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GB/T 20801.3-2020 English PDF (GBT20801.3-2020)

GB/T 20801.3-2020 English PDF (GBT20801.3-2020)

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GB/T 20801.3-2020: Pressure piping code -- Industrial piping -- Part 3: Design and calculation

This Part of GB/T 20801 specifies the basic requirements for the design and calculation of pressure pipelines. These basic requirements include design conditions, design criteria, piping components and their pressure design, pipeline stress analysis, etc. This Part applies to the design and calculation of pressure piping, which is defined within the scope of GB/T 20801.1.
GB/T 20801.3-2020
GB
NATIONAL STANDARD OF THE
PEOPLE REPUBLIC OF CHINA
ICS 23.040
J 74
Replacing GB/T 20801.3-2006
Pressure piping code - Industrial piping - Part 3:
Design and calculation
ISSUED ON: NOVEMBER 19, 2020
IMPLEMENTED ON: JUNE 01, 2021
Issued by: State Administration for Market Regulation;
Standardization Administration of PRC.
Table of Contents
Foreword ... 3
1 Scope ... 6
2 Normative references ... 6
3 Terms and definitions ... 14
4 Design conditions and design criteria ... 16
5 Piping components ... 29
6 Pressure design of piping components ... 50
7 Stress analysis of pipeline ... 70
8 Pipe support & hanger ... 85
Appendix A (Informative) Calculation of wind load and seismic load ... 96 Appendix B (Informative) Piping layout ... 105
Appendix C (Informative) Comparison of common industrial valve standards with foreign general petrochemical valve standards ... 121
Appendix D (Informative) General requirements for stem seals of low leakage valves ... 126
Appendix E (Informative) Calculation example ... 129
Appendix F (Informative) Reinforcement calculation by pressure area method ... 140
Appendix G (Normative) Flexibility factor and stress increase factor ... 142 Appendix H (Informative) Dynamic load analysis of valves in piping system when opening and closing ... 146
Appendix I (Informative) Allowable load of static equipment nozzle ... 151 Appendix J (Normative) Corrugated metal expansion joint ... 154
References ... 162
Pressure piping code - Industrial piping - Part 3:
Design and calculation
1 Scope
This Part of GB/T 20801 specifies the basic requirements for the design and calculation of pressure pipelines. These basic requirements include design conditions, design criteria, piping components and their pressure design, pipeline stress analysis, etc.
This Part applies to the design and calculation of pressure piping, which is defined within the scope of GB/T 20801.1.
2 Normative references
The following documents are essential to the application of this document. For the dated documents, only the versions with the dates indicated are applicable to this document; for the undated documents, only the latest version (including all the amendments) is applicable to this standard.
GB/T 150 (all parts) Pressure vessel
GB/T 196 General purpose metric screw threads - Basic dimensions
GB/T 197 General purpose metric screw threads - Tolerances
GB/T 1031 Geometrical product specifications (GPS) - Surface texture:
Profile method - Surface roughness parameters and their values
GB/T 1047 Pipework components - Definition and selection of nominal size GB/T 1048 Pipework components - Definition and selection of PN
GB/T 3287 Malleable cast iron pipe fittings
GB/T 3420 Gray iron castings for pipe fittings
GB/T 3422 Cast-iron pressure pipe made by continuous casting process
GB/T 3733 24?? cone connectors - Straight thread
GB/T 3734 24?? cone connectors - Male
4.1.1 Design pressure
4.1.1.1 General provisions
4.1.1.1.1 The design pressure of each piping component, in the piping system, shall not be less than the pressure, under the most demanding combination of pressure and temperature, that may be encountered in operation, except for the conditions specified in 4.2.3.
4.1.1.1.2 The most demanding working conditions result in piping components with the largest thickness and the highest pressure grade.
4.1.1.1.3 The most demanding combination of pressure and temperature
conditions shall consider the possible operating conditions, which may be caused by the pressure sources (such as pumps, compressors), pressure
pulsations, decomposition of unstable fluids, static heads, failures or operating errors of control devices and valves, environment impacts.
4.1.1.2 Principles for determining design pressure
4.1.1.2.1 The design pressure of the pipeline, which is equipped with a safety relief device, shall not be less than the set pressure of the safety relief device (or the maximum calibrated burst pressure), except for the cases which are specified in 4.1.5 a) 2) and 4.1.5 c) of GB/T 20801.6-2020.
