Excel sheet Download Link: https://www.scribd.com/document/385945712/PSV-Sizing-Tool-API-Based-Calc-Sheets PSV Sizing for Blocked Liquid Discharge Condition PSV Sizing for Blocked Gas Discharge Condition PSV Sizing for Fire Case of Liquid Filled Vessel PSV Sizing for Control Valve Fail Open Case Relief Valve Sizing for Thermal Expansion Restriction Orifice Sizing for Gas Flow Restriction Orifice Sizing for Liquid Flow Single Phase Flow Line Sizing Tool Gas Control Valve Sizing Tool

1. Sr. No. Description Design Practice Reference
1 PSV Sizing for Blocked Liquid Discharge Condition
2 PSV Sizing for Blocked Gas Discharge Condition
3 PSV Sizing for Fire Case of Liquid Filled Vessel API 521 Par 5.15
4 PSV Sizing for Control Valve Fail Open Case API 521, Section 5.10, 2007 edition
5 Relief Valve Sizing for Thermal Expansion API 521 Par 5.14
6 Restriction Orifice Sizing for Gas Flow Perry's Handbook
7 Restriction Orifice Sizing for Liquid Flow Perry's Handbook
8 Single Phase Flow Line Sizing Tool Darcy-Weisbach Equation
9 Gas Control Valve Sizing Tool Fisher's Equation
Guidelines
Notes
API 520 Part 1 Sec 3.8, 7th
Edition
API 520 Part 1 Sec 3.6, 7th
Edition
API recommended practices for the use of Safety Relief Valves in Petroleum & Chemical industries - mostly used are:
1. API Recommended Practice 520 Part I - Sizing, Selection & Installation of Pressure relieving devices in Refineries.
2. API Recommended Practice 520 Part II – Installation of pressure relief systems in Refineries.
3. API Recommended Practice 521 – Guide for Pressure-Relieving and Depressuring Systems.
4. API Standard 526 - Flanged Steel Pressure Relief Valves
5. API Recommended Practice 527 - Seat Tightness of Pressure Relief Valves
6. API Standard 2000 - Venting Atmospheric and Low-Pressure Storage Tanks: Non-refrigerated and Refrigerated
7. API Standard 2001- Fire Protection in Refineries.
The designed pressure relieving devices should be certified and approved under Code,
1. ASME- Boiler and Pressure Vessel Code Section I, and Section VIII, Pressure Vessels.
2. ASME- Performance Test Code PTC-25, Safety and Relief Valves.
The following Excel Sheet serves for training and preliminay design purposes and process specifications but the final design must always be
checked by a subject matter expert and guaranteed for service by an authorized manfucturing vendor.

2. PSV Sizing - Blocked Liquid Discharge [Requiring Capacity Certification]
Equipment No. V-100 PSV SIZING RESULTS
Relief Service Crude Oil Selected Standard Orifice Area [Based on API 526] 6.38
Reason for Relief Blocked Liquid Discharge Selected Orifice Designation P -
PSV INPUT CALCULATIONS
Parameter Value Unit Parameter Value Unit
Flow through vessel / Relieving Rate 300,000 kg/h Flow Rate [Q] 5,556 lit/min
Liquid Density (for specific gravity calc) 900 Specific Gravity [SG] 0.9 -
Liquid Viscosity 450.0 cP 1,980 kPag
RV Set Pressure 18.00 barg 400 kPag
Over Pressure 10 % Percent of Gauge Back Pressure 22.2 %
Back Pressure at Relief Valve Discharge 4.00 barg 0.65 -
Rupture Disc Installed Upstream of RV Yes 0.9 -
Type of Relief Valve Balanced Bellow 0.96 -
2,795
4.33
Reynolds Number [R] 3,951 -
0.96 -
4.51
Selected Orifice Designation P -
6.38
Notes
2. Balanced Bellow type valves should be selected if back pressure is a variable
3. Upstream Relieving Pressure = Set Pressure + Allowable Over Pressure
4. Section VIII, Division I, of the ASME Code requires that capacity certification be obtained for pressure relief valves designed for liquid service.
inch2
kg/m3
Relieving/Upstream Pressure [P1
]
Downstream Pressure [P2
]
Coefficient of Discharge [Kd
]
Combination correction factors for use of rupture discs [KC
]
Correction Factor due to back pressure[KW
]
Initial Orifice Area Sizing (no viscosity correction) [Kv
= 1.0] [AR
]
mm2
inch2
Correction Factor due to Viscosity [KV
]
Orifice Area based on corrected viscosity [Acorr
] inch2
Selected Standard Orifice Area [Aselect
] [ Based on API 526] inch2
1. Conventional and pilot operated valves require no special correction for Kw
(correction due to back pressure)

