Qualification of Lean Duplex Grade Ldx 2101 (UNS32101) for Carcass Material in Flexible Pipes

Unbonded Flexible pipes have inner armour of stainless steel made from a helix structure of an S-shaped continuous strip. Typically the selected stainless steel grade has been AISI 316L (UNS S31603). The recent development of lean duplex materials has provided attractive alternatives due to the increased strength, good corrosion resistance and lower cost.
The carcass in an unbonded flexible pipe is exposed to the conveyed fluid or gas but protected from marine seawater surroundings. This paper describes acceptance criteria for autoclave testing in CO₂ / H₂S environments. Observations are made on initiation of pitting and selective corrosion on LDX 2101 (UNS S32101). Results from both short and long term tests are evaluated in order to validate an acceptable duration for autoclave testing.