Which type of joint is not allowed for copper or copper alloy tubing used for fuel oil?

• A. Soldered
• B. Flared
• C. Compression
• D. Welded

Answer: (D)

When copper or copper alloy tubing is used for fuel oil, joints must seal reliably without creating heat-affected damage to the tubing. Welding copper introduces a lot of heat, which can distort or anneal the thin-walled tube and create a weld zone that’s prone to leakage or failure. The crack- or distortion-prone welds are hard to inspect and test in a fuel-oil system, and codes restrict this practice for copper tubing used in fuel lines. Instead, soldering or brazing (using appropriate filler metals) and mechanical joints like flared or compression provide tight, durable seals at lower temperatures, preserve the tube’s integrity, and are approved for these applications.