Seamless Pipe Wall Thickness Testing Standard

The wall thickness of seamless pipes is one of the key parameters for their load-bearing capacity, strength and safety. Accurate wall thickness testing is crucial to ensuring the quality and application safety of steel pipes. In order to ensure that the wall thickness of seamless steel pipes meets the design requirements, various countries and regions have formulated a series of standards for wall thickness testing of steel pipes. The following is a careful summary of common wall thickness testing standards, covering measurement methods, tolerance ranges, test accuracy, etc. The following are some of the main standards and related information:

International standards and industry standards

1. ISO 1127—Dimensions, shape, weights and tolerances of seamless steel pipes

Standard content: ISO 1127 mainly specifies the requirements for the outer diameter, wall thickness, length, tolerance, etc. of seamless steel pipes. It is applicable to various seamless steel pipes, including general-purpose steel pipes, boiler pipes, oil pipelines, etc.

Wall thickness tolerance: According to this standard, the tolerance of wall thickness should comply with a certain range, for example, the wall thickness should not be less than 1/10 of the specified value and should not exceed the allowable deviation value.

2. ASTM A106 - Standard specification for seamless carbon steel pipe

Standard content: ASTM A106 is for seamless carbon steel pipe, particularly for applications in high-temperature and high-pressure environments. 

Wall thickness tolerance: This standard specifies the permissible deviation in wall thickness of seamless steel pipes. For example, the deviation in wall thickness is typically plus or minus 3% to 5%, depending on the size and application of the pipe.

3. API 5L - Standard for steel pipes for oil and gas Pipelines

Standard content: API 5L is mainly used in the oil and gas industry and specifies the size and performance requirements of different grades of steel pipes.

Wall thickness tolerance: In API 5L, the tolerance of wall thickness is generally within ±12.5%, but the specific tolerance value needs to be adjusted according to the pipe specifications and application.

Chinese Standards

1. GB/T 8163——Seamless steel pipes for general structural use

Standard content: GB/T 8163 is a Chinese standard that specifies the size, weight, tolerance and other requirements of seamless steel pipes. It is applicable to seamless steel pipes for general structural use.

Wall thickness tolerance: According to this standard, the tolerance of steel pipe wall thickness is ±12.5%, and there are special provisions for the tolerance range of small diameter, large diameter and thick wall pipes.

2. GB/T 5310——Seamless steel pipes for boilers

Standard content: GB/T 5310 is a standard specifically for seamless steel pipes for boilers, and is applicable to seamless steel pipes for boiler high-pressure pipelines and other high-temperature and high-pressure environments.

Wall thickness tolerance: This standard has strict requirements on wall thickness tolerance, usually within ±10%. In order to ensure the strength and durability of boiler pipes, this standard has more stringent requirements on wall thickness testing.

3. GB/T 3091——Spiral welded steel pipe for low pressure fluid transportation

Standard content: GB/T 3091 is applicable to steel pipes used for low-pressure fluid transportation and is suitable for some low-pressure piping systems.

Wall thickness tolerance: The tolerance of steel pipe wall thickness is usually ±10%. The wall thickness requirement of this standard is relatively loose, but it still needs to ensure the stability and safety of fluid transportation.

Wall thickness detection method

1. Mechanical measurement method

Vernier caliper: Suitable for testing smaller steel pipes, simple and easy to use, but with lower measurement accuracy.

Outside diameter caliper: used to measure the outside diameter of the steel pipe, and the wall thickness can be indirectly obtained by subtracting twice the wall thickness.

Inside diameter caliper: directly measure the inside diameter of the steel pipe and calculate the wall thickness based on the measured inside and outside diameters.

Number of measuring points: It is usually required to measure the wall thickness of each steel pipe at several locations, especially at the two ends and in the middle of the straight pipe to ensure the uniformity of the pipe.

2. Nondestructive testing

Ultrasonic thickness gauge (UT): Ultrasonic thickness measurement is the most commonly used non-destructive testing method, especially suitable for steel pipes with thicker walls. It can measure the wall thickness of steel pipes by the propagation speed of sound waves.

Working principle: The ultrasonic probe emits high-frequency sound waves, which are reflected back from the steel pipe wall. The wall thickness of the steel pipe is calculated based on the reflection time.

Advantages: non-destructive, rapid measurement, and large-scale application.

Disadvantages: Requires a certain level of technical skills, and the probe must be in good contact with the pipe wall during operation.

Eddy current testing: Suitable for surface quality inspection, mainly checking cracks, corrosion and wear on the surface of steel pipes, but not suitable for wall thickness measurement.

3. X-ray or gamma ray detection

Application: X-rays or gamma rays can penetrate steel pipes and generate images based on the thickness and density differences of the steel pipes. They are used to inspect the thickness and internal defects of the steel pipes.

Applicable: It is mainly used for the inspection of large-diameter thick-walled pipes. It can detect defects on the inner and outer walls of the pipes and obtain the distribution of wall thickness.

4. Wall thickness tolerance standard

For seamless steel pipe wall thickness tolerances, different standards may have slight differences. Usually, the specific tolerance range is specified based on the outer diameter, wall thickness, application and manufacturing process of the pipe. The following are some typical tolerance requirements:

Specific tolerance requirements:

Smaller diameter pipe: For small diameter seamless pipe, wall thickness tolerances are typically looser, such as ±10% or ±12.5%.

Larger diameter steel pipe: For larger diameter steel pipe, especially those used in high pressure, high temperature or harsh environments, the wall thickness tolerance is usually tighter, typically ±5% or ±7.5%.

Steel pipes for special purposes, such as boiler pipes and fertilizer pipes, may have stricter wall thickness tolerance requirements, usually requiring more precise wall thickness control with a deviation of no more than ±5% or ±7.5%.

Other wall thickness detection considerations

Wall thickness uniformity: Wall thickness uniformity is the key to ensuring the quality and pressure-bearing capacity of steel pipes. Situations where the pipe wall is locally too thin or too thick should be avoided, as this may affect the pressure resistance and service life of the pipeline.

Wall thickness at both ends of the pipe: Since the ends of seamless steel pipes may become thinner during the manufacturing process, the wall thickness at both ends of the steel pipe is usually required to meet certain requirements.

Temperature changes in the pipeline: Temperature changes will affect the accuracy of the measuring equipment, so the temperature must be controlled or temperature compensation must be performed during measurement.

Conclusion

Wall thickness testing of seamless steel pipes is very important. Different application scenarios have different requirements for wall thickness. Standards and specifications (such as GB/T 8163, ASTM A106, API 5L, etc.) have clear provisions on the wall thickness tolerance of seamless steel pipes, and usually have comprehensive requirements for outer diameter, wall thickness, material, etc.

Commonly used wall thickness testing methods include mechanical measurement, ultrasonic thickness testing, and X-ray testing. Each method has its own advantages and disadvantages, and the appropriate testing method should be selected according to specific needs.

Read more: How to Choose a Seamless Steel Pipe Manufacturer & Supplier?