Fabrication, applications and weldability
Fabrication, applications and weldability tests shop-floor judgement: consumable control, preparation, fit-up, and whether a material can be welded to the required quality with the available process.
Consumable control
Basic MMA electrodes absorb moisture; re-dry at 300–350 °C for the manufacturer's time, hold at 100–150 °C and issue in heated quivers. SAW flux is baked at about 300–350 °C and kept dry and screened. Stainless consumables are stored separately and never contaminated by carbon steel tools.
Preparation and cleaning
Thermal cutting leaves dross, oxide and a hardened cut edge; grind back for critical welds. Degrease aluminium and stainless before welding - hydrocarbons cause porosity and carbon pickup. Dedicated stainless brushes and discs prevent iron contamination and rust spotting.
Weldability by material
- C-Mn steel: tolerant; watch CEV, thickness and hydrogen.
- Austenitic stainless (304/316): no preheat, interpass below about 150 °C, heat input typically 0.5–2.5 kJ/mm, argon purge on the root, ferrite 5–10 FN to resist hot cracking.
- Aluminium: remove oxide immediately before welding, AC TIG or MIG, high speed to limit distortion; hydrogen porosity is the main risk.
- Duplex stainless: heat input roughly 0.5–1.5 kJ/mm and controlled interpass to keep the ferrite/austenite balance and avoid sigma phase.
Worked example
A 316L pipe root is welded with TIG and an argon purge. The purge excludes oxygen and nitrogen, preventing oxidation and loss of corrosion resistance; low heat input and 150 °C interpass limit sensitisation and distortion. A carbon steel brush would embed iron and cause pitting.
Traps
Preheating austenitic stainless; using the wrong brush; welding over primer or galvanising; forgetting that aluminium oxide melts far above the metal; controlling heat input on paper but not at the arc.