4.1.1.2.2 For the pipeline, which is not equipped with a pressure relief device OR may be isolated or blocked from the pressure relief device, the design pressure shall not be less than the maximum pressure, that may be generated as a result.
4.1.1.2.3 When the pipeline is directly connected to the equipment, as a pressure system, the design pressure of the pipeline shall not be less than the design pressure of the equipment.
4.1.1.2.4 The design pressure of the outlet pipe of the centrifugal pump shall not be less than the closing pressure of the pump.
4.1.1.2.5 For the pipes that transport low boiling point media, such as refrigerants and liquefied hydrocarbons, the design pressure shall not be less than the maximum pressure, that the medium may reach, when the valve is cut off OR when the medium is not flowing.
4.1.1.2.6 When the pipeline is divided into several separate pressure segments by partitions (including jacketed tubes, blind plates, etc.), the design pressure of the partitions shall not be less than the pressure, under the most demanding combination of pressure difference and temperature, which may occur on the pressure chambers on both sides during operation.
4.1.1.2.7 For vacuum pipelines, which are equipped with safety control devices, the design pressure shall be 1.25 times the maximum pressure difference OR 0.1 MPa (whichever is smaller), AND be designed according to external
pressure conditions. For vacuum pipelines without safety control devices, the design pressure takes 0.1 MPa.
4.1.2 Design temperature
4.1.2.1 General provisions
4.1.2.1.1 The design temperature of each piping component, in the piping system, shall be determined, according to the temperature, under the most demanding combination of pressure and temperature, that may be encountered in operation.
4.1.2.1.2 The design temperature of different piping components, in the same piping, can be different.
4.1.2.1.3 When determining the design temperature, it shall consider the influence of fluid temperature, ambient temperature, sunlight radiation, heating or cooling medium temperature, pipeline insulation, heat transfer.
4.1.2.2 Principles for determining the design temperature
4.1.2.2.1 For pipelines without external thermal insulation, when the medium temperature is lower than 65 ??C, the design temperature of the piping
components is the same as the medium temperature; however, it shall consider the sunlight radiation or other factors that may cause the medium temperature to rise. When the temperature is higher than or equal to 65 ??C, the design temperature of the piping components shall be determined, in accordance with the following requirements:
a) For valves, pipes, flanged ends, welded pipe fittings, take 95% of the medium temperature;
b) For flanges other than loose flanges, 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) It is also possible to take the measured average wall temperature or the average wall temperature, which is calculated based on heat transfer.
4.1.2.2.2 The design temperature of the external insulated pipe is generally taken as the medium temperature. However, it can also be taken from the measured average wall temperature OR the average wall temperature, which 4.1.3.3 Temperature and displacement load
Temperature and displacement load refers to the load, which is caused by temperature and displacement of the piping system, including:
a) Load due to constraints: When the temperature changes, the axial force and moment, which are generated by the pipeline being restricted, so that the pipeline cannot expand and contract freely;
b) Load caused by end point displacement: The load, which is caused by the displacement of the pipe support & hanger OR the equipment connected
to the pipe;
c) Loads due to different expansion characteristics: Loads resulting from differences in thermal expansion factors of materials, such as bimetallic pipes, jacketed pipes, non-metallic lined pipes, etc.;
d) Loads formed by temperature gradients: Loads, which are formed by
stresses in the pipe wall, due to temperature changes or uneven
distribution, such as pipe bending, which is caused by high-temperature fluid passing through thick-walled pipes or fluid stratified flow.
4.1.3.4 Cyclic load
Cyclic load refers to the fatigue load of the piping system, which is caused by pressure cycles, thermal cycles, other cycles.
4.1.3.5 Shock
Shock refers to the impact force caused by external or internal conditions, including impact caused by media flow, changes in media flow rate, pressure fluctuations, liquid flashing, water hammer, liquid or solid blows, explosions, eruptions.
4.1.3.6 Vibration
Vibration refers to vibration, which is caused by shock, pressure pulsation, turbulence, compressor resonance, wind load. For the piping design, layout, support, it shall be able to eliminate excessive and harmful vibration effects. 4.1.4 Additional thickness
4.1.4.1 Corrosion margin
The piping design shall have sufficient corrosion margin. The corrosion margin shall be determined, according to the expected service life and the corrosion rate of the medium to the material; it shall also consider the factors, such as erosion and local corrosion.
