GB/T 18442.7-2017Static vacuum insulated cryogenic pressure vessels— Part 7: Rules of pressure strengthening for inner vessels (English PDF)

3.1 Terms and definitions

The terms and definitions defined in GB/T 18442.1 as well as the followings apply to this document.

3.2 Symbols

The following symbols apply to this document.

A - Elongation after break, %;

Di - Inner diameter of cylinder or head, mm;

5.1 Steel plate

5.1.1 The designation and mechanical properties of the steel plate shall comply with the requirements of Table 1. The supply status is solid solution heat treatment and meets the requirements of GB/T 150.2 and GB/T 24511.

5.1.3 The sampling quantity and position of tensile test shall be in accordance with the provisions of GB/T 24511 and GB/T 150.2.

5.1.4 The tensile sample size and test method shall comply with the provisions of GB/T 228.1.

5.1.5 When the tensile strength of steel plate is higher than 720 MPa, the welding procedure assessment shall be re-carried out according to 7.4.1. It shall be used after it is assessed as qualified.

5.2 Steel pipes and pipe fittings

5.2.1 The materials for steel pipes and pipe fittings shall comply with the provisions of GB/T 18442.2.

5.3 Forgings

Stainless steel forgings in contact with the medium shall comply with the provisions of GB/T 18442.2 and NB/T 47010. Level is not lower than level III.

5.4 Welding materials

5.4.1 Welding materials shall comply with the corresponding provisions of GB/T 18442.2 and NB/T 47018.1~47018.4.

5.5 Overseas designation material

When the inner vessel uses overseas designation, it shall be in accordance with Annex B.

5.6 Other material

When using the materials other than Table 1 and Table B.1 to manufacture the inner vessels with the pressure strengthening technology, it shall also comply with the relevant provisions of TSG 21.

6.1 General

6.1.1 In addition to the provisions of this Part, the design of the inner vessels shall also comply with the provisions of TSG 21, GB/T 150 and GB/T 18442.3.

6.1.5 The product nameplate shall be marked with "pressure strengthening vessel", the symbol is "PS".

6.2 Load

6.2.1 When designing the inner vessel, the corresponding load and its combination shall be considered in accordance with the provisions of GB/T 18442.3.

6.2.2 In the process of pressure strengthening treatment, the reaction force and the strengthening pressure load generated at the support of the inner vessel shall also be considered.

6.3 Allowable stress

6.3.1 The allowable stress of the steel plate for the cylinder and the head is determined according to Table 2.

6.4 Calculation of internal pressure

The strength calculation of the inner vessels shall be in accordance with the provisions of GB/T 150.3. Other relevant calculations are in accordance with the provisions of GB/T 18442.3.

6.5 Calculation of external pressure

6.5.1 The calculation of external pressure stability of each component shall comply with the provisions of GB/T 150.3. The external pressure curve shall be selected according to the corresponding material at 20°C.

6.7 Strengthening pressure

The strengthening pressure pk is calculated according to formula (1).

6.8 Pressure of pressure resistance test

The pressure of pressure resistance test shall comply with the provisions of GB/T 18442.3.

6.9 Pressure of leak test

Perform according to the provisions of GB/T 18442.3.

6.10 Structure design

6.10.1 Except the last closed ring welds, the type A and type B weld joints shall be full penetration butt joints. Closed ring welds allow the use of butt joints with permanent backing.

6.10.5 In the design of the structure, the influence of the plastic deformation of the inner vessel on the low-temperature insulation performance of the vessel, the installation of the outer casing and the piping system shall also be considered.

7.1 General

7.1.1 In addition to the provisions of this Part, the manufacture, inspection and acceptance of the inner vessels shall also meet the requirements of other parts of GB/T 18442 and design documents.

7.2 Material preparation

7.2.1 The cylinder's adjacent tube of the inner vessel shall preferably use the same batch number and the same thickness of the steel plates. When using different batch materials, the difference of Rp0.2 of adjacent tube materials shall not exceed 30 MPa.

7.2.2 The steel plate for the inner vessel seal head shall be made of S30403 or S31603 material.

7.2.3 The splicing head shall be selected from the same batch number of steel plates.

7.3 Processing and forming

7.3.1 The processing of the inner vessel shall comply with the relevant provisions of GB/T 18442.4.

7.4 Welding

7.4.1 Welding procedure assessment

7.4.1.1 Before the welding of the inner vessel, the welding procedure assessment shall be carried out in accordance with the requirements of NB/T 47014 and this Part.

7.4.1.2 The welding joints of the welding procedure assessment test piece shall have no defects such as undercuts, cracks, surface pores, welding slag, pits, welds, etc.

7.4.1.4 When the pre-tensile test piece is made into a sample, the weld height is removed by mechanical means to make it flush with the base material. The sample's sampling method, specification and processing shall comply with the corresponding provisions of GB/T 228.1, GB/T 229, GB/T 2653 and NB/T 47014, respectively.

7.4.4 Weld seam welding rework and welding after strengthening

7.4.4.1 After cylinder type A, B weld joints and adapters of which the nominal diameter is greater than 50mm are welding reworked with cylinder type D weld joint, the pressure strengthening treatment shall be re-carried out. And it shall be approved by the manufacturer's technical leader.

7.4.5 Product welding test piece

7.4.5.1 The product welding test piece shall be prepared piece by piece. The test piece shall be welded at the same time at the extension of the longitudinal weld of the cylinder section and at the cylinder section. Before strengthening, perform longitudinal welding for the inner vessel of which the geometric volume is less than or equal to 5 m³. […]

7.5 Nondestructive testing

7.5.1 Testing before pressure strengthening implementation