API Recommended Practice 591, “User Acceptance of Refinery Valves”, provides end-users or other interested parties testing procedures and acceptance criteria for evaluating a manufacturer’s valves. United Valve performs RP 591 testing for both end-users and manufacturers. Our integrated NDE capabilities, along with decades of valve experience, give us the ability to verify quality and find problems or idiosyncrasies with a particular valve design.
The basic test procedure requires that a number of valves be randomly selected from a distributor or manufacturer’s stock. First the valves are pressure tested in accordance with API 598 or other applicable test document. Next, the valves are subjected to an extensive visual and dimensional inspection, followed by radiography of the castings. Chemical analysis and hardness tests are also performed on several critical components.
The most critical inspection for gate, ball, plug and butterfly valves is the stem to ball/wedge/plug tensile test. This test is designed to determine the first point of failure between the shaft and the closure member. To meet the requirements of RP 591, the first point of failure must occur outside the valve pressure boundary.
United Valve is certified by major refiners to perform RP591 testing. The test results are used to help determine possible inclusion on their acceptable manufacturers list (AML).