Seamless steel pipes, straight-seam welded steel pipes, forged steel pipes, precision steel pipes, high-precision precision steel pipes, and other steel pipes will cause the steel pipe body to have different degrees of curves in the longitudinal direction (i.e., length direction) 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 absolutely 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 the curvature or straightness of the steel pipe.
For the standard of steel pipe straightness, the requirements are not high in general fluid transportation pipelines. This kind of steel 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 like those producing roller equipment pay special attention to the detection of the straightness of steel pipes 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 of forged steel pipes is the best, 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. There is a three-roll straightening process in the production process of this type of steel pipe, which can basically meet the customer’s 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.
Generally speaking, there are two ways to calculate straightness or curvature:
1. Local curvature of seamless steel pipe or straight seam steel pipe: 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. 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.
2. Total curvature of the entire length 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 entire length of the pipe should be: 0.03÷10m×100%=0.3%
Post time: Feb-05-2025