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

3.1 Piping system

Pipelines, which are determined by the same design conditions AND connected to each other.

3.2 Elevated temperature fluid service

The use temperature of the material is in a working condition where the high-temperature strength reduction factor W of the welded joint is less than 1 (see 4.2.7 and Table 5), which is equivalent to the working condition where the working temperature is within the allowable stress temperature range, which is determined by the long-term strength of the material.

3.3 Fluid service

A comprehensive term, which involves the application of piping systems;

takes into account fluid properties, operating conditions and other factors;

forms the basis of piping system design.

3.4 Severe cyclic conditions

3.5 Branch connection fitting

The integral reinforcing fittings, which connect the branch to the trunk pipe, through butt welding connection, socket welding connection, threaded connection.

3.6 Rating value

The pressure value of the piping components, which are specified by the standard.

4.1 Design conditions

4.1.1 Design pressure

4.1.2 Design temperature

4.1.3 Load conditions

4.1.4 Additional thickness

4.1.5 Environmental influence

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.

4.2.2 Pressure-temperature design criteria of piping system

The pressure-temperature design of the piping system shall meet the following requirements.

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.

4.2.3.4 Occasional changes in pressure, which exceed the design conditions, shall be limited to any of the following ranges.

4.2.4 Allowable stress

4.2.5 Factor of longitudinal welded joint Phiw

The longitudinal welding joint factor Phiw, of pipes and butt-welded fittings, shall be determined, according to the criteria specified in Table 3 or Table A.3 of GB/T 20801.2-2020.

4.2.6 Casting's quality factor PhiC

4.2.6.1 The casting quality factor PhiC of iron castings (grey cast iron, ductile iron, malleable cast iron) takes 1.0.

4.2.6.2 Except for cast iron, static metal castings in Table A.1 of GB/T 20801.2-

2020 shall be visually inspected, according to JB/T 7927.It shall not be lower than the requirements of grade B. The casting's quality factor shall be taken as 0.8.

4.2.6.3 For castings that require additional non-destructive testing, it can use

the casting quality factor in Table 4.However, the change in the casting quality factor PhiC does not affect the pressure-temperature ratings of the piping components.

4.2.7 High temperature strength reduction factor W of welded joints

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

5.1.3 Bend

5.1.4 Miter elbow (shrimp elbow)

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.

5.1.6 Flanging joint

5.1.7 Branch pipe connection and its fittings

5.1.8 Flange

5.1.9 Gasket

5.1.10 Fasteners

5.2 Selection of connection form of piping components

5.2.1 General provisions

The selection of the connection form of the piping components shall be compatible with the pipeline material and fluid working conditions. Meanwhile, it shall consider the influence of pressure, temperature, external load on the sealing performance and mechanical strength of the connection joint, under the expected use and test conditions.

5.2.2 Welded joints

5.2.3 Flange connection

5.2.4 Expansion joint

5.2.5 Thread-sealed pipe thread connection

5.2.5.1 The pipe thread type of the thread seal shall meet the requirements of

Table 11.

5.2.6 Straight thread connection

The straight thread connection joint can adopt the structure, as shown in Figure 4, to be sealed by a pair of contact surfaces (non-threaded sealing); it is only suitable for grade GC3 pipelines.

5.2.7 Connection of flaring and non-flaring compression fittings

5.2.8 Packed connector

The packed connector shall meet the following requirements.

5.3 Type and size standards of piping components

6.1 Straight pipe

6.1.1 Symbols

6.1.2 Internal pressure design of straight pipe

The internal pressure design of the straight pipe shall meet the following requirements.

6.1.3 Design of external pressure (or vacuum) of straight pipe

The external pressure (or vacuum) design of the straight pipe shall meet the following requirements.

6.2 Bend or elbow

6.2.1 Symbols

6.2.2 Internal pressure design of bend or elbow

The calculated thickness of the bend or elbow (located at alpha/2) shall be determined, according to formula (3).

6.2.3 Design of external pressure (or vacuum) of bend or elbow

The design of the external pressure (or vacuum) of the bend or elbow shall be carried out, in accordance with the provisions of 6.1.3.The calculated length L is taken as the distance, between two adjacent support lines, on the straight pipe, including those along the axis of the bend or elbow.

6.3 Miter elbow

6.3.1 Symbols

6.3.2 Internal pressure design of miter elbow

The internal pressure design of the miter elbow shall meet the following requirements.

6.3.3 The external pressure (or vacuum) design of the miter elbow

The external pressure (or vacuum) design of the miter elbow shall be carried out, in accordance with the provisions of 6.1.3; however, the calculated length L shall be taken as the distance, between the two adjacent support lines of the straight pipe, including the axis of each segment of the miter elbow.

