GB/T 4732.1-2024 Pressure vessels design by analysis - Part 1: General requirements
1 Scope
1.1 GB/T 4732 specifies the requirements for the construction of steel pressure vessels (hereinafter referred to as "vessels") designed by the analytical design method, and provides a design method based on elastic stress analysis or elastoplastic stress analysis and failure mode. This document specifies the general requirements for the material, design, fabrication, inspection and acceptance of vessel designed by analysis design method.
1.2 The design pressure in GB/T 4732 is applicable to:
a) The vessel with pressure greater than or equal to 0.1MPa and less than 100MPa;
b) The vessel with vacuum degree greater than or equal to 0.2MPa.
1.3 The applicable design temperature range specified in GB/T 4732 is determined according to the temperature range applicable to each part.
1.4 The following vessels are not covered in the applicable scope of GB/T 4732:
a) Vessels with a design pressure less than 0.1MPa and vacuum degree less than 0.02MPa;
b) Pressure chambers (e.g.: pump casings, compressor housings, turbine enclosure, hydraulic cylinders, etc.) as a whole or part in rotating or reciprocating mechanical equipment;
c) Vessels with neutron radiation damage failure risk in nuclear-energy plant;
d) Vessels subjected to direct flame heating;
e) Vessels with the inside diameter (for a non-circular section, it refers to the maximum geometric size of boundary in the section of vessels. For example: the diagonal line of a rectangle; the long axes of oval) less than 150mm;
1.5 Boundary scope of vessel structure
1.5.1 When the vessel is connected to an external pipe:
a) The groove end face of the first girth joint of welded connection;
b) The end face of the first threaded joint of threaded connection;
c) The first flange sealing surface of flanged connection;
d) The first sealing surface of connection by special connecting piece or pipe fittings.
1.5.2 Pressure closure, flat covers and fasteners for connected pipes, manholes, handholes, etc.
1.5.3 The welded joints between non-pressure elements and pressure elements.
1.5.4 Non-pressure elements directly connected to the vessels, e.g. support, skirt, etc.
1.5.5 Overpressure relief device of vessel (see GB/T 150.1).
2 Normative references
The following documents contain provisions which, through reference in this text, constitute provisions of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 150.1 Pressure vessels - Part 1: General requirements
GB/T 151 Heat exchangers
GB/T 4732.2 Pressure vessels design by analysis - Part 2: Materials
GB/T 4732.3 Pressure vessels design by analysis - Part 3: Formulae method
GB/T 4732.4 Pressure vessels design by analysis - Part 4: Stress classification method
GB/T 4732.5 Pressure vessels design by analysis - Part 5: Elastic plastic analysis method
GB/T 4732.6 Pressure vessels design by analysis - Part 6: Fabrication, inspection and testing and acceptance
GB/T 12337 Steel spherical tanks
GB/T 26929 Terminology for pressure vessels
JB/T 4756 Nickel and nickel alloy pressure vessels
NB/T 47041 Vertical vessels supported by skirt
NB/T 47042 Horizontal vessels on saddle supports
TSG 21 Supervision regulation on safety technology for stationary pressure vessel
TSG R0005 Supervision regulation on safety technology for transportable pressure vessel
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T 26929 and GB/T 150.1 and the following apply.
3.1.1
pressure
force acting vertically on a unit surface area of a vessel
Note: It refers to gauge pressure herein, unless otherwise indicated.
3.1.2
operating pressure
maximum pressure possibly reaching on the top of vessel under normal working condition
3.1.3
design pressure
maximum pressure set at the top of a vessel
Note: Design pressure, together with the corresponding design temperature, is taken as the basic design load conditions of a vessel, and it is not lower than the operating pressure.
3.1.4
calculation pressure
pressure used to determine the thickness of the element under the corresponding design temperature
Note: The calculation pressure includes the surcharge load such as static pressure of liquid column.
3.1.5
test pressure
pressure on the top of a vessel during pressure test or leakage test
3.1.6
maximum allowable working pressure; MAWP
maximum pressure allowed on the vessel top at corresponding specific temperature
Note: It is calculated according to the effective thickness of each pressure part of the vessel and by taking into account all the loads borne by the part, and the minimum value is taken. When the maximum allowable working pressure is not indicated in the design document of the pressure vessel, the design pressure of the vessel is considered to be the maximum allowable working pressure.
3.1.7
design temperature
set metal temperature of part, i.e. the average temperature along the metal section of the part, under normal operating conditions of vessel
Note: The design temperature, together with the corresponding design pressure, is taken as the basic design load conditions of the vessel. The upper limit of the design temperature is called the maximum design temperature, while the lower limit of the design temperature is called the minimum design temperature.
