Tank Design & Emission Loss Calculator

Shell sizing per ASME Section VIII, self-supporting cone/dome roof & flat bottom sizing per API 650, plus fixed-roof and floating-roof evaporation loss estimation per EPA AP-42 Chapter 7.1

US CUSTOMARY METRIC / SI

Project Data

Project Name

Tank Tag No.

Engineer

Load a Literature Example

1.1 Process & Sizing Basis

Liquid Throughput lb/hour

Liquid Density ρ_L lb/ft³

Storage / Days Needed days

Design Height/Diameter Ratio (H/D)

Freeboard Allowance % of liquid level

The required liquid working volume is sized from throughput × days ÷ density. Diameter is first solved from V = (π/4)·D²·H using your target H/D ratio, then the actual liquid level is computed for that diameter, and the freeboard allowance is added on top to get the final shell height — so the diameter sizing and the final geometry are always consistent.

1.2 Design Pressure & Shell (ASME Sec. VIII, UG-27)

Design Gauge Pressure, Pg psi

Design Safety Margin

Max. Allowable Stress f psi

Welded Joint Efficiency E

Corrosion Allowance c in

1.3 Roof & Bottom (API 650)

Field-erected atmospheric storage tanks use a thin, self-supporting cone or dome roof and a flat bottom plate — not a pressure-rated ASME torispherical head. Roof thickness follows the API 650 self-supporting roof formula (governed by a minimum nominal thickness floor); the bottom is sized to a minimum nominal plate thickness, both plus corrosion allowance. This roof type matches the one used in Module 2.

Roof Type

Roof Slope (cone) ft/ft

Roof Plate Min. Nominal Thickness in

Bottom Plate Min. Nominal Thickness in

2.1 Tank Geometry & Roof Type

🔗 Synced with Module 1

Tank Diameter, D ft

Tank Shell Height, Hs ft

Roof Type

Roof Slope (cone only) ft/ft

Dome Roof Radius, RR (dome only) ft

2.2 Throughput & Fluid Properties

Annual Net Throughput, Q bbl/year

Number of Turnovers, N

Liquid Density ρ_L lb/ft³

Vapor Density ρ_v lb/ft³

Molecular Weight, Mv lb/lb-mol

Liquid Temperature, TL °R

Max. Ambient Temp °R

Min. Ambient Temp °R

Vapor Pressure Basis

Estimate from vapor density Enter Pva directly

"Estimate from vapor density" back-calculates Pva = ρv·R·TL/Mv via the ideal gas law — a quick approximation. For real fluids/mixtures, enter the true vapor pressure from Antoine data or a lab report for a more accurate result.

2.3 Standing Storage Loss Factors

Paint / Solar Absorptance Factor, α

Daily Solar Insolation, I Btu/ft²-day

Working Loss Product Factor, Kp

3.1 Tank Geometry & Roof Construction

🔗 Synced with Module 1

Tank Diameter, D ft

Roof Construction

No. of Fixed-Roof Support Columns, Nc

Effective Column Diameter, Fc ft

3.2 Throughput & Fluid Properties

Annual Net Throughput, Q bbl/year

Shell Clingage Factor, Cs bbl/1,000 ft²

Vapor Density ρ_v lb/ft³

Liquid Density ρ_L lb/ft³

Molecular Weight, Mv lb/lb-mol

Liquid Temperature, TL °R

Atmospheric Pressure, PA psia

Vapor Pressure Basis

Estimate from vapor density Enter Pva directly

3.3 Rim Seal & Deck Factors

Seal Type Preset (AP-42 Table 7.1-8, welded/riveted tanks, wind < 15 mph)

Zero-Wind Seal Factor, KRa lb-mol/ft-yr

Wind Speed Factor, KRb lb-mol/(mph)ⁿ ft-yr

Wind Speed Exponent, n

Avg. Ambient Wind Speed, v mph

Product Factor, Kc

3.4 Deck Fittings (AP-42 Table 7.1-12)

Deck fitting loss is often the largest single loss term for internal floating roof tanks — don't skip it. Use actual tank-specific fitting counts where known; "Suggest Typical Fittings" fills in AP-42's typical counts (Tables 7.1-11, 7.1-13, 7.1-14, 7.1-15) by tank diameter and construction type as a starting point only.

