Key concepts of submerged arc welding, explained by a submerged arc welding flux manufacturer.

According to manufacturers of submerged-arc welding flux, submerged-arc welding is an automated welding process in which a continuously fed welding wire generates an electric arc beneath a layer of flux. It is also known as submerged-arc automatic arc welding, or simply submerged-arc welding. During welding, the wire feeder of the welding machine automatically feeds the welding wire, strikes the arc on the strike plate, and maintains a constant arc length to carry out the weld. In front of the welding wire, granular flux continuously flows out of the hopper and is sprinkled over the joint surface of the workpiece. The electric arc burns beneath the flux layer, melting the workpiece, the welding wire, and the flux; the molten metal forms a weld pool, while the slag from the melted flux covers the surface of the weld pool. 
According to manufacturers of submerged-arc welding fluxes, the welding process for submerged-arc welded steel pipes is submerged-arc welding, employing both filler metal deposition and granular shielding agents. Pipe diameters can reach up to 1,500 mm, and LSAW is the English abbreviation for longitudinal submerged-arc welded steel pipe. For larger pipe diameters, two steel plates can be rolled and joined to form a double-seam weld. The production technologies for longitudinal submerged-arc welded steel pipes include JCOE forming technology and spiral submerged-arc welding technology. 
Characteristics of submerged-arc-welded steel pipes: Larger-diameter pipes can be produced from narrower billets, and pipes of different diameters can also be manufactured using billets of the same width. This results in low production costs, a simple process, and ease of producing large-diameter pipe products. Most large-diameter welded pipes are manufactured using spiral submerged-arc welding. 
According to submerged-arc welding flux manufacturers, the principal stress in a straight-seam steel pipe acts only perpendicular to the pipe’s direction of lower impact resistance, whereas in a spiral-welded steel pipe, this direction does not coincide with the pipe’s axis of lower impact resistance. This discrepancy turns defects along the weld length of spiral-welded pipes into an advantage. 
According to manufacturers of submerged-arc welding flux, spiral welded steel pipes are produced from coiled steel strip using the hot-extrusion process and are welded using automatic dual-wire submerged-arc welding. 
1. A weld gap control device shall be used to ensure that the weld gap meets the welding requirements, with strict control over pipe diameter, misalignment, and weld gap. 
2. The head and tail of the strip steel are welded using single- or double-wire submerged arc welding, followed by automatic submerged arc welding after coiling into a steel pipe. 
3. The weld seams are inspected using an online, continuous ultrasonic automatic flaw detection system to ensure that the spiral welds undergo non-destructive testing. If any defects are detected, the system automatically triggers an alarm and applies a marking spray. Production personnel can adjust process parameters at any time to promptly eliminate defects. 
4. Prior to forming, straighten, trim, plane, clean the surface, and pre-bend the strip material. 
5. A pressure gauge with electrical contacts is used to control the pressure in the cylinders on both sides of the conveyor, ensuring smooth transport of the strip material. 
6. According to submerged-arc welding flux manufacturers, after each batch of steel pipes is cut, it must undergo a rigorous first-piece inspection procedure that verifies the pipes’ mechanical properties, chemical composition, weld fusion quality, and surface finish, followed by nondestructive testing. Only after confirming that the manufacturing process meets all specifications may formal production commence. 
7. According to submerged-arc welding flux manufacturers, components exhibiting continuous ultrasonic testing indications on the weld seam shall be subjected to manual ultrasonic and radiographic examination. If defects are detected, they shall be repaired and then re-inspected by nondestructive testing until it is confirmed that the defects have been completely eliminated. Submerged-arc welding has evolved into dual-wire and multi-wire submerged-arc welding, further enhancing welding efficiency and finding extensive application in structural steel construction, pile driving, fluid transportation, long-distance pipeline systems, and other fields.