Straight seam steel pipes are steel pipes with welds parallel to the longitudinal direction of the steel pipe. They are usually divided into metric electric welded steel pipes, electric welded thin-walled pipes, transformer cooling oil pipes, etc. The production process of straight seam welded pipes is simple, with high production efficiency, low cost and rapid development. The strength of spiral welded pipes is generally higher than that of straight seam welded pipes. Narrower billets can be used to produce welded pipes with larger diameters, and billets of the same width can also be used to produce welded pipes with different diameters. However, compared with straight seam pipes of the same length, the weld length increases by 30~100%, and the production speed is lower.


First, straight seam steel pipe fault handling:
1. Misalignment. This is a common problem in pre-welding. Misalignment exceeds tolerance, which directly leads to the downgrading or scrapping of steel pipes. Therefore, the amount of misalignment needs to be strictly controlled during pre-welding.
1) When the whole or most of the steel tube billet is out of tolerance, it is usually because of:
① The opening seam is not adjusted in place; ② The joint roller is not adjusted in place (the circumferential angle of the roller is not correct, or the center line of the tube billet is the axis, the left and right rollers are asymmetric, or the radial extension of the relative rollers is inconsistent), and there is no rounding; ③ The pre-bent edge is not pre-bent in place, and the plate edge is on the straight edge.
2) When the head or tail of the tube billet is out of tolerance, it is usually because of:
① The position of the inlet and outlet rollers is incorrect; ② The center of the ring frame is not correct; ③ The joint roller is not well rounded, and the position error of a single roller; ④ The forming is not good (the concave and convex of the two ends of the tube billet after forming is large; ⑤ The width of the opening seam is more than 150mm); ⑥ It is caused by the pressure fluctuation of the hydraulic system.
2. Back weld nodules and burn-through.
If the back weld nodules are removed, it will take time and affect the normal progress of the production process; if they are not removed, it will affect the internal welding forming and the tracking of the internal welding seam. Burn-through affects the internal and external welding and needs to be filled. The reasons for the occurrence of reverse weld nodules and burn-through are usually ① the joint is not tight, or the hydraulic system pressure is too low; ② the forming is not good, the roundness error is large; ③ the pre-welding technical parameters are not properly selected. The welding current and arc voltage should be matched with the appropriate welding speed. Excessive line energy or too low a welding speed makes it easy to produce reverse weld nodules and burn-through.
3. Porosity.
The pre-welding weld porosity causes internal defects in the internal and external welding. The pre-welding weld porosity is usually caused by ① poor maintenance gas, such as rich water, insufficient pressure, and flow, etc.; ② the welding machine is partially blocked, the gas hood formed by the maintenance gas is uneven, and harmful gases are stirred; ③ there is rust and oil on the groove.
4. Poor weld forming.
Poor weld forming affects the subsequent internal and external welding tracking, affects the stability of the welding process, and then affects the welding. Weld formation is closely related to line energy. As welding current, arc voltage, and welding speed increase, weld penetration, and weld width decrease, resulting in poor weld formation. When pores occur in the weld, poor weld formation often occurs.
5. Spatter.
Spatter in pre-welding easily burns the surface or groove of the steel pipe, and is not easy to remove, which affects welding and the outer surface of the steel pipe. The main reason for the spatter is that the protective gas composition is incorrect or the technical parameters are incorrect. The proportion of argon in the protective gas should be adjusted.

Second, straight seam steel pipe production technology:
1. The production of straight seam steel pipes can be divided into two periods, namely the forming period and the production period after forming. The production of large-diameter self-seam submerged arc welded steel pipes abroad is divided into 4 types according to the forming method: UOE forming; roll bending forming; step-by-step die forming; and step-by-step bending forming. After the forming period is completed, the subsequent production period of large-diameter self-seam steel pipes includes a series of basically similar process processes.
2. Plate edge processing welding groove. There are two processing methods: milling and planning. On both sides of the plate, there can be one or more milling and planing heads. Depending on the thickness of the plate, the groove can be processed into an I-shaped, single-V V, or double-V groove with blunt edges. For extremely thick steel pipes, the outer seam can be milled into a U-shaped groove, the purpose of which is to reduce the consumption of welding materials and improve productivity, while the root is wider to prevent welding defects. Positioning welding is commonly known as pre-welding. It is usually carried out with CO2 gas protection welding, the purpose of which is to stabilize the steel pipe, which is particularly useful for the subsequent submerged arc welding and can prevent burn-through.
3. To quickly identify welding defects, wave flaw detection and X-ray flaw detection are immediately carried out after the welding operation is completed, and defects are repaired in time. After welding, the roundness and straightness of the steel pipe generally cannot meet the requirements of relevant standards and technical conditions. Sizing and straightness are used in the pipe manufacturing plant and are completed by mechanical cold expansion. The test pressure can be as high as more than 90% of the yield strength of the steel pipe material.