新型HFW焊管的耐腐蚀性能

李霄; 李磊磊; 牛辉; 黄晓辉; 韦奉; 吕祥鸿

LI Xiao,LI Lei-lei,NIU Hui,HUANG Xiao-hui,WEI Feng,LYU Xiang-hong.Corrosion Resistance Analysis of New HFW Welded Pipe[J],52(4):251-260

Corrosion Resistance Analysis of New HFW Welded Pipe

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DOI：10.16490/j.cnki.issn.1001-3660.2023.04.022

KeyWord:HFW welded pipe ε-Cu phase antibacterial steel microbial corrosion SRB

Author	Institution
LI Xiao	Xi’an Key Laboratory of High Performance Oil and Gas Field Materials, School of Material Science and Engineering, Xi’an Shiyou University, Xi’an , China
LI Lei-lei	Xi’an Key Laboratory of High Performance Oil and Gas Field Materials, School of Material Science and Engineering, Xi’an Shiyou University, Xi’an , China
NIU Hui	Welded Pipe Research Institute of Baoji Petroleum Steel Pipe, Shaanxi Baoji , China;National Petroleum and Natural Gas Pipe Engineering Technology Research Center, Shaanxi Baoji , China
HUANG Xiao-hui	Welded Pipe Research Institute of Baoji Petroleum Steel Pipe, Shaanxi Baoji , China;National Petroleum and Natural Gas Pipe Engineering Technology Research Center, Shaanxi Baoji , China
WEI Feng	Welded Pipe Research Institute of Baoji Petroleum Steel Pipe, Shaanxi Baoji , China;National Petroleum and Natural Gas Pipe Engineering Technology Research Center, Shaanxi Baoji , China
LYU Xiang-hong	Xi’an Key Laboratory of High Performance Oil and Gas Field Materials, School of Material Science and Engineering, Xi’an Shiyou University, Xi’an , China

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Abstract:

The new Cu-bearing High Frequency Welding (HFW) steel for welded pipes is prepared by Cu alloying, using a 150 kg vacuum induction furnace, forging the ingot into a billet, followed by solution treatment at 1 050 ℃. The treated billet is made into a steel plate using a controlled rolling and cooling process, with a 1 h ageing precipitation at 550 ℃. The treated steel plates are rolled into round tubes which are welded by high frequency welding technology. The Cu alloying improves the surface properties of the material and gives it good antibacterial properties. This paper investigates the corrosion behaviour of the new Cu-bearing HFW welded pipe base material and welded joint, conventional welded pipe material L360, in the SRB environment for simulated corrosion experiments to explore its corrosion resistance and reveal the bactericidal mechanism of the antibacterial relative microorganisms in the material. The experimental solution is a simulated microbial corrosion environment solution, the microorganism used in this paper is sulfate-reducing bacteria (SRB) for corrosion experiments. The SRB strain was activated by using SPX-250B biochemical incubator at 37 ℃. The activated SRB solution was injected into a Cl‒ solution at a concentration of 34 000 mg/L. Corrosion specimens were taken from welded Cu-bearing steel base material, welded joint and L360 pipeline steel and machined using high-precision wire-cutting to produce 50 mm×10 mm×3 mm corrosion hangers. The corrosion weight loss test was selected at a temperature of 37 ℃ and the test period was 30 days. Before the experiments, the specimens were ground with steel sandpaper to eliminate mechanical processing traces, and the de-oiled and dehydrated specimens were placed in a dryer to dry, and the size and mass of the experimental hangings were recorded to 0.001 mm and 0.1 mg respectively. The corrosion products were removed from the specimens for weighing and calculating the corrosion weight loss rate, the uniform corrosion rate was calculated according to NACE SP 0775-2018 standard, the samples Cu-bearing steel and L360 immersed in SRB solution were removed after the experiment, the specimens with biofilm were first immersed in 2.5% glutaraldehyde/phosphate (NaCl content 8.7 g/L; KH2PO4 content 0.4 g/L; K2HPO4 1.23 g/L) buffer solution for 30 min. The specimens were dehydrated and fixed in alcohol at 20%, 50%, 75% and 100% concentrations for 10 min and then dried and stored. The surface information of the specimens was subsequently observed using a GIMI500 field emission scanning electron microscope and energy spectrum analysis of the relevant areas. The microstructure of Cu-bearing steel is granular bainite and polygonal ferrite with a small amount of pearlite. The analysis of the microstructure of Cu-bearing steel reveals that the Cu-bearing steel precipitated phase is nano-Cu-rich phase and the matrix is α-Fe; the microstructure of L360 is polygonal ferrite and lamellar pearlite. The results of SRB corrosion experiments showed that the corrosion rates of Cu-bearing steel base material, welded joint and L360 in SRB solution were 0.007 1 mm/a, 0.023 9 mm/a and 0.010 0 mm/a, respectively, and their maximum pitting rates were 0.025 9 mm/a, 0.174 0 mm/a and 0.254 0 mm/a, respectively, with the pitting rate of L360 being 10 times higher than that of Cu-bearing steel. Through corrosion products, bacteria distribution and morphology of scanning electron microscopy observation found that the surface of Cu-bearing steel ladle corrosion products in Cu elements aggregation, the surface was not found to be structurally intact biofilm, corrosion media in the material surface hydrolysis generated by Cu ions effectively destroy the corrosion of the initial rapid attachment to the metal surface biofilm, thus forming a residue on the metal surface, near the shrinkage and tissue fluid spillage of bacteria found. Cu-bearing steel weld zone biofilm structure is intact, there are a large number of bacteria adsorption and good bioactivity, microbial corrosion under the film to produce corrosion pits caused by local film rupture, pitting corrosion is serious. After HFW welding joint weld zone pitting corrosion susceptibility is enhanced and corrosion resistance is reduced. Cu-bearing steel will form biofilm by rapid adsorption of SRB on the material surface at the early stage of corrosion, and the non-uniformity of SRB biofilm increases the active site of corrosion. The surface Cu-rich phase at the bottom of the biofilm is hydrolyzed, and the Cu ions from the hydrolysis are purposefully aggregated at the center of the biofilm. When free Cu ions come into contact with bacteria, they enter inside the biofilm to disrupt its cell wall and membrane structure or disrupt the biological environment, and the bactericidal effect of Cu ions from the center of the biofilm to the outside is from strong to weak. The aggregation of Cu ions had the most significant bactericidal effect at the center of the biofilm, and partially shriveled and dehydrated bacteria were found at the edge of the envelope produced after biofilm death.