GB/T 20801.3-2020 English PDF (GB/T20801.3-2020)

GB/T 20801.3-2020: Pressure piping code - Industrial piping - Part 3: Design and calculation
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GB/T 20801.3-2020
GB
NATIONAL STANDARD OF THE
PEOPLE’S 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 and 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 and 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 low...