Pressure piping code - Industrial piping - Part 4: Fabrication and assembly
1 Scope
This part of GB/T 20801 specifies the basic requirements for pressure piping fabrication and assembly. These basic requirements include provisions on fabrication, welding, preheating, heat treatment, assembly and erection, and piping cleaning.
This part is applicable to the fabrication and assembly of pressure piping components defined in GB/T 20801.1.
2 Normative references
The following referenced documents are indispensable for the application 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 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 aluminium 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
GB 50236 Code for construction of field equipment, industrial pipe welding engineering
NB/T 47014 Welding procedure qualification for pressure equipment
TSG ZF001 Safety technical supervision regulations for safety valves
TSG Z6002 Examination rules for welding operators of special equipment
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3 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T 20801.1-2020, GB/T 20801.2-2020, GB/T 20801.3-2020, GB/T 20801.5-2020, GB/T 20801.6-2020 and the following apply.
3.1
manufacture
production process of products such as pipes, piping components or piping supports
3.2
fabrication
preparations before the erection of pipings
Note: It includes cutting, threading, grooving, forming, bending, welding and assembling assemblies into components, which may be done in workshop or on site.
3.3
assembly
process of connecting two or more piping components together (including piping prefabrication) by bolts, welding, bonding, threading, brazing, soldering or sealing elements according to the design documents
3.4
erection
process of completely fixing a piping system on the designated position and bracket according to the design documents
Note: It includes all on-site fabrication, assembly, checking and test of the system according to the specification requirements.
3.5
isometric diagram
diagram that each piping is drawn as a 3D view of piping represented by a single line according to the drawing method of axonometric projection
3.6
hot bending
process of fabricating the bend when the temperature is higher than the critical point AC1 of metal
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3.7
cold bending
process of fabricating the bend when the temperature is lower than the critical point AC1 of metal
3.8
pipe-segments to be prefabricated
pipe-segment, which is determined and can be processed in advance, selected according to the isometric diagram before the piping is fabricated and processed
3.9
pipe-segments for dimension adjustment
pipe-segment, which is determined and can be processed after measuring the erection dimension, selected according to the isometric diagram before the piping is fabricated and processed
3.10
tack weld
weld used to keep the weldment in position until the final weld is completed
3.11
weldment
assembly made by welding all components of a member
Note: The weldment includes two parts, namely base metal and welded joint.
3.12
welding procedure qualification
process of preparing test piece and specimen according to the requirements of the pre-welding procedure specification and conducting test and evaluating the result in order to verify the correctness of the proposed welding procedure of weldments
3.13
welding procedure qualification report
document recording relevant test data and results during welding procedure qualification
3.14
welding procedure specification
document of technical details which is prepared based on the welding procedure qualification report and practical experience to directly guide welding production
Note: It includes detailed regulations on welding joint, base metal, welding material, welding position, preheating, electrical characteristics and operation technology to ensure the reproducibility of welding quality.
3.15
welding performance qualification
process of evaluating the operation performance of welders
3.16
preheating
process of heating the base metal before or during the forming, welding or cutting process
3.17
interpass temperature
instantaneous temperature of multi-pass weld and adjacent base metal before welding the next pass
3.18
post weld heat treatment
thermal process that can change the structure and properties of welded joint or welding residual stress
3.19
pipework components
general term for all kinds of parts and components connected or assembled into a piping system, including piping components and piping supports
3.20
final closure point
the last connection port to be assembled between two fixed positions in a piping system
Note: The final closure point of the piping may be connected by welding (butt joint, welded connector) or flange connection.
3.21
misalignment at the final closure point
deviation of the final closure point of the piping when it is assembled without external force, which may be decomposed into the misalignment deviation values in the transverse direction (X and Y axes) and the axial direction (Z-axis). Transverse (X and Y axes) deviation value indicates the deviation degree of the center lines of the end faces of two connected pipe segments; axial (Z-axis) deviation value indicates the gap between the parallel sections at the ends of two connected pipe segments
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3.22
length of assembly pipe
length of assembled pipe segments in a certain direction (X, Y or Z-axis), that is, the sum of the accumulated lengths of pipe segments in other two directions (transverse or axial) extending from the closure point to both ends to the nearest two fixed positions in the piping system
4 General requirements
4.1 The piping manufacturing, fabrication and erection units shall have an administrative license meeting the requirements of relevant laws and regulations on pressure piping safety supervision. Piping fabrication and erection units shall establish corresponding quality assurance system and meet the following requirements:
a) It shall have a sound quality management system and fabrication and erection process documents, and the process documents (such as construction organization design and construction scheme, etc.) shall be approved by the owner (or its entrusting party) before being used for piping fabrication or erection;
b) The personnel participating in piping fabrication and erection shall have corresponding abilities and perform their respective duties;
c) The metrological instruments used shall pass the verification and be used within the validity period.
