Quality Standards for Seamless Precision Tube

The quality standards for seamless precision tube mainly include the following aspects:

Dimensional accuracy

The dimensional deviations of the outer diameter, wall thickness and other dimensions of seamless precision tubes should be strictly controlled within a small range to ensure that they can cooperate with other components during installation and use. The following are the relevant dimensional requirements:

1. The outer diameter tolerance adopts a gradient control system of ±0.1mm (precision grade) to ±0.3mm (industrial grade).

2. The wall thickness deviation implements a dual-track standard of ±5% (relative tolerance) or ±0.05mm (absolute tolerance).

3. The roundness error requirement is ≤0.8%OD, and it must reach ≤0.5%OD under special working conditions.

4. The straightness deviation is ≤1.5mm/m, and the high-precision scene requires ≤0.5mm/m.

5. The verticality of the end face is controlled within ±1°, and the precision connection part requires ±0.5°.

Surface quality

The surface should be smooth, free of defects such as cracks, folds, rolling, delamination, scarring, etc. Any surface defects may affect the appearance quality of the pipeline as well as its corrosion resistance and fluid flow performance during use. The following are surface modification indicators:

1. Roughness control Ra 0.4-0.8μm (fluid pipe) to Ra≤0.2μm (ultra-high clean system).

2. Hardened layer depth 50-200μm (nitriding treatment pipe).

3. Oxide film thickness 3-7μm (anti-oxidation treatment pipe).

Chemical composition

The chemical composition of seamless precision pipes should meet the requirements of the corresponding standards. For example, carbon structural steel should contain a specified proportion of carbon, manganese, silicon and other elements, while alloy structural steel should contain specific alloy elements. The stability of the chemical composition is crucial to ensure the mechanical properties and corrosion resistance of the pipeline. For example, the chemical composition of carbon steel pipe and mild steel pipe needs to be strictly controlled. Excessive carbon content will make the steel pipe brittle, while the addition of alloy elements can improve the strength, toughness and other properties of the steel pipe.

Mechanical properties

Including tensile strength, yield strength, elongation and other indicators. Good mechanical properties ensure that the pipeline can withstand various loads without rupture or excessive deformation during operation. The following are the relevant strength and toughness requirements:

1. Tensile strength 410-650MPa (conventional grade) to ≥900MPa (ultra-high strength pipe).

2. Yield strength ratio 0.65-0.90, yield strength ratio graded control.

3. Vickers hardness 180-320HV30, gradient matching working condition requirements.

4. Charpy impact energy ≥27J (-20℃ working condition).

5. Fracture toughness KIC ≥60MPa·m^1/2 (pressure-bearing key parts).

6. Bending radius ≤3D (thin-walled pipe) to ≤8D (thick-walled pipe).

Non-destructive testing

Non-destructive testing is required, such as ultrasonic testing, eddy current testing, etc., to detect whether there are defects such as cracks, slag inclusions, and pores inside the pipeline. The level of flaw detection should be determined according to the use requirements and design standards of the pipeline. It is usually required to achieve a certain flaw detection pass rate to ensure the quality and safety of the pipeline. In the production process of seamless steel pipe, non-destructive testing is a key link to ensure the quality of pipes. For high-end uses such as hydraulic tubes and precision tubes, the flaw detection standards are particularly strict.

Flattening test and expansion test

These two tests are used to test the plastic deformation capacity of the pipeline and the quality of the welded joints. The flattening test requires that the pipeline be flattened to a specified degree under a certain pressure without breaking, and the expansion test is to expand the end of the pipeline to a certain angle and diameter to observe whether it has defects such as cracks. These tests can ensure that the pipeline can adapt to various deformation conditions during use. For seamless precision tubes used for pup joints and pipe flanges connections, flattening and expansion tests can verify their reliability and sealing in practical applications.

Summary

The quality standard of seamless precision tubes is a comprehensive system that covers requirements in multiple aspects such as size, surface, chemical composition, mechanical properties and flaw detection. Only when the corresponding standards are met in all aspects can the quality and reliability of seamless precision tubes be guaranteed to meet the use needs of different fields and industries.

Read more: Difference between seamless pipe and seam pipe