TMCP Linepipe Materials, Welding Specifications and their Applications in NACE Region 3 Severe Sour Service

Abstract

Abstract Large diameter TMCP (Thermo-Mechanically Controlled Process) pipeline steel has been used widely in the past for NACE sour service pipelines application successfully. TMCP pipeline material has the benefits of good mechanical properties, good weldability, and cost competitive over alternate material such as Quench and Temper (Q&T) steel, especially for large diameter and long-distance pipeline. However, the recent pipeline project incident has shown detrimental local variations in the TMCP mechanical properties i.e., increased ID surface hardness leading to Sulfide Stress Cracking (SSC) from the Local Hard Zones (LHZ) or hard spots. This has led to the concerns over the use of TMCP steels on severe sour service in NACE region 3 application. This paper is to share the recent works carried out by the steel mill and Company on the use of TMCP steels for severe sour NACE region 3 application, and to address the potential risk of SSC by implementing the number of control measures e.g. Steel mill TMCP optimization, the steel plate surface hard spot detection system implementation, material specification in term of strength, line-pipe ECA, laybarge welding technique adopted and early welding qualification specifications. This paper also addresses control measures that have been in placed in minimizing the risk TMCP material deterioration during pipeline girth weld application.