A tank should not be gauged when the roof is in the critical zone. If this situation occurs, inform the person in charge at the terminal and request product be pumped into or out of the tank so that the liquid level is no longer in the critical zone. Alternately, request the use of another tank. If these requests cannot be met, contact your supervisor for further instructions. If the displacement of the floating roof increase due to accumulations of water, snow or ice, it will be necessary to remove or estimate the additional weight. For custody transfer, if water snow or ice cannot be removed, it is best to keep the same conditions for both opening and closing, if possible.
From a measurement perspective, they are both accounted for in the same manner. The floating roof will displace a certain volume of liquid, equal to its own weight. This displacement must be accounted for. We will review how this is done in the "calculation" section. 3.2.7.1 Critical Zone Floating roofs have supports or legs that support the roof , approximately three to six feet off the tank floor, when the tank is empty or nearly empty. When the roof is fully afloat, none of the roof supports are touching the floor of the tank, then a roof correction will apply. When the roof is fully supported on its legs, no liquid is touching the roof, then a roof correction will not apply. The zone between that point where the roof supports are just touching the tank floor, yet the roof is still fully supported by the liquid; and that point where the roof is fully supported on its legs and the liquid is touching but not supporting the roof, is called the critical zone. The section of the tank that forms the critical zone is clearly marked on the tank's capacity table.
66,378.17 9
43,472.42
20,573.27
9
9
66,105.52 10 43,199.69 10 20,300.88 65,832.87 11 42,926.96 11 20,028.49 65,560.23 39 42,654.23 46 19,756.10
10 11 53
65,287.58 1 65,014.93 2 64,742.29 3 64,469.64 4 64,196.99 5 63,924.35 6 63,651.70 7 63,379.05 8 63,106.41 9
42,381.50 42,108.77 41,836.04 41,563.31 41,290.58 41,017.85 40,745.12 40,472.39 40,199.66
19,483.71 19,211.32 18,938.93 18,666.54
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
18,394.10 18,121.66 17,849.22 17,593.28 17,334.33 17,072.39 16,807.45 16,539.51 16,268.57 15,996.14 15,723.71
62,833.76 10 39,926.93 10 62,561.11 11 39,654.20 11 62,288.47 40 39,381.47 47
10 11 54
62,015.82 1 61,743.17 2 61,470.53 3 61,197.88 4 60,925.23 5 60,652.59 6 60,379.94 7
39,108.74 38,836.01 38,563.28 38,290.55 38,017.82 37,745.09 37,472.36
1 2 3 4 5 6 7
1 2 3 4 5 6 7
15,451.28 15,178.85 14,906.42 14,633.99
38
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