What are the technical requirements for LSAW steel pipe?

What are the technical requirements for LSAW steel pipe?

The technical requirements and inspection of LSAW steel pipe are based on the GB3092 "Welded Steel Pipe for Low-Pressure Fluid Transport" standard. The nominal diameter of the welded pipe is 6~150mm, the nominal wall thickness is 2.0~6.0mm, and the length of the welded pipe is usually 4~10 meters. It can be shipped from the factory in fixed length or multiple lengths. The surface of the steel pipe should be smooth, and defects such as folding, cracks, delamination, and lap welding are not allowed. The surface of the steel pipe is allowed to have minor defects such as scratches, scratches, weld dislocations, burns and scars that do not exceed the negative deviation of the wall thickness. Thickening of the wall thickness at the weld and the presence of internal weld bars are allowed.

Welded steel pipes should undergo mechanical performance tests, flattening tests and expansion tests, and must meet the requirements stipulated in the standard. The steel pipe should be able to withstand the internal pressure of 2.5Mpa and maintain no leakage for one minute. It is allowed to use eddy current flaw detection method instead of hydrostatic test. Eddy current flaw detection is carried out in accordance with the standard GB7735 "Eddy Current Flaw Detection Inspection Method for Steel Pipes". The eddy current flaw detection method is to fix the probe on the frame, keep a distance of 3~5mm between the flaw detection and the weld, and rely on the rapid movement of the steel pipe to conduct a comprehensive scan of the weld. The flaw detection signal is automatically processed and automatically sorted by the eddy current flaw detector. To achieve the purpose of flaw detection. After flaw detection, the welded pipe is cut to the specified length with a flying saw, and is rolled off the production line via a flip frame. Both ends of the steel pipe should be flat-chamfered and marked, and the finished pipes should be packed in hexagonal bundles before leaving the factory.

Welded pipe processing method:

Welded pipes are steel pipes whose welds are parallel to the longitudinal direction of the steel pipe. The strength of steel pipes is generally higher than that of LSAW steel 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. So what are its processing methods?

1. Forging steel: A pressure processing method that uses the reciprocating impact of a forging hammer or the pressure of a press to change the blank into the shape and size we require.

2. Extrusion: It is a steel processing method in which metal is placed in a closed extrusion cylinder and pressure is applied on one end to extrude the metal from a prescribed die hole to obtain a finished product of the same shape and size. It is mostly used for the production of non-ferrous metals. Material steel.

3. Rolling: A pressure processing method in which the steel metal blank passes through the gap (of various shapes) between a pair of rotating rollers. Due to the compression of the rollers, the cross section of the material is reduced and the length is increased.

4. Drawing steel: It is a processing method that draws the rolled metal blank (shaped, tube, product, etc.) through the die hole to reduce the cross-section and increase the length. Most of them are used for cold processing.

Pre-welding of welded pipes:

Pre-welding includes joints and welds.

1. The joint seam (that is, the forming seam) has no wrong edge or the wrong edge is less than the specified value. Generally, the wrong edge amount is ≤ 8% of the plate thickness, and the maximum value shall not exceed 1.5 mm.

2. It is necessary to ensure that the weld seam has appropriate penetration depth and deposition amount. It is necessary to ensure that there is no cracking or burn-through after welding, and the height of the weld seam must be controlled so that the weld reinforcement height of the external welding seam is not affected.

3. The welding bead is continuous and shaped to facilitate subsequent external welding.

4. The weld does not have defects such as welding deviation, pores, cracks, slag inclusions, burn-through, and back weld burrs, and the center deviation of the weld is required to be ≤1mm.

5. No arc burn, small splash, and no impact on the pipe end bevel and surface.

6. The welding seam matches the base metal, and the physical and chemical properties of the welding seam metal meet the requirements.

Essentials of welded pipe welding:

The forming methods for manufacturing large-diameter LSAW steel pipe include UOE forming method, roller forming method (CFE), CE forming, etc. For most forming methods, the last step is to expand the full length of the welded tube blank to improve the shape of the welded steel tube. Diameter expansion has become an important process in the production of large-diameter LSAW steel pipe to ensure the finished pipe. Diameter expansion is a pressure processing process that uses hydraulic or mechanical means to apply force from the inner wall of the steel pipe to expand the steel pipe outward in the radial direction. The mechanical method is simpler and more efficient than the hydraulic method. It is used in the diameter expansion process of several large-diameter LSAW steel pipe pipelines in the world. Mechanical diameter expansion uses the segmented sector blocks at the end of the diameter expander to move along the radial direction. Expansion is a process in which the tube blank achieves plastic deformation of the entire tube length in a step-by-step manner along the length direction.

1. Preliminary rounding stage. The sector blocks are opened until all the sector blocks are in contact with the inner wall of the steel pipe. At this time, the radius of each point in the inner circular tube of the steel pipe within the step range is almost the same, and the steel pipe is initially rounded.

2. Nominal inner diameter stage. The sector block starts to reduce its movement speed from the front position until it reaches the required position, which is the required inner circumferential position of the finished pipe.

3. Rebound compensation stage. The sector block starts from the second stage position and further reduces the speed until it reaches the required position. This position is the inner circumferential position of the steel pipe before rebound required by the process design.

Seamless steel pipe VS welded pipe

1. In appearance, the difference between seamless steel pipes and welded steel pipes is that the welded pipes have welding bars on the inner wall, while the seamless ones do not.
2. The pressure of seamless steel pipes is higher, and that of welded pipes is generally about 10 MPa. Nowadays, welded pipes are made seamless.

Seamless steel pipes are formed in one step during rolling. Welded steel pipes need to be rolled and then welded, generally with spiral welding and direct welding. The performance of seamless pipes is better, but of course the price is higher.