The most common welding techniques used for 31803 duplex stainless steel include:

1. Gas tungsten arc welding (GTAW) – also known as TIG welding, is a high-quality welding process that produces precise and clean welds. GTAW is commonly used for thin sections and delicate structures, and it provides excellent control over the heat input.

2. Gas metal arc welding (GMAW) – also known as MIG welding, is a versatile welding process that is commonly used for thicker sections and larger components. GMAW produces high-quality welds and is relatively fast compared to other welding techniques.

3. Shielded metal arc welding (SMAW) – also known as stick welding, is a simple and versatile welding process that uses a consumable electrode coated in flux. SMAW is commonly used for thicker sections and in outdoor environments, and it produces strong and durable welds.

4. Flux-cored arc welding (FCAW) – is a versatile welding process that uses a hollow wire filled with flux. FCAW is commonly used for thicker sections and in outdoor environments, and it produces high-quality welds with good penetration.

5. Plasma arc welding (PAW) – is a high-precision welding process that uses a concentrated plasma arc to produce precise and clean welds. PAW is commonly used for thin sections and delicate structures, and it provides excellent control over the heat input.

Overall, the choice of welding technique for 31803 duplex stainless steel will depend on the specific application and the required properties, such as strength, corrosion resistance, and aesthetic appearance. It is important to select the right welding technique and parameters to ensure that the welds are strong, durable, and corrosion-resistant.