Troubleshooting and Production Technology of Straight Seam Steel Pipe

Straight seam steel pipe is a steel pipe whose weld seam is 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 rapid. The strength of the spiral welded pipe is generally higher than that of the straight seam welded pipe, and the welded pipe with a larger diameter can be produced with a narrower billet, and welded pipes with different diameters can be produced with the same width billet. But compared with the straight seam pipe of the same length, the weld length is increased by 30~100%, and the production speed is lower.

Straight seam steel pipe troubleshooting:

1. Wrong side.

This is a common problem in pre-welding, and the wrong side is out of tolerance, which directly leads to the degradation or scrap of the steel pipe. Therefore, it is necessary to strictly control the amount of misalignment during pre-welding.

When the whole or more than half of the steel pipe blanks are out of tolerance, it is usually because:

①The adjustment of the opening seam is not in place;

②The adjustment of the seam pressure roller is not in place (the circumferential angle of the pressure roller is wrong, or the middle line of the tube blank is the axis, the left and right pressure rollers are asymmetrical, or the radial elongation of the relative pressure rollers is inconsistent), and there is no rounding;

③The pre-bending edge is not pre-bent in place, and the edge of the board is caused by the appearance of a straight edge.

When the head or tail of the tube blank is out of tolerance, it is usually because:

① The orientation of the import and export roller table is wrong;

② The middle of the ring frame is wrong;

③The pressure circle of the joint pressure roller is not good, and the position of a single pressure roller is wrong;

④ The forming is not good (the difference between the two ends of the formed tube blank is large;

⑤The opening seam width is more than 150mm);

⑥Caused by pressure fluctuations in the hydraulic system.

2. Welding bumps and burn-through on the reverse side.

If the back welding bump is removed, it will take time and affect the normal progress of the production process; if it is not removed, it will affect the welding shape of the internal welding and the tracking of the internal welding seam. Burn-through affects internal and external welding and needs to be filled. The causes of back weld bumps and burn-through are usually ① not tight joints, or the pressure of the hydraulic system may be too low; ② poor forming and large roundness error; ③ improper selection of pre-welding technical parameters. 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 reverse welding bumps and burn through.

3. Stomata.

Porosity in the pre-welded seam causes internal defects in the inner and outer welds. Pores in the pre-welded seam are usually caused by ① insufficient protective gas, such as high moisture content, poor pressure, and flow, etc.; ② the welding machine has some blocked protective gas, and the gas cover is uneven, and harmful gas is disturbing; ③ There is rust on the groove, oil pollution, etc.

4. Poor weld formation.

Poor weld formation affects subsequent internal and external welding tracking, affects the stability of the welding process, and thus affects welding. Welding seam formation is closely related to line energy, welding current, arc voltage, welding speed increase, weld penetration depth, and fusion width decrease, resulting in poor welding seam formation. Poor weld formation also often occurs when porosity occurs in the weld.

5. Splash.

Splash during pre-welding is easy to burn the surface or groove of the steel pipe, and it is not easy to remove, thus affecting the welding and the outer surface of the steel pipe. The main reason for splashing is that the composition of the maintenance gas is wrong or the technical parameters are wrong, and the proportion of argon in the maintenance 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 post-forming production period. The production of foreign large-diameter self-seam submerged arc welded steel pipes is divided into four types according to the forming method: UOE forming; roll forming; step-by-step die forming; step-by-step bending forming. After the forming period is over, the subsequent manufacturing period of large-diameter self-seamed steel pipes includes a series of basically similar processes.

2. Process the welding groove on the edge of the plate. There are two processing methods: milling and planning. On both sides of the board, there may be one or more milling and planning heads. According to 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 especially 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, and the root is wider to avoid welding defects. Tack welding is commonly referred to as pre-welding. It is generally carried out with CO2 gas-shielded welding, and its purpose is to stabilize the steel pipe, which is especially useful for subsequent submerged arc welding to prevent burn-through.

3. To identify welding defects as soon as possible, conduct wave detection and X-ray detection immediately after the welding operation is completed, and repair in time if defects are found. 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 to complete through mechanical cold expansion. The test pressure can be as high as more than 90% of the yield strength of the steel pipe material.