4.1.4.2 Other additional quantities
When determining the minimum thickness of piping components, it shall include the margin, which is needed for corrosion, erosion, thread depth or groove depth. In order to prevent possible damage, collapse or instability, due to overload stress and deformation, which are caused by support, icing, backfilling, transportation, loading and unloading, it shall consider increasing the thickness of the piping wall.
4.1.5 Environmental influence
4.1.5.1 Pressure
For the fluid in the blocked pipeline, it shall consider the pressure rise, which is caused by expansion, due to the heating of the environment, OR the pressure drop or even the vacuum of the pipeline, which is caused by the cooling of the environment.
4.1.5.2 Temperature
When the design temperature of the piping system is lower than 0 ??C, it shall consider the influence of the failure of valves, pressure relief devices or discharge pipes, which is caused by surface condensation and freezing, as well as the low temperature, on flexibility analysis and material selection. 4.1.6 Design requirements for piping layout and specific piping systems For the piping layout and specific piping systems, such as discharge pipelines, buried pipelines, flammable and toxic media pipelines, steam pipelines, low- temperature pipelines, the design requirements for pipeline insulation and electrostatic grounding are as shown in Appendix B.
4.2 Design criteria
4.2.1 Pressure-temperature design criteria for piping components
The pressure-temperature design of piping components shall adopt one of the methods specified in 4.2.1.1 ~ 4.2.1.4.
4.2.1.1 Pressure-temperature rating method
The pressure-temperature rating of the piping components shall be determined, in accordance with the following requirements:
a) Except as otherwise specified in this Part, for the piping components that have specified pressure-temperature ratings in Table 13, THEN, the
maximum allowable working pressure, at the design temperature, shall be in accordance with the pressure-temperature ratings, which are specified also be determined, based on the confirmatory pressure test.
4.2.1.4 Other methods
In addition to the methods specified in 4.2.1.1, 4.2.1.2, 4.2.1.3, the maximum allowable working pressure of piping components can also be determined, by comparative empirical analysis, stress analysis or experimental stress analysis. 4.2.2 Pressure-temperature design criteria of piping system
The pressure-temperature design of the piping system shall meet the following requirements:
a) In addition to the provisions of 4.2.3, the design pressure of the pipeline shall not be greater than the minimum value of the maximum allowable
working pressure of all piping components in the piping system, at the
design temperature, which is determined according to 4.2.1;
b) When connecting pipes under different fluid conditions, the rating of the separating valve shall be determined, according to the harsh conditions. However, the pipes located on either side of the valve shall be designed, according to the corresponding working conditions.
4.2.3 Allowable range of change of pressure and temperature
4.2.3.1 When determining the design pressure and design temperature, it shall consider the pressure and temperature changes, that occur during the
operation of the piping system.
4.2.3.2 The pressure and temperature of grade GC1 piping shall not exceed the design range.
4.2.3.3 In addition to meeting the following conditions and the requirements of 4.2.3.4, the design conditions of grades GC2 and GC3 pipelines shall be determined, according to the most demanding combination of pressure and temperature changes:
a) There are no piping components of cast iron or other brittle metal materials, in the piping system;
b) The nominal stress of the pipeline, which is caused by the pressure, does not exceed the yield strength of the material, at the corresponding
temperature;
c) The total stress complies with the provisions of 7.5.5;
d) During the expected life of the piping system, the total number of pressure- temperature changes, which exceeds the design conditions, is not more
than 1000;
e) The upper limit of pressure fluctuation is not greater than the test pressure of the piping system;
f) Continuous and periodic changes do not change the operational safety performance of all piping components, in the piping system;
g) The lower limit of the temperature change is not less than the minimum use temperature of the material, which is specified in GB/T 20801.2;
h) The pressure difference of the valve closing element does not exceed the maximum rated pressure difference, which is specified by the valve
manufacturer.
4.2.3.4 Occasional changes in pressure, which exceed the design conditions, shall be limited to any of the following ranges:
a) The magnitude and frequency of the pressure, which exceeds the
pressure rating, at the corresponding temperature, OR the nominal stress of the pipeline, as caused by the pressure, which exceeds the allowable stress value of the material, shall meet one of the following conditions: 1) The range of change is not more than 33%; the duration of each change does not exceed 10 h; the cumulative change time per year does not
exceed 100 h;
2) The range of change is not more than 20%; the duration of each change does not exceed 50 h; the cumulative change time per year does not
exceed 500 h.
b) When the fluctuation is self-limiting (such as pressure relief), under the condition that each change duration does not exceed 50 h AND the
cumulative change time does not exceed 500 h per year, THEN, the
pressure rating's change range is not more than 20%, OR the amplitude
of the nominal stress of the pipeline exceeds the allowable stress value of material, for not more than 20%.
