For non-destructive testing of seamless steel pipes upon leaving the factory, is eddy current testing or ultrasonic testing a better choice?~

It’s difficult to say whether eddy current testing or ultrasonic testing is better for the non-destructive testing of seamless steel pipes prior to shipment. The inspection of austenitic stainless steel pipes on-site is carried out using eddy current testing; for carbon steel pipes, ultrasonic testing is generally the only option available. Eddy current testing cannot be used for carbon steel pipes; if it is necessary to use eddy current testing, special probes are required (expensive and custom-made). The 2507 material you mentioned is a duplex steel. According to the requirements of GB 21833, eddy current testing can be used as a substitute for hydraulic testing for duplex steel pipes, but ultrasonic testing must be carried out on each individual pipe; this is presumably the standard requirement set by national regulations.

Why can’t eddy current testing be used for carbon steel pipes?

As mentioned earlier, ordinary eddy current testing cannot be used for carbon steel pipes; instead, far-field eddy current testing must be employed. An article by Cheng Huayun from Hefei General Machinery Research Institute provides a detailed introduction; those with a spirit of exploration might want to take a look.

I learned that --------------------------- I heard from people who work in flaw detection that stainless steel 304 cannot be subjected to magnetic particle testing because it has no magnetism. Can carbon steel pipes be inspected using magnetic particle testing? Is eddy current testing a type of magnetic particle testing?

Far-field eddy current technology is based on a special physical phenomenon—the far-field eddy current effect—and it is a low-frequency eddy current testing technique capable of penetrating metal pipe walls. Far-field eddy current technology is particularly suitable for the inspection of ferromagnetic materials such as austenite-ferrite duplex stainless steels, ferritic stainless steels, Cr-Mo steels, and carbon steels. When testing heat exchange tubes, an internal probe is placed inside the tube to be inspected; this probe has an excitation coil as well as one (or two) measurement coils ； The distance between the excitation coil and the measurement coil is 2-3 times the diameter of the tube. A low-frequency alternating current is applied to the excitation coil, and the magnetic field lines (energy) generated propagate outward through the wall of the tube. In the far-field region, they pass through the wall of the tube, which has surface defects, and propagate inward again, where they are detected by the measuring coil.