3. PSV Sizing - Blocked Gas Outlet [Non Fire Case]
Equipment No. V-100 PSV SIZING RESULTS
Relief Service Fuel Gas FLOW CONDITION BEHAVIOUR SUBCRITICAL FLOW
Reason for Relief Blocked Gas Discharge Selected Standard Orifice Area [Based on API 526] 3.60
Selected Orifice Designation M -
PSV INPUT CALCULATIONS - CRITICAL FLOW
Parameter Value Unit Parameter Value Unit
Flow through vessel / Relieving Rate [W] 15,000 kg/h Mass Flow [W] 33,069 lb/h
1.30 - Coefficient [C] 347 Unit
Gas Compressibility Factor [Z] 0.85 - 94.5 psia
Gas Molecular Weight [MW] 65.0 lb/lbmol 627 Rankine
Relieving Temperature 75 0.975 -
RV Set Pressure 5.00 barg Percent of Gauge Back Pressure 80.0 %
Over Pressure 10 % 1.00 -
Back Pressure at Relief Valve Discharge 4.00 barg 1.00 -
Rupture Disc Installed Upstream of RV No CALCULATIONS - SUB CRITICAL FLOW
Type of Relief Valve Conventional 72.7 psia
FLOW CONDITION BEHAVIOUR Ratio of Back Pressure to Upstream Relieving Pressure [r] 0.77 -
Critical Flow Pressure Ratio 0.55 - 0.86 -
94.5 psia PSV SIZING RESULTS - BASED on API 526
51.5 psia 3.39
2.5 barg Selected Orifice Designation M -
FLOW CONDITION BEHAVIOUR SUBCRITICAL FLOW 3.6
Notes
2. Balanced Bellow type valves should be selected if back pressure is a variable
3. Upstream Relieving Pressure = Set Pressure + Allowable Over Pressure
4. Section VIII, Division I, of the ASME Code requires that capacity certification be obtained for pressure relief valves designed for liquid service.
inch2
Ratio of Specific Heats [k = CP
/CP
-R]
Relieving/Upstream Pressure [P1
]
Relieving Temperature of Inlet gas to PSV [T]
0
C Coefficient of Discharge [Kd
]
Correction Factor due to back pressure[KB
]
Combination correction factors for use of rupture discs [KC
]
Downstream Pressure [P2
]
Coefficient of Subcritical Flow [F2
]
Upstream Relieving Pressure [P1
]
Critical Flow Nozzle Pressure [Pcf
]
Calculated Orifice Area [Acalc
] inch2
Selected Standard Orifice Area [Aselect
] [ Based on API 526] inch2
1. Conventional and pilot operated valves require no special correction for Kw
(correction due to back pressure)

