Welding Process of Pressure Vessels
1.Material Preparation
Select approved materials (ASME SA-516, SA-387, stainless steel, etc.).
Check material certificates (MTC).
Perform cutting by plasma, oxy-fuel, or mechanical means.
Edges prepared with beveling (usually V, U, or double-V grooves).
Surface cleaning (grinding, shot blasting, degreasing).
2. Joint Design
Common joints:
Longitudinal & circumferential seams
Nozzle-to-shell welds
Head-to-shell welds
Weld joint design must comply with ASME Section VIII, Div. 1 & IX or EN 13445.
3. Welding Process Selection
Depending on thickness, position, and material:
SMAW (Shielded Metal Arc Welding / Stick Welding) – versatile, common for carbon steel.
GTAW (Gas Tungsten Arc Welding / TIG) – root pass, thin materials, stainless steel.
GMAW (Gas Metal Arc Welding / MIG/MAG) – faster, used for production welding.
SAW (Submerged Arc Welding) – for long seams, high deposition rate.
FCAW (Flux Cored Arc Welding) – thick sections, high productivity.
4. Welding Procedure Specification (WPS)
Must be qualified by Procedure Qualification Record (PQR).
Defines:
Process (SMAW, GTAW, etc.)
Welding positions (1G, 2G, 5G…)
Preheat & interpass temperature
Filler metals (ASME Section II, Part C)
Shielding gases (for TIG/MIG)
Heat input control
5. Welding Execution
Preheating (typically 50–200°C, depending on material).
Root pass often with GTAW for quality.
Fill & cap passes with SMAW, SAW, or GMAW.
Interpass cleaning between passes.
Temperature control with thermocouples.
6. Post-Weld Heat Treatment (PWHT)
For thick-walled vessels or alloy steels.
Relieves residual stresses, improves toughness.
Usually at 600–750°C (per ASME requirements).
7. Inspection & Testing
Visual Inspection – every pass.
NDT (Non-Destructive Testing):
Radiographic Testing (RT) – internal defects
Ultrasonic Testing (UT) – thickness, flaws
Magnetic Particle Testing (MT) – surface cracks (ferrous metals)
Dye Penetrant Testing (PT) – surface cracks (stainless, non-ferrous)
Hydrostatic Test – vessel filled with water, pressure raised to 1.3–1.5× design pressure.
Pneumatic Test (with safety precautions) when hydrotest not feasible.
8. Documentation
Welding records, welder qualifications, WPS/PQR.
Material traceability reports.
NDT & PWHT reports.
Final ASME “U-Stamp” or equivalent certification.
✅ Summary: Pressure vessel welding requires strict material control, qualified procedures, skilled welders, and thorough inspection/testing to meet ASME, EN, or ISO standards.
Would you like us to make you a flowchart diagram of the welding process of pressure vessels (step-by-step from material prep → welding → inspection → certification)? By that way you’ll have a clear visual reference.
