What are the acceptance standards for stainless steel welded pipes in the construction industry

The acceptance standards for stainless steel welded pipes in the construction industry mainly cover several aspects. Here are the details:

Appearance quality acceptance

Surface defects: The surface of the welded pipe should be smooth, without cracks, folds, bends, delamination, streaks, and scars. Minor scratches, pits, etc., with a depth not exceeding the negative deviation of the pipe wall thickness, are allowed.

Color and luster: The surface color of the stainless steel welded pipe should be uniform and consistent, without obvious color differences, and should have the metallic luster of stainless steel. There should be no rust, oxide scale, etc., which may affect the appearance and corrosion resistance.

Weld appearance: The weld should be uniform and neat, without pores, slag inclusions, incomplete penetration, incomplete fusion, etc. welding defects. The weld height should comply with relevant standards, generally not exceeding the specified value, and the weld should smoothly transition with the base material.

Dimension accuracy acceptance

Outer diameter: Use calipers or external diameter micrometers and other measuring tools to measure the outer diameter of the pipe at different positions. The size should comply with the allowable deviation range specified in the corresponding standards. For some common stainless steel welded pipes used in construction, the allowable deviation of the outer diameter may be within ±0.5% to ±1%.

Wall thickness: Use wall thickness measuring instruments or ultrasonic thickness gauges and other equipment to measure the wall thickness of the pipe. The wall thickness deviation should be within the standard range to ensure the strength and load-bearing capacity of the pipe.

Length: Use steel tape measures or other length measuring tools to check whether the length of the pipe meets the requirements of the contract or relevant standards. The length allowable deviation is generally ±5mm to ±10mm.

Straightness: Place the pipe on a horizontal platform and measure its straightness using a string or straightedge. The straightness deviation should generally not exceed 1.5mm/m to 2.0mm/m.

Material and chemical composition acceptance

Material certificate: Check the material certificate provided by the supplier to confirm whether the material grade, chemical composition, etc., of the stainless steel welded pipe comply with the design requirements and relevant standards.

Chemical composition analysis: Use spectrometers and other equipment to conduct chemical composition analysis of the pipe to detect the content of main alloy elements such as chromium (Cr), nickel (Ni), and molybdenum (Mo) within the specified range.

Mechanical property acceptance

Tensile test: According to the requirements of relevant standards, take samples from the pipe and conduct a tensile test on a tensile testing machine to determine the tensile strength, yield strength, and elongation after fracture of the pipe, etc. The results should comply with the standard requirements for the material and specification.

Bending test: During the bending test, place the sample on the bending testing machine and perform bending according to the specified bending angle and bending diameter. After the test, check the bending part of the sample. There should be no cracks, fractures, etc., at the bending part.

Flattening test: For some special-purpose stainless steel welded pipes, a flattening test may be required. Place the pipe sample on the flattening testing machine and conduct the test according to the specified flattening rate and flattening degree. The pipe should not have cracks, fractures, etc. after the test.

Process performance acceptance

Welding process qualification: Check the welding process qualification report to confirm whether the welding process has been verified and whether it complies with relevant standards and design requirements. The welding process qualification should include welding methods, welding materials, welding parameters, etc.

Weld flawless detection: Use flawless detection methods such as ultrasonic testing, radiographic testing, magnetic particle testing, etc., to inspect the weld for defects. The detection ratio and qualified level should comply with the design documents and relevant standards.

Other acceptance

Pressure test: For stainless steel welded pipes used for fluid transportation, a pressure test should be conducted to verify the sealing and strength of the pipe. The test pressure is generally 1.25 times to 1.5 times the design pressure. The pipe should have no leakage or deformation within the specified test time. Cleaning and purging: After the pipeline installation is completed, cleaning and purging should be carried out to remove debris, oil, and other substances from the pipeline. The quality of cleaning and purging should comply with relevant standards, and it can be inspected and accepted by checking the cleanliness of the cleaning solution and the condition of the inner surface of the pipeline after purging.