Measuring method of steel pipe straightness

Seamless steel pipe, straight seam welded steel pipe, forged steel pipe, precision steel pipe, high-precision precision steel pipe, etc. steel pipes will cause different degrees of curves in the longitudinal direction (i.e. length direction) of the steel pipe body during the production process. However, the degree of curve of some finished steel pipes can be seen visually with the naked eye. Such steel pipes are already unqualified products. As long as they are regular manufacturers, such products are not allowed to leave the factory. Some require special instruments and equipment to measure their straightness.

This degree of curve is expressed in numbers, which is called steel pipe curvature or steel pipe straightness. For the standard of steel pipe straightness, the requirements are not high in general fluid transportation pipelines. This kind of pipe mainly requires the concentricity of the pipe mouth to facilitate the welding of the pipeline. However, if steel pipe is used in processing machinery and equipment, especially rubber rollers, central shafts, etc., they have high requirements for straightness or curvature, and this is also a very important indicator for them.

Because it involves a processing volume issue, the size of the processing volume directly affects the size of the production cost. If the processing cannot be completed, the steel pipe will be directly scrapped. Therefore, manufacturers similar to roller equipment pay special attention to the detection of steel pipe straightness when purchasing seamless steel pipes or straight seam steel pipes.

Among the three seamless steel pipes, straight seam steel pipes, and forged steel pipes, the straightness is the best forged steel pipe, because its outer diameter is turned out little by little by the processing equipment, so the straightness is generally not a problem. Seamless steel pipes are second. The production process of this kind of steel pipe has a three-roll straightening process (for high precision requirements, there are 6-roll straightening machines, 9-roll straightening machines, and 12-roll straightening machines. For pipes with ultra-high straightness requirements, computer-controlled multi-functional integrated hydraulic straightening machines imported from South Korea are used), which can meet customers' requirements for straightness. The worst is the straight steel pipe. Although the basic process also has this process, it is all made of steel plates or coils. If the internal stress inside the steel cannot be released well, it will also cause deformation of the steel pipe after processing.

There are generally two ways to calculate straightness or curvature:

First, the local curvature of seamless steel pipes or straight seam steel pipes: that is, use a one-meter-long ruler to measure the maximum curvature of the steel pipe and measure its chord height (mm), which is the local curvature value, and its unit is mm/m, and the expression method is 2.5mm/m. This method is also applicable to the curvature of the pipe end.

Second, the total curvature of the steel pipe: use a thin rope to tighten from both ends of the pipe, measure the maximum chord height (mm) at the end of the steel pipe, and then convert it into a percentage of the length (in meters), which is the total curvature of the length of the steel pipe. For example: if the length of the steel pipe is 10m, and the maximum chord height is measured to be 30mm, then the curvature of the full length of the pipe should be 0.03÷10m×100%=0.3% For steel pipes with higher straightness requirements.