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Environmentally Assisted Cracking of High Strength PH Nickel Alloys for HPHT Applications

Environmentally assisted cracking of high strength PH nickel alloys 725 945X and 955 were evaluated under subsea HPHT environments. The two primary environments of interest in this effort were in 3.5wt% NaCl pH = 8.2 under cathodic polarization at low temperature 40F and in sour service environments at elevated temperature and pressure (350F/400F and 125psia CO2/0.08psia H2S). Fatigue crack growth rate and static crack growth rate measurements were performed in both the environments. The alloys exhibited excellent resistance to fatigue and stress corrosion cracking but did not exhibit a strong frequency dependence. There was no evidence of stable static crack growth even at very high values of stress intensity factor (90ksiÖin).However tests performed under cathodic polarization revealed that the fatigue crack growth rate exhibits a strong dependence on frequency for various DK values. In all cases stable static crack growth rate (CGR) was observed for all the alloys tested. In case of 725 CGR values on the order of 10-6mm/s were obtained at K values as low as 50ksiÖin whereas for 945X required a stress intensity factor of about 80 ksiÖin to obtain similar CGR’s suggesting that the 945X was more resistant to cracking under hydrogen embrittlement conditions than 725.

Product Number: 51319-12794-SG
Author: Thodla Ramgopal
Publication Date: 2019
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51312-01477-Environmental Effects on Fatigue Crack Growth Rates in Sour Environments

Product Number: 51312-01477-SG
ISBN: 01477 2012 CP
Author: Ramgopal Thodla
Publication Date: 2012
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