Acceptance method and problem handling of straight seam steel pipes

First, acceptance of straight seam steel pipes:

1. The inspection and acceptance of straight seam steel pipes shall be carried out by the supplier's technical supervision department.

2. The supplier shall ensure that the delivered straight seam steel pipes meet the requirements of the corresponding product standards. The buyer has the right to inspect and accept according to the corresponding product standards.

3. Straight seam steel pipes shall be submitted for acceptance in batches, and the batching rules shall comply with the requirements of the corresponding product standards.

4. The inspection items, sampling quantity, sampling location, and test methods of straight seam steel pipes shall comply with the requirements of the corresponding product standards.

5. If a certain item of the straight seam steel pipe test results does not meet the requirements of the product standards, the unqualified ones shall be selected, and double the number of samples shall be randomly taken from the same batch of straight seam steel pipes for re-inspection of the unqualified items. If the re-inspection results (including any indicator required for 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 structure. 2) Microstructure.

6. For straight seam steel pipes with unqualified re-test results (including those with unqualified microstructure in the initial test results and items that are not allowed to be re-tested), the supplier may submit them for acceptance one by one; or re-heat treat them (the number of re-heat treatments shall not exceed two times) and submit them for acceptance in a new batch.

7. If there is no special provision in the product standard, the chemical composition of the straight seam steel pipe shall be accepted according to the smelting composition.

Second, measures to deal with common problems in the pre-welding of straight seam steel pipes.

1. Misalignment: This is a common problem in pre-welding. Misalignment beyond tolerance directly leads to the downgrading or scrapping of steel pipes. Therefore, the amount of misalignment must be strictly controlled during pre-welding. When the whole or most of the steel pipe billet has misalignment beyond tolerance, it is generally due to:

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 incorrect, or the left and right rollers are asymmetrical with the center line of the tube billet as the axis, or the radial elongation 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 full of straight edges.

When the head or tail of the tube billet is out of tolerance, it is generally due to;

1) The position of the inlet and outlet rollers is incorrect;

2) The center of the ring frame is incorrect;

3) The rounding of the joint rollers is not good, and the position of individual rollers is deviated;

4) The forming is not good (the height difference between the two sides 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-throughs: Back weld nodules, if, time-consuming, affect the normal production process; if not, they 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 back weld nodules and burn-throughs are generally ① The joint is not tight, and it may also be that the pressure of the hydraulic system is too low; ② The forming 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. Excessive line energy or too low welding speed makes it easy to produce back weld nodules and burn-throughs.

3. Porosity: Porosity in the pre-welding weld leads to internal defects of internal and external welding. Porosity in pre-welded welds is generally caused by ① poor shielding gas, such as moisture, insufficient pressure, and flow, etc.; ② the welding gun is partially blocked, the shielding gas forms an uneven gas hood, and harmful gases are stirred; ③ there is rust and oil on the groove.

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 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.

5. Spatter: Spatter in pre-welding can easily burn the surface or groove of the steel pipe, thereby affecting welding and the outer surface of the steel pipe. The main reason for the spatter is the incorrect composition of the shielding gas or the incorrect process parameters. The proportion of argon in the shielding gas should be adjusted.