What is the purpose of steel pipe cold bending test?

The purpose of cold bending test

The quality of steel pipes is assessed by inspecting the process performance of seamless pipe or welded pipe. Master the test methods for steel pipe bending (cold bending) performance and the evaluation methods for steel pipe quality, and use instruments and equipment correctly.

specimen preparation

1) There should be no scratches on the curved outer surface of the test piece;

2) When processing the sample, the affected area caused by shearing or flame cutting should be removed;

3) When the sample diameter is less than 35mm, no processing is required and the test can be carried out directly. If the power of the testing machine allows, specimens with a diameter of no more than 50mm can also be tested with full-section specimens;

4) When the diameter of the steel pipe is greater than 35mm, it should be processed into a specimen with a diameter of 25mm, and the original surface on one side should be retained during processing. During the bending test, the original surface should be located outside the bend;

5) The length of the bending specimen depends on the diameter of the specimen and the bending test device. The length of the specimen is usually determined according to the formula: l=5d+150.

experiment process

(1) Semi-guided bending
One end of the sample is fixed and bent around the diameter of the bend center. The test piece is bent to the specified bending angle or cracks, cracks or fractures occur.

(2) Guide bending
A. The sample is placed on two fulcrums, and a bending center of a certain diameter is applied to apply pressure between the two fulcrums of the sample to bend the sample to a specified angle or cause cracks, cracks or breaks.
b. When the sample is bent at two fulcrums according to a certain bending center diameter until the two arms are parallel, the test can be completed at one time, or it can be bent first and then placed between the flat plates of the testing machine, and continue to apply pressure until the two arms are parallel. The arms are parallel. At this time, a gasket of the same size as the bending center diameter can be added for testing. When the test requires bending until the two arms contact, first bend the sample to the state as shown in the figure, then place it between the two flat plates, and continue to apply pressure until the two arms contact.
c The test should be carried out under constant pressure, and the test force should be applied slowly. The distance between the two rollers is [(d+2.5a)±0.5a], and no change is allowed during the process.
d The test is conducted at 10℃~35℃ or under controlled conditions (23±5)℃.

Test results and analysis

According to the following five test result evaluation methods, if there are no cracks, cracks, or breaks, the test piece is qualified.
(1) When the metal on the outer surface of the curved part of an intact specimen has basically no visible defects caused by bending deformation, it is called intact.

(2) Microcracks When there are basically small cracks in the metal on the bent outer surface of the specimen, with a length of no more than 2mm and a width of no more than 0.2mm, it is called microcracks.

(3) Cracks basically appear on the metal on the curved outer surface of the specimen. When the length is greater than 2mm, but less than or equal to 5mm, and the width is greater than 0.2mm, but less than or equal to 0.5mm, it is called a crack.

(4) Cracks: There are basically obvious cracks in the metal on the bent outer surface of the specimen. When the length is greater than 5mm and the width is greater than 0.5mm, it is called a crack.

(5) Fracture When a crack appears on the curved outer surface of the fractured specimen that runs along the width and its depth exceeds 1/3 of the thickness of the specimen, it is called fracture.
Note: As long as one of the specified lengths and widths of microcracks, cracks and cracks reaches a certain range, they should be evaluated according to this grade.