4. Rel i ef Val v e Si zi n g
Top opic ics s t o be Cov Cove ere red d General Sizing
Sizing Pro P roced cedur ure e APII ‘KA’ AP ‘KA’ vs. ASME ASME ‘KA’
Gas / Vap apor or Sizi izin ng – Son onic ic F lo low w
Equations, Variables, Units of Measure Gas P ro rope pert rties ies Back Pressure Rupture Disc
Gas / Vapor Sub-Sonic Flow
Equations, Variables, Units of Measure Pressure & Vacuum
Top opic ics s t o be Cov Cove ere red d Steam Sizing
Equations, Variables, Units of Measure Sec. VIII vs. Sec I Sonic vs. Subsonic
Liquid Sizing
Equations, Variables, Units of Measure Back Pressure
Fire Sizing
AP I 521 API 521 – Unw Unwet ettted Ve Vessels ssels APII 521 AP 521 – We Wettted Ve Vessels ssels APII 200 AP 2000
Mus ustt Co Co ns nsid ide er The The On e Wo r s t Cas e Sc en ar i o Blocked Blo cked Disc Discha harge rge Ext xte ern rna al Fire Fir e Thermal Exp Expa ans nsio ion n Runaway Re React ctio ion n Tub ube e Rup Ruptu ture re In Hea Heat Exc xchang hange er
Basi Ba sic c Siz Sizin ing g Pr Pr oc oce edu dure re Establish Set Pressure of PSV Determine Required Relief Capacity Select PSV Size That Will Flow At Least Tha Th at Capacity At Th The e Relieving P ress ssu ure
API A PI & A SME ‘K ‘ K A’ Val Valu u es In 1962, the th e ASME ASME Se Sec t i o n VIII Co Co d e Was Revi vised, sed, Requ quir irin ing g Tha hatt “ K” Be Us Us ed In Si Si zi ng Cal cu cull ati tion ons s (10% Saf et y Fac t o r ) In s t ead of o f “ K D”
K = K D x 0. 0.90 90
The NB “Red Book The Book” ” is a Bi-Annual publication of the Pressure Relief Device Certifications by the National Board of Boiler and Pressure Vessel Inspectors. The NB allows advertise The sed d deviations from the R ed Book “K” and “A” values, however… Advertised KA AS ME KA
(per NB Red Book) Book)
Si n c e 1962, mos mo s t PRV man man u f ac t u r er s have Ove versta rstate ted d the their ir “ K” va value lues s, and an d Unde ndersta rstate ted d the their ir “ A” va value lues s.
API A PI vs v s A SME Ori Or i f i c e Ar A r eas AGC A GC JOS-E J OS-E Seri Ser i es API A PI DESIGNATION DESIGNATION
API A PI EFFECTIVE A REA (SQ IN)
ASME A SME / NB CERT. CERT. AREA A REA (SQ IN)
D E F G H
0.110 0.196 0.307 0.503 0.785
0.124 0.221 0.347 0.567 0.887
API A PI vs v s A SME Ori Or i f i c e Ar A r eas AGC A GC JOS-E J OS-E Seri Ser i es API A PI DESIGNATION DESIGNATION
API A PI EFFECTIVE A REA (SQ IN)
ASME A SME / NB CERT. CERT. AREA A REA (SQ IN)
J K L M N
1.287 1.838 2.853 3.600 4.340
1.453 2.076 3.221 4.065 4.900
API A PI vs v s A SME Ori Or i f i c e Ar A r eas AGC A GC JOS-E J OS-E Seri Ser i es API A PI DESIGNATION DESIGNATION
API A PI EFFECTIVE A REA (SQ IN)
ASME A SME / NB CERT. CERT. AREA A REA (SQ IN)
P Q R T
6.380 11.05 16.00 26.00
7.205 12.47 18.06 29.35
Exampl xample e of Dif iffere ferent nt Manu nufactu facturers rers KA Valu lue es “ J” Ori rifi fice ce (API (API = 1.287 in 2) NATIO NA TIONAL NAL BOA BOARD RD
CATALOG
K
A,, in A i n 2 [ c m 2]
KA
K
A,, in A i n 2 [ c m 2]
KA
FARRIS POPRV
0.859
