Export Pipeline Material Selection for Extreme Sour Service Application

Abstract

AbstractWith recent sour gas field discoveries, material selection for export pipeline carrying the sour gas and liquid is one of the key challenges in commercializing the fields especially for the large diameter and long tie-back export pipeline, and it is the focus of this paper. Both CRA clad and Carbon Steel (CS) pipes have been used for sour service pipelines with different benefit and drawback. The study was performed to investigate both technical and commercial feasibility of the two material options. Facility concept has been differentiated between options as CRA clad pipe do not require gas and liquid dehydration and treatment. The conceptual study cover design, fabrication, installation, operation, RAM and risk assessment aspects to identify the key strength and challenges including cost estimation for life cycle cost evaluation. Material selection review including project benchmarking for TMCP CS for sour service has been performed. CRA clad option provides the lowest corrosion and cracking risk leading to minimum requirement for offshore processing facility. However, additional or larger facilities are needed at onshore gas plant such as Slug Catcher and PW treatment. Two main concerns for CRA clad pipe are the buckling due to exporting > 150 deg C fluids and the supply of CRA clad pipes for such a large quantity. TMCP CS option is more conventional for export pipeline with the main concern on the susceptibility for Sulfide Stress Cracking for sour service especially after the Kashagan incident. The study investigates the recent development of LHZ mitigation actions in manufacturing process, new pre-qualification recently published for extreme sour service and project benchmarking for similar H2S concentration. It has been concluded TMCP CS, with qualified manufacturer, is suitable for the extreme sour service application. Life cycle cost estimation indicate CRA clad option is significantly more expensive than CS option with the risk on the supply of cladded pipe. Cracking risk on TMCP CS for extreme sour service is high but manageable with the proven project record and therefore CS option is opted as development concept with the lower development cost than that for CRA clad.