Duplex Steel S31803 Elbow Butt Weld Fittings are stainless steel, a type of stainless steel designed to improve resistance to pitting, high strength, stress corrosion, crevice corrosion and cracking. Duplex steel S31803 tee butt welded pipe fittings are often used in chemical process industries: such as sulfuric acid production, nitric acid process, phosphoric acid process, ethylene oxide, polypropylene production, PVC, equipment for handling organic and fatty acids, chemical storage and tankers, thermal switch, etc.