Welding

Stick welding (SMAW) is portable, tolerates wind and suits field repairs. MIG/MAG is highly productive and suits volume fabrication in a sheltered shop. TIG gives clean, well-controlled welds on stainless, aluminum and thin sheet, but is slower.

Electrodes and wires are classified by AWS (for example A5.1 for carbon steel electrodes and A5.18 for solid wire) or the equivalent ISO standards. The designation tells you weld metal strength, welding positions, coating type or suitable shielding gas. Choose based on the base metal and the welding procedure specification (WPS) where one exists.

At minimum: a welding helmet with the correct shade filter, leather gloves, flame-resistant clothing and safety footwear. The work area needs fume extraction or ventilation, especially when welding galvanized or stainless steel. Gas cylinders must be chained upright and fitted with the correct regulator for the gas.

Welding fume contains metal oxides and toxic gases, and is especially hazardous with stainless steel (hexavalent chromium) or galvanized steel. Local extraction with a hood near the arc is far more effective than general ventilation. Confined spaces need fresh air supply and an attendant outside.

Oil, paint, rust and moisture on the joint generate gas in the weld pool, causing porosity and cracking. Grind or brush about 20 to 25 mm each side of the joint to bright metal. Aluminum and stainless need dedicated brushes to avoid iron contamination.

Thick sections, steels with high carbon equivalent and cast iron usually need preheat to slow cooling and avoid hydrogen cracking. Preheat temperature is set by the welding procedure, based on steel chemistry, thickness and joint restraint. Check it with temperature indicating crayons or a contact thermometer.