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GB/T 20801.4-2020 (GB/T20801.4-2020)

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GB/T 20801.4-2020: PDF in English (GBT 20801.4-2020)
GB/T 20801.4-2020
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 23.040
J 74
Replacing GB/T 20801.4-2006
Pressure Piping Code - Industrial Piping - Part 4:
Fabrication and Assembly
ISSUED ON: NOVEMBER 19, 2020
IMPLEMENTED ON: JUNE 1, 2021
Issued by: State Administration for Market Regulation;
Standardization Administration of the People’s Republic of
China.
Table of Contents
Foreword ... 3 
1 Scope ... 5 
2 Normative References ... 5 
3 Terms and Definitions ... 6 
4 General Rules ... 9 
5 Inspection and Acceptance Inspection of Pipework Components and
Materials ... 10 
6 Fabrication of Piping ... 13 
7 Welding ... 20 
8 Preheating... 36 
9 Heat Treatment ... 39 
10 Assembly and Erection ... 49 
11 Stainless Steel and Non-ferrous Metal Piping ... 58 
12 Piping Cleaning, Purging and Rinsing ... 60 
Appendix A (Informative) Evaluation Method for Misalignment of Piping at
Closure Point ... 63 
Appendix B (Informative) Flange Joint Bolt Tightening Method and Erection
Target Load ... 71 
Pressure Piping Code - Industrial Piping - Part 4:
Fabrication and Assembly
1 Scope
This Part of GB/T 20801 specifies the basic requirements for the fabrication and
assembly of pressure piping. These basic requirements include regulations on
fabrication, welding, preheating, heat treatment, assembly, erection and piping
cleaning, etc.
This Part is applicable to the fabrication and assembly of pressure pipework
components defined in the scope of GB/T 20801.1.
2 Normative References
The following documents are indispensable to the application of this document. In
terms of references with a specified date, only versions with a specified date are
applicable to this document. In terms of references without a specified date, the latest
version (including all the modifications) is applicable to this document.
GB/T 985.1 Recommended Joint Preparation for Gas Welding, Manual Metal Arc
Welding, Gas-shield Arc Welding and Beam Welding
GB/T 985.2 Recommended Joint Preparation for Submerged Arc Welding
GB/T 985.3 Recommended Joint Preparation for Gas-shield Arc Welding on Aluminum
and Its Alloys
GB/T 985.4 Recommended Joint Preparation for Welding on Clad Steels
GB/T 13927 Industrial Valves - Pressure Testing
GB/T 20801.1-2020 Pressure Piping Code - Industrial Piping - Part 1: General
GB/T 20801.2-2020 Pressure Piping Code - Industrial Piping - Part 2: Materials
GB/T 20801.3-2020 Pressure Piping Code - Industrial Piping - Part 3: Design and
Calculation
GB/T 20801.5-2020 Pressure Piping Code - Industrial Piping - Part 5: Inspection and
Testing
GB/T 20801.6-2020 Pressure Piping Code - Industrial Piping - Part 6: Safeguarding
directly guide the welding production, which are formulated in accordance with the
welding procedure qualification report and the combined practical experience.
NOTE: it includes detailed provisions on butt-welded joint, base material, welding material,
welding position, preheating, electrical characteristics and operating techniques,
in order to ensure the reproducibility of welding quality.
3.15 Welding Performance Qualification
Welding performance qualification refers to the process of evaluating the operating
skills of welding operators.
3.16 Preheating
Preheating refers to the process of heating the base material before or during the
forming, welding or cutting process.
3.17 Interpass Temperature
Interpass temperature refers to the instantaneous temperature of multi-pass weld and
the adjacent base material before welding the next weld pass.
3.18 Post Weld Heat Treatment
Post weld heat treatment refers to the thermal process that can change the structure
and performance of welded joint or the welding residual stress.
3.19 Pipework Components
Pipework components is a general term for various parts and components connected
or assembled into a piping system, including piping components and pipe-supporting
elements.
3.20 Final Closure Point
Final closure point refers to the last connector for assembly between two fixed
positions in the piping system.
