Influence of external tensile stress on corrosion and trench formation of low alloy steel in a low H₂S content sour corrosion environment

Abstract

The influence of external tensile stress on corrosion and trench formation of low alloy steel in a low H 2 S content sour corrosion environment was investigated. These experiments were conducted with steel for pipelines, and electrochemical methods were used. The results showed that external stress increases the amount of corrosion weight loss and trench depth by promoting the anodic dissolution reaction, and stress concentration was proven to be one of the driving forces for trench formation due to localized corrosion. Based on the experimental findings, the mechanism of trenching was discussed from the viewpoint of promotion of the anodic dissolution reaction by dislocations.

Influence of dislocation on sour corrosion of carbon steel in a low H2S sour environment

“…It has been reported in previous studies that the anodic solubility of steels is promoted by applying external plastic stress of 105% AYS (actual yield strength) in a sour corrosion environment. [ 42 ] The promotion of anodic dissolution by dislocations has been explained based on the terrace–ledge–kink model, [ 31,32 ] and has also been suggested experimentally, for example, by Damjanovic and Bockris, [ 43 ] who showed that the dissolution current of a high‐index plane (hip) with many steps was up to three orders of magnitude higher than that of a low‐index plane with few slip steps. The reason for the increase in the amount of anodic reaction due to the increase in the dislocation density observed in this study can also be explained reasonably by the terrace–ledge–kink model.…”

“…In the SSC observed in sour corrosion environments, it has been experimentally confirmed that localized corrosion, which is an initial process of SSC, is promoted by stress concentration. [ 42 ] In a plastic stress concentration field, strong activation of anodic dissolution based on similar lattice defects may be one of the driving forces. However, since SSC in a sour corrosive environment is a phenomenon observed in steel materials that are continuously subjected to external stress, it is necessary to consider the involvement of various influencing factors and the possibility of complicated corrosion phenomena.…”

Sulfide Stress Cracking (SSC) of Low Alloy Linepipe Steels in Low H₂S Content Sour Environment

“…The authors examined the SSC mechanism in the low H 2 S partial pressure condition of 0.15 bar for the general X65 grade (YS ≥ 450 MPa) material as a low alloy steel line pipe, and clarified that the transgranular microcrack formation process is the anodic dissolution control based on the APC mechanism. 28) In addition, it was clarified that the local dissolution was promoted by plastic deformation 29) and higher material hardness, 30) and it was estimated from compact tension (CT) test with pre-crack that the initiation and propagation process of SSC crack was caused by HE mechanism. 16) However, since there exist multiple factors such as microscopic structural morphology and crystal orientation distribution of bainite structure, microscopic elasto-plastic deformation of tensile surface with increasing applied stress, and sour environmental conditions such as H 2 S partial pressure and pH, it is not clear how these factors relate to the initial corrosion pit and groove formation process and SSC crack initiation and propagation process.…”

Effect of Surface Hardness and Hydrogen Sulfide Partial Pressure on Sulfide Stress Cracking Behavior in Low Alloy Linepipe Steel

“…19,28,29) Investigation of the SSC mechanism based on the 0.15 bar H 2 S environment revealed that the generation process was dominated by anodic dissolution (local dissolution process: APC) and that local dissolution was promoted by plastic stress concentration and material hardening. 30,31) Due to the high corrosiveness of the hard microstructure on the steel surface, the hard microstructure is preferentially dissolved, and the area where the hard microstructure is dissolved becomes a stress concentration area in the presence of stress. Therefore, introduction of dislocations by stress acts as a driving force, and the part is fixed as a preferential dissolution site.…”

“…in the solution environment progresses. 30) That is, when corrosion starts, anions migrate toward the anode (electrophoresis), and as a result, Cl − ions and Fe 2 + ions form iron chloride at the anode (inside the pitting portion), and iron hydroxide Fe (OH) 3 and hydrochloric acid HCl are formed by a hydrolysis reaction, lowering the pH of the environment in the local corrosion zone. 32) This localized lowering of pH causes further dissolution of iron and provides an additional driving force for localized corrosion growth.…”