Critical Assessment 17: Mechanisms of hydrogen induced cracking in pipeline steels

Abstract

Hydrogen induced cracking (HIC) remains a prominent issue for oil and gas exploration in challenging environments. This assessment discusses HIC in light of hydrogen transport through pipeline steel microstructures and crack initiation and propagation processes. While there has been significant research in hydrogen permeation through steel alloys, additional understanding is necessary in microstructures specific to pipeline steels. Furthermore, a standard model for crack initiation and propagation processes needs to be established; a fracture mechanics based model, which has been used by some researchers, is presented in the present paper to predict crack propagation. Advanced characterisation techniques can help elucidate mechanisms of hydrogen induced crack growth. Ultimately, linking hydrogen transport and cracking processes during HIC will enable optimised alloy and microstructure design.

Assessment of Critical Hydrogen Concentration in As‐Cast and Hot‐Rolled Billets in Medium Carbon Steels

“…Figure 6 shows some hydrogen-induced cracks in both Steel Grade A and Steel Grade B, and most of such cracks are located in central segregated zone. This is a well-known phenomenon widely investigated in the past, [31][32][33] which is related to the fact that impurities (e.g., P, S, Sb) as well as C and Mn tend to accumulate in the segregated areas, therefore increasing the probability of occurrence of HIC.…”

Effect of Cold-Rolling on Hydrogen Diffusion and Trapping in X70 Pipeline Steel

“…Traps in the microstructure are generally categorized into two based on the binding energy of each trap with hydrogen. Findley et al reported that 60kJ per mole is the critical binding energy for dividing traps into irreversible or reversible traps [12]. While reversible traps temporarily store hydrogen, the irreversible traps more permanently store the hydrogen.…”

Initiation of hydrogen induced cracks at secondary phase particles

“…Hydrogen induced internal cracking and blistering can occur in metals subjected to high fugacity hydrogen environments, such as high pressure hydrogen gas environments or under extreme cathodic charging conditions, even without the application of an external load or residual stress, though such stresses can contribute to HIC [5,6]. HIC occurs, for instance, in oil and gas sour service pipelines where hydrogen ingress into steel from H 2 S occurs [7]. Also hydrogen flakes as found in reactor pressure vessels [8] are an example of HIC and could be artificially reproduced by intensive electrochemical hydrogen charging [9].…”