The straight seam steel pipe is a steel pipe with the weld seam parallel to the longitudinal direction of the steel pipe. It is usually divided into metric electric welded steel pipe, electric welded thin-walled pipe, transformer cooling oil pipe, and so on. The production process of straight seam welded pipe is simple, the production efficiency is high, the cost is low, and the development is fast. The strength of the spiral welded pipe is generally higher than that of the straight seam welded pipe. However, compared with the same length of straight seam pipe, the length of the weld is increased by 30~100%, and the production speed is lower.
Troubleshooting of straight seam steel pipe:
1. Wrong side. This is a more common problem in pre-welding, and the wrong side is out of tolerance, which directly leads to the degradation or rejection of the steel pipe. Therefore, it is necessary to strictly control the amount of misalignment during pre-soldering. When the whole or half of the steel tube billet is out of tolerance, it is usually because ① the opening seam is not adjusted properly; ② the seam pressure roller is not adjusted properly (the circumferential viewpoint of the pressure roller is wrong, or the center line of the tube blank is The axis, the left, and right pressure rollers are asymmetric, or the radial elongation of the opposite pressure rollers is inconsistent), there is no rounding; ③ The pre-bending edge is not pre-bent in place, and the edge of the plate is rich in the appearance of the straight edge.
When the head or tail of the tube blank is out of tolerance, it is usually because ① the orientation of the inlet and outlet rollers is wrong; ② the middle of the ring frame is wrong; ④ Poor forming (the difference between the two ends of the tube blank after forming is large; ⑤ The width of the opening seam is more than 150mm); ⑥ Caused by the pressure fluctuation of the hydraulic system.
2. Welding on the reverse side, burn through. If the back welding flash is removed, it will take time and affect the normal progress of the production process; if it is not removed, it will affect the internal welding formation and the tracking of the internal welding seam. Burn through, affect the internal and external welding, and need to be replenished. The reasons for the occurrence of back welding and burn-through are usually ① the seam is not tight, or it may be that the pressure of the hydraulic system is too low; ② the molding is not good, and the roundness error is large; ③ the pre-welding technical parameters are not selected properly. The welding current and arc voltage should be matched with the appropriate welding speed. If the line energy is too large or the welding speed is too low, it is easy to produce a reverse welding flash and burn through.
3. Stomata. Porosity in pre-welded welds causes internal defects in front and rear welding. Porosity occurs in pre-welded welds, usually because ① the maintenance gas is insufficient, such as rich in moisture, and the pressure flow is not enough; ② the welding machine shows some uneven gas cover caused by blocking the maintenance gas, and the harmful gas stirs people; ③ there is rust on the groove, oil pollution, etc.
4. Poor weld formation. Poor weld formation affects the tracking of the subsequent internal and external welding, affects the stability of the welding process, and then affects the welding. The welding seam forming is closely related to the line energy. The welding current, arc voltage, and welding speed increase, and the welding seam penetration depth and width decrease, resulting in poor welding seam forming. Poor weld formation often occurs when porosity occurs in the weld.
5. Splash. The spatter in pre-welding can easily burn the surface or groove of the steel pipe, and it is not easy to eradicate, and then affect the welding and the outer surface of the steel pipe. The reason for the splash is mainly to maintain the wrong composition of the gas or the wrong technical parameters, and the proportion of argon in the gas should be maintained.
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 methods: UOE forming; roll forming; step-by-step molding; step-by-step bending. After the forming period is completed, the subsequent production period of the large-diameter self-sealing steel pipe involves a series of basically similar technological processes.
2. Welding groove for edge processing of plate. There are two methods of processing: milling and planing. On both sides of the board, there can be one or more milling and planning heads. Depending on the thickness of the plate, the groove can be processed into an I-shaped, single-V, or double-V groove with a blunt edge. For very thick steel pipes, the outer seam can be milled into a U-shaped groove, the purpose is to reduce the consumption of welding materials and improve the productivity, and the root is wider to prevent welding defects. Tack welding is commonly known as pre-welding. Generally, CO2 gas maintenance welding is used to make the steel pipe stable, which is very useful for the subsequent submerged arc welding and can prevent burn-through.
3. To quickly identify the welding defects, wave flaw detection and X-ray flaw detection are carried out immediately after the welding operation, and the defects are found and repaired in time. After the welding is completed, the roundness and straightness of the steel pipe generally cannot meet the requirements of the relevant specifications and technical requirements. The sizing and straightness are used in the pipe factory and completed by mechanical cold expansion.