Straight seam steel pipes are steel pipes with welds that are longitudinally parallel to 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 pipe is simple, the production efficiency is high, the cost is low, and the development is rapid. The strength of spiral welded pipes is generally higher than that of straight seam welded pipes. Welded pipes with larger diameters can be produced from narrower billets, and welded pipes with different diameters can also be produced from billets of the same width. However, compared with straight seam pipes of the same length, the weld length is increased by 30~100%, and the production speed is lower.
Troubleshooting of straight seam steel pipes:
1. Wrong side. This is a common problem in pre-welding. Misalignment will directly lead to the downgrading or scrapping of the steel pipe. Therefore, the amount of edge deviation needs to be strictly controlled during pre-welding. When the whole or more than half of the steel pipe blank shows misalignment, it is usually because:
①The opening seam is not adjusted in place;
② The seaming pressure roller is not adjusted in place (the circumferential angle of the pressure roller is wrong, or the middle line of the tube blank is used as the axis, the left and right pressure rollers are asymmetrical, or the radial elongation of the opposite pressure rollers is inconsistent), and there is no rounding;
③The pre-bent edge is not pre-bent in place, causing the edge of the board to be too straight.
When the head or tail of the tube blank shows misalignment, it is usually because:
①The orientation of the inlet and outlet rollers is wrong;
②The center of the ring frame is wrong;
③The seam-joining pressure roller is not rounded well, and the position of a single pressure roller is wrong;
④ Poor forming (the unevenness of the two ends of the formed tube blank is quite different;
⑤The opening seam width is more than 150mm);
⑥ Caused by pressure fluctuations in the hydraulic system.
2. Welding flash and burn-through on the reverse side. If the welding flash on the back side is removed, it will be time-consuming and affect the normal production process; if it is not removed, it will affect the internal welding shape and the tracking of the internal welding seam. Burn-through affects internal and external welding and needs to be replenished. The reasons for the occurrence of welding spatter and burn-through on the back side are usually ① the seam is not tight, or 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 improperly selected. The welding current and arc voltage must be matched with the appropriate welding speed. If the line energy is too high or the welding speed is too low, it is easy to produce back welding nodules and burn-through.
3. Stomata. Pre-weld weld porosity causes internal defects in the internal and external welds. The occurrence of pores in pre-welded welds is usually due to ① insufficient protective gas, such as being rich in moisture and insufficient pressure and flow; ② the welding machine has uneven gas covers formed by some blocking protective gas, and harmful gases are disturbing; ③ there is rust on the groove, oil pollution, etc. caused.
4. Poor weld formation. Poor weld formation affects the subsequent internal and external welding tracking, affects the stability of the welding process, and thus affects the welding. Welding seam formation is closely related to line energy. As welding current, arc voltage, and welding speed increase, welding seam penetration depth and width decrease, resulting in poor welding seam formation. When pores occur in the weld, poor weld formation often occurs.
5. Splash. Spatter during pre-welding can easily burn the surface or groove of the steel pipe and is difficult to remove, thus affecting the welding and outer surface of the steel pipe. The main reason for splashing is that the composition of the protective gas is incorrect or the technical parameters are incorrect. The proportion of argon in the protective gas should be adjusted.
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 manufacturing period after forming. The production of foreign large-diameter self-seam submerged arc welded steel pipes is divided into four types according to the forming methods: UOE forming; roll bending forming; progressive molding forming; and progressive bending forming. After the forming process is completed, the subsequent manufacturing process of large-diameter self-sewing steel pipes includes a series of basically similar processes.
2. Process welding grooves on the edge of the plate. There are two processing methods: milling and planning. On both sides of the board, there can be one or more milling and planning heads. Depending on the plate thickness, the groove can be processed into an I-shaped, single-V, or double-V groove with blunt edges. For particularly 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 productivity, while the root is wider to avoid welding defects. Position welding is commonly known as pre-welding. Generally, CO2 gas protection welding is used to stabilize the steel pipe, which is particularly useful for subsequent submerged arc welding to prevent burn-through.
3. To quickly identify welding defects, conduct wave flaw detection and X-ray flaw detection immediately after the welding operation is completed, and repair the defects in time if any defects are found. After welding, the roundness and straightness of the steel pipe generally cannot meet the requirements of relevant standards and technical conditions. The sizing and straightness are used in the pipe factory and are achieved through mechanical cold expansion. The test pressure can be as high as more than 90% of the yield strength of the steel pipe material.