In Oil & Gas industries, Cr-Ni-Mo stainless steels and Ni-Cr-Mo alloys with Pitting Resistance Equivalent Number (PREN) lower than 40 could be selected for Rigid Production subsea risers, pipeline, and associated structure’s piping, according to a CO2/H2S corrosion assessment that considers all steady and transient conditions foreseen to operate the reservoir.
However, there are frequently some localized corrosion concerns for these materials during the installation and pre-commissioning of the line, when the internal surface of the line could be in contact temporarily with untreated seawater. These concerns systematically lead to discard the selection of these materials and to select, for conservative purpose, UNS N06625 that is admitted immune to localized corrosion in ambient seawater in international standard and operator’s specification, whatever the outcomes of the CO2/H2 corrosion assessment.