API CODE IS NOT GIVING ELABORATE DESIGN GUIDELINES FOR ROOF. SECTION 3.10.1 (C)DEFINES THAT THE SELF-SUPPORTING DOME ROOF IS SUPPORTED ONLY AT ITS PHERIPHERY. HOWEVER THE SUPPORTED ROOF IS DEFINED THAT THE ROOF WHICH IS SUPPORTED EITHER BY RAFTERS/ GIRDERS / COLUMNS.

CONSIDER A LARGE DIAMETER DOME ROOF TANK (SAY AROUND 40 METERS) WHICH IS NECESSARILY TO BE SUPPORTED WITH A SYSTEM OF RAFTERS AND GIRDERS AND IT IS IMPOSSIBLE TO FABRICATE THE DOME WITHOUT RAFTERS/ GIRDERS. WITH THIS SCENARIO, THE CLAUSE 3.10.6 OF API 650 IS NOT APPLICABLE FOR THE ROOF MINIMUM PLATE THICKNESS? OR THE DOME ROOF CAN BE DESIGNED AS PER CLAUSE 3.10.6.1?

I REQUEST CLARIFICATION ON THIS POINT.

I suggest you send your query directly to the API code committee, and get an opinion directly from them.