Microstructural and mechanical factors influencing high pH stress corrosion cracking susceptibility of low carbon line pipe steel

• Different mechanical and microstructural features for SCC and non-SCC affected pipe.
• Lower residual stress/strain below the outer surface for the non-SCC affected pipe.
• Different GB character and grain orientations between the two types of samples.
• Lower CGR measured in laboratory high pH SCC tests for non-SCC affected specimens.
• Low residual stress, low HAB fraction and {1 1 0}〈1 1 0〉 texture improve SCC resistance.

Several adjacent gas pipe sections were obtained from the field. These pipe sections had nominally identical manufacturing, construction, coating and operational conditions. Some sections were unaffected by stress corrosion cracking (SCC), whereas surrounding sections were affected by SCC. Slight differences in mechanical and microstructural properties were found between the two types of section. Residual stress/strain and hardness close to the outer surface of the pipes and high angle boundary fraction values were lower for the non-cracked pipe sections. Predominant 〈1 1 0〉//ND texture was also found at the outer surface of the non-cracked pipe sections. These characteristics lead to a lower crack growth rate in laboratory SCC experiments. These features being mainly a result of the line pipe steel manufacturing operations, appropriate metallurgical processes leading to low residual stress (6.2%YS), relatively low fraction of high angle boundaries (about 0.75) and predominant {1 1 0}〈1 1 0〉 texture in the material (or in the near surface) are expected to greatly improve the stress corrosion cracking resistance of line pipe steels on the field.