Welding Method of Square Pipe

Square tube is a steel tube made from strip steel rolled by a process. Generally, the strip steel is unpacked, flattened, rolled and welded to form a round tube, which is then rolled into a square tube and then sheared to the required length.

Square tubes are commonly used in various building structures and engineering structures, such as house beams, bridges, power transmission towers, lifting and transportation machinery, ships, industrial furnaces, reaction towers, container racks, and warehouse shelves. It plays a very important role in the construction industry. So how is the square tube welded?

Square tube welding according to the process requirements for processing butt welding bevel, pre-gap splicing; and the design of the welded joint is the weaker link in the welding project. The bevel form has a very important role in controlling the internal quality of the weld and the manufacturing quality of the welded structure.

Process requirements are that the first layer of the weld must be welded through, to ensure that the back side is well formed, welding current, arc voltage, wire feed speed and welding speed, etc. can be adjusted according to the equipment model; in order to reduce the square tube welding deformation, the principle of welding production is taken from the middle to the two sides in layers and sections of symmetric jump welding, resulting in smaller welding deformation than straight through welding, which is conducive to the dispersion and release of stress and avoid complex stresses in welding. Straight through swing welding when welding the narrower plastic deformation zone formed only once, and due to continuous swing welding, heat input is large, the heat area is large, the plastic deformation area caused by compression is large, and thus the post-weld shrinkage deformation is large.

When jump welding in layers and sections, each layer cross-section is very small, the heat required is small, and each layer is divided into several sections for jump welding, each welding section is basically a re-establishment of the temperature field on the cold steel plate, each time there is a narrower plastic deformation zone, so the average width of the plastic deformation zone than the corresponding layered through welding is small, longitudinal shrinkage is also small, compared to the straight through continuous once-filled swing welding deformation is even smaller.

What are the requirements of the square tube again?

1. the allowable deviation of the wall thickness of the square tube, when the wall thickness is not greater than 10mm shall not exceed the nominal wall thickness of plus or minus 10%, when the wall thickness is greater than 10mm for the wall thickness of plus or minus 8%, except for the corner and the wall thickness of the weld area.

2. The usual delivery length of square tube is 4000mm-12000mm, with 6000mm and 12000mm being the majority. Square pipe is allowed to be delivered in short and non-scheduled lengths of not less than 2000mm, and can also be delivered in the form of interface pipe, but the interface pipe should be removed when the demand side is in use. The weight of short and non-scheduled products shall not exceed 5% of the total delivery quantity, and for the theoretical weight of square tube greater than 20kg/m shall not exceed 10% of the total delivery quantity.

3. The curvature of the square tube shall not be more than 2mm per meter, and the total curvature shall not be more than 0.2% of the total length.