Title: /
Foam Dam Clarification
Date: / November 13, 2012Contact: / Name: / MarilynShores
Company: / Explorer Pipeline
Phone: / 918-493-5178
E-mail: /
Purpose: / To allow commercially available (carbon, galvanized or stainless steel) foam dams to be bolted onto floating roofs
Source: / Larry Hiner’s email
Revision: / 10
Impact: / Authorizes a practice that was inadvertently disallowed (but continues to be installed at owner/operator’s request).
Background: / The 11th Edition added the sentence: “The dam shall be attached to the top deck plateby a continuous fillet weld on the foam side.”
Proposal: / Add further details for foam dams
Rationale: / Bolted-on foam dams cause less interference with other components on the floating roof than welded dams and can be moved out of the way for seal inspections or other work.
Since most bolted-on dams are galvanized or stainless steel, there is no corrosion issue. For corrosive atmospheres, replacement of the welded dam is more difficult.
Proper recognition of the potential of water entering the pontoons through deteriorated seals around the bolt holes caused them to be prohibited.
NFPA asked API to submit our recommendation during the open solicitation timeframe. We will do so, but there is no assurance that it will be adopted. Also, their next issue is not due to be published (with or without stainless steel dams) until 2014. It should be noted that their documents are not mandatory nor are they international.
Therefore, the information presented in NFPA 11 is transferred to this standard and the reference to NFPA dropped. This also makes our document more complete, rather than forcing users to look elsewhere for this information.
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C.3.15.2 Foam Dams
A foam dam, if specified on the Data Sheet, Line 32, shall be installed on top plates of pontoon or roof deckat least 300 mm (12 in.) but no more than 600 mm (24 in.) from the tank shell to contain foam fire-fighting solution. The foam dam shall be a minimum of 300 mm (12 in.) high and extend at least 50 mm (2 in.) above the lower of the secondary seal or any burnout panel, measured at its highest contact point with the shell. The foam damshall be fabricated from 10 gauge (0.134 in.) or thicker steelplate with support braces installed on the side of the foam dam closest to the center of the tank at a circumferential spacing of approximately 1.5 m (5 ft) on center. Bottom of plate shall have 10-mm (3/8-in.) slotted weep holes. 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.
C.3.15.2 Foam Dams
A foam dam, if specified on the Data Sheet, Line 32, shall be designed to retain foam at the seal area, at a depth to cover the seal area while causing the foam to flow laterally to the point of seal rupture. The top of the foam dam shall beat least 300 mm (12 in.) but no more than 600 mm (24 in.) from the tank shell. The foam dam shall be a minimum of 300 mm (12 in.) high and extend at least 50 mm (2 in.) above the secondary seal, a combustible secondary seal using a plastic-foam log, or any burnout panel, measured at its highest contact point with the shell.
The foam damshall be fabricated from 10-gauge (0.134in.) steel, 18-gauge (0.050 in.) stainless steel, or other sufficiently fire resistantmaterial. Support braces shall be installed on the side of the foam dam closest to the center of the tank at a circumferential spacing of approximately 1.5 m (5 ft.) on center, but do not need to be welded to the floating roof and should not be permanently affixed.
A bolted foam dam shall be attached to the outer rim, the rim angle, or to an angle that has been welded to the deck or pontoons. A welded foam dam shall be installed on the top plates of the pontoon or roof deck.The angle for attaching a bolted foam dam or any welded foam dam to the deck or pontoonsshall be continuously welded on the foam side.
To allow drainage of rainwater, the foam dam bottom or attachment angle shall be slotted on the basis of 278mm2 of slot area per m2 of dammed area (0.04 in2 of slot area per ft2 of dammed area), with a maximum drain slot heightof 9.5 mm (3/8 in.). Bolts should not penetrate the deck or pontoons.
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