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

First, the regulations for thick-walled steel pipes in engineering projects: the corresponding regulations and various regulations for the actual selection and use of thick-walled pipe fittings. When thick-walled steel pipes and thick-walled pipe fittings are selected or used, they must first follow the relevant regulations and regulations, especially for pipelines that transport extremely or highly hazardous fluid media, flammable media, and high-pressure gases. Under this premise, the type of pipe fittings is mainly determined based on the purpose and use conditions (pressure, temperature, fluid medium). The following mainly lists the relevant regulations/specifications for reference only.

1. Special Equipment Supervision Law;

2. Special Equipment Inspection Regulations;

3. Pressure Pipeline Management and Supervision Regulations;

4. Special Equipment Supervision and Inspection Regulations;

5. Special Equipment Design/Manufacturing/Installation Supervision and Management Regulations (Drafted);

6. Pressure Pipeline Technical Supervision Regulations (Drafted);

7. Industrial Metal Pipeline Technical Specifications (Drafted).

Second, problems in the selection standards for thick-walled steel pipes:

1. Formulated from the standard system. In the project, there are standards for pipe materials, but there are no corresponding standards for forgings or castings. The reality is that the standards for forgings of pipe fittings borrow the standards for forgings of pressure vessels, without considering the differences between the two, such as welding, film inspection, and other regulations.

2. The standards for pipe fittings vary greatly, and the content lacks consistency and systematicity, resulting in contradictions in the connection, and causing inconvenience in use.

3. There is no type test standard for pipe fittings. Only GB12459 and GB13401 standards specify 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 implementation standards to ensure the manufacturing of pipe fittings.

The weight formula of thick-walled seamless pipe is: [(outer diameter-wall thickness)*wall thickness]*0.02466=kg/meter (weight per meter).

Third, determination of the strength grade of thick-walled steel pipes:

1) For pipe fittings that express their grade or specify a pressure-temperature rating in nominal pressure, the pressure-temperature rating specified in the standard shall be used as the basis for their use, such as GB/T17185;

2) For pipe fittings that only specify the nominal thickness of the straight pipe connected to them in the standard, their applicable pressure-temperature rating shall be determined according to the benchmark 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 pressure-bearing strength shall be determined through verification tests.

4) For others, the basis for their use shall be determined by pressure design or analytical analysis by relevant regulations. In addition, the strength grade of pipe fittings shall not be lower than the pressure under the severe working conditions that the entire pipeline system may encounter during operation.