For annular plates thicker than 1/2", what is the requirement for the weld size in relation to the shell plate thickness?

• A. The weld size must be equal to the shell plate thickness
• B. The weld size must exceed the shell plate thickness
• C. The weld size should match the annular-plate thickness but not exceed the shell plate thickness
• D. The weld size should be half the annular-plate thickness

Answer: (C)

The correct choice indicates that for annular plates thicker than 1/2", the weld size should match the thickness of the annular plate but must not exceed the thickness of the shell plate. This requirement aligns with the general practice in tank design where weld sizes are determined based on the thickness of the components being joined.

In this case, ensuring that the weld size matches the annular plate thickness ensures adequate strength and integrity in the welded joint. Furthermore, it is important that the weld size does not exceed the shell plate thickness to avoid over-welding, which could lead to unnecessary material stress and potential defects in the weld joint.

This balance in sizing helps maintain the structural integrity of the tank and ensures that the welded areas can withstand the operational pressures without compromising safety or performance. It reflects the principles outlined in API 650 for creating reliable and resilient welded tanks for oil storage.