Diameter expansion technology and detection methods of straight seam steel pipes

Generally speaking, the diameter of steel pipe can be divided into outer diameter, inner diameter, and nominal diameter. The outer diameter of a steel pipe whose material is a straight seam steel pipe is represented by the letter D, followed by the outer diameter size and wall thickness. For example, a seamless steel pipe with an outer diameter of 108 and a wall thickness of 5MM is represented by D108*5. A plastic pipe is also expressed by the outer diameter, such as De63. Others such as reinforced concrete pipes, cast iron pipes, galvanized steel pipes, etc. are expressed by DN. In design drawings, the nominal diameter is generally used to express it. The nominal diameter is artificially specified for the convenience of design, manufacturing, and maintenance. A kind of standard, also called nominal diameter, is the specification name of steel pipe (or pipe fitting). The nominal diameter of the steel pipe is not equal to its inner diameter and outer diameter. For example: there are several types of straight seam steel pipes with a nominal diameter of 100MM, such as 102*5, 108*5, etc. 108 is the outer diameter of the steel pipe, and 5 represents the wall thickness of the steel pipe. , therefore, the inner diameter of the steel pipe is (108*5-5) = 98MM, but it is not equal to the difference between the outer diameter of the steel pipe minus twice the wall thickness. It can also be said that the nominal diameter is close to the inner diameter, but not equal to the inner diameter. A specification name for the diameter of a steel pipe. The nominal diameter is used in design drawings. The purpose is to determine the structural dimensions and connection dimensions of steel pipes, pipe fittings, valves, flanges, gaskets, etc. based on the nominal diameter. The nominal diameter is represented by the symbol DN. , if the outer diameter is used in the design drawings, a pipeline specification comparison table should also be made to indicate the nominal diameter and wall thickness of a certain pipeline.

Straight seam steel pipe diameter expansion technology:

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 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 to further reduce the speed from the second stage position until it reaches the required position. This position is the inner circumferential position of the steel pipe before rebound is required by the process design.

4. Pressure-maintaining and stable stage: The sector-shaped block remains stationary in the inner circumferential position of the steel pipe for some time before springing back. This is the pressure-maintaining and stable stage required by the equipment and diameter expansion process.

5. Unloading return stage: The sector block rapidly retracts from the inner circumferential position of the steel pipe before rebounding until it reaches the initial expansion position. This is the minimum shrinkage diameter of the sector block required by the expansion process.

Common testing methods for straight seam steel pipes:

1. As a result of the straight seam steel pipe test, if a certain item does not meet the requirements of the product standard, the unqualified ones should be singled out, and double the number of samples should be taken from the same batch of straight seam steel pipes to test the unqualified items. recheck. If the re-inspection result fails, the batch of straight seam steel pipes shall not be delivered. If the following inspection items fail the initial inspection, re-inspection is not allowed.

2. For straight-seam steel pipes with unqualified re-inspection results, the supplier may submit them for acceptance one by one; or they may re-heat-treat them and submit a new batch for acceptance.

3. If there are no special provisions in product standards, the chemical composition of straight seam steel pipes shall be inspected according to the melting composition.

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

5. The supplier guarantees that the delivered straight seam steel pipes comply with the corresponding product standards. The purchaser has the right to inspect and accept products according to corresponding product standards.

6. 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.

7. The inspection items, sampling quantity, sampling locations, and test methods of straight seam steel pipes shall be by the provisions of the corresponding product standards.