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Investigation of Sulfide Stress Crack Propagation Using Sour Pipe Burst in Tubulars with Simulated Defects under Pressure

Seamless oil country tubular goods (OCTG) with defined chemistry and toughness, e.g. API 5CT C110, are utilized as production casing in sour wells globally. These grades must withstand high pressures and mild sour conditions to maintain the integrity of the well and, as such, should resist both sulfide stress crack (SSC) initiation and potential propagation from defects in service. A laboratory study was conducted to assess the tendency of crack propagation from two defined types of defects, electro-discharge machined (EDM) notches and fatigue cracks, simulating potential as-delivered OCTG tubulars. The tubulars were subjected to a variety of test conditions including two temperatures, 4ºC and 24ºC, internal pressures ranging from 550 to 1,100 bar, and exposure to a modified NACE TM0177 Solution B equilibrated with 7% H2S/N2 gas purge. The applied pressure and depth of defects were used to determined applied stress intensity values, K, for each condition to compare tests with one another and to traditional small-scale evaluations per NACE TM0177 Method D, single edge notched tensile (SENT), and constant K compact tension (CT). The findings indicated that tendency towards SSC propagation was principally dependent on type of defect, temperature, and applied K. Threshold K values for SSC propagation from EDM-type defects were higher than determined from any of the small-scale evaluation methods. Fatigue pre-cracks were demonstrated to be more aggressive in promoting SSC propagation compared to EDM-type defects.
Product Number: 51324-20420-SG
Author: Brian Chambers; Bostjan Bezensek; Sebastian Cravero; Pedro Olivo; Octavio Albores
Publication Date: 2024
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