 13Cr-5Ni-2Mo (P110), 13Cr-5Ni-2Mo
(Q135), and 13Cr-3Ni-1Mo (P110). Based on the results of the conducted electrochemical
investigations, it can be concluded that 5Ni-2Mo (P110/Q135) steels exhibit the lowest cor-
rosion rate in a CO
2
-saturated environment (0.056–0.100 mm/year), while 13Cr-3Ni-1Mo
steel shows the highest corrosion rate (0.409 mm/year). The corrosion rate of 13Cr-4Ni-
1Mo steel was the median—0.156 mm/year.
Metals 2023, 13, x FOR PEER REVIEW 11 of 14
1b
Not observed MnS ~0.5–2.0 -
2a
Al
2
O
3
+
Ti,Nb-N,C+
MnS
~3.2–12 2.1–5.4
2b
Al
2
O
3
+
Ti,Nb-N+
MnS
~3.2–6.2 1.5–4.1
3
Al
2
O
3
+
Ti,Nb-N,C+
MnS
~2.5–6.4 1.7–3.3
The results of electrolytic etching should be carefully assessed in conjunction with
the results of electrochemical studies. For instance, in the case of the 13Cr-5Ni-2Mo (Q135)
samples, sulfides with molybdenum-containing carbo-nitride inclusions are observed.
This confirms the earlier assumptions regarding the influence of inclusions on passivation
processes. In comparison, the 13Cr-3Ni-1Mo sample exhibits less favorable inclusion char-
acteristics than the 13Cr-4Ni-1Mo sample, including size and dissolution coefficient.
The high values of K
D
, as well as the presence of large inclusions, explain the occur-
rence of pits on the surface of the 13Cr-3Ni-1Mo steel sample after SSC testing.
4. Discussion
Electrochemical studies of the samples of P110 tubing made of 13Cr-2Ni-grade steel
after service revealed that pH critically affects the materials resistance in the corrosion-
active environment. The most aggressive environment for this material was found to be a
3% NaCl solution saturated with CO
2
, with a pH value less than 3.0 at a temperature of 60
°C. In this environment, four experimental closest analogs of 13Cr-Ni-Mo-alloyed steels
were tested for comparison: 13Cr-4Ni-1Mo (P110), 13Cr-5Ni-2Mo (P110), 13Cr-5Ni-2Mo
(Q135), and 13Cr-3Ni-1Mo (P110). Based on the results of the conducted electrochemical
investigations, it can be concluded that 5Ni-2Mo (P110/Q135) steels exhibit the lowest cor-
rosion rate in a CO
2
-saturated environment (0.056–0.100 mm/year), while 13Cr-3Ni-1Mo
steel shows the highest corrosion rate (0.409 mm/year). The corrosion rate of 13Cr-4Ni-
1Mo steel was the median—0.156 mm/year.
Al2O3+
Ti,Nb-N,C+
MnS
~2.5–6.4 1.7–3.3
4. Discussion
Electrochemical studies of the samples of P110 tubing made of 13Cr-2Ni-grade steel
after service revealed that pH critically affects the material’s resistance in the corrosion-
active environment. The most aggressive environment for this material was found to be a
3% NaCl solution saturated with CO
2
, with a pH value less than 3.0 at a temperature of
60
◦
C. In this environment, four experimental closest analogs of 13Cr-Ni-Mo-alloyed steels
were tested for comparison: 13Cr-4Ni-1Mo (P110), 13Cr-5Ni-2Mo (P110), 13Cr-5Ni-2Mo
(Q135), and 13Cr-3Ni-1Mo (P110). Based on the results of the conducted electrochemical
investigations, it can be concluded that 5Ni-2Mo (P110/Q135) steels exhibit the lowest
corrosion rate in a CO
2
-saturated environment (0.056–0.100 mm/year), while 13Cr-3Ni-1Mo
steel shows the highest corrosion rate (0.409 mm/year). The corrosion rate of 13Cr-4Ni-1Mo
steel was the median—0.156 mm/year.

Metals 2023,13, 1805 12 of 14
The results of autoclave tests in a 5% NaCl and 0.5% acetic acid solution with a pH
of 3–4 at a temperature of 80
◦
C for 240 h showed that the samples of 13Cr-4Ni-1Mo steel
(0.0019 mm/year), 13Cr-5Ni-2Mo—P110 (0.0007 mm/year), and 13Cr-5Ni-2Mo—Q135
(0.0025 mm/year) exhibited low corrosion rates without critical pittings. For the samples
of 13Cr-3Ni-1Mo steel, passivation was absent under the conditions of the autoclave tests,
which was manifested by the presence of a uniform layer of corrosion products on the
surface. The corrosion rate of 13Cr-3Ni-1Mo steel was 0.0106 mm/year.
