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Problems existing in the regulations and selection standards for thick-walled steel pipes in projects

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Thick-walled steel pipes are stipulated in the project: the corresponding laws and regulations for the actual selection and use of thick-walled pipe fittings. When thick-walled steel pipes are selected or used, thick-walled pipe fittings must first comply with the corresponding laws and regulations, especially for transportation. Situations that are extremely or highly hazardous to pipelines such as fluid media, flammable media, and high-pressure gases. Under this premise, the type of pipe fittings is mainly determined based on the purpose and usage conditions (pressure, temperature, fluid medium). The following mainly lists relevant regulations/norms for reference only.

1. Special Equipment Supervision Law;
2. Special equipment inspection regulations;
3. Regulations on pressure pipeline management and supervision;
4. Special equipment supervision and inspection regulations;
5. Special equipment design/manufacturing/installation supervision and management regulations (formulated);
6. Technical supervision procedures for pressure pipelines (formulated);
7. Technical specifications for industrial metal pipes (formulated).

Problems in the selection standards of thick-walled steel pipes:
1. The standard system is formulated based on the standard system. There are standards for pipes used in engineering, but there are no corresponding standards for forgings or castings. The reality is that the pipe fitting forging standards borrow from the pressure vessel forging standards without considering the differences between the two, such as welding, film inspection, and other regulations.
2. The standard level of pipe fittings varies widely, and the content lacks consistency and systematicness, resulting in contradictions in connection, and causing inconvenience in use.
3. There are no type test standards for pipe fittings. Only the GB12459 and GB13401 standards stipulate the pressure calculation for the burst test of steel butt-welded seamless pipe fittings and steel plate butt-welded pipe fittings. There are no other types of test standards or execution standards to ensure the manufacture of pipe fittings.
The weight formula of thick-walled seamless pipes is: [(outer diameter-wall thickness)*wall thickness]*0.02466=kg/meter (weight per meter).

Determination of strength grade of thick-walled steel pipe:
1) Pipe fittings whose grade is expressed by nominal pressure or whose pressure-temperature rating is specified should be based on the pressure-temperature rating specified in the standard, such as GB/T17185;
2) The standard only stipulates the nominal thickness of the pipe fittings connected to the straight pipe, and its applicable pressure-temperature rating is determined according to the benchmark pipe grade specified in the standard, such as GB14383~GB14626.
3) For pipe fittings that only specify outer dimensions in the standard, such as GB12459 and GB13401, their pressure-bearing strength should be determined through confirmatory tests.
4) For others, pressure design or analytical analysis should be carried out by relevant regulations to determine the basis for their use. In addition, the strength level of pipe fittings should not be lower than the pressure under severe working conditions that the entire pipeline system may encounter during operation.




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