Serviceability of 35KhF steel in hydrogen-sulfide media
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SERVICEABILITY OF 35KHF STEEL IN HYDROGEN-SULFIDE MEDIA H. V. Chumalo
UDC 620.194
Corrosion and corrosion-mechanical properties of 35KhF low-alloyed steel in hydrogen-sulfide media are investigated. The corrosion resistance and resistance to hydrogen-induced cracking of the steel of different heats in NACE solution and artificial seawater, and its resistance to hydrogen-sulfide stress corrosion cracking in the NACE solution are determined. It is shown that 35KhF steel can be used for the manufacture of critical components of a lift string for pumping-over stratal water. Keywords: steel, hydrogen sulfide, corrosion cracking, corrosion resistance, hydrogen-induced cracking, stratal water.
Hydrogen sulfide contained in process products of many industries is an extremely aggressive component, which causes corrosion, corrosion-hydrogen, and corrosion-mechanical fracture of equipment. Structural materials are chosen taking into account their mechanical properties and results of the corrosion resistance and crack resistance in process media, which are partially obtained from the experience of operation and, in the stage of design, on the basis of laboratory investigations. NACE Standard MR0175-96 [1] specifies conditions for gas and oil fields under which materials resistant to hydrogen-sulfide stress corrosion cracking (HSSCC) should be used. The threshold stress determined in the NACE hydrogen-sulfide solution (5% NaCl + 0.5% CH 3COOH + H 2 Ssat ., pH 3–4, 20°C) for 720 h is considered an nonstandard but generally accepted criterion of the resistance of steels to HSSCC, and if SSC 0.8 0.2 , steel is serviceable. In operation of equipment in media with a high hydrogen-sulfide content (oil, gas, and stratal water), cracks form in steel as a result of not only HSSCC, but also hydrogen-induced cracking (HIC). By the latter we mean the initiation of cracks in the absence of loads under the action of a high pressure of molecular hydrogen near internal defects (inclusions), delaminations, and surface blistering. Hydrogen-induced cracking manifests itself in the formation of internal structural cracks oriented predominantly along the direction of rolling of pipes and other components. For steels, investigations of the susceptibility to HIC are performed because this test is mandatory for choosing materials for pipelines and other equipment intended for transportation of products with hydrogen-sulfide impurities. It should be noted that the susceptibility of steels to HSSCC depends on the concentration and partial pressure of H 2 S . If in fields with a relatively insignificant content of hydrogen sulfide, materials with increased resistances to HSSCC and HIC are used, this leads to unjustified equipment costs for fields, and if materials with insufficient resistances to HSSCC and HIC are used, fracture of equipment may occur with unforeseeable consequences. In what follows, we investigate the serviceability of 35KhF low-alloyed steel in hydrogen-sulfide media and assess the possibility of its using for the manufacture o
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