The resistance to sulfide stress cracking (SSC) was evaluated according to NACE
TM0177, Method A, on cylindrical samples immersed in a solution of 5% NaCl and 0.5%
acetic acid, saturated with 10% H
2
S, for 720 h. The results showed that only the sample of
13Cr-4Ni-1Mo steel did not fracture during the testing. The samples of 13Cr-5Ni-2Mo (P110),
13Cr-5Ni-2Mo (Q135), and 13Cr-3Ni-1Mo (P110) steels exhibited a high susceptibility to
SSC, fracturing after 150, 170, and 250 h of testing, respectively. Secondary cracks were
observed on all fractured samples, and pitting was observed on the samples of 13Cr-5Ni-
2Mo (P110) and 13Cr-3Ni-1Mo steels.
The evaluation of non-metallic inclusions (NMIs) using the electrolytic extraction
method showed that the samples of 13Cr-4Ni-1Mo steel contained inclusions of more favor-
able shape, size, and chemical composition compared to the other steels. The occurrence of
pitting in 13Cr-3Ni-1Mo steel after SSC testing can be attributed to the presence of large
manganese sulfide inclusions. The pitting in 13Cr-5Ni-2Mo (Q135) steel after SSC testing
can be attributed to the presence of corrosion-active molybdenum carbide inclusions.
Based on the results of the study, increasing the nickel and molybdenum content in
steels of this class does not lead to a directly proportional increase in corrosion resistance in
a model environment approximating operational conditions. The research has shown that
high-strength 13Cr materials, slightly inferior to supermartensitic ones, due to increased
carbon content, may still exhibit satisfactory resistance in CO
2
environments and low con-
centrations of H
2
S. Furthermore, metallurgical quality and chemical composition influence
the formation of specific non-metallic inclusions, relevant to this type of material, which
have a significant impact on the corrosion resistance of stainless steel.
Thus, among the investigated steel types, 13Cr-4Ni-1Mo steel proves to be the most
optimal, demonstrating high resistance to SSC, low corrosion rates under aggressive auto-
clave test conditions, satisfactory results in electrochemical testing, and containing more
favorable types of small-sized non-metallic inclusions.
5. Conclusions
Tests were carried out to determine the corrosion characteristics of experimental
steel grades with the determination of resistance to sulfide stress corrosion cracking, the
determination of the corrosion rate in autoclave tests under conditions close to opera-
tional, and the determination of the corrosion-electrochemical characteristics in a CO
2
-
saturated environment. The influence of the chemical composition, structure and metallur-
gical quality, and production technology on the corrosion properties of the studied steels
is determined.
1.
Tests were carried out to determine the corrosion characteristics of experimental steel
grades with the determination of resistance to sulfide stress corrosion cracking, the
determination of the corrosion rate in autoclave tests in conditions close to opera-
tional, and the determination of the corrosion-electrochemical characteristics in a
CO2-saturated environment.
2.
When tested to determine the resistance to sulfide cracking under stress in accordance
with NACE TM-0177, Method A, at a load of 80% of the minimum yield strength, all
test steels showed a tendency to crack. However, steel 13Cr-4Ni-1Mo (P110) did not
fracture during the tests, although there are cracks on two of the three samples.
3.
According to the results of electrochemical studies carried out in a CO
2
-saturated
environment at pH 2.8–3 and a temperature of 60
◦
C, it was shown that 13Cr-4Ni-

Metals 2023,13, 1805 13 of 14
1Mo (P110), 13Cr-5Ni-2Mo (P110), and 13Cr-5Ni-2Mo (Q135) steels have the lowest
corrosion rate.
4.
The results of autoclave tests at a pH of 3–4 and a partial pressure of carbon dioxide
of 3 MPa at a total pressure of 5 MPa in a CO
2
-saturated solution at a temperature of
80
◦
C are consistent with the results of electrochemical tests. It has also been shown
that steel 13Cr-4Ni-1Mo (P110), 13Cr-5Ni-2Mo (P110), and 13Cr-5Ni-2Mo (Q135) have
the highest corrosion resistance in a CO
2
-saturated environment. Steel 13Cr-3Ni-1Mo
(P110) had the lowest corrosion resistance during autoclave tests.
5.
The metallurgical quality, shape, size, and type of non-metallic inclusions allow one
to obtain an economically alloyed 13Cr-type steel of martensitic class with satisfactory
resistance in CO2and H2S environments: 13Cr-4Ni-1Mo.
Author Contributions:
Conceptualization, A.D. and E.A.; data curation, O.S., N.D. and K.L.; investi-
gation, A.D., E.A. and V.K.; methodology, A.D. and D.S.; project administration, A.D., E.A., N.D. and
A.A.; resources, O.S., N.D. and K.L.; supervision, A.D., E.A. and K.L.; validation, A.D.; visualization,
A.D. and V.K.; writing—original draft, A.D. and V.K.; writing—review and editing, A.D. and E.A. All
authors have read and agreed to the published version of the manuscript.
Funding:
The research is partially funded by the Ministry of Science and Higher Education of
the Russian Federation as part of the World-class Research Center program: Advanced Digital
Technologies (contract No. 075-15-2022-311 dated 20 April 2022).
Data Availability Statement: Not applicable.
Conflicts of Interest: The authors declare no conflict of interest.
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