The pass rate of NDT re-inspection after seamless steel tube repair is affected by the repair process, defect type, and the stringency of the testing standards. The industry average pass rate is approximately 70%-85%, but the pass rate for critical pressure-bearing pipe fittings is usually below 70%.
Key factors affecting the pass rate:
1. Defect depth and location
The pass rate for shallow scratches and abrasions (<30μm) after repair can reach over 90%.
For deep damage involving more than 10% of the wall thickness or repair near the weld area, the pass rate drops to 50%-60% due to the tendency for residual stress or microcracks.
2. Standardization of repair process
Using standardized grinding and turning processes and operated by certified personnel increases the pass rate to over 80%.
Manual, arbitrary grinding or lack of smooth transitions often results in failure during re-inspection due to stress concentration.
3. Inspection Standards and Equipment Accuracy
Using high-sensitivity ultrasonic testing (UT) or eddy current testing (ET) equipment can detect micron-level nascent defects, leading to a higher initial rejection rate, but ensuring long-term safety.
According to GB/T 5777-2019 standard, if the echo signal in the repaired area exceeds the equivalent of a Φ2mm flat-bottom hole, the pipe is rejected, directly affecting the pass rate.
4. Usage Scenarios Restrictions
For repaired pipes used in non-pressure-bearing structural components or decorative applications, the inspection is more lenient, and the pass rate can reach 90%.
Steel pipes used in high-pressure fluid transportation systems, even after repair, are not allowed to be re-inspected and put back into use; they are directly treated as scrap, therefore, no pass rate statistics are available.
