51314-3793-Comparison of C110 Critical Stress Intensity Factor (KISSC) Data in CO2 and H2S Environments with Varying H2S Concentrations and Applied Loads

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Product Number: 51314-3793-SG

ISBN: 3793 2014 CP

Author: Samar Saha

Publication Date: 2014

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Critical Stress Intensity Factor (KISSC) data are used in the design of high-strength low-alloy (HSLA) steel casing used for oil exploration and extraction in sour environments. KISSC is dependent on the sourness (H2S concentration and pH) of the testing environment as well as the applied testing load. Current API and NACE Standards as used in North America for C110 material address the determination of KISSC in 100% and 7% (mild and buffered sour environment) H2S with balance of the carrier gas being N2. The European Standard (EFC Publication 16) recommends a different testing environment namely a test solution that is buffered to a different pH level and the carrier gas for testing in weak H2S environments is CO2. This paper presents Critical Stress Intensity Factor (KISSC) data generated for two heats of standard mill produced C110 casing (microalloyed 4130 type steel). Double Cantilevered Beam (DCB) samples from this material were tested in both NACE and EFC solutions to the requirements of NACE Standard TM0177 Method D in various sour environments (3.5% 7.0% 14% 22.0% 50% and 100% H2S - balance CO2 or N2) under a range of applied loads (wedges 20 25 30 35 and 40 mils thick ). The KISSC data generated under the NACE and EFC environments are compared. A simplified approach for KISSC compliance and KIimit determination of C110 material exposed to various H2S environments is discussed for field use by the oil well designers.