Fitting / Construction Detail	Count, NF	KFi (lb-mol/yr)

Tank Profile Sketch

Not to true scale between diameter and height.

Tank Geometry Results

Inside Diameter, Di -

Outside Diameter, Do -

Straight Shell Height, H -

Overall Tank Height -

Liquid Level, hl -

Freeboard -

Design Pressure & Thickness

Design Pressure -

Shell Thickness, tt -

Roof Plate Thickness, th -

Roof Rise -

Bottom Plate Thickness -

Areas, Volume & Weight

Circumference -

Shell Surface Area -

Roof Surface Area -

Bottom Surface Area -

Total Steel Volume -

Approx. Steel Weight -

Tank Working Capacity -

Fixed Roof Loss Results

Liquid Level, hl -

Roof Outage, HRO -

Vapor Space Outage, HVO -

Vapor Space Volume, Vv -

Vapor Pressure, Pva -

Vented Vapor Saturation, Ks -

Vapor Space Expansion, KE -

Annual Losses

Working Loss, Lw -

Standing Storage Loss, Ls -

Total Loss, Lt -

Total Loss (Volume) -

Floating Roof Loss Results

Vapor Pressure, Pva -

Vapor Pressure Function, P* -

Annual Losses

Rim Seal Loss, LR -

Withdrawal Loss, LwD -

Deck Fitting Loss, LF -

Deck Seam Loss, LD -

Total Loss, LT -

Total Loss (Volume) -

Engineering Reference & Technical Basis

1. Shell Thickness (ASME Sec. VIII Div. 1, UG-27)

Circumferential (hoop) stress governs a thin cylindrical shell under internal pressure:

t = \dfrac{P \cdot R}{S \cdot E - 0.6 \, P} + CA

where P = design pressure, R = inside radius, S = allowable stress, E = joint efficiency, CA = corrosion allowance.

2. Roof & Bottom Sizing (API 650, self-supporting cone/dome + flat bottom)

Field-erected atmospheric tanks use a thin self-supporting roof, not a pressure-rated ASME head. Cone and dome roof thickness are minimum-thickness governed; the bottom is a flat plate at minimum nominal thickness (no dish/head geometry):

t_{roof,cone} = \max\left(\dfrac{D}{400\cos\theta},\; t_{min}\right) + CA $$ $$ H_R = R_R - \sqrt{R_R^2 - R_S^2}, \qquad $$ $$ t_{roof,dome} = \max\left(\dfrac{D}{400},\; t_{min}\right) + CA $$ $$ t_{bottom} = t_{min,bottom} + CA

D = tank diameter, θ = roof slope angle, R_R = dome radius (defaults to D), R_S = shell radius, t_min ≈ 3/16 in (roof) and t_min,bottom ≈ 1/4 in (bottom) by default, both editable. Self-supporting cone roofs require slope between 2:12 and 9:12 (0.1667–0.75 ft/ft, 9.5°–37°) per API 650; self-supporting dome roofs require a crown radius between 0.8D and 1.2D.

3. Design Pressure & Hydrostatic Head (shell only)

Design pressure is the hydrostatic head of liquid at the design liquid level, converted to psi, plus the tank's design gauge pressure — not atmospheric pressure, which acts equally on both sides of the shell and produces no net stress:

P_{hydrostatic} = \dfrac{\rho_L \cdot 4.883 \cdot g \cdot h_l}{101325}\times 14.7 $$ $$ P_{design} = SF\left(P_{hydrostatic} + P_g\right)

ρ_L in lb/ft³, h_l in ft, g = 9.8 m/s², P_g = design gauge pressure (psi) — use ~0 for a freely-vented tank, or the breather-vent setting (commonly ~0.03 psig) otherwise. The constant 4.883 combines the lb/ft³→kg/m³ (16.0185) and ft→m (0.3048) conversions so the hydrostatic bracket evaluates to atmospheres before the 14.7 psi/atm conversion.