4.2 The fabrication and erection of pipings shall be carried out according to the design documents and the requirements of this part. If it is necessary to modify design documents and substitute engineering materials, it shall be approved by the original design unit, and a written document shall be issued.
4.3 The piping fabrication and erection units should adopt the information management system of piping welding, and timely input and save the relevant data of pipework components, welding, heat treatment, checking, test, etc.
4.4 The piping fabrication and erection units shall establish and properly keep the necessary construction records and supporting documents. After the completion of the piping erection work, the fabrication and erection units shall submit at least the following technical documents and materials to the owner:
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a) As-built drawings of piping erection (including piping isometric diagram, design modification documents and material substitution sheets). Changes such as design modification and material substitution shall be marked directly on the as-built drawing. The piping isometric diagram shall at least include the material, specification and furnace batch number of piping components, actual dimensions of pipe segment, weld position, weld No., welder code, non-destructive testing method, local or sampling nondestructive testing weld position, weld repairing position, heat treatment weld position, etc.
b) Product certificate, quality certificate, re-inspection report, or test report of piping components, supports and welding materials.
c) Inspection records and inspection and test reports of piping fabrication and erection. Inspection records of piping fabrication and erection shall include piping welding checking records, weld repair checking records, piping concealment records, piping heat treatment curve records and reports, etc.
d) Quality certificate of piping erection. If piping components or piping supports are fabricated on site, the quality certificates of piping components and piping supports shall also be submitted.
5 Inspection and acceptance of pipework components and materials
5.1 Acceptance of material marking and quality certificates
The marking and quality certification documents of pipework components and materials shall be accepted in accordance with the design documents and the requirements of 9.1 and 9.2 in GB/T 20801.2-2020, and shall also meet the following requirements:
a) The supplier (manufacturer) shall provide various property data or inspection results according to the requirements of design documents and supply contracts, and shall comply with those specified in the design documents and product standards;
b) If the property data or inspection results provided by the quality certification documents do not meet the requirements of product standards and design documents, or if the recipient has any objection to the property data or inspection results, necessary verification tests or supplementary tests shall be conducted;
c) The marking of pipework components and materials shall be clear and complete, and can be traced back to the product quality certificate.
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5.2 Appearance inspection
Pipework components and materials shall be checked for their materials, specifications, models and quantities according to the requirements of design documents and product standards, and their appearance quality and geometric dimensions shall be checked and accepted piece by piece. The results shall meet the requirements of design documents and corresponding product standards.
5.3 Material inspection
For piping components made of Cr-Mo alloy steel, nickel-containing low-temperature steel, stainless steel, nickel and nickel alloy, titanium and titanium alloy materials, the content of main alloy elements shall be checked by positive material identification (PMI) or other methods before use, and the quantity shall meet the following requirements:
a) For GC1 piping, the inspection quantity shall be 10% of each inspection lot and at least one piping component shall be randomly selected for inspection;
b) For other pipings, the inspection quantity shall be 5% of each inspection lot and at least one piping component shall be randomly selected for inspection.
Note: Each inspection lot indicates a batch of pipework components or materials with the same furnace batch number, the same model and specification and arrived at the same time.
5.4 Valve pressure test
5.4.1 The valves shall be subjected to pressure test, and the quantity shall meet the following requirements:
a) The valves used in GC1 pipings shall be subjected to shell pressure test and sealing test piece by piece;
b) For valves used in GC2 pipings, 10% of each inspection lot shall be sampled for shell pressure test and sealing test, and at least one valve shall be tested;
c) For valves used in GC3 pipings, 5% of each inspection lot shall be sampled for shell pressure test and sealing test, and at least one valve shall be tested;
d) With the consent of the designer or the owner, the valves that have been subjected to pressure test under witnessing piece by piece in the manufacturer and have the record of test under witnessing may be exempted from the pressure test.
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5.4.2 The pressure test methods, procedures and test results of valves shall meet the requirements of design documents and supply contracts. If no requirement is specified, the requirements given in GB/T 13927 shall be met.
5.4.3 With the consent of the designer or the owner, the gate valve with nominal pressure less than or equal to PN100 and nominal diameter greater than or equal to DN600 may be subjected to the pressure test along with the piping system, and the sealing test may adopt color printing method.
5.4.4 The safety valve shall be verified according to the requirements of TSG ZF001 and design documents.
5.4.5 If jacket pressure test is carried out on valves with jackets, the test pressure shall be 1.5 times the design pressure of jackets.
