NB/T 47015-2023Welding specification for pressure vessels (English PDF)

4.1 General provisions

4.1.1 In addition to complying with the provisions of this document, the welding of pressure vessels shall also comply with the technical requirements of the design documents.

4.1.2 In addition to the provisions of this document, any results that have been proven effective through welding test research and practice, after being approved by the relevant parties and included in the enterprise standard, can be used for pressure vessel welding.

4.2 Welding materials

4.2.1 Welding materials include welding rods, welding wires, welding strips, flux, gases, electrodes, gaskets.

4.2.2 The welding seams of pressure vessel's pressure components, the welds welded to pressure components, the welding electrode, welding wire, welding strip, welding flux for positioning welds melted into permanent welds, shall comply with the provisions of NB/T 47018.

4.2.3 The gas used for gas shielded welding of pressure vessels shall comply with the provisions of GB/T 39255.

4.2.4 Principles for selecting welding materials.

The mechanical properties of weld metal shall match those of the parent material. The mechanical properties of weld metal, which is welded according to a reasonable welding process, shall meet the requirements of NB/T 47016 and design documents.

When necessary, other properties shall not be lower than the corresponding requirements of the parent material.

4.2.5 The manufacturing (installation) organization shall master the weldability of welding materials; the welding materials used for pressure vessels shall have a welding test or practice basis.

4.2.6 Welding materials shall have a product quality certificate; the user organization shall accept or re-inspect according to the provisions of the quality management system and relevant standards and design documents.

4.3 Weld position

The weld position is divided into four types. flat weld, vertical weld, lateral weld, overhead weld. The specified methods and ranges are shown in Appendix A.

4.4 Welding procedure qualification and welders

For the following types of welds, the welding procedure shall be qualified according to NB/T 47014; the welder shall be qualified according to TSG Z6002 "Examination rules for welding operators of special equipment".

a) Pressure component welds;

b) Welds welded to pressure components;

c) Positioning welds of the above welds (referring to welding procedure), positioning welds welded into the above permanent welds (referring to welders);

d) Overlay welding and repair welding on the surface of the parent material of the pressure component.

4.5 Preparation before welding

4.5.1 Site

4.5.1.1 The site of high-alloy steel pressure vessels shall be separated from other types of materials; anti-scratch pads shall be laid on the ground.

4.5.1.2 Non-ferrous metal pressure vessels shall be manufactured in a dedicated site or dedicated space; corresponding protective measures shall be taken.

4.5.2 Welding groove

4.5.2.1 The welding groove shall be selected from standard grooves or designed by itself according to the design drawings and process conditions. The groove form and size shall consider the following factors.

a) Welding method;

b) Type and thickness of parent material;

c) Minimum weld filler metal;

d) Avoid welding defects;

e) Reduce welding deformation and residual stress;

f) Facilitate welding protection;

g) Convenient operation for welders;

h) The groove of composite materials should reduce the dilution rate of transition layer weld metal; it is easy to distinguish the interface between the base layer and the cladding layer when welding the corrosion-resistant layer.

5.1 Welding methods Applicable

welding methods are gas welding, arc welding, submerged arc welding, gas tungsten arc welding, gas metal arc welding, plasma arc welding, gas electric vertical welding, stud welding, electron beam welding, strip electrode cladding.

5.2 Welding materials

5.2.1 In addition to complying with the provisions of this document, welding materials for steel pressure vessels shall also comply with the provisions of relevant safety technical specifications, welding material standards, product standards, technical documents.

5.2.2 The Cr, Mo, V content of the weld metal of welding materials for heat-resistant

low-alloy steel shall not be lower than the specified values of the corresponding parent material standards.

5.2.3 The Cr and Ni content of the weld metal of austenitic stainless steel materials shall not be lower than the specified values of the corresponding parent material standards.

When necessary, its corrosion resistance shall not be lower than the corresponding requirements of the parent material.

5.2.4 When welding non-austenitic parent materials with welding materials that generate austenitic weld metal, the additional stress caused by the different expansion coefficients of the parent material and the weld metal shall be carefully considered.

5.2.5 The user of welding materials can select appropriate welding materials based on experience and test data. The welding materials recommended for commonly used steel designations can refer to Table D.1 in Appendix D.

5.2.6 When welding steels of different steel designations, the principles for selecting welding materials are as follows.

a) When welding between low-carbon steels, between low-carbon steels and low-alloy steels, between low-alloy steels, the selected welding materials shall ensure that the tensile strength of the weld metal is higher than or equal to the lower limit of the tensile strength of the parent material on the lower strength side; meanwhile it should not exceed the upper limit specified by the standard of the parent material on the higher strength side.

b) When welding low-carbon steel, low-alloy steel and austenitic stainless steel, when the design temperature is higher than 370 °C, nickel-based welding materials shall be used.

c) When welding low-carbon steel, low-alloy steel and ferritic stainless steel or duplex stainless steel, welding materials suitable for welding dissimilar steels can be used. Duplex steel welding materials can also be used for welding with duplex stainless steel.

d) When welding between heat-resistant low-alloy steels or between heat-resistant low-alloy steels and other low-alloy steels, welding materials with low chromium and molybdenum content should be selected.

