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.
Dereham (/ˈdɪərəm/), also known as East Dereham, is a town and civil parish in the Breckland District of the English county of Norfolk. It is situated on the A47 road, about 15 miles (25 km) west of the city of Norwich and 25 miles (40 km) east of King's Lynn.
The civil parish has an area of 21.51 km2 (8.31 sq mi) and, in the 2001 census, had a population of 15,659 in 6,941 households; the population at the 2011 census increased to 18,609. Dereham falls within, and is the centre of administration for, Breckland District Council. The town should not be confused with the Norfolk village of West Dereham, which lies about 25 miles (40 km) away.
Since 1983, Dereham has been twinned with the town of Rüthen in North Rhine-Westphalia, Germany. It is also twinned with Caudebec-lès-Elbeuf, France. In spite of the reunification of Germany in 1990, the sign on the A47 at the entrance to Dereham from the Swaffham direction still refers to Rüthen being in West Germany; this sparks periodic comment in the local press.