GB/T 20801.4-2020 English PDF (GBT20801.4-2020)

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GB/T 20801.4-2020: Pressure piping code - Industrial piping - Part 4: Fabrication and assembly
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...