Development and application of pipes with polymer lining and coating in the system of in-field flow lines rated for 4 MPa max pressure has been one of the most successful anti-corrosion projects of Tatneft PJSC. Collars with ring gaskets are used to protect non-lined weld junction against corrosive environment. For 12 years of operation, no failures from internal corrosion have been registered, so, the Company considered application of these pipes in the formation pressure maintenance system with 21 MPa max pressure. Calculations and tests showed that the pipe design would not provide a reliable anti-corrosion protection of weld junctions at high pressure, so, efforts were made to improve the pipe’s weld junction design. Bench tests of pipes under 27 MPa pressure demonstrated good results, and currently pipes are tested in field conditions. Since pipe ends have been cold-worked to expand them, the diameter loss because of protective collars is negligible. Protective collars are placed in expanded pipe-end sections and are further fixed in place by welded spigots, which protects them against axial displacement while scraper-pig injection or other operations. Other advantages include absence of human-mistake factor while fitting and assembly of pipes in field, ease of assembly of pipe joints with the help of a screw jack, reliable anti-corrosion protection.
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