Purpose of cold bending test
The quality of steel pipes is assessed by inspecting the technological properties of seamless pipe or welded steel tube. Master the test method of steel pipe bending (cold bending) performance and the uation method of steel pipe quality, and use instruments and equipment correctly.
Specimen preparation
1) There shall be no scratches on the curved outer surface of the test piece;
2) When the sample is processed, the affected area formed by shearing or flame cutting should be removed;
3) When the diameter of the sample is less than 35mm, it does not need to be processed, and it can be tested directly. If the energy of the testing machine allows, the test piece with a diameter of not more than 50mm can also be tested with a full-section test piece;
4) When the diameter of the steel pipe is greater than 35mm, it should be processed into a test piece 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 on the outside of the bend;
5) The length of the bending specimen depends on the diameter of the specimen and the bending test device. Usually determine the length of the specimen according to the formula: l=5d+150.
Experiment procedure
(1) Semi-guided bending
One end of the sample is fixed, and it is bent around the diameter of the bend center. The specimen is bent to the specified bending angle or cracks, cracks or fractures appear.
(2) guide bending
a. The sample is placed on two fulcrums, and a bending center of a certain diameter is applied between the two fulcrums of the sample to apply pressure, so that the sample is bent to a specified angle or cracks, cracks or breaks appear.
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 to continue to apply pressure until the two arms of the test are parallel. At this point, a gasket of the same size as the diameter of the bend center can be added for testing. When the test needs to be bent until the two arms touch, first bend the sample to the state shown in the figure, and then place it between the two flat plates and continue to apply pressure until the two arms touch
c The test should be performed under steady pressure, and the test force should be applied slowly. The distance between the two rollers is [(d+2.5a)±0.5a], and no changes are allowed during the process.
d The test is carried out at 10°C~35°C or under control conditions (23±5)°C.
Test Results and Analysis
According to the following five test result uation methods, if there is no crack, crack or break, the test piece is qualified.
(1) When the metal on the outer surface of the bending part of the intact test piece basically has no defects caused by bending deformation visible to the naked eye, it is called intact.
(2) Microcracks When the metal on the curved outer surface of the test piece basically has small cracks, the length of which is not greater than 2mm and the width is not greater than 0.2mm, it is called a microcrack.
(3) Cracks basically appear on the metal on the curved outer surface of the test piece. 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 The metal on the curved outer surface of the test piece basically has obvious cracks, and when the length is greater than 5mm and the width is greater than 0.5mm, it is called a crack.
(5) Fracture When the curved outer surface of the fractured specimen has cracks penetrating 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 length and width of micro-cracks, cracks and cracks reaches a certain range, it should be uated according to this level.
The quality of steel pipes is assessed by inspecting the technological properties of seamless pipe or welded steel tube. Master the test method of steel pipe bending (cold bending) performance and the uation method of steel pipe quality, and use instruments and equipment correctly.
Specimen preparation
1) There shall be no scratches on the curved outer surface of the test piece;
2) When the sample is processed, the affected area formed by shearing or flame cutting should be removed;
3) When the diameter of the sample is less than 35mm, it does not need to be processed, and it can be tested directly. If the energy of the testing machine allows, the test piece with a diameter of not more than 50mm can also be tested with a full-section test piece;
4) When the diameter of the steel pipe is greater than 35mm, it should be processed into a test piece 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 on the outside of the bend;
5) The length of the bending specimen depends on the diameter of the specimen and the bending test device. Usually determine the length of the specimen according to the formula: l=5d+150.
Experiment procedure
(1) Semi-guided bending
One end of the sample is fixed, and it is bent around the diameter of the bend center. The specimen is bent to the specified bending angle or cracks, cracks or fractures appear.
(2) guide bending
a. The sample is placed on two fulcrums, and a bending center of a certain diameter is applied between the two fulcrums of the sample to apply pressure, so that the sample is bent to a specified angle or cracks, cracks or breaks appear.
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 to continue to apply pressure until the two arms of the test are parallel. At this point, a gasket of the same size as the diameter of the bend center can be added for testing. When the test needs to be bent until the two arms touch, first bend the sample to the state shown in the figure, and then place it between the two flat plates and continue to apply pressure until the two arms touch
c The test should be performed under steady pressure, and the test force should be applied slowly. The distance between the two rollers is [(d+2.5a)±0.5a], and no changes are allowed during the process.
d The test is carried out at 10°C~35°C or under control conditions (23±5)°C.
Test Results and Analysis
According to the following five test result uation methods, if there is no crack, crack or break, the test piece is qualified.
(1) When the metal on the outer surface of the bending part of the intact test piece basically has no defects caused by bending deformation visible to the naked eye, it is called intact.
(2) Microcracks When the metal on the curved outer surface of the test piece basically has small cracks, the length of which is not greater than 2mm and the width is not greater than 0.2mm, it is called a microcrack.
(3) Cracks basically appear on the metal on the curved outer surface of the test piece. 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 The metal on the curved outer surface of the test piece basically has obvious cracks, and when the length is greater than 5mm and the width is greater than 0.5mm, it is called a crack.
(5) Fracture When the curved outer surface of the fractured specimen has cracks penetrating 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 length and width of micro-cracks, cracks and cracks reaches a certain range, it should be uated according to this level.
