Which type of joint is primarily used for seams in all riveted boiler shells?

The correct answer is a lap joint, which is primarily used in seams for riveted boiler shells due to its structural advantages and ability to handle various stresses. In a lap joint, two pieces of material overlap one another, allowing for a large surface area that can be effectively secured with rivets. This design enhances strength and helps to distribute the load across a broader area, reducing stress concentrations that might occur with other joint types.

Riveted lap joints are especially suitable for the high-pressure environments found within boiler shells. The overlapping sections create a robust seal that minimizes the risk of leaks and ensures that the boiler can contain steam and high-pressure water efficiently. The joint's configuration also provides accessibility for riveting, which is essential during the assembly of the boiler.

In contrast, while butt joints, screwed joints, and welded joints each have their own applications and advantages in different contexts, they are not typically used for riveted seams in boiler shells. Butt joints can require more precise alignment and often need additional reinforcement to manage the stresses involved. Screwed joints might not provide the necessary strength under high pressure and temperature conditions, and welded joints, although strong, may introduce issues with material integrity due to welding heat affecting the surrounding metal properties. Therefore, the lap joint is