Qualification of TMCP Pipe for Severe Sour Service: Mitigation of Local Hard Zones

Abstract

Abstract C-Mn steels are extensively used as line pipe material for sour service oil and gas applications, i.e. in the presence of hydrogen sulfide (H2S), because of their ease of fabrication, weldability and significantly lower cost compared to Corrosion Resistant Alloys (CRAs). However, use of C-Mn steel in sour conditions can be limited by its susceptibility to various hydrogen damage mechanisms such as sulfide stress cracking (SSC) and hydrogen induced cracking (HIC). Presently, there are several industry standards which provide guidelines for materials selection and qualification testing to ensure the integrity of carbon steel pipelines in sour service. In recent years, examples of line pipe susceptibility to SSC have occurred due to undetected Local Hard Zones (LHZs) produced during steel plate manufacture. A companion paper (Fairchild, et al, [1]) describes historical and one newly recognized root causes for LHZs. Due to this newly recognized root cause, the adequacy of the current industry practice for specifying and qualifying C-Mn line pipe for severe sour service should be evaluated. In this work, a new approach to monitoring steel plate manufacture during Thermo Mechanical Controlled Processing (TMCP) in order to manage LHZs is explained. Results from implementing this qualification approach will be discussed. In addition, several gaps were identified in the current test methods and various potential modifications to address these gaps were identified. Based on the results of these studies, recommendations to the test methods are made to improve the robustness in the materials qualification process used for sour pipeline projects.