Formation of Microgrooving on C110 casing steel after Sulfide Stress Cracking Test

NACE TM0177 is a commonly employed materials qualification standard specifying how Sulfide Stress Cracking (SSC) tests must be conducted and interpreted to verify the suitability of material application in sour service. This standard specifies through the so-called method A test (a tensile uniaxial environmental cracking test) that a material could be considered acceptable for sour service as long as no failure is evidenced after 720 hours of exposure, and no initiation of environmental cracking is observed on the reduced length of the specimen after macrographic observations. After cross-sectional observations, so-called “micro-grooves” can sometimes be evidenced on the surfaces of non-failed specimens. Such features can hardly be interpreted as SSC crack initiation sites considering their shape and depth. Experience, however, shows that the formation of these microgrooves appears to be dependent on test conditions and type of load. This paper presents the results of investigations on the parameters influencing the micro-groove formation on C110 steel after the method A uniaxial tensile SSC test. Test parameters influencing the groove formation are studied, and the results suggest that grooving is not considered as SSC initiation for the testing conditions used in this work

Fracture Failure Analysis of C110 Oil Tube in a Western Oil Field

There was an oil pipeline fracture found in the unlock process of Z well in western oilfield.The reason that made the oil tube fracturewassystematically studied usingmacroscopic analysis,physical and chemical property test,scanning electron microscope with an energy dispersive X-ray spectrometer and X-ray diffraction analysis.The results suggested that the requirement of relevant standard for C110 steel grade was satisfied with the chemical component and mechanical property of oil tube.The perforation of oil tube made H2S in the fluid medium enter the oil set of connected rings. In addition, the high-pressure gas left by gas contained certain H2S and O2 so that the tubewould fracture and be invalid under the combined action of sulfide stress corrosion and oxygen corrosion.