Why do Stainless Steel Pressure Vessels have Rounded Ends?

Stainless steel pressure vessels have rounded ends as part of their design so they can safely contain their high pressure contents. Pressure applies a force over the entire surface area of the vessel. Rounding the ends prevents stress from building up like it would at a sharp corner. It’s one of many design choices that make pressure vessels strong and reliable.

Why are sharp corners bad for pressure vessels?

Pressure vessels are made from a sturdy, flexible material like stainless steel formed into a cylinder with rounded caps on either end. They can withstand pressure applied internally by a fluid, or externally if the inside is put under vacuum.

The forces applied on the vessel walls spread throughout the material, evenly distributing the load. If the load is concentrated in the material, that small portion of the wall will experience a much higher force than the areas around it, and the material is much more likely to deform or crack.

Sharp corners are notoriously bad for evenly spreading out stress in a material, since the forces meeting at the corner will push against each other instead of moving past each other or canceling each other out. To make matters worse, corners often are made with welds, which can further concentrate stresses.

How do welds impact stainless steel pressure vessels?

Welding metal pieces involves applying a filler metal and heating a small area to join the pieces together. With stainless steel welds, it’s important to have them performed by experts that can match the right filler metal to the type of stainless steel used and know how to handle the heat distribution in the metal.

Mismatched filler metals will have different material properties than the rest of the vessel, so the weld won’t respond the same to an applied pressure. This creates a stress concentration in the weld.

Heating the material while creating the weld can also cause the piece to warp and even locally change the material properties if not done by a professional.