Acceptance of straight seam steel pipe:
1. The inspection and acceptance of straight seam steel pipes shall be carried out by the technical supervision department of the supplier.
2. The supplier ensures that the delivered straight seam steel pipe meets the requirements of the corresponding product standards. The purchaser has the right to conduct inspection and acceptance according to the corresponding product standards.
3. Straight seam steel pipes should be submitted for acceptance in batches, and the batching rules should comply with the provisions of the corresponding product standards.
4. The inspection items, sampling quantities, sampling locations, and test methods of straight seam steel pipes shall be in accordance with the provisions of the corresponding product standards.
5. In the test results of straight seam steel pipes, when a certain item does not meet the requirements of the product standard, the unqualified ones should be picked out, and double the number of samples should be taken from the same batch of straight seam steel pipes to carry out the unqualified items. recheck. If the re-inspection results (including any index required by the project test) are unqualified, the batch of straight seam steel pipes shall not be delivered. The following inspection items are not allowed to be re-inspected when the initial inspection fails:
1) There are white spots in the low-magnification tissue.
6. For straight seam steel pipes with unqualified re-inspection results (including unqualified microstructures in initial inspection results, and re-inspection items are not allowed), the supplier may submit them for acceptance one by one; or re-heat treatment (the number of re-heat treatments shall not exceed two times) ), to submit a new batch for acceptance.
7. If the product standard does not make special provisions, the chemical composition of the straight seam steel pipe shall be checked and accepted according to the smelting composition.
Solutions to common problems in pre-welding of straight seam steel pipes
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 scrapping of the steel pipe. Therefore, it is required to strictly control the amount of misalignment during pre-welding. When the whole or most of the steel tube billets are out of tolerance, it is generally due to:
1) The adjustment of the opening seam is not in place;
2) The adjustment of the seam pressure roller is not in place (the circumferential angle 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 roller is inconsistent), there is no pressure round ;
3) The pre-bending edge is not pre-bent in place, which is caused by the phenomenon that the plate edge is abundant in the straight edge.
When the head or tail of the tube blank is out of tolerance, it is generally due to;
1) The position of the import and export roller table is wrong;
2) The center of the ring frame is wrong;
3) The seam pressure roller is not well rounded, and the position of individual pressure rollers has deviated;
4) The forming is not good (the height difference between the two sides of the formed tube blank 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 back, burn through.
Welding on the back, if it is time-consuming, will affect the normal production process; no, it will affect the internal welding formation and the tracking of the internal welding seam. Burn-through, which affects internal and external welding, needs to be filled. The causes of back welding and burn-through are generally: 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 deviation is large; ③ the pre-welding process parameters are improperly selected. 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 back welding flash and burn through.
Pre-weld seam porosity causes internal defects in internal and external welds. Pores in pre-welded welds are generally due to ① poor shielding gas, such as moisture content, insufficient pressure flow, etc.; ② uneven gas cover formed by partial blockage of shielding gas in the welding torch, and harmful gas agitates; ③ there is rust on the groove, Oil pollution, etc.
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. Weld formation is closely related to line energy. The welding current, arc voltage, and welding speed increase, and the weld penetration and width decrease, resulting in poor weld formation. When pores are generated in the weld, poor weld formation often occurs.
Splash in pre-welding is easy to burn the surface or groove of the steel pipe, and it is not easy, thus affecting the welding and the outer surface of the steel pipe. The reason for the splash is mainly due to the wrong composition of the shielding gas or the wrong process parameters, and the proportion of argon in the shielding gas should be adjusted.