Welding Requirements and Heat Treatment for Marine Low-Pressure Air Bottles
This standard specifies the welding and heat treatment requirements during the manufacturing of air cylinders (pressure vessels), aiming to ensure that the quality of product weld joints meets design, safety, and relevant standard specifications. All welding operations, quality control, and heat treatment activities shall comply with the specific provisions of this standard and referenced standards such as GB 11038, in order to guarantee the structural integrity, safety, reliability, and long-term service performance of the air cylinders. The main contents cover pre-welding preparation, personnel and procedure qualification, weld quality requirements, product test plate management, non-destructive testing, as well as heat treatment conditions and controls
Overview
1. Welding
1.1 Pre-Welding Preparation
1.1.1 Before welding, oxides, moisture, oil stains, and other contaminants that may affect welding quality shall be removed from the surface of the weld joint edges within a zone of at least 25 mm from the groove.
1.1.2 Tack welds and edge defects that may affect welding quality shall be removed before welding.
1.1.3 Low-hydrogen or ultra-low-hydrogen welding materials shall be used for welding air bottles. Regular testing and inspection shall be carried out in accordance with the manufacturer's instructions for the welding materials.
1.1.4 Misalignment between the two plate surfaces of butt welds on air bottles shall not exceed 10% of the plate thickness at any point. For longitudinal seams, the misalignment shall not exceed 3 mm; for circumferential seams, it shall not exceed 4 mm.
1.2 Welder Qualification and Welder Marking
Shall comply with the relevant provisions of GB 11038.
1.3 Welding Environment and Welding Procedure Qualification
Shall comply with the relevant provisions of GB 11038.
1.4 Welds
1.4.1 Weld surfaces shall be uniform and dense, free from cracks, weld spatter, pores, slag inclusions, undercut, arc craters, incomplete filling, lack of penetration, lack of fusion, or other visible defects. Any such defects shall be removed before non-destructive testing. Spatter on both sides of the weld must also be removed.
1.4.2 Weld surfaces may be flush with the base metal or slightly thicker at the center of the weld, but the transition in the weld reinforcement shall be gradual. The weld shall not have a flat or sharp-angled profile.
1.4.3 After surface defects or mechanical damage are removed by grinding, the thickness of the weld shall not be less than the negative tolerance thickness of the base metal.
1.4.4 Cross-shaped welds are not permitted in the assembly welding of air bottle cylinders. The distance between the longitudinal welds of the head and the cylinder section or between two cylinder sections shall not be less than 200 mm.
1.4.5 If unacceptable defects are found in a weld, they shall be repaired after removal. The number of repairs at the same location shall not exceed two. After repair, X-ray inspection and heat treatment shall be performed as required.
1.4.6 For single-side welding, appropriate measures shall be taken to ensure complete penetration at the weld root and to minimize deformation caused by shrinkage of the weld metal.
1.5 Welding Test Plates
1.5.1 The material grade and thickness of the welding test plates for air bottles shall be the same as those of the cylinder. The groove of the test plate shall be identical to that of the cylinder weld.
1.5.2 Test pieces are generally not required for circumferential seams. However, if the cylinder has only circumferential seams or if the processes used for circumferential and longitudinal seams differ significantly, one simulated test piece for the circumferential seam shall be welded.
1.5.3 The welding of test plates shall employ the same method, procedure, heat treatment, and the identical electrodes, welding wires, and fluxes as used for the product welding. The test plates shall undergo heat treatment in the same furnace as the cylinder.
1.5.4 The product welding test plates shall be welded by the welder performing the product welding. After welding, the welder's and inspector's identification codes shall be permanently marked (e.g., stamped) on the test plates.
1.5.5 Test specimens required for air bottles shall be prepared and tested in accordance with the provisions of GB 11038.
1.5.6 The results of the product welding tests for air bottles shall conform to the requirements specified in Table 4 of GB 11038.
1.6 Non-Destructive Testing
1.6.1 The scope of non-destructive testing shall comply with the stipulations in the following table.
Scope of Non-Destructive Testing
Testing Method | Pressure Vessel Class | |
Class I | Class II | |
Where P, δ, t are all less than the limits specified for Class I, but either P > 1.57, δ > 16, or t > 150 | Where P ≤ 1.57 and δ ≤ 16 and t ≤ 150 | |
Radiographic Testing (X-ray) | Welds of the test plate shall undergo 100% inspection. For product welds, a spot check of no less than 10% shall be performed. | — |
Magnetic Particle or Penetrant Testing | For welds on components such as pipes, columns, reinforcement plates, stubs, and branch pipes that have not undergone radiographic inspection, a 10% spot check by magnetic particle or penetrant testing shall be performed. | — |
1.6.2 For air bottles classified as Class II pressure vessels, the test plates may be exempted from X-ray radiographic inspection. However, the test plates for the initial product shall undergo 100% X-ray radiographic inspection in accordance with the requirements for Class I pressure vessels.
1.6.3 For low-pressure air bottles falling under GJB 14.1A, the test plates shall undergo 100% radiographic inspection.
1.6.4 For medium-low pressure air bottles falling under GJB 14.1A, more than 25% of the longitudinal butt welds and more than 15% of the circumferential welds shall undergo radiographic inspection. Film evaluation shall be performed according to GB 3323. The weld quality for longitudinal seams shall meet at least Class I, and for circumferential seams, at least Class II.
1.6.5 For air bottle products classified as Class I pressure vessels, the evaluation of butt weld radiographs shall be performed according to GB 3323. The weld quality for longitudinal seams shall meet at least Class I, and for circumferential seams, at least Class I.
1.6.6 When a head is fabricated by splicing several steel plates, at least 10% of the welds shall undergo X-ray radiographic inspection before forming. After forming, 100% radiographic inspection shall be performed. Film evaluation shall be conducted according to GB 3323. The weld quality for longitudinal seams shall meet at least Class I, and for circumferential seams, at least Class I.
1.6.7 For air bottles subjected to partial inspection, the manufacturer remains responsible for the quality of the untested portions.
2. Heat Treatment
2.1 Cold-formed heads must undergo normalizing heat treatment and non-destructive testing.
2.2 The following air bottles may be exempted from post-weld heat treatment:
a) Air bottles classified as Class I pressure vessels, when made of carbon steel with a welded component thickness of less than 30 mm and an operating temperature not exceeding 150°C; or when made of carbon-manganese steel with a welded component thickness of less than 20 mm and an operating temperature not exceeding 150°C.
b) All air bottles classified as Class II pressure vessels.
2.3 For air bottles requiring overall heat treatment, if overall treatment is impractical due to limitations, segmented heat treatment is permitted, provided the entire length of the weld seam is subjected to the heat treatment.
2.4 The temperature and holding time for the heat treatment of air bottles shall comply with the provisions of GB 11038.
