China technical requirements for seamless steel pipes for high pressure gas cylinders

1. Requirements of steel material.

The steel material for the high-pressure gas cylinder is a kind of dead steel without aging, which is usually melted by an alkaline open hearth furnace, an electric furnace and an oxygen blowing alkaline converter, and some kinds of steel must be melted by electroslag or vacuum. casting, the main ones are manganese steel, Chromium molybdenum or other alloy steel, carbon steel is rarely used. The demand for chemical composition is:

carbon-manganese steel: C≤0.40%, S≤0.030%, P≤0.035%, S + P≤0.060%.

Chromium-molybdenum and other alloy steels: C≤0.40%, S≤0.035%, P≤0.030%, S + P≤0. 055%, other elements have been specified.

The chemical composition requirements of alloy steel for special ultra-high strength light gas cylinders are as follows: S≤0.010%, P≤0.015%, S + P≤0.020%. In addition, there are strict requirements for non-metallic inclusion and low-strength steel structure. White spot, residual shrinkage hole, separation layer, slag inclusion and other defects are not allowed in low-power tissue.

2. Physical Ownership Requirements.

To ensure the safe use of high-pressure vessels, high tensile strength and elasticity strength are required, as well as high elongation and impact resistance. The ordinary cylinder using the ambient temperature is -20~60, while the cold area is -40~60; The former are usually treated with normalization or standardization + tempering with carbon-manganese steel cylinder, the second is usually a quenching treatment with Cr-Mo steel or another alloy steel cylinder. According to GB5099-94, these two types of steel must be performed: V-shaped low-temperature impact test of 20°C and 50°C respectively after heat treatment. Its impact resistance, buckling and elongation resistance ratio must reach the corresponding specified value. Seamless steel billet pipes that are obtained after heat treatment must also meet the specified value requirements.

3. Process and metallographic inspection.

According to the requirements of the cylinder manufacturer, it is required to perform flattening or cold bending tests on the seamless steel pipe, which must be performed in accordance with GB13440. For steel pipe samples after normalizing or normalizing + tempering, the grain size (100 times) must be greater than or equal to grade 6, the band structure must be less than or equal to grade 3.0, and the wechtenstein structure must be less than or equal to grade 2.0. The microstructure of the tempered steel tube samples should be tempered. In addition, the depth of the decarbonization layer of the tube body is also required.

4. Dimensional accuracy.

The cylinder wall thickness is designed for a minimum wall thickness, such as the international standard ISO 4705, DOT of American, DIN4664 of Germany and JISB 8230/8241 of Japan. The calculation of the minimum wall thickness is based on creep strength. The minimum wall thickness in the GB5099 standard is changed to the ISO4705 standard and calculated according to the performance resistance. Once the minimum wall thickness is provided, the seamless steel pipe for the high-pressure cylinder must ensure that the deviation of the wall thickness cannot be less than the minimum wall thickness to meet the requirements of the cylinder body thickness. According to the terms of the specified minimum wall thickness, the thinner the wall, the higher the accuracy of the wall thickness, the lighter the weight of the cylinder, the greater the volume, or the lower the weight-capacity ratio, the better The quality of the cylinder is. According to the requirements of GB5099, the deviation of the seamless steel tube wall thickness of the medium and small gas cylinder body supplied by the steel pipe factory is generally +15/-10%. The deviation of the outer diameter of the supplied seamless steel pipe is generally D 1.25%. The wall thickness and deviation from the outer diameter of the large volume gas cylinder tube shall be determined by agreement between the supplier and the supplier in accordance with the specific specifications.

5. Surface quality and inspection.

The surface quality of the gas cylinder directly affects the safety and aesthetics of the gas cylinder. Therefore, the inner and outer surface of the steel pipe must be free of defects such as cracks, bends, scars, separation, rolling and bending, pitting, etc., which must be removed. The wall thickness after removal should be greater than the negative deviation from wall thickness or the minimum wall thickness required by the design. In order to further ensure the quality of the entire pipe body section, the seamless steel pipe before delivery will undergo ultrasonic inspection according to GB 5777 and GB 8163 standard.