4. Tank Sizing from Working Volume

Diameter is solved from the required liquid working volume using a single, user-specified height-to-diameter ratio k = H/D — the same ratio used later for the actual shell height, so the initial sizing and the final geometry stay consistent:

V = \frac{\pi}{4}D^2 H, \qquad H=kD $$ $$ D = \sqrt[3]{\dfrac{4V}{\pi k}}

5. Fixed Roof Standing Storage & Working Loss (AP-42 Ch. 7.1)

L_s = 365 \, V_v \, W_V \, K_E \, K_S $$ $$ K_S=\dfrac{1}{1+0.053\,P_{VA}\,H_{VO}} $$ $$ \Delta T_V = 0.72\,\Delta T_A+0.028\,\alpha\, I, \qquad $$ $$ K_E \approx \Delta T_V / T_{LA} $$ $$ L_w = 0.001\, M_V\, P_{VA}\, K_N\, Q\, K_P, \qquad $$ $$ K_N=\begin{cases}1 & N\le 36\\ (180+N)/6N & N>36\end{cases}

V_v = vapor space volume, W_V = vapor density, H_VO = vapor space outage, ΔT_A = daily ambient temperature range, I = solar insolation, N = annual turnovers, T_LA = daily average liquid surface temperature (°R). The K_E ≈ ΔT_V/T_LA form omits the AP-42 vapor-pressure-range term (ΔP_V−ΔP_B)/(P_A−P_VA) as a simplification — for volatile stocks with a wide daily temperature swing, cross-check against the full AP-42 equation.

6. Floating Roof Rim Seal, Withdrawal, Deck Fitting & Deck Seam Loss (AP-42 Ch. 7.1)

L_R = (K_{Ra}+K_{Rb}V^n)\,D\,P^*\,M_V\,K_C, \qquad $$ $$ P^*=\dfrac{P_{VA}/P_A}{\left[1+\left(1-P_{VA}/P_A\right)^{0.5}\right]^2} $$ $$ L_{WD} = 0.943\,\dfrac{Q\,C_S\,W_L}{D}\left(1+\dfrac{N_C F_C}{D}\right) $$ $$ L_F = F_F\,P^*\,M_V\,K_C, \qquad F_F=\sum_i N_{F_i} K_{F_i}, \qquad $$ $$ K_{F_i} = K_{Fa_i} + K_{Fb_i}(K_v V)^{m_i} $$ $$ L_D = K_D\,S_D\,D^2\,P^*\,M_V\,K_C

W_L = liquid density in lb/gal (converted internally from the lb/ft³ input). N_C = 0 for external floating roofs (no fixed roof/columns). L_D applies to bolted decks only. Wind speed V is forced to zero for internal and domed external floating roofs — the fixed roof blocks wind at the rim (K_v=0.7 wind correction applies only to external tanks). K_Ra, K_Rb, n and the deck fitting K_Fa, K_Fb, m factors are taken directly from AP-42 Tables 7.1-8 and 7.1-12.

7. Assumptions & Limitations

Shell sizing uses a single uniform ASME Sec. VIII thickness rather than the course-by-course API 650 1-foot method — reasonable for small/medium vessels, not a substitute for a full API 650 design on large field-erected tanks.
Roof and bottom thickness are minimum-thickness/self-supporting-geometry governed, not pressure-stress calculated — matching real API 650 cone/dome-roof, flat-bottom tank practice rather than a pressure-vessel head. Confirm the minimum nominal thickness inputs against the API 650 edition governing your project.
"Estimate from vapor density" derives vapor pressure via the ideal gas law — adequate for light pure hydrocarbons, approximate for mixtures. Use direct Pva entry (Antoine/lab data) where accuracy matters.
"Suggest Typical Fittings" fills deck-fitting counts from AP-42's typical tables (7.1-11, 7.1-13, 7.1-14, 7.1-15) by diameter and construction type only — always replace with actual tank-specific counts when known, per AP-42's own preference for tank-specific data over typical-value tables.
K_E omits the AP-42 vapor-pressure-range and breather-vent terms (see item 5); solar insolation and liquid/ambient temperatures are editable defaults — confirm against location data governing your project.
All results are preliminary sizing/estimation figures for early engineering.

References

ASME Boiler & Pressure Vessel Code , Section VIII, Division 1 — UG-27 (cylindrical shell hoop stress).
API Standard 650 "Welded Tanks for Oil Storage" — self-supporting cone/dome roof and flat bottom minimum thickness requirements; full course-by-course shell design on large atmospheric tanks.
US EPA, AP-42 Compilation of Air Pollutant Emission Factors, Chapter 7.1 "Organic Liquid Storage Tanks" (basis of the TANKS emissions estimation methodology).