The American Petroleum Institute published Chapter 12, Section 1, Part 1 of its Manual of Petroleum Measurement Standards titled, “Calculation of Static Petroleum Quantities – Up- right Cylindrical Tanks and Marine Vessels” in 1996.
This standard has introduced a significant change in how shore tank quantities are calculated.
The New Correction Upright cylindrical tanks have capacity tables based upon a specific tank shell temperature which is usually 60°F in USA. If the actual tank shell temperature differs from the capacity table tank shell temperature, the volumes extracted from that table will need to be corrected, accordingly.
Determining the shell expansion factor is a three step process;
- calculate the temperature of the tank shell,
- determine the correction and
- apply the correction.
- Calculate the Temperature of the Tank Shell:
On a non-insulated tank this is done by adding 7/8 [0.875] of the product temperature to 1/8 [0.125] of the ambient air temperature and then rounded to the nearest degree.
- Determine the Correction:
For mild steel tanks that were calculated using a tank shell temperature of 60°F, this can be easily achieved by entering the table in Appendix “B1” of the new standard with the temperature of the tank shell. The factor can be read directly from the table.
The “Appendix B” table of correction factors will apply in most situations; however, tanks that contain heated products often have capacity tables that were calculated using a tank shell temperature other than 60°F. Alternately, tanks containing specialty products such as corrosive chemicals may be constructed from something other than mild steel, such as stainless steel. In this case it will be necessary to use the formula found in section 9.1.3 of the new standard to calculate the correction factor. This formula is:
CTSh = 1 + 2α∆T + α2 ∆T2
Where:
α = Linear coefficient of expansion of the tank shell material
∆T = Tank Shell Temperature (TSh) minus Base Temperature (TB)
The Base Temperature (TB) is the tank shell temperature for which the capacity table volumes were calculated to.
- How to apply the factor:
The correction must be applied to the table volume after it has been corrected for free water; and, before any correction is made for the floating roof, if applicable.
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Are your expeditor(s) and independent surveyor(s) aware of this API procedure?
Have they been using it for determining the final out-turn figures in order to ascertain the cargo quantity more accurately and to reduce the “paper” losses?
Are they aware about taking the ambient temperature accurately and correctly?
Are they aware about the Linear coefficient of expansion of the tank shell material?
If not, you are at risk of significant “paper” losses which might affect your KPI for cargo losses.
For more information on storage tanks shell expansion factor or any other Loss Control & Expediting information and how we can help you reduce your losses contact;
Capt. Anurag Srivastava at anurag@ocsol.net
Capt. Anurag has extensive experience and knowledge about Loss Control & Expediting.