6.1 Welding methods

The welding methods applicable to aluminum pressure vessels are gas welding, tungsten inert gas shielded welding, metal inert gas shielded welding, plasma arc welding.

6.2 Welding materials

6.2.1 In addition to complying with the provisions of this document, welding materials for aluminum pressure vessels shall also comply with the provisions of relevant safety technical specifications, welding material standards, product standards and technical documents.

6.2.2 To ensure the corrosion resistance of the weld metal, when the parent material is pure aluminum, it should use welding wire with a purity not lower than that of the parent material; when the parent material is aluminum-magnesium alloy or aluminum-manganese alloy, it should use welding wire with a magnesium content or manganese content not lower than that of the parent material.

6.2.3 The recommended welding wire models for commonly used aluminum materials can refer to Table D.2 in Appendix D. The manufacturer can select suitable welding materials based on experience and test data.

6.2.4 The surface of the welding wire and the filler wire shall be kept bright and smooth.

It can be observed visually and with a 20x magnifying glass. There shall be no burrs, pits, scratches, oxide scale, cracks, folds, inclusions. The welding wire shall not have knots, waves, bends and other defects that affect continuous wire feeding.

6.2.5 Argon is commonly used as shielding gas; helium or a mixture of the two can also be used. The purity of argon shall not be less than 99.9%. Cylindered argon shall not be used when the pressure is less than 0.5 MPa.

6.2.6 It is recommended to use cerium tungsten electrode for tungsten inert gas shielded welding; pure tungsten electrode, thorium tungsten electrode, etc. can also be used.

6.3 Groove preparation

6.3.1 The groove form and size for gas shielded welding refer to GB/T 985.3.

6.3.2 Groove processing shall be cold processing method, or plasma cutting. Before welding, the groove shall be ground or cold processed to remove oxides, until the metallic luster is exposed and polished flat.

6.4 Cleaning before welding

6.4.1 The weld groove, backing, welding wire shall be cleaned before pairing and welding. The surface of the groove and the area within 50 mm on both sides shall be strictly cleaned to remove moisture, dust, metal chips, oil, paint, oxide film, hydrogen-containing substances, and attachments. The surface oil stain shall be removed with organic solvents such as acetone first; then the surface oxide film shall be removed mechanically or chemically; however, grinding wheels or sandpaper shall not be used. The mechanical or chemical cleaning methods are as follows.

a) Mechanical cleaning. The groove and the surfaces on both sides can be cleaned by cutting to reveal the metallic luster. The cutting tool can be an electric milling cutter or a scraper. For thinner oxide films, reamer and stainless steel wire brush can also be used for cleaning.

b) Chemical cleaning. 5% ~ 10% sodium hydroxide solution at a temperature of about 70 °C shall be used; soak for 30 s ~ 60 s; then rinse with water; soak in about 15% nitric acid at room temperature for 2 minutes; then rinse with warm water.

6.4.2 The cleaned weldment and welding wire shall be kept dry and protected; welding shall be carried out in time without water marks, alkali marks or contamination.

6.4.3 If the weldment and welding wire are not welded for more than 8 hours after cleaning, meanwhile there are no effective protection measures, they shall be cleaned again before welding.

7.1 Welding method

The welding methods applicable to titanium pressure vessels are tungsten inert gas shielded welding, metal inert gas shielded welding, plasma arc welding.

7.2 Welding materials

7.2.1 In addition to complying with the provisions of this document, welding materials for titanium pressure vessels shall also comply with the provisions of relevant safety technical specifications, welding material standards, product standards and technical documents.

7.2.2 The content of impurity elements such as nitrogen, oxygen, carbon, hydrogen, iron in the welding wire shall be strictly controlled; strips cut from the parent material to be welded shall not be used as welding wire.

7.2.3 The recommended welding wire models for commonly used titanium materials can be referred to Table D.3 in Appendix D. Manufacturers can select suitable welding materials based on experience and test data.

7.2.4 When different designations of titanium materials are welded, titanium welding wire or filler wire shall be selected according to the provisions of the design documents; when the design documents do not make provisions, welding wire and filler wire shall be selected according to the base material with better corrosion resistance and lower strength grade.

7.2.5 The storage of titanium welding wire and filler wire shall be kept dry; the relative humidity shall not be greater than 60%.

7.2.6 Argon is commonly used as shielding gas; helium or a mixture of the two can also be used. The purity of argon shall not be less than 99.99%. It should not be used when the pressure of cylindered argon is less than 0.5 MPa.

