Non-destructive testing techniques for tube sheet surface defects

Non-destructive testing (NDT) techniques for tube sheet surface defects mainly include magnetic particle testing, penetrant testing, and eddy current testing. Magnetic particle testing utilizes the magnetization characteristics of ferromagnetic materials, identifying surface defects such as cracks and folds by observing the accumulation and distribution of magnetic particles at the defect site. Penetrant testing uses capillary action to allow a penetrant to seep into open defects, and then a developer is applied to reveal the defect morphology. Eddy current testing is based on the principle of electromagnetic induction and is suitable for rapid online inspection of conductive materials.

These techniques can effectively detect defects such as cracks, scratches, and scabs on the tube sheet surface without damaging the tube sheet structure. Magnetic particle testing has high sensitivity for ferromagnetic tube sheets but is only suitable for surface and near-surface defects; penetrant testing provides a visual display of defects but relies on manual observation; eddy current testing is fast and suitable for automated production scenarios.

In practical applications, the appropriate technique should be selected based on the tube sheet material and defect type. For example, austenitic stainless steel tube sheets are best inspected using penetrant or eddy current testing, while carbon steel tube sheets can prioritize magnetic particle testing. The test results must be evaluated in conjunction with relevant standards and specifications to ensure the safety and reliability of the tube sheet.