4. PSV Sizing - Fire Case - Liquid Filled Vessel
Equipment No. V-100 PSV SIZING RESULTS
Relief Service Vapour FLOW CONDITION BEHAVIOUR CRITICAL FLOW
P&ID No. xx-xx-xx-xx Selected Standard Orifice Area [Based on API 526] 0.11
Reason for Relief Liquid Filled vessel [Fire Case] Selected Orifice Designation D -
EQUIPMENT INPUT PSV INPUT CALCULATIONS - CRITICAL FLOW
Parameter Value Unit Parameter Value Unit Parameter Value Unit
Tank Diameter [D] 4.50 m Relieving Rate [W] 4,352 kg/h Mass Flow [W] 9,594 lb/h
Tank Length [T/T] [L] 21.00 m 1.39 - 355 Unit
Tank with Boot Yes - Gas Compressibility Factor [Z] 0.53 - 1,769 psia
Boot Diameter 1.20 Gas Molecular Weight [MW] 79.3 lb/lbmol 989.6 Rankine
Boot Height 2.00 Relieving Temperature 277 0.975 -
Mounting Horizontal - RV Set Pressure 100.00 barg Percent of Gauge Back Pressure 3.5 %
Vessel and Boot Head Hemispherical - Over Pressure 21 % 1.00 -
Tank Elevation w/o considering Boot [H] 5.5 m Back Pressure at Relief Valve Discharge 3.5 barg 1.00 -
Tank Elevation with Boot [H] 2.9 m Rupture Disc Installed Upstream of RV No CALCULATIONS - SUB CRITICAL FLOW
Operating Liquid Level [HLL/NLL] [F] 4.0 m Type of Relief Valve Conventional 65 psia
Drainage & Fire Fighting Measures Available - FLOW CONDITION BEHAVIOUR Ratio of Back Pressure to Upstream Relieving Pressure [r] 0.04 -
Latent Heat of Vaporization
150 kJ/kg Critical Flow Pressure Ratio 0.53 - 0.14 -
64 BTU/lb 1,769 psia PSV SIZING RESULTS - BASED on API 526
Is the Vessel Insulated Yes - 938 psia 0.04
Thermal Conductivity of Insulation 3.00 W/m.K 62.8 barg Selected Orifice Designation D -
% Piping Exposed to Fire 20 % FLOW CONDITION BEHAVIOUR CRITICAL FLOW 0.11
Environmental Factor [F] 0.0399 -
CALCULATIONS - CRITICAL FLOW
Parameter Value Unit
6.90 m
6.90 m
4.00 m
4.00 m
β 141.1 degrees
292.64
3,150.0
Heat Load [Q] 618,730 BTU/hr
Vapour Flow Rate
9,594 lb/h
4,352 kg/h
Notes
2. Balanced Bellow type valves should be selected if back pressure is a variable
3. Upstream Relieving Pressure = Set Pressure + Allowable Over Pressure
4. Section VIII, Division I, of the ASME Code requires that capacity certification be obtained for pressure relief valves designed for liquid service.
5. The wetted area computed with hemispherical ends is considered approximately equal to wetted area with elliptical heads since margin is added to account for piping. The difference is expected to be accomodated in the margin
inch2
Ratio of Specific Heats [k = CP
/CV
] Coefficient [C] [SQRT(lbm.lbmol.R/lbf.hr]
Relieving/Upstream Pressure [P1
]
Relieving Temperature of Inlet gas to PSV [T]
0
C Coefficient of Discharge [Kd
]
Correction Factor due to back pressure[KB
]
Combination correction factors for use of rupture discs [KC
]
Downstream Pressure [P2
]
Coefficient of Subcritical Flow [F2
]
Upstream Relieving Pressure [P1
]
Critical Flow Nozzle Pressure [Pcf
]
Calculated Orifice Area [Acalc
] inch2
Selected Standard Orifice Area [Aselect
] [ Based on API 526] inch2
K1 [ISO 23521]
K1
[Effective Total Height of Liquid Surface]
E1 [ISO 23521]
E1
[Initial Liquid Level]
Wetted Surface Area [Awet
]
m2
f2
1. Conventional and pilot operated valves require no special correction for Kw
(correction due to back pressure)

