Sour Service Challenges

Abstract

Abstract Material selection for sour service is generally based on International Standards. Sometimes there are project conditions that are not properly covered, therefore additional investigations are needed. This fact can arise conflictual discussions between the lay contractor and the field operator, regarding first the selection of the laboratory, and then the method and extent of the weld qualification campaign: disagreements may impact the installation schedule as well as significantly affect the operational requirements. The subject is crucial in field development projects, in both shallow and deep waters, when performance requirements are particularly demanding. In the meantime, field experience shows failure conditions in sour service due to erroneous design choices, inaccuracies during construction, unexpectedly severer flow conditions and/or poor mechanical performance of both line pipe and welds. Therefore, the upstream community is currently involved in joint industry initiatives that aim to establish international consensus on updating guidelines, aiming to include the lesson learnt from recent project outcomes. The challenges of sour service mainly regard material selection in case of long distance export pipelines from offshore fields, as well as the allowance of functional and environmental load effects on flowlines, i.e., the permissible number and entity of either few high stress cycles on high temperature high pressure flowlines or many small stress cycles on risers and free spans. In this paper an outline of sour service in offshore projects will be given, with comments on the state of the art from the designer and laying contractor's viewpoint. In particular, lessons learnt from recent experiences are discussed, in relation with the efforts for standardization currently undertaken by international certification bodies.