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

Solution (By Examveda Team)

Option A: Electrical Resistance Welding: This method is generally used for thinner materials.
It wouldn't be practical or efficient for such a thick plate because generating enough heat to fuse the entire thickness evenly would be extremely difficult.

Option B: Electroslag Welding: This is the MOST SUITABLE option.
Electroslag welding is specifically designed for welding THICK materials in a SINGLE PASS.
It uses a molten slag to protect the weld pool and allows for deep penetration, making it ideal for joining these boiler drum plates.

Option C: Plasma Torch Welding: While plasma welding is precise, it's typically used for THINNER materials or for specialized applications where high precision is needed.
It can be used on thicker materials with multiple passes, but it's not the most efficient for this application.

Option D: Submerged Arc Welding: Submerged arc welding is also suitable for welding THICKER materials, but usually requires multiple passes.
While it could potentially be used, electroslag is generally preferred for very thick sections like 20 cm because of its single-pass capability, which reduces time and potential defects.

Therefore, the best answer is B: Electroslag.