5. PSV Sizing - Control Valve Fail Open
Equipment No. V-100 PSV SIZING RESULTS
Relief Service Fuel Gas FLOW CONDITION BEHAVIOUR CRITICAL FLOW
Reason for Relief Control Valve Fail Open Selected Standard Orifice Area [Based on API 526] 26.00
Selected Orifice Designation T -
CONTROL VALVE INPUT PSV INPUT CALCULATIONS - CRITICAL FLOW
Parameter Value Unit Parameter Value Unit Parameter Value Unit
6.49 barg Flow through vessel / Relieving Rate [W] 61,012 kg/h Mass Flow [W] 134,508 lb/h
109 psia 1.25 - Coefficient [C] 342 Unit
4.63 barg Gas Compressibility Factor [Z] 0.98 - 90.4 psia
82 psia Gas Molecular Weight [MW] 19.4 lb/lbmol 551 Rankine
35.0 Relieving Temperature [CV Outlet] 32.7 0.975 -
Gas Molecular Weight [MW] 19.37 kg/kmol RV Set Pressure 4.50 barg Percent of Gauge Back Pressure 0.0 %
1.25 Over Pressure 16 % 1.00 -
768.0 - Back Pressure at Relief Valve Discharge 0.00 barg 1.00 -
Gas Compressibility Factor [Z] 0.9791 Rupture Disc Installed Upstream of RV No CALCULATIONS - SUB CRITICAL FLOW
CALCULATIONS Type of Relief Valve Balanced Bellow 14.7 psia
Parameter Value Unit FLOW CONDITION BEHAVIOUR Ratio of Back Pressure to Upstream Relieving Pressure [r] 0.16 -
27 psia Critical Flow Pressure Ratio 0.56 - 0.31 -
Pressure Drop Ratio [x] 0.25 - 90.4 psia PSV SIZING RESULTS - BASED on API 526
1.00 - 50.2 psia 23.55
0.89 - 2.4 barg Selected Orifice Designation T -
0.81 - FLOW CONDITION BEHAVIOUR CRITICAL FLOW 26
Expansion Factor [Y] 0.885 -
Flow Behaviour across Control Valve SUB CRITICAL -
Mass Flow through Control Valve 61,012 kg/h
Notes
2. Balanced Bellow type valves should be selected if back pressure is a variable
3. Upstream Relieving Pressure = Set Pressure + Allowable Over Pressure
4. Section VIII, Division I, of the ASME Code requires that capacity certification be obtained for pressure relief valves designed for liquid service.
inch2
Control Valve Inlet Pressure [P1
]
Ratio of Specific Heats [k = CP
/CV
]
Control Valve Outlet Pressure [P2
]
Relieving/Upstream Pressure [P1
]
Relieving Temperature of Inlet gas to PSV [T]
Control Valve Inlet Temperature [T1
] 0
C 0
C Coefficient of Discharge [Kd
]
Ratio of Specific Heats [k = CP
/CV
] Correction Factor due to back pressure[KB
]
Control Valve Cv
Combination correction factors for use of rupture discs [KC
]
Downstream Pressure [P2
]
Pressure Drop [ΔP] Coefficient of Subcritical Flow [F2
]
Upstream Relieving Pressure [P1
]
Piping Geometry Factor [Fp
]
Critical Flow Nozzle Pressure [Pcf
]
Calculated Orifice Area [Acalc
] inch2
Ratio of Specific Heat Factor [Fk
]
Rated Pressure Drop Factor [xT
] Selected Standard Orifice Area [Aselect
] [ Based on API 526] inch2
1. Conventional and pilot operated valves require no special correction for Kw
(correction due to back pressure)

6. Relief Valve Sizing - Thermal Expansion
Equipment No. V-100 PSV SIZING RESULTS
Relief Service Fuel Gas Selected Standard Orifice Area NPS 3/4" x NPS 1"
Reason for Relief Thermal Expansion 1.91
INPUT Notes
Parameter Value Unit 1. Since the flowrates are very small for Thermal expansion cases the safety valve size of
850 NPS 3/4" x NPS 1" (DN 20 x DN25) should be sufficient as per API 521 Par. 5.14.2
53.1
API Gravity 35.0
Total Heat Transfer Rate [H]
1000.0 kJ/s
3,412,140 BTU/hr
Specific Heat of Trapped Fluid [C]
2.00 kJ/kg.K
0.4777
Cubic Expansion Coefficient [B] 0.00050
Specific Gravity (SG) 0.850 -
RESULTS
RV Flow Rate
8.40 USGPM
1.91
RV Flow Rate [m3
/h]
Density of Liquid (ρ)
kg/m3
lb/f3
0
API
BTU/lb 0
F
1/0
F
m3
/h

