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Test Protocol for Assessing the Sulfide Stress Cracking Resistance of Low Alloyed Steels in High Temperature High Pressure Sour Environments

High Pressure and High Temperature wells are very critical and require special attention to avoid well integrity issues. High pressure requests the use of very high strength low alloyed steels, above 965 MPa (140 ksi), while even trace of hydrogen sulfide implies significant partial pressures of H2S, much higher than the limit of 0.05 psi (3.5 mbar) provided by NACE MR0175 / ISO 15156 standard. Consequently, and despite a high temperature that reduces the risk of cracking, it is crucial to assess the resistance to Sulfide Stress Cracking of materials. However low alloyed steels experience high corrosion rates when exposed to standardized test solutions at elevated temperatures, leading to difficulties of controlling the mechanical stress loading, with a load rising in NACE TM0177 Method A and declining in four-points bending test. In addition, close attention shall be paid to both the evolution of the mechanical properties of the materials with the temperature and the appropriate sequence of sour gas introduction with regards to the temperature control. This paper discusses the most appropriate testing protocol for overcoming these issues and provides experimental results obtained in the frame of the qualification of 965 MPa (140 ksi) controlled yield grade for HPHT applications. 

Product Number: 51320-14588-SG
Author: Florian Thebault, Jonathas Oliveira, Julien Millet
Publication Date: 2020