This paper summarizes the investigation and findings of a root cause failure analysis (RCFA) related to the failure of 25 Cr, UNS S32750, Super Duplex Stainless Steel (SDSS2507) tubes inside three subsea umbilicals off the western equatorial coast of Africa and the adjoining topsides equipment made of 316L Stainless Steel, UNS S31603 (SS316L).

The RCFA determined that a particular type of low-dosage hydrate inhibition chemical (LDHI) being used during normal service conditions, caused internal pitting corrosion that resulted in numerous leaks in weld zones and base metal of the SDSS2507 tubes, necessitating the replacement of all three umbilicals. The topsides SS316L equipment exposed to this chemical experienced similar damage for the same reasons.

Subject
Pits, Materials, Tubes, Anodic polarization curves, Inspection, Seawater, Acidity, Mechanical failure, Fluids, Pitting, Stainless steel, Chlorides, Samples
Keywords:
umbilical, 25 Cr super duplex stainless steel 2507 UNS S32750 (SDSS2507), low dose hydrate inhibitor (LDHI), pitting, critical pitting temperature (CPT), potentiodynamic anodic polarization curves, ASTM G1501, ASTM G482, ASTM G53, 316L stainless steel UNS S31603 (SS316L)
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2011
Association for Materials Protection and Performance (AMPP)
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