Which of the following processes is not suitable for the construction of boilers?

Soldering is not suitable for the construction of boilers primarily because it does not provide the strength and durability required for high-pressure applications. Boilers operate under significant pressure and temperature conditions, necessitating joints and materials that can withstand these stresses without failure.

Welding, on the other hand, creates strong and robust joints by melting the base metal and allowing it to cool, forming a solid connection that can handle high pressures. Similarly, brazing, which involves joining materials using a filler metal melted at a lower temperature than that of the workpieces, is also commonly used in high-pressure applications and can provide sufficient strength when done properly. Forging is a process used to shape metals and may be involved in creating certain boiler components but does not pertain directly to joining materials in the same context as welding, soldering, or brazing.

Thus, soldering, which typically uses a lower melting point filler material and is often employed in low-pressure systems or for electronic connections, is inadequate for the stringent requirements of boiler construction.