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GB 50128-2014 English PDF (GB50128-2014)

GB 50128-2014 English PDF (GB50128-2014)

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GB 50128-2014: Code for construction and acceptance of vertical cylindrical steel welded storage tanks

GB 50128-2014
UDC GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 87.040
G 51
P GB 50128-2014
Code for Construction of Vertical Cylindrical Steel
Welded Storage Tanks
ISSUED ON: APRIL 15, 2014
IMPLEMENTED ON: JANUARY 1, 2015
Issued by: Ministry of Housing and Urban-Rural Development of the
People's Republic of China;
General Administration of Quality Supervision, Inspection
and Quarantine of the People's Republic of China.
Table of Contents
Foreword ... 5
1 General Provisions ... 7
2 Terms ... 7
3 Material Acceptance ... 8
4 Prefabrication ... 9
4.1 General Requirement ... 9
4.2 Shell Plate Prefabrication ... 11
4.3 Bottom Plate Prefabrication ... 13
4.4 Floating Roof Prefabrication ... 15
4.5 Top Plate Prefabrication of Fixed Roof ... 16
4.6 Accessories Prefabrication ... 17
5 Assembly ... 17
5.1 General Requirement ... 17
5.2 Foundation Inspection ... 18
5.3 Tank Bottom Assembly ... 19
5.4 Shell Plate Assembly ... 20
5.5 Fixed Roof Assembly ... 24
5.6 Floating Roof Assembly ... 24
5.7 Accessories Installation ... 25
6 Welding ... 25
6.1 General Requirement ... 25
6.2 Welding Procedure Qualification and Welding Procedure Specification ... 26 6.3 Welding Material ... 26
6.4 Welding Construction ... 27
6.5 Welding Sequence ... 29
6.6 Repair and Rework ... 30
7 Inspection and Acceptance ... 32
7.1 Welding Seam Appearance Inspection ... 32
7.2 Welding Seam NDT Test and Leakage Test ... 33
7.3 Tank Geometry and Dimension Inspection ... 36
7.4 Hydro-test ... 37
7.5 Project Completion ... 39
Appendix A Fillet Welding Seam Test Specimen Preparation and Inspection for T-shape Joint ... 41
Appendix B Storage Tank Foundation Settlement Observation Method ... 43 Appendix C Acceptance Forms ... 45
Explanation of Wording in This Code ... 57
List of Quoted Standards ... 58
1 General Provisions
1.0.1 This code is formulated to standardize the construction of vertical cylindrical welded steel tanks, guarantee the engineering quality and make it advanced in technology, cost-effective, safe and applicable.
1.0.2 This code is applicable to the construction of vertical cylindrical welded steel tank body at and close to normal pressure for storing petroleum and petrochemical products and other similar liquids, including accessories welded with the tank, but not applicable to the construction of buried tank, tank holding extremely and highly hazardous medium and artificial refrigerant fluid tank.
1.0.3 Tanks shall be constructed according to design documents. In case design documents are required to be revised, written consent of the original design organization shall be first obtained.
1.0.4 Prefabrication, installation and inspection of tanks shall be performed with qualified measuring tools with the same accuracy grade.
1.0.5 The construction of vertical cylindrical welded steel tanks shall not only meet those specified in this code, but also those in the current relevant standards of the nation. 2 Terms
2.0.1 Annular/sketch bottom plates
The tank bottom plates at the outermost side of the lower part of the shell plate, including annular edge plates and non-annular edge plates.
2.0.2 Fixed roofs
The tank roofs with peripheral parts connected, in fixed method, with the tank shell top, mainly including self-supporting cone roof, supporting cone roof and self-supporting dome roof etc.
2.0.3 Floating roofs
Roofs which lifts with the liquid level, including external floating roof and internal floating roof, and mainly being single-deck floating roof, double-deck floating roof, open-top bulk-headed floating roof and floating roof on floats etc.
2.0.4 Wind girder
Member arranged onto the shell to make it stronger to resist wind.
2.0.5 Auto vent
The venting device which opens/closes automatically when the floating roof rises or restores to be in bracing state.
2.0.6 Floating roof drains
Equipment which drains the rainwater on external floating roof out of the tank under normal conditions.
3.0.6 Material re-inspection shall meet the requirements of the design documents. 3.0.7 In case of any doubt about material quality, re-inspection shall be performed by the party purchasing such material.