4.2.4 Allowable stress
4.2.4.1 The allowable stress of metal materials AND the allowable stress of bolt materials shall meet the requirements of Table A.1 and Table A.2 in GB/T 20801.2-2020.
Note: The allowable stress value in the Table does not include the longitudinal welded joint factor ??w of the material, the high-temperature strength reduction factor of the welded joint W, the casting quality factor ??C (see Table 4).
5 Piping components
5.1 Selection of piping components
5.1.1 General provisions
The piping components shall be selected, according to the nature of the fluid, various possible operating conditions, the requirements of the external environment, economic rationality.
5.1.2 Pipes and butt-welding fittings
5.1.2.1 For pipes and butt-welding fittings, which are selected in accordance with Table A.1 and Table 13 of GB/T 20801.2-2020, the calculation of wall thickness shall comply with the relevant requirements in Chapter 6 of this Part. 5.1.2.2 For the pipes, which are selected in accordance with Table A.1 and Table 13 of GB/T 20801.2-2020, it shall also consider the design conditions and various possible operating conditions.
5.1.2.3 The restrictions on the use of pipes and butt-welded fittings materials shall comply with the relevant requirements of GB/T 20801.2.
5.1.2.4 Butt-welding pipe fittings, which are used for GC1 pipes and severe cyclic conditions, shall meet the following requirements:
a) Meet the minimum wall thickness requirements in Appendix B of GB/T
12459-2017;
b) Use reducer pipes with folded edges, AND the half cone angle is not more than 30??.
5.1.2.5 Adopt the piping system of L290 (X42) ~ L555 (X80) in GB/T 9711. The butt-welding pipe fittings shall meet the relevant requirements of GB/T 29168.2. 5.1.3 Bend
5.1.3.1 The production of the bend shall comply with the relevant requirements of GB/T 20801.4.
5.1.3.2 The minimum wall thickness of the bend shall meet the requirements of 6.2.
5.1.3.3 The bends, which have wrinkles and waves (see Figure 1 of GB/T
20801.4-2020), shall not be used for grade GC1 pipelines and severe cyclic conditions.
5.1.3.4 Adopt the piping system of L290 (X42) ~ L555 (X80) in GB/T 9711. The bend shall meet the relevant requirements of GB/T 29168.1.
5.1.4 Miter elbow (shrimp elbow)
5.1.4.1 The use of miter elbows shall meet the following requirements:
a) The design pressure P ??? 2.0 MPa; the design temperature is lower than the creep temperature of the material;
b) If the variable direction angle ?? of the miter elbow is greater than 45??, it is only applicable to grade GC3 pipelines;
c) If the variable direction angle ?? of milter elbow is greater than 22.5??, it shall not be used for grade GC1 pipelines and severe cyclic conditions;
d) If the variable direction angle ?? of milter elbow is less than or equal to 3??, it can be used as straight pipes, instead of miter elbows.
5.1.4.2 In addition to meeting the requirements of 5.1.4.1, non-standard miter elbows shall be pressure designed, in accordance with Chapter 6. The welding and fabrication shall also meet the relevant requirements of GB/T 20801.4. 5.1.5 Short radius elbow
The short radius elbow and short radius return elbow (R = 1.0D) shall meet the requirements of GB/T 12459.
If the thickness of the inner arc side wall of the plane, where the elbow center line is located, is not less than 1.25 times the nominal wall thickness of the pipe fitting, the maximum allowable working pressure is the same as the maximum allowable working pressure, which is determined in 4.2.1.3 a).
If the thickness of the inner arc side wall is less than 1.25 times the nominal wall thickness of the pipe fitting, the maximum allowable working pressure shall not be greater than 80% of the maximum allowable working pressure, which is determined according to 4.2.1.3 a).
5.1.6 Flanging joint
5.1.6.1 The selection of flanging joints shall comply with the requirements of the corresponding standards, which are listed in Table 13.
5.1.6.2 The welded flanging joints, which are made on site, shall meet the following requirements:
a) It shall use the basic type of welded flange joint, which is specified in Figure 1. However, for severe cyclic conditions, it shall use the fillet corner

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