What is the defect of large-diameter straight seam welded pipe?

تاريخ:2018-04-12 رأي:2342
Large diameter welded pipe, more common in industrial and civil construction electrical, water supply and drainage, fire fighting and support structure. Due to the production of such pipes, the rolling, coiling, and straight-line welding processes are used. Most of the welding of the welded pipe uses a high-frequency wave welding process, so it is customarily called a "high-frequency welded pipe." Small-diameter pipe, using this process, the technology is relatively simple, easy to control defects. When the large-diameter welded pipe is manufactured, because of the large size of its blank, some manufacturing defects such as concentricity of the finished product, smoothness of the surface, and surface finish are inevitably caused by some influences of the processing machinery and processes. There are also indicators such as voids, missing welds, and welding defects that may exceed original expectations. In addition, the material weldability index of the pipe is also a major factor affecting the quality of the finished product.

Recently, the large-diameter welded pipe used as a pipe is generally produced by a spiral welding process, which avoids the defects of the longitudinal welded pipe.

Large diameter welded pipe overall heat treatment process
The overall heat treatment is characterized by: in the process of processing, there is no temperature difference in the wall, no residual stress, heating and holding time can be adjusted to adapt to more complex heat treatment specifications, but also can be automatically controlled by a computer, but the roller type furnace equipment is complex and operating costs are high. Large-diameter welded pipe overall heat treatment: it can be divided into online heat treatment and off-line heat treatment.

Welded pipe heat treatment:
After the large-diameter welded pipe is welded, two or more sets of intermediate frequency circular induction heating devices are used to heat the whole pipe. The required temperature is heated to normal temperature within 900-920°C for a short period of time. After normal cooling below °C, the overall tube organization was improved.

Welding pipe offline normal heat treatment in furnace:
The overall heat treatment equipment for the large-diameter welded pipe of the welded pipe consists of a chamber furnace and a roller hearth furnace. Nitrogen or hydrogen-nitrogen mixed gas is used as a protective atmosphere to achieve no oxidation or light. Due to the lower production efficiency of the chamber furnace, a roll-bottom type continuous heat treatment is currently used.