Where are single-welded lap joints permitted according to API 650?

• A. On vertical plates only
• B. Bottom and roof plates
• C. Only in internal structures
• D. On transition plates

Answer: (B)

Single-welded lap joints are permitted on bottom and roof plates according to API 650 due to considerations regarding structural integrity and the specific pressures and forces that these areas experience. The allowable single-welded lap joints in these locations provide a practical solution for joining sections of material while allowing for reasonable tolerances in construction.

In the context of bottom and roof plates, the design calls for effective sealing of the tank while minimizing the potential for leaks, as these are critical areas susceptible to environmental exposure and fluid retention. The single weld can provide adequate strength, provided that the design meets the relevant code requirements and that proper welding practices are upheld.

Other locations, such as vertical plates or transition plates, often have different performance requirements and stress distributions, which can lead to increased risks of failure if single-welded lap joints were utilized instead. Thus, the preference for bottom and roof plates reflects the balancing of structural performance with construction feasibility outlined in the API 650 guidelines.