Rim Seal Foam Dam

[KiwiTanks]

My questions are in 2 parts...
We are constructing a 32m dia floating roof tank to API650, with fire protection to NFPA11.

Part 1
NFPA11 Table 5.3.5.3.1 indicates spacing between the foam discharge outlets depending on the 'foam dam'. It is not clear if the measurements for the foam dam are for the height (as per 5.3.5.4.3.1 & 2), or the distance from the shell (as per 5.3.5.4.4).

To minimise the number of foam pourers, we would like to go for the "610mm Foam Dam". However this leads in to the next part...

Part 2
For construction constraints adding a 610mm high dam will make transportation of bulkheads to the site difficult, and welding them on on-site will add precious days we don't have in the time line (welding, blasting, painting etc).
Therefore the contractor has asked if they can bolt on the dam.
In API650 it states that the bottom edge of the dam must be seal welded to the pontoon (Not sure if NFPA has this). The contractor wants to weld on a small dam about 150mm high, (welding, blasting, painting etc in the shop), and later on, bolt on the remainder of the dam. Is it acceptable to do this?

From an Inspection point of view I don't like the detail as it will promote corrosion, and bolts to maintain etc, but for Construction this would be beneficial.

 

[IFRs]

Do you have an internal or external floating roof?

Per API 650 Section H.5.9 (internal floating roofs): "A foam dam, if specified on the Data Sheet, Line 32, shall be fabricated and installed in compliance with NFPA 11."

Per API 650 Section C.3.15.2 (external floating roofs) "The dam shall be attached to the top deck plate by a continuous fillet weld on the foam side. See NFPA 11 for additional information regarding foam dams."

NFPA says: "The foam dam shall be welded or otherwise fastened to the floating roof."