11.1 Cladding to Provide a Corrosion-Resistant Layer

The application of stainless material to a lower alloy steel is an economic method of producing reactor pressure vessels or pressure vessels for such applications as the chemical industry, where a thick-walled vessel is needed with internal corrosion protection. There are several different welding methods that can be used:

• Submerged arc welding using a solid wire electrode, often Twin Arc double wire, or using a flux cored wire.

• Submerged arc welding using a broad but thin strip electrode.

• Strip electrode welding with a flux that enables the process to be carried out using the electroslag principle, i.e. without an arc, but with the heat being generated by resistance heating in the molten slag. See "Electroslag welding" on page 93

• Plasma cladding.

• Thermal spraying: see Page 110.

The aim is to achieve a sound weld, but with little melting of the underlying material. In this respect, the electroslag method is preferable to ordinary submerged arc welding, as it penetrates less into the substrate material and so results in less mixing of the weld metal. Several of the ordinary submerged arc welding methods can of course be used, but it may be necessary to apply two or more layers until a sufficiently pure layer of weld metal is produced.

Cladding is often performed by mechanised methods, as there are often larger areas to be covered.

11.2 Hardfacing

Application of high-abrasion-resistance alloys by welding is a method of repairing machine parts or other metallic items that...