5.5 Other inspections
If other inspection and acceptance requirements (such as nondestructive testing, hardness inspection, etc.) are put forward for pipework components and materials in design documents, they shall be met. The inspection method, quantity and results shall meet the requirements of the design documents and relevant standards.
5.6 Disposal of rejected products
5.6.1 If one piece of pipework components and materials is rejected during sampling inspection, testing or test, the inspection lot subjected to the sampling inspection, testing or test shall be deemed as rejected, and the batch of pipework components and materials shall not be used, or the batch of pipework components and materials shall be subjected to inspection, testing or test piece by piece, and the acceptable ones may still be used.
5.6.2 During sampling inspection, testing or test of pipework components and materials, records and material identification markings shall be made, and rejected products shall be isolated.
5.7 Material storage
Pipework components and materials shall be properly stored during fabrication and erection, and shall not be confused or damaged. Pipework components and materials of stainless steel and non-ferrous metals shall not contact with carbon steel and low alloy steel during storage. Pipes, valves and pipe fittings that are not erected for the time being shall be subjected to pipe orifice closure.
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6 Piping fabrication
6.1 Cutting and groove processing
6.1.1 Cold cutting or thermal cutting may be adopted for cutting pipework components and materials. Where thermal cutting is adopted, the surface slag and surface layer affecting the piping welding quality shall be removed by machining or grinding.
6.1.2 Carbon steel and carbon manganese steel may be cut and its groove may be prepared by machining or flame cutting. Low-temperature nickel steel and alloy steel should be cut and its groove should be prepared by machining.
6.1.3 Stainless steel and non-ferrous metal shall be cut and its groove shall be prepared by machining or plasma cutting. If stainless steel, nickel and nickel alloy, titanium and titanium alloy, zirconium and zirconium alloy are cut or ground with grinding wheels, special grinding wheels shall be used.
6.1.4 Mechanical damage to the surface of pipework components and materials shall be avoided during processing, fabrication and erection. Repair welding or grinding shall be carried out on the positions with serious scars, and the wall thickness of the ground place shall not be less than the design wall thickness.
6.2 Marking transplantation
6.2.1 During the fabrication process of piping components, the original markings of materials shall be checked and preserved as far as possible. If the original markings cannot be preserved, the material identification shall be carried out again by transplantation, and the engineering uniform code or color marking of piping components may also be adopted for the material identification.
6.2.2 The marking method shall be based on the principle of not causing damage or pollution to materials, and hard printed markings shall not be used for low-temperature steel, stainless steel and non-ferrous metals. If austenitic stainless steel and non-ferrous metal materials are marked with color marks, the printed colors shall not contain substances that damage the materials, such as sulfur, lead and chlorine.
6.2.3 If marking methods other than hard printing or engraving are adopted, the fabricator shall ensure that there will be no confusion between different materials, such as separate treatment (time and place) or distinguishing color bands.
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6.3 Bend
6.3.1 When fabricating the bend, appropriate bending process and equipment shall be adopted according to pipe material properties, working conditions of conveying fluid and bending radius of pipe.
6.3.2 Two methods can be used for bend fabrication: hot bending and cold bending.
6.3.3 If welded pipe is used for bend fabrication, the weld shall avoid the tension (compression) zone.
6.3.4 The out-of-roundness, fold and thinning of bends shall meet the following requirements:
a) The out-of-roundness shall meet the following requirements:
1) The out-of-roundness u (%) of the bend shall be calculated using Formula (1):
(1)
where,
u——the out-of-roundness of the bend;
Dmax——the maximum measured outer diameter of the same section, mm;
Dmin——the minimum measured outer diameter of the same section, mm;
2) For bends under internal pressure, the out-of-roundness shall not exceed 8%; for bends under external pressure, the out-of-roundness shall not exceed 3%.
b) The fold height hm on the inner side of the bend shall not be greater than 3% of the pipe outer diameter D1, and the wave spacing a shall not be less than 12hm. Where, hm is the average height of two adjacent folds and shall be calculated using Figure 1 and Formula (2):
(2)
where,
hm——the fold height, mm;
D2——the outer diameter at the convex part of the fold, mm;
D3——the outer diameter at the concave part of the fold, mm;
D4——the outer diameter at the convex part of the adjacent fold, mm.
Figure 1 Fold and wave spacing of bend
c) The wall thickness of the pipe before bend fabrication should meet those specified in Table 1. The minimum thickness after bend fabrication shall not be less than the design thickness of straight pipe.
