AWS WHC-4.06:2010

Clad and Dissimilar Metals
Scope : Clad metals are laminar composites consisting of a metal or alloy, with a metal or alloys of different chemical composition applied to one or more sides by welding casting, drawing, rolling, surfacing, chemical deposition, or electroplating. In this chapter, the term dissimilar metal refers to the welding of chemically different metals (for example, aluminum, copper and nickel) or microstructurally different alloys of a particular element (for example, carbon steel and stainless steel). Dissimilar metal combinations comprise one or more base metals and one or more filler metals that make up the final weld metal after melting and mixing during welding. A series of weld metals that vary significantly in composition may exist within a single welded joint; each weld bead may have individual compositional characteristics.1, 2 Combining dissimilar metals in a weldment allows the use of the best properties of each metal, and serves the special requirements of industries such as aerospace, power generation, petroleum, chemical, pharmaceutical, transportation, mining, and other industries. The welding of clad and dissimilar metals is especially important when the weldment is to be used in corrosive applications or is exposed to thermal cycles during service. An example of an application in a corrosive atmosphere is shown on the cover page of this chapter, a deepwater subsea pipeline manifold. Manifolds are fabricated using high-strength low-alloy forgings and piping from materials such as heat treated AISI 4130, AISI 8630, and F22 chrome-molybdenum steels. In many cases these materials are clad on the ID surfaces with a corrosion-resistant alloy and then joined together using special welding techniques to prevent degradation of strength, toughness, and corrosion resistance. These manifolds are designed to withstand high internal pressure, external pressure, internal corrosive fluids, external sea water exposure and expected to remain in service without maintenance for up to 25 years. The information in this chapter addresses the fusion welding of clad and dissimilar metals. It does not address joining methods, such as brazing, in which there is insignificant alloying between the base metal and the added weld metal. The use or application of the techniques and guidelines presented in this chapter requires sufficient engineering, prefabrication testing, and fabrication controls to confirm in advance that the specific application requirements will be met by the completed product.