In a pressure vessel, what is a type 2 weld joint?

A type 2 weld joint refers specifically to a single-welded butt joint that includes a backing strip. This type of joint is characterized by its structural integrity and is used in pressure vessels to ensure a strong, leak-tight connection between two pieces of material. The single-welded butt joint configuration allows for effective welding across the thickness of the material, with the backing strip providing support during the welding process and ensuring proper fusion of the weld material to the base metal.

The use of a backing strip is significant because it helps to prevent defects such as undercutting and allows for better control over the weld penetration. In pressure vessel applications, which operate under high pressure, it's crucial that the welds are designed to resist stress and potential failure. A single-welded butt joint with a backing strip meets these requirements effectively, making it suitable for pressure vessels.

The other options described different types of weld configurations that do not correspond to the definition of a type 2 weld joint. Each of those alternatives serves different purposes or applications, but only the configuration involving a single-welded butt joint with a backing strip aligns with the characteristics that define a type 2 weld joint in the context of pressure vessels.