NOTE: the connection mode of the final closure point can be welding (butt joint and socket
welding joint) or flange connection.
3.21 Misalignment at the Final Closure Point
Misalignment at the final closure point refers to the deviation of the final closure point
when being assembled without external force, which can be decomposed into
misalignment of three directions: transverse (X, Y axes) and axial (Z axis). The
misalignment in the transverse (X, Y axes) direction indicates the degree of deviation
between the center lines of the end faces of two connected pipe segments. The
misalignment in the axial (Z axis) direction indicates the amount of clearance between
the parallel sections of the ends of two connected pipe segments.
3.22 Length of Assembly Pipe
Length of assembly pipe refers to the length of assembled pipe segment in a certain
direction (X, Y or Z axis), that is, the sum of the cumulative length of pipe segments in
the other two directions (transverse or axial) extending from the closure point to the
two ends to the nearest two fixed positions in the piping system.
4 General Rules
4.1 The organization manufacturing, fabricating and erecting the piping shall have an
administrative license that complies with the requirements of relevant laws and
regulations for pressure piping safety supervision. The organization fabricating and
erecting the piping shall establish a corresponding quality assurance system and
comply with the following stipulations:
a) In possession of a sound quality management system, and documents on the
fabrication and erection process. The process documents (such as:
construction organization design and construction schemes, etc.) shall be
approved by the proprietor (or its entrusting party) before they can be used
for piping fabrication or erection;
b) The personnel participating in the fabrication or erection of the piping shall
have the corresponding capabilities and perform their respective duties;
c) The measuring instruments used shall be qualified and within the validity
period.
4.2 The fabrication and erection of the piping shall be carried out in accordance with
the design documents and the stipulations of this Part. When it is necessary to modify
the design documents and substitute engineering materials, it shall be approved by the
original design organization, and a written document shall also be issued.
4.3 The organization fabricating and erecting the piping should adopt a piping welding
information management system, and timely input and save the relevant data of
pipework components, welding, heat treatment, inspection and testing, etc.
4.4 The organization fabricating and erecting the piping shall establish and properly
keep the necessary construction records and certification documents. After the
completion of the piping erection project, the organization fabricating and erecting the
piping shall submit at least the following technical documents and materials to the
proprietor:
a) Piping erection as-built drawing (including piping isometric diagram, design
complete, and can be traced back to the product quality certification
documents.
5.2 Appearance Inspection
The pipework components and materials shall be checked for their materials,
specifications, models and quantities in accordance with the stipulations of the design
documents and product standards. In addition, the inspection and acceptance
inspection of appearance quality and geometric dimensions shall be carried out one
by one. The results shall comply with the stipulations of the design documents and the
corresponding product standards.
5.3 Material Inspection
For piping components made of chromium-molybdenum alloy steel, nickel-containing
low-temperature steel, stainless steel, nickel and nickel alloy, titanium and titanium
alloy materials, before use, positive material identification (PMI) or other methods shall
be adopted to check the contents of main alloy elements. The quantity shall satisfy the
following requirements:
a) For GC1 piping, the inspected quantity shall be spot inspection at 10% of each
inspection lot and not less than 1 piping component;
b) For other piping, the inspected quantity shall be random inspection at 5% of
each inspection lot and not less than 1 piping component.
NOTE: each inspection lot represents a batch of pipework components or materials
that have the same furnace batch number, the same model and specification,
and arrive at the same time.
5.4 Valve Pressure Test
5.4.1 The valves shall receive pressure test, and the quantity shall satisfy the following
requirements:
a) Valves used for GC1 piping shall be subject to shell pressure test and sealing
test one by one;
b) Valves used for GC2 piping shall be subject to shell pressure test and sealing
test in accordance with random inspection at 10% of each inspection lot, and
the quantity shall be not less than one;
c) Valves used for GC3 piping shall be subject to shell pressure test and sealing
test in accordance with random inspection at 5% of each inspection lot, and
the quantity shall be not less than one;
d) With the consent of the designer or the proprietor, valves undergoing pressure
test one by one at the manufacturer and have the test records may be
exempted from the pressure test.