4 Prefabrication
4.1 General Requirement
4.1.1 Sample plate for tank prefabrication and installation inspection shall meet the following requirements:
1 the chord length of arc-shaped sample plate shall not be less than 1.5m in case the curvature radius is less than or equal to 12.5m or 2m in case the curvature radius is greater than 12.5m.
2 the length of linear sample plate shall not be less than 1m.
3 for the arc-shaped sample plate for measuring weld angularity, its chord length shall not be less than 1m.
4.1.2 The method to prefabricate the tank shall not damage the base material or reduce the performance of base material.
4.1.3 Cutting of tank members and processing of weld groove shall meet the following requirements:
1 carbon steel and low alloy steel members should be machined or processed by way of automatic and semi-automatic flame cutting; stainless steel members shall be machined or processed by way of plasma cutting;
2 if the operating temperature is less than the following temperature listed, steels shall not be cut:
1) -16℃ for common carbon steels;
2) -12℃ for low alloy steels.
4.1.4 Weld groove shall be processed to be flat and smooth, free from slag inclusion, delamination or crack and other defects; hardened surface layer generated on weld groove due to flame and plasma cutting shall be removed.
4.1.5 As for shell plate of which the minimum yield strength specified in the standard is greater than 390MPa, if its weld groove is processed by way of flame cutting, groove surface shall be subjected to magnetic particle or penetrant testing after the removal of hardened layer, and testing methods and criterion of acceptability shall meet the requirements of 7.2.9 of this code.
4.1.6 If no required in design documents, groove type and dimension of welded joints shall be selected according to the current national standards Recommended Joint Preparation for Gas Welding, Manual Metal Arc Welding ,Gas-shield Arc Welding and Beam Welding (GB/T 985.1) and Recommended Joint Preparation for Submerged Arc Welding (GB/T 985.2); types of butt joints for electro-gas welding and submerged arc welding respectively for longitudinal welding seam and circumferential welding seam of the tank shall also meet the following requirements:
Figure 4.1.6-2 -- Butt Joint Formed Through Submerged Arc Welding of Circumferential Welding Seam 4.1.7 Common carbon steel members shall not be subjected to cold sizing and cold bending in case the operating ambient temperature is less than -16℃, nor the low alloy steel members in case the operating ambient temperature is less than -12℃.
4.1.8 Deformation, damage and corrosion shall be avoided in the preservation, transport and on-site stacking of tank members.
4.1.9 Prefabrication of stainless steel tank shall also meet the following requirements: 1 stainless steel materials shall not contact with carbon steel and materials for storing peroxides;
2 stainless steel plate shall not be stamped with embossed marks or portrayed with labels, but be marked with colourant easy to scrub;
3 stainless steel plate and members should be hoisted with lifting belt, and transport mould shall be provided with protection measures;
4 stainless steel plate and members shall not be hammered directly with hammer, and the surface shall be free from scratch, bruise, arc scratch and corrosion, and shall be smooth; 5 stainless steel members shall not be formed by way of fire bending;
6 dedicated grinding disk or belt shall be used to polish the stainless steel materials. 4.1.10 All prefabricated members of the tank shall be with serial number once finished, and be marked clearly with paint or other methods.
4.2 Shell Plate Prefabrication
4.2.1 Cutting plan shall be drawn before prefabrication of tank shell plate and meet the following requirements:
1 longitudinal welding seams of shell plates at various rings should be staggered ring by ring along the same direction, and the clearance between longitudinal welding seams of shell plates at adjacent rings should be 1/3 of the plate length and shall not be less than 300mm.
2 the distance between the longitudinal welding seam of the shell plate at bottom ring and the butt welding seam of the sketch bottom plate shall not be less than 300mm. 3 the distance from shell opening to longitudinal and circumferential welding seams center of the tank shell, as well as to the fillet welding seam at the uttermost end of the tank shell shall meet the following requirements:
1) the distance from nozzle or reinforcement plate outer edge to longitudinal and circumferential welding seams of the tank shell shall be greater than 8 times the size of the relatively large weld leg and no less than 250mm in case the shell thickness is greater than 12mm and the nozzle as well as shell plate won't be subjected to stress relief heat treatment after welding.
