On-line Eddy Current Flaw Detection of Welded Stainless Steel Pipes

  • By:Iris Liang
  • Date:2021/10/18

With the rapid development of science and technology and industrial production, companies have higher and higher requirements for material performance. However, current metallurgical technology cannot provide perfect materials. At the same time, various types of equipment will also produce various defects during the manufacturing process, such as welding cracks, incomplete penetration, welding leakage and other quality problems, internal surface cracks, peeling, pulling wires, scratches, pits, bumps, etc. Spots, corrosion and other defects, as well as residual internal debris, foreign objects and other extras in the inner cavity of the product, etc. These problems may damage the entire organization, cause major equipment and personal accidents, and cause major losses to enterprises and workers.

 Therefore, in this context, the value and significance of non-destructive testing is particularly important.

1. The necessity of eddy current testing for welded pipes

Industrial welded stainless steel pipes are widely used in industrial fields such as fluid transportation, heat exchangers, and aerospace. Therefore, there must be no cracks, cracks, unwelded welding and other defects in the weld, and there must be no excessive scratches, crushing and other defects on the surface. Because welded pipe has the characteristics of continuous and rapid production on the production line, it is difficult to guarantee the quality of welded pipe only by manual post-inspection. The eddy current flaw detection method has the advantages of fast detection speed, no need to couple with the surface of the workpiece, and high detection sensitivity, which is suitable for quality control and quality inspection of welded pipe production.

2. The function of eddy current flaw detector

The online eddy current flaw detection of the steel pipe production line refers to the flaw detection that is synchronized with the production process on the production line, which is mainly used for the quality control of the production process; if users have requirements in this regard, generally speaking, Hangao Tech (SEKO Machinery) is for users All are equipped with online eddy current flaw detection. Its advantages are: saving space and simplifying process steps. When the damage is detected, the instrument can automatically alarm and automatically mark the scratched or unfused place.

3. Selection of standard sample tube


The detection result is judged by the comparison of the artificial defect and the natural defect display signal in the comparison sample. The steel pipe of the comparison sample and the steel pipe to be inspected should have the same nominal size and chemical composition. The surface state and heat treatment state are similar, that is, they should have similar electromagnetic properties.


In the production process of welded pipes, it is easy to find a test machine standard sample tube that meets the notch size specified by the standard. This standard sample tube contains not only open cracks in the weld, but also cracks or dark cracks and unfusion. These defects are continuous and slow. Transitional, referred to as slow-change injury or natural injury. Therefore, a section of welded pipe that meets the notch size requirements and contains natural flaws can be selected as the standard sample tube for eddy current flaw detection.

4. Alarm device

During online flaw detection, if an over-standard defect is found, the defect signal amplitude enters the alarm area, and the instrument will automatically alarm. The instrument has an alarm logic output circuit that can connect to the external sound-light alarm and send out an alarm signal. The defective welded pipe can be separated by automatic or manual inspection to achieve the purpose of quality control of the welded pipe.




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