A standard NACE hydrogen induced crack test was used to evaluate the resistance of two compositions of X70 steel (X70-X and X70-B) under severe (pH = 2.7 and 100% H~2~S) and mild (pH = 5.5 and 100% H~2~S) sour service conditions. An ultrasonic technique was developed to quantify the severity of hydrogen cracking in both steels as a function of test conditions, steel type and time.  In this procedure, a series of local ultrasonic measurements were taken for each test sample to determine a local crack to backwall signal ratio (LCBR).  The local LCBR values were integrated over the entire sample to give a global crack to backwall ratio (GCBR). The larger the value of GCBR, the greater the severity of hydrogen cracking in the sample. Energy dispersive X-ray spectroscopy (EDX) and glancing angle X-ray diffraction (XRD) were used to characterize the surface corrosion products that formed during testing. For severe sour service conditions, the GCBR value reached an asymptotic value of approximately 0.4 and 0.5 for X70-X and X70-B steels, respectively, after 2 days of testing. For mild sour service conditions, the GCBR value reached an asymptotic value of approximately 0.2 for X70-B steel after 32 days of testing. The onset of cracking of X70-X steel occurred between 32 and 64 days. XRD measurements showed the formation of FeS deposits on both steels tested under mild sour service after 8 days of testing. EDX mapping confirmed the presence of high sulfur content over a significant fraction of the surface. XRD measurements of X70-B steel under severe sour service after 8 days did not show the presence of FeS. The surface FeS is believed to alter hydrogen ingress into the steel making it difficult to directly compare the measured GCBR values obtained under mild and severe sour service.


Evaluation of Hydrogen Induced Cracking Resistance of X70 Pipeline Steel Under Severe and Mild Sour Service Conditions Using Ultrasonic Analysis

Division / Sponsors: 
Pipeline Systems Division

Paper Proceedings: https://asmedigitalcollection.asme.org/IPC/IPC2020/volume/84447

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