Final answer:
A double-V edge preparation is specified in welding for reducing distortion, improving penetration and fusion, and increasing the strength of the joint.
Step-by-step explanation:
A welding procedure might specify a joint with a double-V edge preparation for several reasons. This type of joint preparation is often used because it can help to reduce distortion in the finished weldment. This is because the weld volumes are more evenly distributed on both sides of the joint, which helps to balance the heat input and reduce the uneven expansion and contraction that can lead to warping. Additionally, a double-V joint allows for better penetration and improved fusion at the root of the joint, as access for the welding process is easier than in a single-V joint. These factors contribute to the overall increased strength of the joint, making a double-V edge preparation a valuable choice in certain applications.