5.4.2 The pressure test methods, procedures and test results of the valves shall comply
with the stipulations of the design documents and the supply contracts. When there is
no such stipulation, they shall comply with the stipulations of GB/T 13927.
5.4.3 With the consent of the designer or the proprietor, for gate valves with a nominal
pressure less than or equal to PN100 and a nominal diameter greater than or equal to
DN600, the pressure test may be carried out with the piping system; the color printing
method may be used for the sealing test.
5.4.4 The calibration of the safety valves shall be carried out in accordance with the
stipulations of TSG ZF001 and the design documents.
5.4.5 When valves with jackets are subject to a jacket pressure test, the test pressure
shall be 1.5 times the jacket design pressure.
5.5 Other Inspections
When the design documents put forward other inspection and acceptance inspection
requirements (such as: non-destructive testing and hardness inspection, etc.) for the
pipework components and materials, they shall be satisfied. The inspection methods,
quantities and inspection results shall comply with the stipulations of the design
documents and the relevant standards.
5.6 Disposal of Non-Conforming Products
5.6.1 During sampling inspection, detection or testing of the pipework components and
materials, if one piece is disqualified, then, the inspection lot represented by the
sampling inspection, detection or testing shall be deemed as disqualified; this
inspection lot of pipework components and materials must not be used. Or the
inspection lot of pipework components and materials shall be inspected, detected or
tested one by one, and the qualified ones may still be used.
5.6.2 During sampling inspection, detection or testing of the pipework components and
materials, records and material identification marks shall be made, and the disqualified
products shall be isolated.
5.7 Material Storage
During the fabrication and erection process, the pipework components and materials
shall be properly kept, and shall not be mixed or damaged. During the storage,
stainless steel and non-ferrous metal pipework components and materials shall not
come into contact with carbon steel or low-alloy steel. The orifices of the pipes, valves
and fittings that are not temporarily installed shall be closed.
medium in the jacket, and the expansion and contraction of the inner pipe and the outer
pipe; its material shall be the same as the inner pipe. The geometric sizes, installation
position and spacing of the positioning plate shall comply with the stipulations of the
design documents and the relevant standards.
6.7.5 The welding, heat treatment, examination, inspection and testing of the jacketed
pipes shall comply with the corresponding clauses of this Part and the relevant
stipulations of GB/T 20801.5-2020.
6.8 Hangers and Supports
6.8.1 The form, materials, processing sizes and accuracy of the piping hangers and
supports shall comply with the stipulations of the design documents, the relevant
standards and product technical documents.
6.8.2 The assembly dimensions and welding mode of the piping hangers and supports
shall comply with the stipulations of the design documents. After fabrication, the welds
shall be visually inspected, and welding deformations shall be corrected. All threaded
connections shall be locked in accordance with the design requirements.
6.8.3 The welds in the hangers and supports that require full penetration shall be
subject to radiographic testing and ultrasonic testing, and shall comply with the relevant
stipulations of GB/T 20801.5-2020. The inspection quantity shall be not less than 20%,
and the weld length shall be not less than 200 mm.
6.8.4 The hangers and supports qualified in the fabrication shall receive rust-proof
treatment and shall be properly classified and stored. Alloy steel hangers and supports
shall be marked with the material.
7 Welding
7.1 Welding Procedure Qualification and Welding Performance
Qualification
7.1.1 The welding of piping pressure-bearing parts and pressure-bearing parts, as well
as the welding of pressure-bearing parts and non-pressure-bearing parts, shall adopt
qualified welding procedures and be welded by qualified welders.
7.1.2 The welding procedure qualification shall comply with the stipulations of NB/T
47014. The impact test requirements shall comply with the stipulations of 8.2 in GB/T
20801.2-2020.
