Pipeline fittings (elbows, adaptors, T-couplings, etc.) are more exposed to stress-corrosion fracture than straight sections of a pipeline. The research and tests were performed to enhance performance of oilfield pipeline systems. A test batch of steel 13HFА (high-grade steel containing 0.13% of carbon, chrome and vanadium) pipeline fittings was manufactured to be mounted on oil and gas line pipes featuring improved mechanical properties and extra-high resistance to corrosive oilfield media. Field (bypass) tests of the pipeline fittings (elbows, adaptors, T-couplings, etc.) test batch were run (for 19, 23 and for 42 months) in an operational in-field flow line and oil-gathering line of a West-Siberian oilfield with high contents of dissolved H2S and CO2 as well as with bacterial contamination. Changes in structural and mechanical performance and corrosion resistance were measured prior to and after the tests. General corrosion, local corrosion and bacterial corrosion rates were quantified in course of the tests. The structure, chemical and phase composition of corrosion products as well as their change versus the time of testing were identified. Specific features of stress-corrosion fracture and changes of general and local corrosion rates versus time in service are identified for each type of pipe fittings. High intensity of bacterial corrosion in pipeline fittings as compared with pipeline straight sections is pointed out. Heat treatment conditions are proposed that form the 13HFА structural condition which gives pipeline fittings persistent properties and corrosion resistance for continuous operation in oilfield media with contents of carbon dioxide.
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