Materials, Consumables and Preparation
Material knowledge
Understand carbon and low-alloy steels, stainless steels (austenitic, ferritic, duplex), aluminium alloys, and their weldability issues. Key concepts: carbon equivalent and preheat for hardenable steels, hydrogen cracking risk, sensitisation in austenitic stainless (chromium carbide precipitation), and the oxide film on aluminium requiring AC or DCEP cleaning action.
Consumables
Match filler to base metal and specification. Know electrode classification basics (e.g. E7018: 70 ksi tensile, all-position, low-hydrogen), the need to store low-hydrogen electrodes in holding ovens, and re-drying requirements. For GMAW/FCAW, understand wire diameter, flux-cored types (rutile, basic, metal-cored) and their positional and toughness behaviour. For GTAW, filler and tungsten electrode type (thoriated, lanthanated, ceriated) and grinding to a point.
Preparation
Joint preparation determines weld quality: clean surfaces free of oil, paint, rust, moisture and scale; correct bevel angle, root gap and root face; backing or purge for root protection. Preheat and interpass control reduce cracking. Distortion control via sequencing, backstep, balanced welding and restraint.
Traps
- Using a cellulose or rutile electrode where low-hydrogen is specified.
- Storing 7018 in the open; it must be in a heated quench oven.
- Welding aluminium with DCEN and expecting cleaning action.
- Ignoring preheat on thick or high-carbon-equivalent steel.
Rule of thumb
Low-hydrogen electrodes: keep in a holding oven at about 100-150 °C after opening; re-dry per manufacturer if exposed. If in doubt, dry rather than risk hydrogen cracking.