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If you know the gross fabricated weight, skip the information on calculating the weight and go directly to either "Cost Data for Pressure Vessels, Columns, and Reactors” or “Cost Data for Alloy Steel Pressure Vessels & Columns,” later in this section.Calculating the Weight
You need to know certain design data (diameter, length, design pressure, and temperature) to estimate the vessel’s weight. If possible, review the process flow diagrams or ask a process engineer for help.
If you do not have the information, do a preliminary design of a pressure vessel either manually or by using a computer program. See Figure 401-1 for resources.
For In This Manual Other Sources
Designing a Pressure Vessel Manually ASME Boiler & Pressure Vessel Code, Section VIII, Division 1
Designing a High-Pressure Vessel Manually
ASME Boiler & Pressure Vessel Code, Section VIII, Division 2
Mechanical & Structural Design Chevron Pressure Vessel Manual, Volumes 1 & 2
Updating Costs to Current Date Section 301 Figure 401-1. Resources for Estimating Columns and Vessels
Gross Fabricated
Weight DEFINITION
The gross fabricated weight is equal to the net fabricated weight times a factor that allows for plate over-thickness tolerance, clips, bosses, and tray supports as follows:
W(Gross Fabricated)=W(Net Fabricated) x Fv (or Fc) Where:
For Vessels: Fv = 1.0 + 0.10 (3,000/WNF)0.5
For Columns: Fc = 1.0 + 0.225 (10,000/WNF)0.8
Net Fabricated
Weight DEFINITION
The net fabricated weight is the sum of the following component weights (pounds):
WNF = W(shell) + W(heads) + W(skirt) + W(saddles) + W(nozzles) + W(manways) + W(trays)
Weight of Shell W(shell) = 0.890 x Ts (D + Ts) x Hs
Where:
Ts = Commercial plate thickness in inches
D = Inside diameter in inches
Hs= Tangent-to-tangent height (length) in inches
Steel plate is available in thickness increments of 1/16 inch up to 2 inches, and 1/8-inch increments above 2 inches (design thickness plus corrosion allowance, rounded up to commercial plate thickness).
Weight of Heads W(heads) = 0.58 × D1.9 x Th (per head for ellipsoidal heads)
Where:
Th = Design head thickness in inches, including corrosion allowance and forming
allowance (see Figure 401-2) D = Inside diameter in inches
Thickness without Forming Allowance ≤ 150" OD >150" OD < 1" 1/16" 1/8" ≥ 1", but < 2" 1/8" 1/8" ≥ 2", but < 3" 1/4" 1/4" ≥ 3", but < 3.75" 3/8" 3/8" ≥ 3.75", but < 4.25" 1/2" 1/2" ≥ 4.25" 3/4" 3/4"
Weight of Skirt W(skirt) = 0.890 × Tsk× (D + Tsk) × Hsk
Where:
Tsk = Skirt thickness in inches
D = Skirt inside diameter in inches Hsk = Skirt height in inches
Weight of Saddles W(saddles) = 0.877 × (Do)1.59 (two medium-weight, 120o saddles)
Where:
Do = Outside vessel diameter in inches
Weight of Nozzles Columns
W(nozzles) = 20.14 x (capacity, cu.ft.)0.48
Nozzle weight: Not to exceed 2500 lbs
Vessels
For vessels ≤ 36 inches in diameter, allow two nozzles weighing a total of 100 lbs
For vessels > 36 inches in diameter:, allow two nozzles weighing a total of 150 lbs
Weight of Manways W(manways)
See Figures 401-3 through 401-5.
Number of Trays Assumed # of 18-inch Manways
≤ 10 trays: 2
> 10 trays and ≤ 30 3 > 30 trays Estimate1
1 Manways = Shell Length (feet) + 2
30
For packed columns: A manway is required above and below each bed.
