Welding and joining
Brazing and soldering: what goes wrong and where to inspect
Brazed joints connect copper tubes in refrigeration and HVAC, aluminium heat exchangers, carbide tools and electrical contacts, using a filler metal that melts below the base metal.
01How the process works
The joint is heated by torch, induction or in a furnace; the filler alloy flows into a narrow gap by capillary action. Flux or a controlled atmosphere protects surfaces. Soldering works the same way at lower temperatures.
Gap control, cleanliness and temperature decide whether the filler wets and fills the joint. Voids, incomplete fill and flux residues cause leaks or corrosion later. Procedure and operator qualification apply to pressure containing joints.
- Cleaning and fit-up. Surfaces cleaned, gaps set.
- Flux or atmosphere. Flux applied or furnace atmosphere prepared.
- Heating. Joint heated to brazing temperature.
- Filler flow. Filler melts and fills by capillarity.
- Cleaning and test. Residues removed; leak and visual tests.
02What typically goes wrong
| Defect | Typical cause | How it is found |
|---|---|---|
| Incomplete fill and voids | Gap, temperature, cleanliness | Sectioning, ultrasonic, X-ray |
| Leaks | Voids through the joint | Helium or pressure leak test |
| Flux residues | Insufficient cleaning | Visual |
| Overheating and erosion | Excess temperature | Visual, section |
| Cracks | Thermal stress | Visual, PT |
| Lack of wetting | Oxides, contamination | Visual |
03Where an inspector should look
Before production
- Brazing procedure and operator qualification
- Filler and flux certificates
During production
- Temperature control
- Joint cleanliness
After production
- Leak test 100% for pressure parts
- Sample sectioning
- Visual of fillets
04Standards and references
ISO 13585 (brazer qualification), ISO 13134 (brazing procedure tests), EN 14324 (brazing guidance).
Standards are named for orientation. The applicable edition and acceptance criteria are those in your contract and specification.