3.1.8
test temperature
metal temperature of the vessel shell during pressure test or leakage test
3.1.9
minimum design metal temperature
minimum metal temperature of each part under various possible conditions expected during the operation of the vessel when such vessel is designed
3.1.10
required thickness
thickness calculated according to the corresponding equation or method specified in GB/T 4732 based on the related loads
3.1.11
design thickness
sum of required thickness and corrosion allowance
3.1.12
nominal thickness
sum of design thickness and negative deviation of material thickness, rounded up to the thickness under the standard specification of material
3.1.13
effective thickness
thickness obtained by deducting the corrosion allowance and negative deviation of material thickness from the nominal thickness
3.1.14
minimum required fabrication thickness
minimum thickness required to ensure meeting the design requirements after the pressure part is fabricated
3.1.15
low-temperature pressure vessel
vessels made of low alloy steel, duplex stainless steel and ferritic stainless steel with a design temperature of less than -20℃ and those made of austenitic stainless steel with a design temperature of less than -196℃
3.1.16
equivalent stress
combined stress defined by strength theory and as the a criterion for strength judgment under random stress states
Note: The third strength theory is generally adopted in the design based on the formulae method in GB/T 4732.3; while the fourth strength theory is adopted in the design and strength calculation based on the stress classification method in GB/T 4732.4, and the strength design based on the elastic plastic stress analysis method in GB/T 4732.5.
3.1.17
gross structural discontinuity
discontinuity of geometry, material or load, which may change the stress or strain of the structure in a large range, and have significant effect on the overall stress distribution and deformation of the structure
Example: Examples of gross structural discontinuity, such as the connection between the head, flange, nozzle, support and the shell, as well as the connection between the shells with different diameters or different wall thicknesses.
3.1.18
local structural discontinuity
discontinuity of geometry, material or load, which may change the stress or strain of the structure in a small range, and have no significant effect on the overall stress distribution and deformation of the structure
Note: Examples of local structural discontinuity, such as small transition fillet, connection between shell and small accessory, and the incomplete penetration weld.
3.1.19
normal stress
stress component orthogonal to the section under consideration
Note 1: Also known as "direct stress".
Note 2: Generally, the normal stress distribution along the thickness of the component is not uniform, which can be decomposed into three components: membrane stress uniformly distributed along the thickness, bending stress linearly distributed and peak stress distributed non-linearly.
3.1.20
shear stress
stress component tangent to the section under consideration
Note: Also known as "tangential stress".
3.1.21
membrane stress
stress component uniformly distributed along the thickness of the section, it is equal to the average stress along the thickness of the section under consideration
3.1.22
bending stress
normal stress varies linearly in the direction of thickness, and proportional to the distance from the neutral axis
Note: For the nonlinear stress, the bending stress may be obtained by equivalent linearization.
3.1.23
primary stress
normal stress or shear stress required to balance the pressure and other mechanical load
Note 1: For ideal plastic materials, the total plastic flow caused by the primary stress is not self-restricted, that is, when the plastic zone within the structure is extended to a mechanism geometrically variable, the limit state is reached. Even if the load is no longer increased, unrestricted plastic flow is still generated until failure.
Note 2: The primary stress is divided into general primary membrane stress, primary local membrane stress and primary local membrane stress.
3.1.24
general primary membrane stress
Pm
primary membrane stress with influence scope covers the whole structure
Note: In the plastic flow process, the general primary membrane stress will not be redistributed, which will directly lead to structural failure.
Example: Examples of general primary membrane stress, such as the membrane stress caused by balancing the internal pressure and distributed load in various shells.
3.1.25
primary local membrane stress
PL
primary membrane stress with stress level greater than the general primary membrane stress, but the influence range is limited to the local region of the structure
Note 1: When plastic flow occurs locally in the structure, such stresses will be redistributed. If not restricted, when the load is transferred from one part of the structure (high stress region) to another part (low stress region), excessive plastic deformation will be generated and cause failure.
Example: An example of primary local membrane stress, the membrane stress caused by external load and torque at the fixed support or connected pipe of the shell.
Note 2: Even the local membrane stress caused by gross structural discontinuity has the nature of secondary stress, it is still regarded as primary local membrane stress for convenience and reliability.
Note 3: The local stress zone refers to the area where the longitude extension distance is not greater than when the equivalent stress exceeds 1.1Sm (where, R is radius of second curvature of the surface of shell in this region, that is, the distance from the rotation axis of the shell to the middle surface of the shell along the normal direction of the middle surface; δ is the minimum wall thickness in the region). Two adjacent stress regions with local membrane equivalent stresses greater than 1.1Sm are separated from each other, the distance between them along the longitude is greater than or equal to [where, Rm=(R1+R2), δm=(δ1+δ2). R1 and R2 is the radius of second curvature of the surface of shell in the two regions considered, respectively. δ1 and δ2 is the minimum thicknesses for each considered region].
3.1.26
primary bending stress
Pb
bending stress that is linearly distributed along the thickness of the section required to balance the pressure or other mechanical load
Example: The bending stress caused by pressure at the center of a flat cover reflects an example of a primary bending stress.
