Full penetration welds are required for which type of joints?

• A. Pressure-retaining joints
• B. Cosmetic joints
• C. Temporary seals
• D. Non-pressure piping joints

Answer: (A)

Full penetration welds are required for joints that must contain pressure. When a weld goes through the entire thickness of the joint, there is no through-thickness path where leakage or a failure could start, providing the full strength and leak-tightness needed for pressure-retaining components. If the weld only partially penetrates, lack of fusion or a through-thickness flaw could allow leakage or failure under internal pressure, which is unacceptable for vessels or piping that must hold pressurized contents.

Cosmetic joints are designed mainly for appearance and do not need the structural guarantees required for pressure containment. Temporary seals are meant to be removable or replaceable, often using gaskets or other sealing methods rather than a full-thickness weld. Joints in non-pressure piping may not be subjected to internal pressure, so they do not inherently require full penetration to meet strength requirements.