Seamless X60QOS and X65QOS linepipes are widely used for Sour Service offshore and onshore applications. Sour Service refers to the risk of hydrogen related cracking, such as by Sulfide Stress Cracking (SSC). The International standard NACE MR0175 / ISO 15156 provides requirements for assessing the resistance to SSC, specifically on how to qualify for use in region 3 of the environmental severity diagram (Figure 1 in paragraph 7.2.1.2 of part 2). Qualification requires exposing materials in an acid solution saturated by 1 bar of H2S (NACE TM0177 Solution A) and to apply a tensile stress above 80% AYS by means of different methods: uniaxial tensile, C-ring or Four-Point Bend. However, for very sour fields presenting H2S partial pressures much greater than 1 bar, the preservation of the SSC resistance might be questioned and is presently a major concern for the O&G industry.

The present paper is dedicated to the evaluation of the SSC resistance of seamless quenched and tempered X65 grades including the girth weld in the standard NACE TM0177 Solution A up to 15 bar of H2S partial pressure. Corrosion tests consisted of four-point bend tests performed in autoclave vessels and different test configurations were investigated, including specimen sampling location through the wall thickness, surface preparation and root bead condition (ground flush or intact).

Subject
Hydrogen sulfide, Materials, Piping, Sour environments, Girth welds, Micrography, Partial pressures, Stress, Fugacity, Tensile stress, Steel, Sulfide stress cracking, Stress corrosion cracking
Keywords:
Seamless, X60QOS, X65QOS, girth weld, Sulfide Stress Cracking, high H2S partial pressure
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2020
Association for Materials Protection and Performance (AMPP)
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