Super martensitic stainless steel (13Cr-5Ni-2Mo) provides high strength and CO2 resistance. It can be used at high temperature up to 180°C/356°F in high chloride environment. When the well temperature is above 180°C/356°F, Duplex grades 22-5-3 or Super Duplex 25-7-4 grades are commonly selected as per API 5CRA standard.
A new proprietary grade chemistry has been developed to provide improved strength up to 125ksi and higher pitting resistance while maintaining a tempered martensitic microstructure with low delta ferrite content and no detrimental phases or precipitates. Improvement of pitting resistance has been assessed through cyclic polarization curves. Higher sulfide stress cracking (SSC) and stress corrosion cracking (SCC) were assessed through NACE(1) TM 0177 method A 1 at ambient and high temperature. X-ray Photoelectron Spectroscopy (XPS) characterizations provide deep knowledge about passive film compositions underlining the beneficial effect of higher Mo within the grade.
This paper presents the benefit of the improved chemistry on sweet corrosion and sulfide stress cracking in severe downhole environment. It summarizes the effect of different parameters in both production and shut-in conditions to be considered to select cost effective material.