As the service conditions for non-metallics becomes ever more challenging, their reliability and fitness for service evaluation requires more refined levels of testing. For elastomers used in HPHT sour conditions, the need to evaluate their ability to continue to seal requires testing that closer represents them as an elastomer seal and not as an elastomer material. This paper discusses new methods to test new techniques for the use of sour gas to conduct rapid decompression testing and new functional testing techniques to measure their ability to seal. The increased use of composite materials in more aggressive service has required new evaluation approaches to be developed and new standards written to match. This paper also discusses these new test methods for testing at a material and a pipe level within these standards.
Carbon and low alloy steels (CS and LAS, respectively) used for exploration and production in the oil and gas (O&G) industry are normally exposed to environments that may contain H2S in a wide range of concentrations. In aqueous solutions, H2S acts as a cathodic poison.1,2 A cathodic poison inhibits the recombination of atomic hydrogen to H2, and as a result, favors its absorption by the metal.1,2 In the presence of a susceptible microstructure and the simultaneous effect of applied or residual tensile stress, a crack can nucleate and propagate, when a critical concentration of hydrogen is reached in the metal.3 This environmentally assisted cracking (EAC) phenomenon is known as Sulfide Stress Cracking (SSC).2 SSC is commonly addressed as a case of hydrogen embrittlement (HE) damage.2
Alloy UNS N07718 (hereafter abbreviated as 718) is one of the most versatile precipitation-hardened nickel-based corrosion-resistant alloys (CRAs) used for both surface and sub-sea components in oil and gas production service. API 6ACRA1 provides heat treatment windows and acceptance criteria for 718 in these oil and gas production environments, in which the heat treatment is intended to obtain high strength and to minimize the formation of δ-phase at grain boundaries. As pointed out in NACE MR0175 Part 32 (Table 1), field failures of 718 components in sour service are primarily related to stress corrosion cracking (SCC) at elevated temperatures and hydrogen embrittlement in the lower temperature range. The latter is specifically called galvanically induced hydrogen stress cracking (GHSC or GIHSC), which is typically caused by atomic hydrogen uptake from galvanic corrosion or cathodic protection (CP) when 718 is used with steel components in a seawater environment. CP is normally used to protect steel component from corrosion in subsea environments.
Martensitic stainless steel (MSS) well tubulars are favorable due to their high strength and relatively low cost and are therefore widely applied in the Oil & Gas industry. This is especially the case for 13Cr and Super13Cr grades, which are often selected for mildly sour gas fields, where a relatively low content of H2S is present. When selecting martensitic stainless steels for sour service, the susceptibility to Stress Corrosion Cracking (SCC) and Sulfide Stress Cracking (SSC), determined by standard laboratory tests, are the most important selection criteria.