1.430 [9.226]
1.228 [7.925]
0.953
1.287 [8.303]
1.226 [7.910]
CONSOLID. DSOPRV
0.855
1.496 [9.652]
1.279 [8.252]
0.95
1.287 [8.303]
1.223 [7.888]
A GC AGC POPRV
0.877
1.496 [9.652]
1.312 [8.464]
0.975
1.287 [8.303]
1.255 [8.095]
API A PI & A SME ‘K ‘ K A ’ Val Valu u es A PI – Pr API Prel elii m i n ar ary y Si Sizi zin ng ASME A SME – Mo Mod d el els s A c t u al Val Valv v e Perf Per f o r m an anc ce A PI – Us API Uses es A PI 526 Stan St and d ar ard d Or Orii f i c e Ar A r eas ASME A SME – Us Uses es NB NB-18 -18 Ac A c t u al Cer Certt i f i ed Or Orii f i c e Ar A r eas API A PI – Co Coef efff i c i en entt s o f Di Dis s c h ar arg ge
Gas / Vap Vap o r = 0.975 0.975 Liqu Li quid id = 0. 0.65 650 0
ASME A SME – Co Coef efff i c i en entt s o f Di Dis s c h ar arg ge
Use DeDe-rated rated Value (K) fo forr sizin s izing g Varies from fro m Manu Manufactu facturer rer to Manufactu anufacturer rer and Model Typ Type e to Model Typ Type e Ad A d v er ertt i s ed K A A ASME SME KA KA
Gas / Vap o r Si zi n g SONIC Flow - Genera nerally lly When When Set Set Pressure Pressure
15 ps psig ig [1.0 [1.03 3 barg]
E NGLISH UNITS UNITS
A
V MTZ
METRIC UNI UNITS TS VOLUMETRIC FLOW
CKP P1 K b K c 6.32CK
A
V MTZ
OR
A
W TZ
CKP CK P1 K b K c M
17.02C KP1 K b K c OR
MASS FLOW
A
1.316W TZ
CKP CK P1 K b K c M
For ormu mula la Sym ymbo bols ls SYMBOL
A P1 V W Z C KD K Kb Kc T M
DESCRIPIPTION
Calc lcul ula ated Orifi Ori fice ce Ar Are ea Inlet Flowing Flowin g Pressu Pressure re [ P1 = Pset + Pover – Ploss + Patm ] Vol olum ume etr tric ic Flo low w Rate Mass Flow Flo w Rate Rate u nknown own,, assu assume me Z = 1.0 1.0)) Compressibility Factor (if unkn nknown own,, assu assume me C = 315 315)) Gas Ga s Constant Cons tant (if u nkn Ac A c t u al Co Coef efff i c i en entt o f Di Dis s c h ar arg ge [K=0. =0.90 90 x K d ] ASME A SME Coeff Coef f i c i en entt o f Di Dis s c h ar arg g e [K Back Pressu Pressure re Cor orrecti rection on Fact Factor or Rupt upture ure Disc Disc Comb ombination ination Corr orre ecti ction on Facto Factor r Reli Re lie evi ving ng Temp mpe eratu rature re Mol lar W ig ight ht
Units SYMBOL
ENGLISH
METRIC
A P1 V W Z C KD K Kb Kc T M
in2 psia SCFM lb/hr ------------°R = °F + 460
cm2 bara Nm 3/h /hr r kg/hr ------------K = °C + 273 273
Com ompr pre ess ssib ibil ilit ity y Fact ctor or,, Na Natu tural ral Gas, Gas, 0. 0.60 SG SG 1.2
T = ºF [ºC] 500º [260] 400º [204] 300º [149] 200º [93] 100º [38] 0º [-18]
1.1 1.0 0.9 0.8 0.7
MW = 17.40 (0.6 (0 .6 sp gr gr))
0.6 0.5
0
500 [34]
1000 1500 2000 2500 3000 3500 4000 4500 5000 [69] [103] [138] [172] [207] [241] [276] [310] [345]
PRESSURE, psig [barg]
Gas Con onst sta ant k 1
C
520
2 k 1 k k 1
400
380
360
C 340
320 1.0
1.2
1.4
1.6
1.8
2.0
RATIO OF SPECIFIC HEATS, k
Typ ypic ica al Pro Propert perties ies of Gases Gases Gas A CETYLENE ACETYL ENE AIR A IR AMMONIA A MMONIA ARGON A RGON B ENZENE B UTA DIENE CA RB ON DIOXIDE CA RB ON MONOXIDE ETHA NE ETHYL ENE FREON 22 HEL IUM HEXA NE