7.2.7 Tungsten inert gas shielded welding shall use cerium tungsten electrode.

7.3 Groove preparation

7.3.1 The groove form and size for gas shielded welding are shown in Appendix B.

7.3.2 Groove processing shall be done by cold processing. If hot processing is used, the oxide layer and slag on the surface of the groove and both sides shall be removed. The surface and both sides of the groove shall have a silvery white metallic luster.

7.3.3 The groove surface and the area within 25 mm on both sides shall be cleaned to remove oil, nitride, scale, moisture, organic impurities, etc.

7.3.4 Surface cleaning can be done by degreasing, mechanical cleaning, chemical cleaning. When cleaning the surface, do not use oxide solvents and methanol solvents.

Attention shall be paid to removing residual plasticizers from rubber products and preventing the risk of stress corrosion of chloride-containing water. When grinding to remove surface oxides, stainless steel wire brushes or silicon carbide grinding wheels shall be used.

7.3.5 After the welding wire and groove surface are cleaned, if they cannot be stored in a dry environment, such as not welding for 4 hours after cleaning and degreasing, they shall be cleaned again before welding.

7.4 Welding wire and filler wire

The surface of the welding wire and filler wire shall be clean, dry, smooth. There shall be no burrs, dents, scratches, scale, folds, or other defects that affect use. There shall be no contamination by lubricants and other foreign substances. The surface oil and moisture shall be carefully removed before use.

Clean the welding wire and weldment. Do not contaminate them before welding. Do not touch the welding part with your hands. Otherwise, clean them again.

8.1 Welding methods

The welding methods applicable to copper pressure vessels are gas welding, arc welding, submerged arc welding, tungsten inert gas shielded welding, metal arc shielded gas welding, plasma arc welding.

8.2 Welding materials

8.2.1 In addition to complying with the provisions of this document, welding materials for copper pressure vessels shall also comply with the provisions of relevant safety technical specifications, welding material standards, product standards and technical documents.

8.2.2 Strictly control the impurity elements such as oxygen, lead, bismuth, sulfur in the weld metal, to ensure that there are sufficient deoxidizing elements such as silicon, manganese, phosphorus, aluminum, titanium in the welding materials.

8.2.3 The applicable scope of common copper and copper alloy welding materials can refer to Table D.4 and Table D.5 in Appendix D. Manufacturers can select suitable welding materials based on experience and test data.

8.2.4 When welding copper and copper alloys with gas shielded welding, argon gas protection is usually selected. When welding pure copper, or preheating is not allowed, or a larger penetration depth is required, helium or a mixed shielding gas of argon and helium can be used.

9.1 Welding method

The welding methods applicable to nickel pressure vessels are arc welding, tungsten inert gas welding, metal inert gas welding, submerged arc welding, plasma arc welding.

9.2 Welding materials

9.2.1 In addition to complying with the provisions of this document, welding materials for nickel pressure vessels shall also comply with the provisions of relevant welding material standards, product standards and technical documents.

9.2.2 The chemical composition of the deposited metal of the electrode or wire shall be similar to that of the parent material. In order to control welding pores and hot cracks, alloying elements such as titanium, manganese, niobium are generally added to the welding materials.

9.2.3 The recommended welding materials for commonly used nickel and nickel alloys can refer to Table D.6 in Appendix D. The manufacturer can select appropriate welding materials based on experience and test data.

9.2.4 Argon, helium or a mixture of the two is recommended for tungsten inert gas welding; argon or argon-helium mixed gas is recommended for metal arc welding; argon or argon-hydrogen mixed gas is recommended for plasma arc welding.

9.2.5 Cerium tungsten electrode is recommended for tungsten inert gas welding.

9.3 Groove and joint preparation

9.3.1 The groove angle of nickel and nickel alloy welding is large, the root gap is large, the blunt edge height is small. The recommended groove of nickel alloy arc welding butt joint is shown in Figure 4.

9.3.2 The groove can be machined and plasma arc cut.

9.3.3 When welding on one side, measures such as placing a formed liner or protective cover on the back and passing a protective gas can be taken, to ensure the back side is welded through and prevent oxidation.

9.4 Cleaning before welding

9.4.1 Before heating, use a stainless steel wire brush, aluminum oxide, silicon carbide grinding wheel or carbide chisel to clean the welding wire, groove, liner and the material surface within 50 mm on both sides of the groove, as well as using brushes, chisels and other tools that come into contact with the joint to clean it.

9.4.2 Solvents, hydrochloric acid solution or grinding, shot peening, polishing and machining can be used to remove oxides on the surface of the joint, harmful elements that form low melting point eutectics with Ni, and products (oil, paint, coating, marking pen marks, ink, temperature pen marks, cutting fluid, workshop dust, etc.). […]