Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding, is an arc welding process that uses a non-consumable tungsten electrode to produce the weld. The weld area and electrode are protected from oxidation or other atmospheric contamination by an inert shielding gas (argon or helium). A filler metal is normally used, though some welds, known as autogenous welds, or fusion welds do not require it. When helium is used, this is known as heliarc welding. A constant-current welding power supply produces electrical energy, which is conducted across the arc through a column of highly ionized gas and metal vapors known as a plasma. GTAW is most commonly used to weld thin sections of stainless steel and non-ferrous metals such as aluminum, magnesium, and copper alloys. The process grants the operator greater control over the weld than competing processes such as shielded metal arc welding and gas metal arc welding, allowing for stronger, higher quality welds. However, GTAW is comparatively more complex and difficult to master, and furthermore, it is significantly slower than most other welding techniques. A related process, plasma arc welding, uses a slightly different welding torch to create a more focused welding arc and as a result is often automated.
Thetford is a market town and civil parish in the Breckland district of Norfolk, England. It is on the A11 road between Norwich and London, just east of Thetford Forest. The civil parish, covering an area of 29.55 km2 (11.41 sq mi), has a population of 24,340.
There has been a settlement at Thetford since the Iron Age, and parts of the town predate the Norman Conquest; Thetford Castle was established shortly thereafter. Roger Bigod founded the Cluniac Priory of St Mary in 1104, which became the largest and most important religious institution in Thetford. The town was badly hit by the dissolution of the monasteries, including the castle's destruction, but was rebuilt in 1574 when Elizabeth I established a town charter. After World War II, Thetford became an "overspill town", taking people from London, as a result of which its population increased substantially. Thetford was the headquarters of Tulip International, large-scale manufacturers of bacon, beef and pork until its closure in 2010.
Thetford railway station is served by the Breckland line and is one of the best surviving pieces of 19th century railway architecture in East Anglia.