Because the program assumes a fixed geometry. Included angle, tip diameter and stickout determine arc shape, penetration profile and arc starting behaviour, and the machine cannot sense that any of them have changed. An inconsistent grind produces wandering arc starts and varying penetration on a program that was qualified and signed off, which is far harder to diagnose than an obvious fault.

Enough to confine argon to the joint and verify it. Purge dams, inflatable bladders or soluble film restrict the volume being purged, tube plugs and caps seal the ends, and an oxygen analyser reading in parts per million confirms the bore before welding. Confining the volume also cuts gas consumption and purge time dramatically on long runs.

It forms a temporary dam close to the joint so only a short length of bore has to be purged, then dissolves and flushes away with the system's first water fill. It suits pipework where a mechanical dam could not be retrieved afterwards. Confirm compatibility with the process fluid and the flushing regime before specifying it.

Square, clean and matched. Autogenous welds have no filler to bridge a gap, so end squareness, concentricity and fit-up tolerance are tighter than for manual welding. Facing and squaring tools cut the end perpendicular to the axis with a consistent finish; abrasive cutting and hand deburring introduce contamination and out-of-square ends that show as inconsistent penetration.

To prevent cross-contamination. Carbon steel particles transferred to stainless by a shared file, brush or clamp insert will rust in service and can initiate pitting, and on nickel alloys and titanium the consequences are more serious still. Dedicated sets per material group, marked and stored separately, are standard practice on high-purity and code work.

Tungsten electrodes and clamp inserts. Electrodes are consumed by each arc start and by any contact with the pool, and inserts wear at the gripping faces so tubes gradually sit less concentrically. Gas diffusers and seals on enclosed heads are next, since leakage degrades shielding long before it is visible on the weld.

Yes on regulated work. Current, voltage, rotation speed, wire feed and gas flow are all qualified variables, so the supply's readings are verified against calibrated instruments at intervals set by the quality system, typically annually or after any repair. Weld coupons run at the start of a shift or a batch provide the practical day-to-day check.