Abstract
Fully-welded ball valves are widely used in the crude oil/natural gas transmission pipelines, and their quality has a direct bearing on the transportation safety of national energy. Two paralleled and symmetrical circular welds are used in the main welds of valve body, and the narrow-gap submerged arc welding (NG/SAW) is used in the welding groove. Because of conditional restrictions, it is impossible for the value to be post-weld heat treatment (PWHT). Therefore, the welds must have high impact toughness and strength. In order to study the welding performance of the base metal, SAW is used in the welding of proving rings of steel LF2 fully-welded ball valves. CTOD tests are applied to welding joints, and the result suggests that the minimum CTOD value of the valve’s welds and heat affected zone (HAZ) is more than 0.15mm. According to the criterion DNV-OS-C401, the welds in the fully-welded ball valve are safe enough without PWHT.
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