Problems Existing in Regulations and Selection Standards of Thick-walled Steel Pipes in Engineering

Thick-walled steel pipes are stipulated in the project: the corresponding regulations and various regulations for the actual selection and use of thick-walled pipe fittings. Extremely or highly hazardous fluid media, flammable media, and high-pressure gas pipelines. Under this premise, the type of pipe fittings is mainly determined according to the purpose and conditions of use (pressure, temperature, fluid medium).
1. Special Equipment Supervision Law;
2. List of special equipment inspection regulations;
3. Pressure pipeline management and supervision regulations;
4. Special equipment supervision and supervision regulations;
5. Special equipment design/manufacture/installation supervision and management regulations (draft);
6. Technical supervision regulations for pressure pipelines (draft);
7. Technical specifications for industrial metal pipelines (draft).

Problems in the selection criteria of thick-walled steel pipes:
1. Starting from the standard system to formulate. For the selection in engineering, there are pipe standards, but there is no corresponding standard for forgings or castings. The reality is that the standard for forgings of pipe fittings borrows the standard for forgings of pressure vessels, without considering the differences between the two, such as welding, film inspection, and other regulations.
2. The standard level of pipe fittings varies greatly, and the content lacks consistency and systematicness, so that there are contradictions in the connection, causing inconvenience in use.
3. There is no type test standard 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-weld pipe fittings. There are no other type test standards or implementation standards to ensure the manufacture of pipe fittings.
Thick-walled seamless pipe weight formula: [(outer diameter-wall thickness)*wall thickness]*0.02466=kg/m (weight per meter).

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