GB/T 20801.1-2025Pressure piping code - Part 1: Industrial piping (English PDF)

3.1 Piping

A system assembled from piping components for the conveying, distributing, mixing, separating, discharging, metering, or shutting off of fluid flow.

Note: In addition to piping components, this includes pipe-supporting elements, but excludes supporting structures such as building frames, pipe racks, bases (pipe piers or foundations).

3.2 Nominal pressure

A parameter representing the pressure rating of a piping component, consisting of the letters PN or Class and a dimensionless number.

3.3 Nominal diameter

Explosion group

The explosion hazard level of flammable gases and vapors, which are classified according to the maximum experimental safe gap (MESG).

3.81 Fire emergency block valve (FEBV)

A block valve that automatically shuts off the fire in the event of a fire without human intervention or external power (electricity, gas, or liquid) supply, possessing fire resistance, antistatic properties, high sealing performance, impact resistance.

5.1 General provisions

5.1.1 Material selection

The construction organization (user organization) or design organization shall select appropriate piping component materials, based on specific usage conditions (including manufacturing, fabrication and installation, media, operating conditions, working environment, testing, etc.) as well as the material usage requirements and limitations specified in this chapter, taking into account the material damage risk. Specific provisions for welding materials are provided in Chapter 7.

5.1.2 Basic technical provisions for materials

5.1.2.1 Tables B.1 and B.2 of Appendix B specify the designations, base material categories, allowable stresses, application ranges of commonly used piping component materials. Materials used for piping components shall also comply with the material standards listed in Tables B.1 and B.2.

The physical performance parameters of the materials are shown in Appendix C. The design and selection of commonly used pipeline materials, damage risks, corresponding engineering measures are shown in Appendix D.

5.1.2.2 In addition to the material standards and designations listed in Tables B.1 and B.2, the following materials may also be used in piping components, provided they meet the requirements and usage restrictions for the corresponding materials in this chapter.

a) Other designations of materials listed in the material standards in Tables B.1 and B.2;

5.6.2 Quality certification

The quality certification of materials shall comply with the following requirements.

a) The material has corresponding quality certification documents;

b) The quality certification documents include the inspection and test results specified in the standards and contract, which shall be traceable.

6.1 Design conditions

6.1.1 Design pressure

6.1.1.1 General provisions

6.1.1.1.1 The design pressure of each piping component in the piping system shall not be less than the pressure under the most severe pressure (including internal and external pressure) and temperature combination conditions, that may be encountered during operation, except as specified in 6.2.3.

6.1.1.1.2 The most severe operating conditions result in the piping components having the maximum thickness and the highest pressure rating.

6.1.1.1.3 The most severe pressure and temperature combination shall take into account operating conditions, that may arise from pressure sources (e.g., pumps, compressors), pressure pulsations, decomposition of unstable fluids, static head, failure or operational errors of control devices and valves, environmental influences.

6.1.1.1.4 When connecting piping with different fluid conditions, the pressure rating of the separating valves shall be determined according to the most severe condition. When multiple valves are used for separation (e.g., with double shut-off and discharge), the pressure rating of all valves shall be determined according to the most severe condition.

If multiple valves operate at different temperatures and are connected to main pipes or equipment and remotely controlled, the type selection of multiple valves can be considered based on different temperatures.

6.1.1.2 Principles for determining design pressure

6.1.1.2.1 For piping equipped with a single safety relief device, the design pressure shall not be less than the set pressure of the safety relief device; for piping equipped with multiple safety relief devices, the design pressure shall not be less than the set pressure of the first safety relief device.

6.1.1.2.2 For piping without safety relief devices or those prone to isolation or blockage from such devices, the design pressure shall not be less than the maximum pressure that may result from this.

6.1.1.2.3 When a pipeline is directly connected to equipment as a pressure system, the design pressure of the pipeline shall not be less than the design pressure of the equipment.

6.1.1.2.4 The design pressure of the centrifugal pump outlet pipeline shall not be less than the pump's shut-off pressure.

6.1.1.2.5 For piping conveying refrigerants or liquefied hydrocarbons with low boiling points, the design pressure shall not be less than the maximum pressure that the medium may reach, when the valve is closed or when the medium is not flowing.

6.1.1.2.6 When a pipeline is divided into several separate pressure-bearing sections by partitions (including jacketed pipes, blind flanges, etc.), the design pressure of the partition shall not be less than the pressure of the most severe pressure difference and temperature combination, that may be encountered in the pressure-bearing spaces on both sides during operation.

6.1.1.2.7 For vacuum piping equipped with safety control devices, the design pressure shall be the smaller of 1.25 times the maximum pressure difference and 0.1 MPa, which shall be designed according to external pressure conditions. For vacuum piping without safety control devices, the design pressure shall be 0.1 MPa.

6.1.2 Design temperature

6.1.2.1 General provisions

6.1.2.1.1 The design temperature of each piping component in the piping system shall be determined, based on the temperature under the most severe pressure and temperature combination conditions that may be encountered during operation.

6.1.2.1.2 The design temperatures of different piping components within the same pipeline may be different.

6.1.2.1.3 When determining the design temperature, the fluid temperature, ambient temperature, solar radiation, temperature of the heating or cooling medium, the effects of pipeline insulation and heat transfer shall be considered.

6.1.2.2 Determination of design temperature

6.1.2.2.1 For piping without external insulation, when the medium temperature is below 65 °C, the design temperature of the piping components is the same as the medium temperature, but factors such as solar radiation or other factors that may cause the medium temperature to rise shall be considered. When the medium temperature is above or equal to 65 °C, the determination of the design temperature of the piping components shall comply with the following provisions.

a) For pipes, valves, flanged short sections, welded fittings, other components with wall thicknesses similar to pipes, take 95% of the medium temperature;

b) For flanges other than loose flanges (including flanges on fittings and valves), take 90% of the medium temperature;

c) For loose flanges, take 85% of the medium temperature;

d) For bolts, take 80% of the medium temperature;

e) The average wall temperature can also be taken as the measured average wall temperature or the average wall temperature obtained from heat transfer calculations.

6.1.2.2.2 For externally insulated piping, the design temperature of the piping components is generally taken as the medium temperature; however, the average wall temperature can also be taken as the measured average wall temperature or the average wall temperature obtained from heat transfer calculations. For piping using tracing or jacketed structures, the influence of heating or cooling on the design temperature shall be considered.

6.1.2.2.3 For internally insulated piping, the design temperature of the piping components shall be determined by heat transfer calculations or tests.

6.1.2.3 Minimum design temperature

The minimum design temperature refers to the lowest temperature of the piping […]