Floating Roof Adjustment - Method 2
The Floating Roof Adjustment (Method 2) is the second of two volume corrections for tanks with a floating roof. Use Method 2 to calculate the displaced volume of material due to these parameter changes.
- Volume change per unit density
- Thermal Expansion
This calculation uses the following equation if the level gauge is greater than or equal to the critical high.
Where:
Vc = volume correction.
Y = adjustment in units of Volume adjustment per API density change.
APIstrapped = API density at strapping, at the observed temperature.
APIobserved = API density at observed conditions.
For calculation of the Volume displacement due to a floating roof based on the roof weight see Floating Roof Adjustment - Method 1.
EXAMPLE: Floating Roof Adjustment - Method 2
The tables below list the example data.
Input Data
| Attribute | Value |
|---|---|
| Product | Crude Oil |
| Reference Temperature | 60 F |
| API Gravity @ 60°F | 40.0 |
| Liquid Temperature | 84.0 F |
| Gauge | 10 ft 5 in |
Strapping Table Data
| Attribute | Value |
|---|---|
| Strapping API @ Strap. Temp. | 35.0 |
| Adjustment | 24.59 bbl / API |
| Strapping Temperature | 80.0 F |
| Critical Zone Height | 5 ft 0 in |
If the level gauge is greater than or equal to the critical zone height, start by calculating the observed density at the liquid temperature of 84.0 F. To do this, determine the volume correction factor. See the data reference for Volume Correction Factor calculation for details. If the level gauge is less than the critical high, then there is no correction.
For crude oil of 40.0 API and temperature of 84.0 °F, the VCF = 0.9879. Therefore, the observed density at 84.0 °F is calculated as shown below. Note that the density is first converted to specific gravity from API before the calculation is made.
Dref = 40 API = 0.8251 SG
VCF = 0.9879
Dobs = VCF * Dref
Dobs = 0.9879 * 0.8250
Dobs = 0.8151 SG = 42.1 API
Using the original equation at the beginning of this section we get the adjustment.
Vc = (35 – 42.1) * 24.59 = -174.59 bbl
See Configuring - Floating Roof Adjustment (Method 2) for details on how to configure this method.