Fixed roof oil storage tank rafter to roof plate weld 1

[Andrewstructure]

I am working on a 150' diameter, 40' tall fixed roof oil storage tank. The roof structure consists of W12 girders, forming an octagon in the middle of the tank radius. W12 rafters bear on the girders in a radial pattern, with steel plate bearing on the rafters.
Does API require the plate be welded to the rafters?

 

[JStephen]

No.
That is sometimes done for corrosion/ coating purposes. Sometimes, external rafters are used for the same reason.
If welded, that is a consideration in the selection, design, and layout of rafters and roof plate, not usually just a matter of throwing a weld on an otherwise unwelded seam.

 

[Geoff13]

See clause 5.10.2.3. Roof plates are only welded to the rafters when approved by the Purchaser (likely for lining) but then the roof is non-frangible.

However if lining is required, then you should reconsider if a supported cone roof is a cost-effective solution. Pretty much impossible to properly seal weld the entire framing system for good paint continuity (roof plate underside laps, rafters to roof plate, rafters to girders, girders to columns, etc, etc).

 

[IFRs]

W12 seems to be a very small girder, especially for a 150 foot tank with a single circle of eight columns.