Butt-welded steel elbow
Butt-welded elbows are steel elbows formed by hot pressing or forging. Their connection method is to directly butt-weld the elbow with the steel pipe. The main manufacturing standards for butt-welded elbows are generally GB/T 12459, GB/T 13401, ASME B16.9, SH 3408, SH 3409, HG/T 21635, HG/T 21631, and SY/T 0510.
Butt-welded elbows generally include 45-degree elbows, 90-degree elbows, 180-degree elbows, etc., and are made of carbon steel, alloy steel, and stainless steel.
Butt-welded elbows are usually welded at the pipeline construction site because different pipelines have different welding standards, requiring on-site welding according to the pipeline weld grade. Butt-welded elbows have weld seams.
After the completion of welding construction, anti-rust or anti-corrosion treatment shall be carried out on butt-welded elbows according to actual conditions or the external environment of the pipeline, so as to avoid corrosion of the elbow at the weld seams, which would result in a short service life of the elbow.
Before welding the butt-welded elbow, to prevent welding deformation, after aligning both ends of the outer tiles on both sides of the integrally assembled elbow, it shall be reinforced with stainless steel arc plates and keels. According to conventional welding methods, argon back purging welding is required. Considering the welding cost and the large diameter of the miter elbow, argon back purging is difficult. Based on the above factors, two welders inside and outside are arranged to perform symmetrical welding simultaneously during welding, which not only effectively solves the problem of argon back purging but also ensures good forming. The welding process of argon tack welding combined with electric welding is adopted. Electrode A022 is selected, and welding wire HOOCr21Ni10 is used. Argon arc welding is used for the root pass of the bottom layer. Before electric welding operation, lime powder is applied within a range of 100 mm on both sides of the weld seam to prevent spatter from adhering to the pipe surface. A low current is adopted for electric welding, with multi-layer and multi-pass continuous welding. After the overall welding is completed, the welding spots and spatters on the surface of the butt-welded elbow are polished. Non-destructive testing is performed on the prefabricated and welded tiles, and pickling and passivation are carried out on the inner and outer weld surfaces. The pickled elbow is then transported to the installation site for on-site installation.