6.4 Pressure design and external load evaluation of pipe flanges and blind flange

6.4.1 Symbols

6.4.2 Pressure-temperature ratings of standard pipe flanges

The standard pipe flanges and blind flanges, which are listed in Table 13, are selected according to the pressure-temperature ratings, which are specified in the standard.

6.4.3 Pressure design verification of standard pipe flanges

With the consent of the designer, the allowable pressure-temperature value (maximum allowable working pressure) of the standard pipe flange can also be determined, according to the design method of non-standard flanges, which are listed in 6.4.4 [Taylor (Taylor Forge) method].

6.4.4 Pressure design of non-standard flanges

The pressure design (maximum allowable working pressure) of non-standard flanges and blind flanges shall comply with the Taylor method, which is specified in GB/T 17186.1.However, the allowable stress of the flange and bolt materials shall comply with the relevant requirements of GB/T 20801.When using the flange tightening measures to control the bolt installation load, the bolt's design load and the flange torque, in the pre-tightened state, are calculated according to the required bolt area Am, regardless of the actual bolt area Ab.

6.4.5 External load evaluation of pipe flanges

When the pipe flange bears an applied axial force or an applied bending moment, it can be evaluated according to one of the following methods.

6.4.6 Flange stiffness

When necessary, the flange rigidity can also be checked, according to the provisions of GB/T 17186.1.

6.5 Blind plate

6.5.1 Symbols

6.5.2 Calculated thickness of blind plate

The calculated thickness of the blind plate shall be calculated, according to formula (14).

6.6 Other piping components

For the pressure design of other piping components, such as reducers, convex heads and flat heads, it shall be carried out in accordance with relevant standards.

6.7 Equal area reinforcement method for branch pipe connections

6.8 Calculation of pressure area method for integrally formed tee and

branch pipe connections

7.1 General provisions

7.1.1 This Chapter gives analysis methods and evaluation criteria, for various

possible loads and stresses, which are generated in piping components.

If it needs to consider the fatigue effect of pressure fluctuations on piping components, it can follow the analysis method and evaluation criteria, which is given in JB 4732.Meanwhile, in the flexibility analysis of 7.5.5, the reduction factor f of the allowable stress range in the formulas (34) and (35) is taken as 1.0.

7.1.2 The flexibility analysis method, which is described in this Chapter, is not

applicable to brittle materials, such as cast iron.

7.1.3 When conducting stress analysis of the piping system, it shall consider

the stiffness of expansion joints and other piping components. The flexibility factor and stress increase factor, of various piping components, can be calculated, according to the formulas listed in Table G.1 in Appendix G. The designer can also use more accurate values, which are obtained by experiments or other methods.

7.1.4 The number, position, type of supports & hangers, in the piping system, have a great influence on the stress distribution of the piping system. In the design, the arrangement of supports & hangers shall be treated with care, to reduce the stress of the pipeline. The design of the piping system shall ensure that, each support & hanger has sufficient strength and appropriate rigidity.

7.2 Scope and method of pipeline stress analysis

7.2.1 All pipelines shall be subjected to stress analysis. In engineering design, it should determine the analysis method and level of detail, according to the temperature, pressure, diameter of the pipeline and the type of connected equipment.

7.3 Symbols

Unless otherwise specified, the symbols in this Chapter are the same as those in Chapter 6.

7.4 Load and its combination conditions

7.5 Static stress analysis and strength conditions

8.1 General provisions

8.1.1 The arrangement and type of pipeline supports & hangers shall be

compatible with the pipeline layout, pipeline flexibility, anti-vibration design, bearing size and rooting conditions of the supports & hangers; the following conditions shall be prevented.

8.2 Material requirements

8.3 Design requirements

8.3.1 General provisions

8.3.2 Structure

8.3.3 Load

8.4 Setting and selection of pipe supports & hangers

8.4.5 Guide frame

The guide frame can be set according to the following principles.

8.4.6 Anti-vibration bracket

The anti-vibration bracket can be set, according to the following principles.

8.4.7 Limiting frame

In order to control the displacement of thermal expansion and contraction of the pipeline OR reduce the thrust or moment of the pipeline on the constraint points (such as equipment nozzles, fixation points, etc.), it may set limiting frames at appropriate positions.

8.4.8 Others

For pipelines with expansion joints, the design of layout, fixation bracket, limiting frame shall meet the requirements of Appendix J. The layout of other types of pipeline supports & hangers shall also meet the requirements of the expansion joint product description.