7.1.3 When the materials required for the welding procedure qualification cannot
satisfy the stipulations of 7.1.2, with the consent of the designer and the proprietor, it
is allowed to use the mode of technical review of the pre-welding procedure
specification to replace the welding procedure qualification, but the following conditions
shall be satisfied at the same time:
a) The welding organization has grasped the characteristics of the metal material
(chemical composition, mechanical properties and welding performance);
b) The welding organization can provide the welding procedure qualification of
other base materials in the same category (same group), and has the
experience (achievements) in the welding;
c) The welder performing the welding has obtained the corresponding
performance qualification;
d) It is able to provide welding procedure qualification of the material that
complies with the requirements of 7.1.2 completed by other organizations.
7.1.4 Before the welding of the piping, in accordance with the welding procedure
qualification report (or the pre-welding procedure specification that has passed the
technical review), the welding procedure specification shall be formulated to guide the
welders’ welding and post-weld heat treatment. The welding procedure specification
shall include at least the following contents:
a) Welding method and type of operation (manual, automatic, semi-automatic);
b) Joint form, size and processing requirements of the welded joint;
c) Standard No., model, specification and relevant requirements of the base
material of the welded joint;
d) Standard No., model, designation, specification and baking requirements of
the welding material;
e) Welding position and welding direction;
f) Preheating and interpass temperature control requirements (preheating
temperature, interpass temperature range, heating mode and range,
measurement method, etc.), and if necessary, post-heating requirements
(post-heating temperature, time, heating and slow cooling modes, etc.);
g) Post-weld heat treatment requirements (heat treatment temperature, heat
preservation time, heating rate, cooling rate, heating and measurement
modes, etc.);
h) Type (composition), mixing ratio (purity), flow rate and other requirements of
the protective gas;
i) Electrical characteristics and process parameters of welding;
j) Essentials and technical measures of welding operation;
b) Alloy steel piping with the lower limit of the standard tensile strength greater
than or equal to 540 MPa.
7.4.5 Welding equipment
The welding equipment and auxiliary equipment shall be able to ensure the normal
operation, safety and reliability of the welding; the instruments shall be regularly
calibrated.
7.5 Basic Requirements for Welding
7.5.1 Welding procedures that pass the welding procedure qualification shall be
adopted. The welds (including the weld metal surfacing for assembly and welding) shall
be welded by qualified welders in accordance with the welding procedure specification.
7.5.2 During the welding, a reasonable welding method and welding sequence shall
be adopted:
a) During the welding of carbon steel and alloy steel, the method of electrode
arc welding, tungsten inert gas shielded arc welding, molten electrode gas
shielded arc welding, self-shielded flux-cored wire arc welding, submerged
arc welding or gas welding may be adopted;
b) During the welding of aluminum and aluminum alloys, the method of tungsten
inert gas shielded arc welding or molten inert gas shielded arc welding may
be adopted;
c) During the welding of copper and copper alloys, titanium and titanium alloys,
zirconium and zirconium alloys, the method of tungsten inert gas shielded arc
welding may be adopted. The method of oxyacetylene (gas welding) welding
may also be adopted for brass;
d) During the welding of nickel and nickel alloys, the method of electrode arc
welding, tungsten inert gas shielded arc welding, molten inert gas shielded
arc welding or submerged arc welding may be adopted.
7.5.3 For piping welds with a chromium content greater than or equal to 3%, or a total
content of alloy elements greater than 5%, when tungsten inert gas shielded arc
welding or molten electrode gas shielded arc welding is used for single-sided welding
of the root pass, the back of the weld shall be filled with argon or other shielding gases,
or other measures shall be taken to prevent the metal of the back weld from being
oxidized.
7.5.4 Except for the demand of welding in separate times due to process or inspection
requirements, generally speaking, each weld shall be continuously welded at one time.
When welding is interrupted for a certain reason, measures like heat preservation and
slow cooling, or post-heating shall be taken in accordance with the process
requirements to prevent the generation of cracks. Before re-welding, the surface of the
weld layer shall be checked, and after confirming that there are no cracks, the welding
may be continued in accordance with the original process requirements.
7.5.5 On the root pass and the cover pass, it is not advisable to use hammering to
eliminate the residual stress.
7.5.6 When welding the valves connected by welding, the adopted welding sequence,
process and post weld heat treatment shall ensure that the sealing performance of the
valve seat is not affected.
