Calculating Inventory Component Mass

The inventory component mass of a component is calculated using the values in the following fields in the Criticality Calculator RBI Component record:

Operating Pressure (P)
Operating Temperature (T)
Diameter (d)
Length (L)

Note: If the component type is Piping, then the value in the Piping Length field is used instead of the value in the Length field.

Percent Liquid Volume (pc)
Molwt (This value is stored in the RepresentativeFluids reference table for the fluid specified in the Process Fluid field in the Criticality Calculator RBI Components record)
Fluid Density (This value is specified in the RepresentativeFluids reference table for the fluid specified in the Process Fluid field in the Criticality Calculator RBI Components record)

Note: If the component is linked to an RBI 581 Risk Analysis, then these values are taken from the corresponding fields in the analysis record instead of the component record.

The inventory component mass of a component is calculated as follows:

Inventory Component Mass = (Liquid Volume x Fluid Density) + (Vapor Volume x Vapor Density)

where:

Liquid Volume = (pc/100) x Volume of the cylinder

Note: The volume of the cylinder is calculated from the values in the Diameter and Length fields in the Criticality Calculator RBI Component record.

Vapor Volume = (1-(pc/100)) x Volume of the cylinder
Vapor Density = (Molwt x (P + 14.7)) / (10.73 x (T + 459.15) x z)

This value is populated in the Inventory Component Mass field in the Common section of the associated RBI 581 Consequence Evaluation.

Example for Calculating Inventory Component Mass

Suppose a component has the following specifications:

Component Type: Heat Exchanger (Shell)
Process Fluid : C6-C8
Operating Pressure: 101 Pounds/Sq Inch Gage
Operating Temperature: 121 Degrees Fahrenheit
Molwt of CO: 28
Diameter: 97.625 inches
Length: 360 inches
Percent Liquid Volume: 50 percent
Fluid Density: 42.704

Given these values:

Volume of the cylinder = (pi x (d/12) x (d/12) x (L/12)) / 4

Volume of the cylinder = ((22/7) x (97.625/12) x (97.625/12) x (360/12)) / 4

Volume of the cylinder = 1560.075 Cubic feet
Liquid volume = (pc/100) x Volume of the cylinder

Liquid volume = (50/100) x 1560.075

Liquid volume = 780.038 Cubic feet
Vapor volume = (1 - (pc/100)) x volume of the cylinder

Vapor volume = (1 - (50/100)) x 1560.075

Vapor volume = 780.038 Cubic feet
Vapor Density = (Molwt x (P + 14.7)) / (10.73 x (T + 459.15) x z)

Vapor Density = (100 x (101 + 14.7)) / (10.73 x (121 + 459.15) x 1)

Vapor Density = 1.859 Pounds per cubic feet
Inventory Component Mass = (Liquid Volume x Fluid Density) + (Vapor Volume x Vapor Density)

Inventory Component Mass = (780.038 x 42.704) + (780.038 x 1.859)

Inventory Component Mass = 34760.526 Pounds

Note: The value in the Inventory Component Mass field on the RBI Component datasheet may slightly differ from the value that is shown in the example. This happens because of rounding off some of the values.