2) the distance shall not be less than 150mm from nozzle or reinforcement plate outer edge to longitudinal welding seam of the tank shell or not less than 2.5 times the tank shell thickness and 75mm from nozzle or reinforcement plate outer edge to circumferential welding seam of the tank shell in case tank shells varying in thickness and nozzles are subjected to post weld heat treatment or the tank shell thicker than 12mm and the nozzle won't be 4.6 Accessories Prefabrication
4.6.1 After being formed by machining, wind girder, stiffening ring, wrapped angle steel, tensile ring, compressive ring and other arc-shaped members shall be inspected with arc-shaped sample plate regarding the corresponding radian and the corresponding clearance shall not be greater than 2mm; their buckling deformation shall be inspected onto the platform while the deformation amount shall not exceed 0.1% of the member length and shall not be greater than 6mm.
4.6.2 Members formed by fire bending shall be free from over-burning.
4.6.3 Adjustment amount should be reserved in the prefabrication of floating roof support. 4.6.4 Prefabrication of reinforcement plate for shell opening shall meet the following requirements:
1 The material of reinforcement plate shall be the same as that of shell plate at opening.
2 Cutting surface of the reinforcement plate shall be flat and smooth while edges and corners shall be rounded; its curvature shall be consistent with that of the shell plate at this position while the permissible deviation shall meet those specified in 4.2.3 of this code. 3 Butt welding seams for spliced reinforcement plate shall be full penetration welding seams.
4 The reinforcement plate shall be with signal hole. The reinforcement plate manufactured with a complete steel plate shall be with one signal hole; The reinforcement plate spliced shall be with one signal hole at each splicing segment. The signal hole should be M6 ~ M10 and at the bolt hole onto the horizontal centre line.
4.6.5 Prefabrication of structural members shall meet the requirements of design documents. 5 Assembly
5.1 General Requirement
5.1.1 Prior to assembly of tank, groove of the member and rust, moisture as well as dirt at the overlapping position shall be cleaned up.
5.1.2 Base metal shall not be damaged in the dismantlement of clamping tools assembled. Craters on the steel plate surface shall be polished until to be smooth; if damaged, base metal shall be repaired according to the requirements of 6.6 of this code.
5.1.3 Assembly of stainless steel tank shall meet the following requirements: 1 Tank shell, tank bottom and accessories shall not be with embossed marks; 2 Stainless steel materials should be adopted for assembling clamping tools, and carbon steel clamping tools shall not contact and be welded with stainless steel tank; if required to be contacted and welded, clamping tools shall be welded with stainless steel isolation plate;
3 Arc scratch shall be avoided in assembly welding.
5.1.4 Safety measures for assembling technology shall be taken in assembling the tank to has been welded.
5.6.6 Before assembly of double-deck floating roof, the welding seam covered by ring plate, partition, truss and reinforcement plate shall be carried out firstly and inspected by vacuum tank and upon it is qualified, the assembly of double-deck floating roof shall be carried out. The weld pass shall be subjected to the top plate and accessories installation upon being qualified.
5.6.7 Assembly of fabricated internal floating roof shall be carried out in accordance with the design requirements.
5.7 Accessories Installation
5.7.1 Nozzle of tank shall meet the following requirements:
1 The position deviation of nozzle center shall not be greater than 10mm and the allowable deviation of connection pipe extension length shall be ±5mm.
2 The curvature of opening reinforcement plate shall be consistent with that of tank. 3 The sealing face of nozzle flange shall be free from overlap and scratch. The flange sealing surface shall be perpendicular with connection shaft unless otherwise specified in the design documents and the flange face shall be perpendicular or horizontal and declined by 1% of flange outer diameter or less and shall not be greater than 3mm; the flange bolt hole shall be installed at mid-span.
5.7.2 Verticality and linearity of the dipping tube and guide tube shall not be greater than 0.1 % of tube height and shall not be greater than 10mm.
5.7.3 In the water filling test of storage tank, the floating roof support height shall be adjusted according to the actual measurement size.
5.7.4 After rotary joint hardwired floating roof drains system has been pre-casted, the dynamic test shall be carried out and the test height shall subject to the highest level of the storage tank in the water filling test.
