External Floating Roof 1. Verify that the top of the roof has a minimum slope of 1:64. If the slope is less than 1:64, the roof is unsatisfactory. 2. Verify that the deck of a pontoon type roof will be in contact with the liquid during normal operation. 3. Verify that the deck plates are joined by continuous full-fillet welds on the top side. Confirm that full-fillet welds that are at least 50 mm (2 in.) long on 250 mm (10 in.) centers are used on the underside of any lap plates that are located within 300 mm (12 in.) of stiffening girders or support legs. 4. Verify that vendor calculations confirm the roof has sufficient buoyancy to remain afloat when the tank contains a liquid with a specific gravity of 0.7 under the following conditions: •
• •
250 mm (10 in.) of rainfall in a 24 hour period, with the- roof intact. However, doubledeck roofs w i t h emergency drains that are designed to prevent the stored liquid from flowing onto the roof may be designed for a lesser rainwater volume as determined by the- drain sizing. In single-deck- pontoon roofs, single-deck and any two adjacent pontoon compartments punctured with no water or live load. In double-deck pontoon roofs, any two adjacent compartments punctured with no water or live load.
If sufficient buoyancy does not exist, the roof is unsatisfactory. 5. Verify that vendor calculations confirm that the pontoons of single-deck roofs will not be permanently distorted under the loads that are specified in Step 4 . Also confirm that the roof sag will not permit any stored liquid to get on the roof through any roof penetrations (e.g. leg sleeves or vents). 6. Verify that each pontoon compartment has a liquid-tight man way. The top edge of the man way necks must be at an elevation that prevents liquid entry into the compartment under the conditions specified in Step 4 . If the man ways are not provided or are inadequate, the roof is unsatisfactory. 7. Verify that each pontoon compartment has vents that protect against internal or external pressure. The ve.nts must be at a level that preve.nts liquid entry into the compartment under the conditions specified in Step 4. If the vents are not provided or are inadequate, the roof is unsatisfactory. 8. Verify that a ladder has been provided that automatically adjust to any roof position. If the ladder is a rolling ladder, verify that it has full-length handrails on both sides and has been designed for a 454 kg (1000 lb.) mid-point load with the ladder in any operating position. If a ladder is not provided or is inadequate, the roof is unsatisfactory. 9. Verify that roof drains are adequate to prevent backflow of stored liquid in case of drain pipe leakage, and to prevent the roof from accumulating a water level greater than design at the
maximum rainfall rate when the roof is floating at the minimum operating level. Verify that a check valve is installed in the drain line at the roof sump to prevent backflow. The drain size must be at least 76.2 mm (3 in.) for roofs that are no larger than 36.6 m (120ft.) in diameter, and at least 101.6 mm (4 in.) for roofs that are larger than 36.6 m (120ft.) in diameter. If the drains are not provided or are undersized, the roof is unsatisfactory. 10. Verify that adequate automatic bleeder vents and rim vents are provided to prevent overstressing of the roof deck or seal membrane. Vents that are capable of evacuating air and gases from underneath the roof during initial filling must be provided. If the ve.nts is not provided or is inadequate, the roof is unsatisfactory. 11. Verify that roof support legs are provided. The support legs must be capable of supporting the roof and a uniform live load of 122 kg / m2 (25 lb / ft2). The length of the legs must be adjustable from the top of the roof. The low-leg position must provide at least 2 m (6.5 ft.) clearance between the lowest portion of the roof and the tank bottom. All tank appurtenances must be cleared by the roof in its lowest position. If the support legs are not provided or are inadequate, the roof is unsatisfactory. 12. Verify that at least two roof manholes with a minimum inside diameter of at least 610 mm (24 in.) have been provided. Verify that all roof manholes that were specified in the purchase specification are provided. If the manholes are not provided or are inadequate, the roof is unsatisfactory. 13. Verify that an adequate sealing device is provided between the periphery of the roof and the tank shell. If the device is not provided or is inadequate, the roof is unsatisfactory. 14. Verify that all bulkheads and rims inside the pontoon or double-deck roofs are continuously welded along their upper edges to the top deck plates. 15. Verify that inlet pipes have been equipped with diffusers, if specified in the purchase specification. 16. Verify that roof centering and anti-rotation devices have been provided. 17. Verify that the additional requirements that are contained in Appendix C of 32-SAMSS005 are satisfied. 18. If an external floating roof has been satisfactory in all steps to this point, the roof is satisfactory for the purposes of this Work Aid. 19. For internal floating roofs, verify the design complies with API-650, Appendix-H.
20. Construction Requirements a) Approximately 200 mm free space must have between external floating roofs and the shell, where the seal will be mounted. The modern seals assure good jam and normal work when the distance between shell and roof is from 100 to 300 mm.
b) Minimal thickness of the steels in the pontoons in the membrane is 5 mm.
(tr > 5 mm) c) The maximal distance between the roof supports of the floating roof must not be bigger than 1000 x tr (thickness of the membrane) d) Distance from roof supports to welding joint in the membrane is not smaller than 300 m m e) W hen there are the girders stiffening the membrane, roof supports must be put in the area in this stiffening. f) The length of the supports is different depending on its status: - during the exploitation- minimal height must grant the tank filling without the liquid jet to touch the vertical board. It is unacceptable that the floating roof in its lowest position to lie upon the technological facilities; - during the repairing works on the tank - the minimal distance depends on considerations for easy doing of the repairing works. It is assumed to be 1800 mm in the lowest point of the roof. g) The floating roof, stepped through its supporting constructions on the bottom or when floats on the liquid must have the slope toward the roof drain not less than 1:100. For insider roofs this slope have not be considered. h) Upon the floating roofs must be constructed foam dam which height must not be less than 300 mm at 1 m from shell of the tank. i) For fixing the roof according to the design conditions the antirotation devices must be considered. They do not allow the rotation of the roof. They must bear the horizontal forces, caused by the rolling ladder, by the uneven load from snow, by wind and by rotation of the stored product when it is mixed or the tank fills. j) The drain pipe must have the diameter not smaller than 3" for the tank which have the diameter D < 36 m. The drain pipe must have the diameter not smaller than 4"for the tanks which have the diameter D > 36 m. k) The pontoons situated on the periphery must be separated by waterproofed barriers and every pontoon must have manhole for inspection. l) In the central part of the roof must have one manhole for inspection, through which people can go to the roof when the roof is in its lower position and the tank is empty.
