Standard X-65 carbon steel pipe material is to be utilized for a flowline and riser system for an on-going project within the Gulf of Mexico. The project-produced fluids are corrosive with CO2 and produced water chemistry being the primary corrosive driving forces. The oil field will utilize water injection for reservoir pressure maintenance and as a consequence souring of the field in the later stages of life could occur. An experimental program of work was undertaken to measure the fatigue “knock-down” factor of sour/brine environments compared to that of laboratory air. Stress-life (S-N) samples were removed from segments of pipe with an outside diameter of 9.625 inch (wall thickness of 1.26 inch) containing fully inspected, production-quality circumferential welds. The environment examined included laboratory air conditions as well as deoxygenated brine supplemented by a gas mix of H2S and CO2. The primary variable changed during the test program was the test frequency. Fatigue testing in the high stress, or flowline, region was performed at 0.01Hz compared to a test frequency of 0.33Hz, utilized for the lower stress region, indicative of riser conditions. For all environmental tests performed, the dissolved oxygen levels were maintained at less than 10 ppb during testing. The measured fatigue life decrease in the curved pipe segments was in the range of 3–12 times when tested under sour brine environmental conditions compared to lab air. The results of this work clearly illustrates the importance of performing environmentally relevant fatigue testing when considering material selection for offshore applications that may contain a sour environment.

This content is only available via PDF.
You do not currently have access to this content.