Seamless Steel Pipe Straightness Measurement

SMLS pipe, longitudinally welded steel pipes (LSAW pipe), forged steel pipes, precision dense steel pipes, high-precision precision steel pipes, and other steel pipes will cause the steel pipe body to bend to varying degrees in the longitudinal direction (that is, the length direction) during the production process. However, the degree of bending of some steel pipe products is visible to the naked eye, and the steel pipe is not a qualified product. As long as it is a regular manufacturer, such products are absolutely not allowed to leave the factory, and some require special equipment to measure straightness.

For the straightness of steel pipes, the requirements are not high in general fluid transportation pipelines. This kind of pipe mainly requires the concentricity of the nozzles to facilitate the welding of the pipeline. However, if steel pipes are used in processing machinery and equipment, especially rubber rollers, middle shafts, etc., they have higher requirements for straightness or curvature, and this is also a very important index for them. Because it involves a processing problem, the amount of processing directly affects the size of the production cost. If it cannot be processed, the steel pipe will be a waste product. Therefore, manufacturers like the production of roller body equipment pay special attention to the straightness of the steel pipe when they buy seamless steel pipes or straight seam steel pipes.

For seamless steel pipes, straight seam steel pipes, and forged steel pipes, the straightness is best to be forged steel pipes. Because the outer diameter is produced by the processing equipment bit by bit, the straightness is generally not a problem. Secondly, seamless steel pipes have a three-roll straightening process in the production process of this steel pipe. The pipes with high straightness requirements use a computer-controlled multi-function integrated hydraulic straightening machine imported from South Korea, which can basically meet the straightness requirements of customers. The worst is the straight steel pipe. Although the basic process also has this process, it is made of steel plate or coil. If the internal stress of the steel cannot be released well, it will also cause the deformation of the steel pipe after processing. .

Pipe Straightness Calculation 

1. Partial Curvature of Seamless Steel Pipe or Straight Seam Steel Pipe

Use a one-meter ruler to measure the maximum bend of the steel pipe and measure the chord height (mm), which is the value of local curvature, and its unit is mm/m, means such as 2.5mm/m. This method is also suitable for tube end curvature.

2.The Total Bending Degree of the Steel Tube

use a thin rope to pull tight from both ends of the tube, measure the maximum chord height (mm) at the bend of the steel tube, and then convert it into a percentage of the length (in meters), which is the length of the steel tube The full-length curvature of the direction. For example: the length of the steel pipe is 10m, and the measured maximum chord height is 30mm, the total length of the pipe is: 0.03+10m*100%=0.3%.

Straightness Requirements for Seamless Pipes

The straightness requirements for seamless steel pipes vary depending on their application. For ordinary fluid transport pipes, the straightness deviation per meter should not exceed 1mm, and the total length deviation should not exceed 0.1% of the total length.

 

Seamless steel pipes for precision machinery have higher requirements, with a straightness deviation of ≤0.5mm per meter to ensure accurate positioning during processing. High-pressure pipelines require a straightness deviation of ≤0.8mm/meter to avoid obstructed media flow or excessive local pressure due to bending.

 

Straightness testing can be performed by placing the steel pipe on a platform and measuring the maximum gap between the pipe and the platform using a feeler gauge, or by using a straightness measuring instrument for automatic detection.

 

Pipes exceeding the standard must be straightened using a straightening machine. Small-diameter pipes can be straightened using pressure, while large-diameter pipes require heated roller straightening to ensure compliance with usage requirements.

 

Pipe Straightness Measurement

Commonly used methods for measuring straightness include the ruler method, collimation method, gravity method, and straightness method.

 

Straightness measurement primarily measures the straightness error of the generatrix of cylinders and cones, the straightness error of guide surfaces of machine tools and other machines, and the straightness error of workpiece guide surfaces. Straightness measurement is an important part of length measurement technology.

 

In addition, straightness errors can be measured using optical flats, laser interferometers, and their straightness measuring accessories, with very high measurement accuracy. The latter can achieve a measurement accuracy of 0.4 micrometers/1000 millimeters. Many machine tool manufacturers now use laser interferometers to measure straightness, flatness, perpendicularity, etc.

 

How to Check Straightness of Pipe

1. Fitting Method

This method uses the principle of comparing the element to be measured with an ideal element. For example, if the cutting edge is considered as the ideal element, it is fitted against the surface to be measured, minimizing the maximum gap between them. This maximum gap is the straightness error of the element being measured.

When the gap is small, a standard optical gap is used for estimation; when the gap is large, a feeler gauge is used for estimation.

 

2. Micrometer Method

Used to measure the straightness of the generatrix or axis of a cylinder.

 

3. Pitch Method

Suitable for measuring long parts. The length to be measured is divided into several small segments, and the relative reading of each segment is measured using a level, autocollimator, etc. Finally, the straightness error is calculated through data processing.

Straightness after cold drawing: 0.7mm/m. Inner diameter roundness: within 0.005mm. Requirements for seamless pipes in South Korea.

 

4. Data Acquisition Instrument with Dial Indicator Method

Measuring Instruments: Runout meter, dial indicator, data acquisition instrument.

Advantages: No need for manual reading, reducing errors caused by manual reading; No need for manual data processing, the data acquisition instrument automatically calculates the parallelism error value.

Measurement Result Alarm: The data acquisition instrument will automatically alarm if the measurement result is outside the straightness tolerance zone.

 

Measurements to Improve the Straightness of Seamless Steel Pipes

In addition to relying on professional testing equipment, manufacturers can also take a series of measures to improve the straightness of seamless steel pipes. For example, introducing advanced straightening equipment for precise straightening of steel pipes; strengthening quality control during production to ensure each process meets requirements; and regularly providing skills training to employees to improve their operational levels.

 

Factors Affecting the Straightness of Seamless Steel Pipes

1. Steel Pipe Manufacturing Process

The straightness accuracy of seamless steel pipes is directly related to the manufacturing process. Traditional seamless steel pipe manufacturing processes require multiple steps such as hot rolling, piercing, annealing, and pickling, all of which affect straightness. Modern manufacturing processes such as hot drawing and cold drawing can effectively improve the straightness accuracy of steel pipes, offering better stability and precision compared to traditional processes.

 

2. Material

Different materials also have a certain impact on the straightness of steel pipes. Different types of materials, due to their special physical properties, affect the shape of the steel pipe, thus affecting its straightness. Therefore, the choice of steel pipe material should be made based on the specific application.

 

3. Equipment and Facilities

The straightness of steel pipes is constrained by the production equipment. The precision of the production equipment directly determines the accuracy of the pipe's straightness. For steel pipes with high straightness deviation requirements, close cooperation between manual labor, equipment, and facilities is necessary to produce high-quality seamless steel pipes.

 

The Importance of Seamless Pipe Straightness

The straightness of seamless steel pipes has a significant impact on their performance. If the straightness does not meet the standards, it will not only affect the appearance quality of the steel pipe but may also lead to problems such as bending and deformation during installation or use. Especially in applications with high precision requirements, such as precision machining equipment and hydraulic pipes, the straightness of seamless steel pipes is a crucial quality indicator.

Read more: Seamless Pipe Thickness or Thermal Conductivity of Seamless Pipe