What is a characteristic of a diagonal stay?

A diagonal stay is characterized by its design to support a boiler's shell and maintain structural integrity under pressure. The correct choice indicates that it is made of flat material similar to the boiler shell. This flat material is essential because it closely matches the shell's structural characteristics, allowing for effective load distribution and support.

Using flat material helps align with the stresses experienced in the boiler, enhancing its ability to withstand pressures and prevent structural failure. It forms a diagonal structure that helps manage the lateral forces acting on the boiler, further promoting stability.

In contrast, stays made from round material would not offer the same effective surface area for load distribution. Additionally, being attached at right angles to the boiler shell is a characteristic of other types of stays rather than diagonal stays, which are typically oriented at an angle to provide enhanced support. Lastly, while welded joints may be present in some designs, a diagonal stay can also incorporate bolted joints or other forms of connection, making the notion of only welded joints too restrictive.