Results from Environmental Assisted Cracking Experiments in O&G Environments for UNS S33207

UNS S33207 is a new hyper duplex stainless steel with a minimum PRE of 50 that has been developed for use in umbilicals. Results from corrosion and mechanical testing show that UNS S33207 has better localized corrosion resistance and higher strength than superduplex stainless steel. The increase in strength is about 20% compared to UNS S32750. In addition the fatigue properties are increased for UNS S33207 compared to superduplex. Earlier has no results from environmental cracking experiments been reported. Sour service and in seawater with cathodic protection are two important environmental assisted cracking environments in many applications in the oil and gas industry. For each environment a test program has been performed and experimental results are given. Both small diameter tubing and material with larger austenite spacing were tested for hydrogen induced stress cracking, HISC. For small diameter tubing no cracking was observed for C-rings at 100 % yield strength when coupled to Zn at 20°C .Results from constant load experiments at a potential at
-1084 mV vs. SCE show that UNS S33207 with an austenite spacing of slightly above 30µm does not initiate cracking at 100% actual yield strength at 4°C. The results are in line with DNV-RP-F112 for duplex stainless steels and these results indicate that USN S33207 has good resistance against HISC.
Results from H₂S-testing at both room temperature and elevated temperature for several heats indicate that UNS S33207 has similar resistance or better resistant against cracking in sour service as superduplex stainless steels.