Molecular “ C” “ k” , Ratio Of Of Factor Specific Weight Specifi c Heats Heats 26 29 17 40 78 54 44 28 30 28 86 4 86
343 356 348 378 329 329 345 356 336 341 335 377 322
1.26 1.40 1.31 1.67 1.12 1.12 1.28 1.40 1.19 1.24 1.18 1.66 1.06
Typ ypic ica al Pro roperti pertie es of Gases Gas HYDROGEN HYDROGEN SUL FIDE METHA NE METHYL MERCA PTON N-B UTA NE NATURAL GAS (SG=0.60) NITROGEN OXYGEN PENTA NE PROPA NE PROPYL ENE STEA M SUL PHUR DIOXIDE VCM
(cont’d)
Molecular Weight
“ C” Factor
“ k” , Ratio Of Of Speci Spe cifi fic c Heats Heats
2 34 16 48 58 18.9 28 32 72 44 42 18 64 62
357 349 348 337 326 344 356 356 323 330 332 348 346 335
1.41 1.32 1.31 1.20 1.09 1.27 1.40 1.40 1.07 1.13 1.15 1.31 1.29 1.18
Back Pr ess Back ssur ure e Cor orre rect ctio ion n Fa Fact ctor or Unbalanc Unbala nced ed Con Conventi ventional onal Direct Spring Spri ng PRV 1.00 0.90
A t 110% of At o f Set Pressu Pressure re
0.80 0.70 0.60
~
0.00 0
10 10
20
30
4 40 0
50
% Bui Built-Up lt-Up Back Back Pressur e (gauge)
Back Pr ess Back ssur ure e Cor orre rect ctio ion n Fa Fact ctor or Balanced Bellows Bellow s Direct Spr Sprin ing g PRV PRV 1.00 0.90
A t 110% of At o f Set Pressu Pressure re
0.80 0.70 0.60 0.50 0
10 10
20
30
4 40 0
% Back Pressure Pressur e (gauge)
50
Effect of o f Ba B ack Pre ress ssure ure on Lift Li ft o f Pressu Press u re Re Rel ief Valv Valve e Ty pes 100 Pilot Operated PRV (Standard)
90 t f i L 80 d e t a R 70 %
Balanced Bellow s Balanced Spring Sprin g Ope Operated rated PRV PRV
Conventional Spring Operated PRV
60 50 0
10
20
30
40
50
% Back Pressure Pressur e (gauge)
90
100
A Per Perff ec ectt No Nozzl zzle e (K D = 1.0) 100
53%
y 80 t i c a p a C 60 d e t a R 40 %
k=1.3
P1
P 2
20
0 0
20
40 60 80 % Back Back Pressu Pressure re
100
Back Pressu Pressure re Cor Correcti rection on Fact Factor or AGC A GC Pis Pi s t o n POPRV (Gases (Gas es)) 1.0
k = 1. 1.0 0 k = 1.2 1.2 k = 1.4
0.8
k = 1.6 1.6 k = 1.8 0.6
k = 2.0 2.0
Kb 0. 4
0.2
0.0 0.0
0. 2
P2
0.4
0.6
0.8
1.0
= Absolute Absolu te Pressu Pressure re Ratio Ratio
PSV Wi t h Ru p t u r e Di s c Att In A Inll et Do PSV Cal c u l at i o n , t h en Ap A p p l y “ Co Com m b i n at atii o n Fac Factt o r ” f o r t h at Mo d el PSV & Mo d el /M /Ma at er i al o f RD* As A s Es Estt ab abll i s h ed b y t h e NB Tes estt i n g . OR Dee-rr ate PS PSV Capac Capacii t y b y 10 10%. %. *List d in back of NB NB “ R d Book” Boo k”
PRV Wi t h Ru p t u r e Di s c Att Ou A Outt l et
No PSV DeDe-R Rati atin n g Neces ecess s ary
Gas / Vap o r Si zi n g SUBSO BSON NIC Flow - Gene enerally rally When Set Set Pressure Pressur e < 15 psig [1. [1.03 03 barg]
E NGLISH UNITS UNITS
A
V MTZ
METRIC UNI UNITS TS VOLUMETRIC FLOW
4645FK D P1
A
OR
A
W TZ
735FK D P1 M
V MTZ
12510 FK D P1 OR
MASS FLOW
A
W TZ
558FK D P1 M
For ormu mula la Sym ymbo bols ls SYMBOL
A P1 V W Z KD M T F
DESCRIPIPTION
