High frequency welded steel pipe if produce control is better, fusion surface of molten metal or oxide will be left. If the cutting of a weld sample polishing, etching, and observed under the optical microscope, the heat-affected zone is shaped like a drum, because the edge of the strip entering into the high-frequency current from the ends of the steel strip and the side edge portions with generating heat. Heat-affected zone slightly darker than the base metal, because the heating of welding carbon steel edge diffusion weld cooling is absorbed in the strip edges. Especially near the edges of the strip into CO and oxygen or carbon dioxide, the remaining iron without carbon, the color lighter.

On the use of high-frequency generator frequency generator past three loops welded pipe: High-frequency generators; solid drive; electronic high-frequency oscillator, and later improved to basically a single loop. There are a variety of high-frequency oscillator output power adjustment methods, such as auto-transformers, reactance method, thyristor law.

High frequency welded steel pipe may be a variety of defects. Each defect has many different names, there is no generally accepted terminology. The following names are given defect, the defect in parentheses another common name: (1) inclusion (burnt black oxide); (2) pre-arc (white burnt oxide); less (3) fusion (open seam); (4) lack of fusion edge (edge waves); (5) Central fusion inadequate (central cold welding); (6) stick welding (cold welding); (7) cast welding (brittle weld); (8) stomata (pinhole); (9) jump welding. These defects are not all but the most common frequency welding defects.