(1) Corrosion method.
The weld seams of welded pipes posing as seamless steel pipes have been polished and should have traces of polishing. After visually identifying the suspected weld seam, polish the pipe end face with sandpaper, and then drop a prepared 5% nitric acid alcohol solution on the end face. If there is an obvious weld seam, it can be proved that it is a polished welded pipe.
(2) Metallographic method.
Since no welding materials are added to the high-frequency resistance welded pipe, its weld is very narrow. The above-mentioned rough grinding and then corrosion method may not be able to directly see the weld. However, since the high-frequency resistance welded pipe is not heat treated after welding, the structure of its weld area is essentially different from the structure of the steel pipe parent material. In this case, the metallographic method can be used. Cut a small sample with a length and width of 40mm at the suspected weld, and perform rough grinding, fine grinding and polishing. After meeting the metallographic inspection requirements, drop nitric acid alcohol solution on the suspected weld. If it is a welded steel pipe, a thin bright band will soon appear at the weld.
This sample was placed under a metallographic microscope to observe the structure of the steel pipe. It can be seen that the overall structure of the steel pipe is a ferrite network, pearlite and a large amount of Widmanstatten structure.
The suspected bright weld strip was placed under a metallographic microscope to observe its structure. Ferrite and a small amount of pearlite were visible, but no Widmanstätten structure was found.
By observing the steel pipe base material and weld under a microscope at the same time, the difference in the structure of the base material and the weld area can be clearly compared.
