Welding Procedure for Pressure Vessels (also often referred to as Welding Procedure Specification, WPS, or Welding Operation Instruction) is a set of technical documents used to guide the welding production of pressure vessels. It serves as a critical basis for ensuring welding quality and safe, reliable operation of equipment. It must be formulated in accordance with national regulations, standards, as well as the structure, materials and service conditions of the pressure vessel. The main contents and requirements typically included in a pressure vessel welding procedure are as follows:
- Scope of ApplicationSpecify the pressure vessels, welded joints, materials and welding methods to which the procedure applies. For example, it applies to manual arc welding, argon arc welding or submerged arc welding of carbon steel, stainless steel or chromium-molybdenum steel.
- Referenced StandardsList the national or industrial standards on which the procedure is based, such as GB 150 Pressure Vessels, NB/T 47014 Welding Procedure Qualification for Pressure Equipment, NB/T 47015 Welding Procedure for Pressure Vessels, etc.
- Welding ConsumablesSpecify the type, grade, size, drying requirements and service conditions of welding materials. For example, the selection of electrodes, welding wires and fluxes must match the base metal, with clear drying temperature and holding time specified.
- Welding EquipmentDescribe the type, performance requirements and maintenance requirements of welding machines to be used, as well as auxiliary equipment required during welding, such as argon shielding devices, preheating devices, etc.
- Welding Parameters (Core Part)This is the core section of the procedure, including:
- Welding processes (SMAW, GTAW, GMAW, SAW, etc.)
- Welding current, voltage and travel speed
- Number of welding layers and passes
- Type and flow rate of shielding gas
- Preheating temperature and interpass temperature
- Postweld heat treatment temperature and holding time
- Groove design, gap and fit-up requirements
- Welded Joint DesignSpecify the structural form, groove dimensions, machining requirements and assembly tolerances of welded joints, such as groove angle and root face size for butt joints, fillet joints and T-joints.
- Pre-welding PreparationIncluding:
- Groove machining and cleaning requirements
- Assembly and tack welding requirements for workpieces
- Preheating method and preheating temperature control
- Removal of oil, rust, moisture from the welding zone
- Welding Operation RequirementsClarify the technical guidelines to be followed by welders during operation, such as welding sequence, electrode manipulation method, crater filling requirements, and measures to prevent defects. For stainless steel or high-alloy steel, emphasis shall also be placed on measures to prevent intergranular corrosion.
- Postweld Heat Treatment (PWHT)Specify whether postweld heat treatment is required, as well as heat treatment temperature, holding time, heating and cooling rates. For example, chromium-molybdenum steel pressure vessels usually require PWHT to relieve residual stresses.
- Quality InspectionSpecify inspection methods and acceptance criteria for welded joints, including:
- Visual inspection (VT)
- Non-destructive testing (RT, UT, MT, PT)
- Mechanical property tests (if required)
- Repair provisions for defective welded joints
- Welding RecordsRequire recording of the welding process for each pressure vessel, including welder code, welding date, welding parameters, heat treatment records, inspection results, etc., for traceability purposes.
- Safety RequirementsClarify safety precautions during welding operations, such as fire prevention, explosion protection, electric shock prevention, and argon asphyxiation prevention.
Summary
The welding procedure for pressure vessels is a systematic and rigorous technical document used to regulate the entire welding process, ensuring that welded joint quality meets design and standard requirements, thereby guaranteeing the safety and reliability of pressure vessels. It is a mandatory document that must be strictly enforced in pressure vessel manufacturing.