Weight of Trays W (trays)
Calculate the weight of carbon steel or stainless steel sieve trays from the following equations. The weight includes
ten-gauge tray plate 3/8-inch downcomers manways
intermediate structural supports shell support rings and bolts
The equations are based on column diameters from 40 to 140 inches. Assumptions:
Full cross-flow trays for diameters of 68 inches or less Half cross-flow trays for larger diameters
You can extrapolate weights of trays outside the 40-to-140-inch diameter range, with the possibility of inaccuracies.
Full Cross-Flow: W(trays) (lbs) = 0.785 × D1.47
Half Cross-Flow: W(trays) (lbs) = 0.244 × D1.82
Where
D = Shell inside diameter in inches Diameter Size
≤ 36 inches 4-inch inspection openings > 36 inches 18-inch manways
Volume # of Manways < 315CF One
> 315CF Two
Figure 401-4. For Vessels, Estimating Size of Openings and Number of Manways by Volume
Design Pressure (psi) Weight (lbs) 4" Inspection Opening Weight (lbs) 18" Manway 0-150 80 500 150-300 120 600 300-400 150 700 400-500 190 800
Figure 401-5. Estimating the Weight of Inspection Openings and Manways Based on Design Pressure
Example Weight Calculation
Design Information
Horizontal pressure vessel, 7 feet inside diameter by 18 feet long, designed for 300 psig, carbon steel material (A-285-C). An ASME Code calculation shows that the shell and head thicknesses will be 1.25 inches and 1.168 inches, respectively (including 1⁄
8" corrosion allowance).
Because the volume is greater than 315 cubic feet, assume two manways. Using the formulas above, the weight calculation is thus:
W(shell) = 20,486 lbs
W(heads) = 2 × 3,069 = 6,138 lbs
W(skirt) (not applicable)
W(saddles) = 1,054 lbs
W(nozzles) = 150 lbs
W(manways) = 2 × 600 = 1,200 lbs
W(trays) (not applicable)
Net Fabricated Weight = 29,028 lbs
Factor = 1.032
Gross Fabricated Weight = 30,000 lbs (rounded)
Cost Calculation CARBON STEEL
To estimate the cost of the above horizontal carbon steel vessel, use equation 1 in “Cost Data for Pressure Vessels, Columns, and Reactors” later in this section.
Cost, $ = 76.5 × (30000 lbs)0.63 = $50,600
This cost is at EDMI = 850. Use the data in Section 301 to adjust it to the current date. Also use the adjustment factors shown with equation 1 if your vessel requires full x-ray or stress relief.
Cost Calculation ALLOY STEEL VESSEL
Suppose the above vessel is to be fabricated from 21⁄
4 Cr-1Mo steel.
Assuming that the weight is still 30,000 lbs, and the corresponding steel vessel cost is $50,600 (as calculated above), the cost of the alloy vessel may be estimated as follows1: (Refer to “Cost Data for Alloy Steel Pressure Vessels & Columns” later in this section.),
1 CALCULATE THE ADJUSTED MATERIAL COST
Approximately 55% of the cost (or $27,800) represents the cost of the steel plate. From the data in Figures 401-10 through 401-12, the plate costs for SA-285-C and SA-387 (21⁄
4-1Mo) are $0.41 and $0.82 per pound,
respectively, for plate less than 11⁄
2 inches thick. The adjusted material cost
is then
$27,800 × ($0.82/$0.41) = $55,600
Although the plate costs shown are at EDMI = 855 while the vessel cost is at a different EDMI, the ratio of the plate costs is independent of EDMI and need not be adjusted.
2 CALCULATE THE ADJUSTED LABOR COST
Approximately 45% of the cost (or $22,800) represents the cost of fabrication labor and related shop overheads. Figure 401-13 gives multipliers for the labor cost relative to carbon steel. The adjusted labor cost is
$22,800 × 1.30 = $29,600
3 CALCULATE THE TOTAL ESTIMATED COST
The total estimated cost for the alloy vessel is the sum of the material and labor costs, or
$55,600 + $29,600 = $85,200
This cost may need adjustment relative to EDMI = 850 and for extras such as full x-ray or stress relief.
1 The shell and head thicknesses must be re-calculated using the allowable stress for the new material which may change the