7. RO Sizing - Gas Flow
Equipment No. V-100 RO SIZING RESULTS
Relief Service Fuel Gas FLOW CONDITION BEHAVIOUR CRITICAL FLOW
RO Tag No. xx-RO-xxx GAS FLOW 6803.0 kg/h
Reason for Relief RO Gas Flow BLOWDOWN ORIFICE SIZE 15.2 mm
RO INPUT CRITICAL FLOW CALCULATIONS
Parameter Value Unit Parameter Value Unit
Gas Flow [W] 6,803 kg/h 63.00 bara
Gas Molecular Weight [MW] 24.52 kg/kmol 8.00 bara
1.18 - 360.8 K
61.99 barg Upstream Gas Specific Gravity [SG] 0.85 -
7.0 barg 0.69 -
87.7 °C 15.22 mm
1.09 β [d/D] 0.3092 -
Gas Compressibility factor [Z] 0.88 - 1.0019 -
Orifice Coefficient [C] 0.84 - 15.20 mm
Upstream Diameter [D] 49.22 mm Orifice Area [A] 182
FLOW CONDITION BEHAVIOUR SUB CRITICAL FLOW CALCULATIONS
Critical Flow Pressure Ratio 0.57 - Parameter Value Unit
63.0 bara Pressure ratio [r] 0.127 -
62.0 barg Expansion Factor [Y] 0.248 -
34.8 barg Blowdown Orifice Area [A] 2622
FLOW CONDITION BEHAVIOUR CRITICAL FLOW Blowdown Orifice Diameter [d] 57.8 mm
Notes
Upstream Pressure [P1
]
Downstream Pressure [P2
]
Ratio of Specific Heats [k = CP
/CV
] Upstream Temperature [T1
]
Upstream Pressure [P1
]
Downstream Pressure [P2
] Critical Expansion Factor (Ycr
)
Upstream Temperature [T1
] Blowdown Orifice Diameter [d] (Ftp
= 1)
Upstream Gas Density [ρ1
] kg/m3
Corrected Ftp
Corrected Blowdown Orifice Diameter [dcorr
]
mm2
Upstream Relieving Pressure [P1
]
Critical Flow Nozzle Pressure [Pcf
] mm2
1. P1
& P2
is computed in Pascals (Pa)

8. RO Sizing - Liquid Flow
Equipment No. V-100 RO SIZING RESULTS
Relief Service Condensate Orifice Mass Flow 36,261 kg/h
RO Tag No. xx-RO-xxx Orifice Volumetric Flow 0.012
Reason for Relief RO Liquid Flow
RO INPUT CALCULATIONS
Parameter Value Unit Parameter Value Unit
850 1.44 bara
0.43 barg 1.01 bara
0.00 barg
Orifice Area [A]
1,963
0.70 - 0.001963
Orifice diameter [d] 50.0 mm Orifice Mass Flow 10.07 kg/s
Orifice Coefficient [C] 0.60 - Orifice Volume Flow 0.0119
Notes
m3
/h
Liquid Density [ρ1
] kg/m3 Upstream Pressure [P1
]
Upstream Pressure [P1
] Downstream Pressure [P2
]
Downstream Pressure [P2
] mm2
Pressure Ratio [P2
/P1
] m2
m3
/s
1. P1
& P2
is computed in Pascals (Pa)
2. In case, Orifice Flow Rate is Known, Use 'Goal Seek' to backcalculate the orifice diameter required