Table 1 Wall thickness of pipe before bend fabrication In: mm
Bending radius R Wall thickness before bend fabrication
R≥6D 1.06td
5D≤R<6D 1.08td
4D≤R<5D 1.14td
3D≤R<4D 1.25td
Note: D is the outer diameter of the pipe and td is the design thickness of the straight pipe.
6.3.5 After the bend of GC1 piping is bent, magnetic particle inspection or penetrant inspection shall be carried out on the bent parts piece by piece, and shall meet the requirements of GB/T 20801.5-2020. The linear defects found shall be ground, and the wall thickness after grinding shall not be less than the design thickness of the straight pipe.
6.4 Plate welded pipe
6.4.1 The fabrication of plate welded pipe shall meet the requirements of design documents and product standards.
6.4.2 The following requirements shall be met when fabricating and erecting the plate welded pipe with a nominal diameter of not less than 400 mm:
a) The length of a single cylindrical section shall not be less than 300 mm, and the longitudinal welds of adjacent cylindrical sections shall be staggered by more than 100 mm. The distance from the outer wall of branch pipe to the weld should not be less than 50 mm.
b) There shall be no more than two longitudinal welds on the same longitudinal weld, and the distance between longitudinal welds shall be no less than 200 mm.
c) For plate welded pipe with reinforcing ring, the butt weld of reinforcing ring shall be staggered with the longitudinal weld of the pipe and not less than 100 mm, and the distance from the reinforcing ring to the girth weld of the pipe shall not be less than 50 mm.
d) The perimeter and pipe end diameter of plate welded pipe shall meet those specified in Table 2.
Table 2 Perimeter tolerance and diameter tolerance of plate welded pipe In: mm
Nominal diameter ≤800 >800~1,200 >1,200~1,600 >1,600~2,400 >2,400~3,000 >3,000
Perimeter tolerance ±5 ±7 ±9 ±11 ±13 ±15
Diameter tolerance 4 4 6 8 9 10
Note: The diameter tolerance is the difference between the maximum and minimum outer diameters of pipe ends (within 100 mm).
e) Edge angle at longitudinal weld [Figure 2a)] (measured respectively on inner wall and outer wall of pipe with sample plate with chord length equal to 1/6 Di and not less than 300 mm) and edge angle at girth weld [Figure 2b)] (checked on inner wall and outer wall of pipe with straight edge), and the E value shall not be greater than 10% of wall thickness plus 2 mm and shall not exceed 5 mm.
a) Longitudinal weld b) Girth weld
Figure 2 Check of edge angles at longitudinal and girth welds
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f) The misalignment of butt weld shall meet those specified in Table 3 and the following requirements:
1) For longitudinal and girth welds that can only be welded from one side, the misalignment of the inner wall shall not exceed 25% of the wall thickness and shall not exceed 2 mm;
2) If assembling the composite steel plate, it shall be based on the clad surface, and the misalignment shall not be greater than 50% of the clad thickness of the steel plate and not greater than 1 mm.
Table 3 Butt weld misalignment of plate welded pipe In: mm
Thickness of base metal T Misalignment
Longitudinal weld Girth weld
T≤12 ≤T/4 ≤T/4
1250 ≤T/16, and ≤10 ≤T/8, and ≤20
g) The straightness tolerance of the plate welded pipe shall not be greater than 0.2% of its length.
h) The welding, post weld heat treatment, check and inspection of plate welded pipe shall meet the requirements in relevant clauses of this part and in GB/T 20801.5-2020.
i) Pressure test shall be carried out on plate welded pipes piece by piece, and the test pressure shall meet the corresponding requirements of GB/T 20801.5-2020. With the consent of the owner or designer, the pressure test method of plate welded pipe may be replaced by full radiographic or ultrasonic testing on longitudinal weld and girth weld specified in GB/T 20801.5-2020.
6.5 Mitre bend
6.5.1 Unless otherwise specified in the design, the fabrication of mitre elbows shall meet the requirements of 6.5.2 ~ 6.5.4. The welding of mitre elbows shall meet the requirements of Clause 7, and the check and inspection of miter elbows shall also meet the relevant requirements of GB/T 20801.5-2020.
6.5.2 The mitre elbow may be prepared according to the composition shown in Figure 3. For mitre elbows with a nominal diameter greater than 400 mm, the number of middle joints may be appropriately increased, but the minimum width of the inner side shall not be less than 50 mm
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 General requirements
5 Inspection and acceptance of pipework components and materials
6 Piping fabrication
7 Welding
8 Preheating
9 Heat treatment
10 Assembly and erection
11 Stainless steel, non-ferrous metal pipings
12 Piping cleaning, purging and rinse
Annex A (Informative) Evaluation method of misalignment at the closure point of pipings
Annex B (Informative) Bolt tightening method and target load of erection of flange joint
