CALCULATION OF TEST PRESSURE FOR ARTERIAL PIPELINES

摘要

Arterial pipelines are classed as critical engineering structures. The failure and shutdown of arterial, industrial, and process pipelines result not only in loss of gas, oil, and petroleum products, but also require expenditures for repair and restoration work; this involves large economic outlays estimated in billions of rubles per year. Pipeline failures are accompanied by explosions, fires, and the pollution of water bodies and the air basin. This exerts a destructive influence on the flora, fauna, and economy of the country. All this suggests extreme urgency to improve the quality and reliability of arterial pipelines by means of their hydraulic testing. The problem of analyzing and ensuring the safety of arterial petroleum pipelines occupies a special place in providing for their reliability. Arterial pipelines represent a system of sequentially connected elements (pipes, fittings, pipe components); the failure of any of these elements will therefore result in shutdown of the transport of the product and economic losses. At the manufacturing plant, each pipe is subjected to short-term (up to 30 sec) hydraulic tests in accordance with GOST 3845-75. At domestic plants, the test pressure does not exceed 0.90-0.95σ_y (σ_y is the normal yield point). Some foreign companies test pipes under a pressure of 1.1σ_y. At the manufacturing plants, the modern means of flaw detection and nondestructive control, which are employed for the short-term tests, do not make it possible to expose all pipe defects. Effective preoperational tests should be conducted to disclose defects of metallurgical and production origin that remain in the pipes as the sheet is rolled and welded during their manufacture, and also defects associated with construction and assembly. Hydraulic tests of arterial pipelines under an elevated pressure result in determination of defects in the metal of the pipe wall, and the longevity of large-diameter pipes is determined by residual defectiveness after the tests. The magnitude of a pipe defect will depend on the parameters of the hydraulic tests (pressure, holding time, number of cycles).