Welding Process Requirements for Nickel-Plated High-Pressure Reactors

　　Nickel-based materials are highly resistant to corrosion by strong alkaline substances. They can be fusion-welded to carbon steel, low-alloy steel, high-alloy steel, as well as other grades of nickel and nickel alloys, and can also be used for surfacing welding on their surfaces. The specific welding procedures have the following requirements:

　　1. For the fusion welding of nickel and nickel alloy linings in high-pressure reactors, tungsten inert gas (TIG) welding and metal inert gas (MIG) welding are commonly used. Plasma welding can also be employed, as can arc welding and submerged arc welding.

　　2. When welding nickel alloys containing chromium or molybdenum onto the inner wall of a high-pressure reactor, it is essential that the weld joints exhibit excellent resistance to intergranular corrosion in their post-weld condition. Therefore, tungsten inert gas (TIG) welding, metal inert gas (MIG) welding, or plasma welding should be used whenever possible; alternatively, shielded metal arc welding (SMAW) may also be employed.

　　3. For the connection between the tube and tube sheet in tubular heat exchangers, welding is recommended; it is advisable to use other shielded welding processes with filler metal.

　　4. To reduce the susceptibility of nickel alloy weld joints to intergranular corrosion in the post-weld condition, it is recommended—starting from the second weld pass during multi-pass welding in high-pressure reactors—to employ forced water cooling on the back side of the weld bead.

　　5. When using nickel-alloy welding wires, it should be noted that certain nickel-molybdenum alloys and some nickel-chromium-molybdenum alloys are not suitable for submerged arc welding.

　　6. When using nickel and nickel alloy welding electrodes, note that nickel-molybdenum alloys and certain nickel-chromium-molybdenum alloys are suitable only for flat welding.