What type of joint creates a gas-tight seal through the melting of materials at high temperature?

The correct answer is that a welded joint creates a gas-tight seal through the melting of materials at high temperature. Welding is a process that involves the joining of metals by melting them together, which typically occurs at temperatures that can reach or exceed the melting point of the base materials. This high-temperature method allows the materials to bond seamlessly, resulting in a very strong joint that is impervious to gas or liquid leaks.

Welded joints are commonly used in various mechanical applications, especially where structural integrity and pressure containment are critical—such as in pipelines, pressure vessels, and structural metalwork. The molten material fuses and, upon cooling, solidifies to form a durable connection, engineered to withstand high-pressure environments without allowing leakage.

In contrast, the other methods listed involve different processes: brazed joints rely on a filler metal that has a lower melting point than the base metals, soldered joints utilize a low-temperature filler to join electrical components or sheet metal, and plastic heat fusion joints involve the heating of thermoplastic materials to fuse them without reaching the melting point. Each of these processes creates a bond through different mechanisms, often without achieving the same level of pressure resistance or gas-tightness as a welded joint.