Which fastener type is most commonly used in boiler construction?

• A. Welded
• B. Bolted
• C. Riveted
• D. Threaded

Answer: (D)

In boiler construction, joints must be strong and leak-tight to handle high pressure and heat. Welding is the main method used because it creates a continuous metal bond across joints, giving uniform strength and eliminating gaps through which steam could leak. This approach also provides smoother interior surfaces and better stress distribution, which are crucial for pressure vessels and reliability under demanding conditions.

Bolts and threaded fasteners come into play mainly where parts must be removable or reworked, such as flanges, gaskets, manways, or access doors. Riveting was common in older boilers, but modern practice has largely moved away from rivets in favor of welding for the shell and major joints. So, the most common approach for the boiler shell and major joints is welding, with bolts and threaded fasteners used to connect removable components rather than form the primary joint.