7.5.7 DO NOT perform arc striking or current testing on the surface of the weldment.
For piping whose design temperature is not higher than 20 C, alloy steel piping with
a relatively great tendency for hardening, stainless steel and non-ferrous metal piping,
their surfaces shall not have defects like arc scratches.
7.5.8 Under one of the following circumstances, the weld root of the single-sided
welding of the piping shall adopt tungsten inert gas shielded arc welding or other
welding process methods that can ensure the quality of the root welding:
a) GC1 piping;
b) Piping with a nominal diameter less than 500 mm and a design temperature
lower than 20 C;
c) Piping with relatively high requirements for internal cleaning and difficulty to
clean after welding;
d) Inlet piping of machines;
e) Other piping specified in the design.
7.5.9 Piping with a nominal diameter greater than or equal to 500 mm should be welded
on both sides of the root on the inside.
7.5.10 For multi-pass welding, after each pass is completed, cleaning and visual
inspection shall be immediately carried out. If defects are found, they shall be
eliminated before proceeding to the next layer of welding.
7.5.11 For welds that require interlayer non-destructive testing, the non-destructive
testing shall be performed after it passes the visual inspection. The non-destructive
testing on the surface shall be carried out before radiographic testing and ultrasonic
testing. After the welds pass the qualification, the welding may be continued.
7.5.12 After the welding is completed, the slag on the surface of the welds and nearby
spatters shall be cleaned up in time.
7.5.13 Each welder shall have a designated identification code. Unless it is otherwise
tc---the effective thickness of the fillet weld, which shall take the smaller value between 0.7Tb
or 6.4 mm;
Tb---the nominal thickness of the branch pipe;
Th---the nominal thickness of the main pipe;
Tr---the nominal thickness of the reinforcement ring or the saddle-shaped reinforcement;
tmin---tb or Tr, whichever is smaller;
Tm---the nominal thickness of the weld of the branch pipe seat. When there is no such
requirement in the design documents or the instruction manual of the branch pipe connector
manufacturer, the thickness shall be the largest thickness of the combined weld joint after the
assembly.
The cover fillet weld of the connection between the branch pipe seat and the main pipe is an
equilateral fillet weld at the longitudinal section, but at other sections, with the aperture ratio of
the branch pipe / main pipe, especially at the cross-section, it may transform to non-equilateral
fillet weld. However, it shall maintain a smooth transition with the joint weld and the surface of
the main pipe.
Figure 10 (continued from previous page)
7.8.2 The joints of the placed welded branch pipes or the plug-in welded branch pipes,
including the integrally reinforced branch pipe seats, shall be fully welded; the
thickness of the fillet weld of the cover surface shall be not less than the effective
thickness of the fillet weld [see Figure 10a) and Figure 10b)].
7.8.3 The welding of the reinforcement ring or the saddle-shaped reinforcement shall
comply with the following stipulations:
a) The reinforcement ring and the branch pipe shall be fully welded; the
thickness of the fillet weld of the cover surface shall be not less than the
effective thickness of the fillet weld [see Figure 10c) and Figure 10d)].
b) The thickness of the fillet weld between the saddle-shaped reinforcement and
the branch pipe connection shall be not less than 0.7tmin [see Figure 10e)].
7.8.4 The thickness of the fillet weld between the outer edge of the reinforcement ring
or the saddle-shaped reinforcement and the main pipe shall be greater than or equal
to 0.5Tr [see Figure 10c), Figure 10d) and Figure 10e)].
7.8.5 The reinforcement ring and the saddle-shaped reinforcement shall fit well with
the main pipe and the branch pipe. A vent hole for the welding of welds and leak
detection shall be opened at the high position of the reinforcement ring or the saddle-
shaped reinforcement (not at the axis of the main pipe). The reinforcement ring and
the saddle-shaped reinforcement may be composed of multiple pieces of splicing, but
......
 
(Above excerpt was released on 2022-03-06, modified on 2022-03-06, translated/reviewed by: Wayne Zheng et al.)
Source: https://www.chinesestandard.net/PDF.aspx/GBT20801.4-2020