9. Single Phase Line Sizing
Piping No. x"-xxx-xxx RO SIZING RESULTS
Service Condensate Pressure Drop [ΔP] 0.0002 bar
From Equipment V-100 Fluid Velocity 0.05 m/s
To Equipment V-200 Flow Behaviour Turbulent -
Friction Factor Equation Colebrook -
PIPE INPUT CALCULATIONS
Parameter Value Unit Parameter Value Unit
Pipe Inner Diameter 102.26 mm 0.00005000 m
Pipe Length 100 m Pipe ID (D) 0.10226 m
Pipe Roughness 50.0 μm Pipe Cross Sectional Area [A] 0.00821
Flowrate 950.0 kg/h 0.000 kg/m.s
Liquid Viscosity [Dynamic] 0.36 cP Volumteric Flow [Q] 1.37
Liquid Density 693.0 Fluid Velocity [V] 0.05 m/s
FRICTION FACTOR [f] CALCULATIONS 9,072 -
Laminar Flow - Friction Factor [f] Flow Behaviour Turbulent -
Parameter Value Unit Pipe Roughness /Pipe ID [ε/D] 0.00049 -
Laminar Flow [f] 0.0071 - Friction Factor Equation Colebrook
Turbulent Flow - Churchill Equation Friction Factor [f] Friction Factor [f] 0.0324 -
Term A 1.30E+19 - 0.02360 kPa
Term B 7.36E+09 - 0.00024 bar
Churchill Equation - Friction Factor [f] 0.0327 - Pressure Drop per 100m [ΔP/L] 0.00024 bar/100 m
Turbulent Flow - Colebrook Equation Friction Factor [f]
Churchill Equation - Friction Factor [f] 0.0324 -
Notes
4. Pressure Drop is estimated using Darcy-Weisbach Equation
Pipe Roughness [ε]
m2
Dynamic Viscosity [μ]
m3
/h
kg/m3
Reynold's Number [NRe
]
Pressure Drop [ΔP]
1. P1
& P2
is computed in Pascals (Pa)
2. If NRe
<= 2100 - Use Laminar Flow Friction Factor
2. If NRe
<= 4000 - Use Churchill Equation
3. If NRe
> 4000 - Use Colebrook Equation

10. Gas Control Valve Sizing
Equipment No. V-100
Service Fuel Gas
CONTROL VALVE INPUT
Parameter Value Unit
6.49 barg
109 psia
4.63 barg
82 psia
35.0
Gas Molecular Weight [MW] 19.37 kg/kmol
1.25 -
768.0 -
Gas Compressibility Factor [Z] 0.9791 -
CALCULATIONS
Parameter Value Unit
27 psia
Pressure Drop Ratio [x] 0.25 -
1.00 -
0.89 -
0.81 -
Expansion Factor [Y] 0.885 -
Flow Behaviour across Control Valve SUB CRITICAL -
Mass Flow through Control Valve 61,012 kg/h
Notes
Sizing is based on Fisher Equation for Gas Flow
Control Valve Inlet Pressure [P1
]
Control Valve Outlet Pressure [P2
]
Control Valve Inlet Temperature [T1
] 0
C
Ratio of Specific Heats [k = CP
/CV
]
Control Valve Cv
Pressure Drop [ΔP]
Piping Geometry Factor [Fp
]
Ratio of Specific Heat Factor [Fk
]
Rated Pressure Drop Factor [xT
]

11. Tank LAH & LAHH Calculator
Parameter Value Unit
Tank Diameter [D] 14 feet
Tank Height [H] 18 feet
Normal Liquid Level [NLL] 6 feet Overfill 18.00 feet
Pump in Flow [Q] 250 USGPM
2,771
20,728 U.S Gallons LAHH 14.74 feet
Time to fill from Overfill to LAHH 15 min
Tank flow in 15 minutes 3,750 U.S Gallons
LAHH to Overfill Volume
16,978 U.S Gallons
2,270 LAH 8.23 feet
Liquid Alarm HH [LAHH] 14.74 f
Time to fill from Overfill to LAH 45 min
Tank flow in 45 minutes 11250 U.S Gallons NLL 6.00 feet
LAH to Overfill
9,478 U.S Gallons
1267
Liquid Alarm H [LAH] 8.23 f Tank Bottom 0.00 feet
Summary
Liquid Alarm HH [LAHH] 14.74 f Legend Input Data
Liquid Alarm H [LAH]
8.23 f
LAH to NLL
2.23 f
Total Volume of Tank [Vtotal
]
f3
f3
f3