Which joint uses heat to join or fuse materials?

• A. Solvent Weld
• B. Fusion
• C. Threaded
• D. Flanged

Answer: (B)

Heat fusion is the process of joining thermoplastic materials by heating the surfaces until they soften and fuse when pressed together, then cooling to form a solid bond. This is how a fusion joint works: pipe and fitting ends are heated to the correct temperature, pressed to meet, and allowed to cool, producing a bond as strong as the pipe itself. It's widely used in irrigation systems with plastics like HDPE because it yields a continuous, leak-free joint without needing solvents or mechanical helpers. Other methods—solvent weld relies on a chemical solvent to soften surfaces to fuse them without heat; threaded joints depend on engaged threads and sealing compounds; and flanged joints use a gasket and bolts—do not use heat to join the material.