Welding of duplex alloys like UNS 31803 is not difficult but it is different than welding austenitic stainless steels like 316L. Control of the ferrite content is important in maintaining the expected corrosion resistance and mechanical properties. Well defined welding procedures will define heat inputs and cooling rates to achieve weldments with optimum ferrite to austenite ratios. Most duplex welding procedure qualification tests include ASTM A923 Method B or C to determine if any intermetallic phases or precipitates were formed and a ferrite measurement by the point count method or an electromagnetic measuring method. Suppliers of duplex alloys are a good source of welding information. Another fine resource is the article "Duplex Stainless Steel Welding: Best Practices," by Messer, Oprea, and Wright published in Stainless Steel World, December 2007 (pg 53-63). This article is available free on-line at the Stainless Steel World website (http://www.stainless-steel-world.net).