Initial Corrosion Behavior of Carbon Steel Q235, Pipeline Steel L415, and Pressure Vessel Steel 16MnNi Under High Humidity and High Irradiation Coastal-Industrial Atmosphere in Zhanjiang
LI Xiaohan1,2, CAO Gongwang2(), GUO Mingxiao1,2, PENG Yunchao3, MA Kaijun3, WANG Zhenyao2()
1School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China 2Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China 3PipeChina Network Corporation Eastern Oil Storage and Transportation Co., Ltd., Xuzhou 221008, China
Cite this article:
LI Xiaohan, CAO Gongwang, GUO Mingxiao, PENG Yunchao, MA Kaijun, WANG Zhenyao. Initial Corrosion Behavior of Carbon Steel Q235, Pipeline Steel L415, and Pressure Vessel Steel 16MnNi Under High Humidity and High Irradiation Coastal-Industrial Atmosphere in Zhanjiang. Acta Metall Sin, 2023, 59(7): 884-892.
The Zhanjiang oil station is located near the sea, and corrosion factors such as Cl-, SO2, humidity, and UV irradiation in the surrounding environment will endanger the service life of the common materials. Carbon steel Q235 is commonly used as an oil tank pressure ring, pipeline steel L415 is used for oil and gas transportation, and pressure vessel steel 16MnNi is commonly used as the outer wall material of an oil tank. These materials are easily corroded when they are directly exposed to the atmosphere, but there have been few studies in recent years on the short-term corrosion behaviour of common metal materials in oil stations in high humidity and high irradiation industrial marine atmosphere environments. In this work, the initial corrosion behaviour of carbon steel Q235, pipeline steel L415, and pressure vessel steel 16MnNi exposed to the real Zhanjiang atmospheric environment for 180 d were studied through weight loss analysis, corrosion product analysis, corrosion morphology observation, and electrochemical analysis. According to the thickness loss data, carbon steel Q235 had the weakest corrosion resistance of the three materials, whereas pipeline steel L415 had the best corrosion resistance. These common materials were exposed to the same atmospheric environment for the same amount of time, resulting in the same corrosion products in the rust layer, which contained α-FeOOH, γ-FeOOH, and Fe3O4. The difference was that the rust layer of carbon steel Q235 contained a high concentration of β-FeOOH, which may have facilitated the corrosion process. The concentration of γ-FeOOH and Fe3O4 varied amongst the three materials. The rust layer of carbon steel Q235 contained more γ-FeOOH and Fe3O4, followed by pressure vessel steel 16MnNi and pipeline steel L415, which had the least γ-FeOOH and Fe3O4. Furthermore, carbon steel Q235 had the thinnest rust layer and the greatest thickness loss, whereas pipeline steel L415 and pressure vessel steel 16MnNi had a thicker rust layer and less thickness loss. The results of electrochemical experiments showed that the rust layer of carbon steel Q235 has the weakest ability to protect the matrix, whereas the rust layer of L415 has the best ability to protect the matrix. Additionally, the synergistic effect of Cl-, SO2, and UV irradiation destroyed the protective layer of the rust layer and accelerated the corrosion.
Table 1 Chemical compositions of Q235, L415, and 16MnNi steels
Fig.1 Microstructures of Q235 (a), L415 (b), and 16MnNi (c) steels
Time
Tmax
Tmin
Cloudy
Rain
Sun
month
oC
oC
d
d
d
7
33
27
14
16
0
8
33
26
14
16
0
9
33
25
16
13
1
10
30
22
20
7
3
11
26
20
20
8
2
12
21
15
21
5
4
Table 2 Changes of Zhanjiang environment conditions over time
Fig.2 Thickness losses of Q235, L415, and 16MnNi steels exposed to Zhanjiang atmospheric environment for 180 d
Fig.3 Low (a, c, e) and locally high (b, d, f) magnified surface morphologies of Q235 (a, b), L415 (c, d), and 16MnNi (e, f) steels at the same time and the same environment for 180 d
Fig.4 Cross-section morphologies of Q235 (a), L415 (b), and 16MnNi (c) exposed to Zhanjiang atmospheric environment for 180 d
Fig.5 XRD spectra of powdered rust Q235, L415, and 16MnNi steels exposed to the same environment and the same time for 180 d
Fig.6 Potentiodynamic polarization curves of Q235, L415, and 16MnNi steels exposed to Zhanjiang atmospheric environment for 180 d (E—potential, i—current density)
Steel
Ecorr / mV
icorr / (μA·cm-2)
Q235
-559.5
107.20
L415
-662.9
77.82
16MnNi
-652.1
86.79
Table 3 Corrosion potential (Ecorr) and corrosion current density (icorr) of Q235, L415, and 16MnNi steels
Fig.7 Nyquist (a) and Bode (b, c) diagrams of Q235,L415, and 16MnNi steels exposed to Zhanjiang atmospheric environment for 180 d
Fig.8 Equivalent circuit of EIS (Rs—the electrolyte resistance, Rr—the rust layer resistance, Rct—the charge transfer resistance, Qr—the rust layer capacitance, Qdl—the double layer capacitance, Zw—the barrier diffusion impedance)
Steel
Rs / (10-4 Ω·cm2)
Qr / (10-9 F·cm-2)
nr
Rr / (Ω·cm2)
Qdl / (10-3 F·cm-2)
ndl
Rct / (Ω·cm2)
Zw / (10-2 Ω·cm2)
χ2 / 10-4
Q235
2.674
5.617
1
40.47
2.216
0.4563
31.39
5.296
3.98
L415
106.7
5.602
1
51.55
1.588
0.3364
72.15
4.795
3.68
16MnNi
13.68
5.160
1
41.46
1.134
0.2762
61.60
5.365
2.61
Table 4 Fitting parameters of the equivalent circuit
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