__________ welding will be the most suitable for butt welding two 20 cms thick boiler drum mild steel plates.

ANS:B - Electroslag

Electroslag welding (ESW) is a welding process that is particularly well-suited for joining thick sections of materials, typically steel plates. It is a method that falls under the category of fusion welding processes. Electroslag welding is characterized by the creation of an electric arc between a consumable electrode and the workpiece, which melts the electrode and a portion of the workpiece, forming a weld pool. Here's a simplified explanation of the electroslag welding process:

1. Preparation: The two workpieces to be welded are aligned and prepared with a small gap between them. The joint area is usually cleaned to remove any contaminants.
2. Electrode placement: A consumable electrode, typically a long, cylindrical metal rod, is fed into the gap between the workpieces. The electrode is positioned vertically or nearly vertically.
3. Flux application: A layer of flux material is applied over the joint area and the electrode. The flux serves multiple purposes, including providing a protective atmosphere, controlling the weld pool, and promoting the formation of a slag layer.
4. Arc initiation: An electrical arc is initiated between the electrode and the workpieces. This arc heats the electrode, causing it to melt and create a pool of molten metal. The intense heat generated by the arc melts the flux, creating a conductive slag layer.
5. Electroslag process: As the electrode melts, droplets of molten metal fall into the weld pool. The slag layer floats on top of the weld pool, protecting it from atmospheric contamination and regulating the cooling rate. The electrode is continuously fed into the weld joint as the process progresses.
6. Weld completion: The welding process continues until the desired weld length is achieved. Once the weld is completed, the slag layer is removed, and the weld joint may undergo further post-weld treatments as needed.

Electroslag welding is known for its high welding speeds and excellent penetration capabilities, making it particularly suitable for joining thick steel plates in applications such as shipbuilding, bridge construction, and pressure vessel fabrication. It is often favored for its efficiency in welding thick materials, although it requires specialized equipment and careful control of process parameters.