Welding and joining
Submerged arc welding: what goes wrong and where to inspect
Submerged arc welding deposits large volumes of weld metal under a blanket of granular flux: longitudinal and circumferential seams of vessels, pipes, wind towers and heavy beams.
01How the process works
The arc burns under flux, which shields the weld and forms a slag. The process is mechanised on tractors, column and boom manipulators or rotators, with single or multiple wires. Heat input is high, so toughness of weld and heat affected zone must be qualified.
Flux moisture, wire and flux combination, heat input and interpass temperature are the critical controls. Slag inclusions between passes and centreline cracking in deep narrow joints are classic problems.
- Joint preparation. Bevel and fit-up on thick plate.
- Flux handling. Flux baked and kept dry.
- Welding. Mechanised passes with controlled heat input.
- Back gouging. Root removed and rewelded where required.
- Inspection. VT, UT or RT, mechanical tests on coupons.
02What typically goes wrong
| Defect | Typical cause | How it is found |
|---|---|---|
| Slag inclusions | Interpass cleaning | RT, UT |
| Centreline cracking | Bead shape, joint geometry | UT, MT |
| Porosity | Damp flux, contamination | RT |
| Low toughness | Excess heat input | Impact tests on production coupons |
| Lack of fusion | Wire position | UT |
| Undercut | Speed, voltage | VT |
03Where an inspector should look
Before production
- WPS with heat input range
- Wire and flux certificates
- Production test coupon plan
During production
- Flux baking and recycling
- Heat input and interpass temperature
- Wire alignment
After production
- UT or RT per code
- Production coupon tests
- Dimensions and ovality
04Standards and references
ISO 14171 and ISO 14174 (SAW wires and fluxes), ASME Section VIII and EN 13445 for vessels.
Standards are named for orientation. The applicable edition and acceptance criteria are those in your contract and specification.