5.7.5 Sealing device shall be protected during transportation and assembly to prevent the damage to the rubber products; during the assembly, attention shall be paid to fire protection. 5.7.6 The paraffin cutter shall be tightly close to shell plate and partial maximum clearance shall not exceed 5mm.
5.7.7 Horizontal projection of rolling ladder central line shall be superposed with track center line and the deviation shall not be greater than 10mm.
5.7.8 Installation of latticed shell shall meet requirements of design documents. 6 Welding
6.1 General Requirement
6.1.1 The welder for storage tank welding must be assessed according to TSG Z6002 Assessment Rules for Special Equipment Welding Operators and upon being qualified in the Nation.
6.5 Welding Sequence
6.5.1 The welding of tank bottom shall use the welding procedure and the welding sequence which may result minimum shrinkage deformation. The welding sequence of tank bottom should meet the following requirements:
1 In case of welding of bottom sketch plates , shorter welding seams shall be welded firstly followed by longer ones; the first pass should be welded with the method of back-step welding or skip welding.
2 The welding of annular bottom plates shall meet the following requirements: 1) Welding shall be applied firstly to welding seams at least 300mm near the outside edge, after completion of the fillet welding seam of tank bottom and wall and before the application of welding of shrinkage joints between the edge plate and the bottom sketch plate, the welding of butt welding seam of
remaining edge plates and bottom sketch plates shall be completed;
2) Welding of the first layer of butt welding seam for annular edge plates should be made in the way that the welders are evenly distributed to weld it
symmetrically;
3) Welding of the first layer of shrinkage joints between edge plates and bottom sketch plates shall be made with the method of back-step or skip welding. 3 The tank bottoms with non-annular edge plates should remain no shrinkage joint. 4 The welding of fillet welding seam connecting tank bottom and shell shall be made after completion of longitudinal seam welding on bottom ring shell and it shall be welded by several pairs of evenly distributed welders, section by section from inside and outside of tank along same direction. The fillet welding seam inside the tank shall be welded firstly followed by the ones outside the tank. The pass of first layer shall be welded with the method of back-step or skip welding.
6.5.2 The welding sequence of shell should meet the following requirements: 1 Longitudinal welding seams shall be welded firstly followed by circumferential ones. On completion of the welding of longitudinal welding seams for shell of two adjoining rings, the circumferential welding seams between them shall be welded; in case the unsymmetrical grooves are adopted, the side with large groove shall be welded firstly followed by that with small groove.
2 When gas shielded welding is used for longitudinal welding seams, the welding should be applied upward. When submerged automatic arc welding is used for circumferential welding seams, the welding machines should be evenly distributed to apply welding along same direction; when shielded metal arc welding is used, the welders should be evenly distributed to apply welding along same direction.
6.5.3 The welding sequence of fixed-roof top plates should meet the following requirements:
1 The inside welding seams should be welded firstly followed by outside ones. For radial long welds, the method of symmetric welding of every other weld should be used and it nominal thickness of steel plates deducting the negative deviation.
2 In case the defect depth or polishing depth exceeds 1mm, it shall be subjected to repair welding and polished to be smooth.
6.6.2 Repair of welding seam surface defects shall meet the following requirements: 1 In case the welding seam surface defect exceeds those specified in 7.1.2 of this code, it shall be polished or shall be subjected to repair welding;
2 The welding seam surface defect shall be removed with angle grinder; in case the welding seam surface is lower than base metal after removal of defect, it shall be subjected to welding repair;
3 The removal depth of undercut and toe crack on both sides of welding seam shall not be greater than 0.5mm, if fails to meet the requirements, shall be subjected to welding repair; 4 The undercut of longitudinal welding for shell steel plates with the minimum standard yield strength greater than 390MPa or low-alloy steel bottom ring shell with the thickness greater than 25mm shall be repaired and polished to smooth transition with base metal.
6.6.3 Rework of internal defect of welding seam shall meet the following requirements: 1 Applicable welding method shall be selected, and rework technique shall be established according to causes of defects.
2 For unacceptable defect inside the welding seam, the buried depth of defect shall be detected and the removal surface of defect shall be determined before welding repair, the removal length shall not be less than 50mm and the removal depth should not be greater than 2/3 of the plate thickness; if carbon arc air gouging is adopted, the defect shall be grinded and grooved after removal.
3 The welding seam after rework shall be subjected to non-destructive testing in accordance with the former me...

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