Calc lcul ula ated Orifi Ori fice ce Ar Are ea Inlet Flowing Flowin g Pressu Pressure re [ P1 = Pset + Pover – Ploss + Patm ] Vol olum ume etr tric ic Flo low w Rate Mass Flow Flo w Rate Rate u nknown own,, assu assume me Z = 1.0 1.0)) Compressibility Factor (if unkn Ac A c t u al Co Coef efff i c i en entt o f Di Dis s c h ar arg ge Mol ole ecu cular lar Weig ight ht Reli Re lie evi ving ng Temp mpe eratu rature re Subs ubsoni onic c Flow Facto Factor r
Units SYMBOL
ENGLISH
METRIC
A P1 V W Z KD M T F
in2 psia SCFM lb/hr ------°R = °F + 460 ---
cm2 bara Nm 3/h /hr r kg/hr ------K = °C + 273 273 ---
Subs ubsoni onic c Flow Facto ctor r
F
2 k 1 k k P2 k P2 k 1 P1 P1
WHERE: k = ratio ratio of specific s pecific hea heats ts For Press Pressur ure: e: P1 = Inlet Flo Flowin wing g Pressure Pressur e [ P1 = Pset + Pover – Ploss + Patm ] P2 = Pres Pressu sure re at Valv Valve e Out Outlet let
[ P2 = Pback + Patm ]
For Vacuu Vacuum: m: P1 = Atmo Atmosph sphe eric Pressure
[ P1 = Patm ]
P2 = Pres Pressu sure re at Valv Valve e Out Outlet let
[ P2 = Pvacuum set + Punder + Patm ]
0.55
k = 1.90
0.50
k = 1.40
0.45
k = 1.00
0.40
F
“ F” Factor
0.35
0.30
A GC Seri AGC Ser i es 90 & 9000
0.25
0.20
0.15 0.10 1.00
0.90
0.80
0.70
0.60
0.50
0.40
P2 = Absolute Absolu te Pressur Pressur e Ra Ratio
St eam Si zi n g SONIC Flow - Genera nerally lly When When Set Set Pressure Pressure
E NGLISH UNITS UNITS
A
W
51.5 K K S K P K b P1 METRIC UNI UNITS TS
A
W
52.5 K K S K P K b P1
15 ps psig ig [1.0 [1.03 3 barg]
For ormu mula la Sym ymbo bols ls SYMBOL
A P1 W K KS KP Kb
DESCRIPIPTION
Calc lcul ula ated Orifi Ori fice ce Ar Are ea Inlet Flowing Flowin g Pressu Pressure re [ P1 = Pset + Pover – Ploss + Patm ] Mass Flow Flo w Rate Rate ASME A SME Coeff Coef f i c i en entt o f Di Dis s c h ar arg ge Sup upe erh rhe eat Corre Corr ect ctio ion n Fact Factor or Hig igh h Pressu Pressure re Cor Correcti rection on Fact Factor or (over 1600 psig) Back Pressu Pressure re Cor orrecti rection on Fact Factor or
Units SYMBOL
ENGLISH
METRIC
A P1 W K KS KP Kb
in2 psia lb/hr ---------
cm2 bara kg/hr ---------
K S – Su Sup p er erh h eat Co Corr r ec ectt i o n Fac Factt o r Set Sat. Pres. Steam oF 280 psig 15 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 350 400 450 500
250 259 287 308 324 338 350 361 371 380 388 395 403 409 416 422 436 448 460 470
1.00 1.00
[ENGLISH]
Tot otal al Stea St eam m Temper emperatur ature, e, o F 300 1.00 1.00 1.00
320 1.00 1.00 1.00 1.00
340 0.99 0.99 1.00 1.00 1.00 1.00
360 0.99 0.99 0.99 0.99 1.00 1.00
380 0.98 0.98 0.99 0.99 0.99 1.00 1.00 1.00 1.00
400 0.98 0.98 0.98 0.98 0.99 0.99 0.99 1.00 1.00 1.00 1.00 1.00
420 0.97 0.97 0.97 0.97 0.98 0.98 0.98 0.99 0.99 0.99 0.99 1.00 1.00 1.00 1.00
440 0.96 0.96 0.96 0.96 0.97 0.97 0.97 0.98 0.98 0.98 0.99 0.99 0.99 0.99 1.00 1.00 1.00
460 0.95 0.95 0.95 0.95 0.96 0.96 0.96 0.96 0.97 0.97 0.97 0.98 0.98 0.98 0.99 0.99 1.00 1.00
480 0.94 0.94 0.94 0.94 0.94 0.95 0.95 0.95 0.95 0.96 0.96 0.96 0.97 0.97 0.97 0.98 0.99 0.99 1.00 1.00
500 0.93 0.93 0.93 0.93 0.93 0.94 0.94 0.94 0.94 0.95 0.95 0.95 0.95 0.96 0.96 0.96 0.97 0.98 0.99 0.99
520 0.93 0.93 0.93 0.93 0.93 0.94 0.94 0.94 0.94 0.94 0.94 0.95 0.95 0.96 0.96 0.96 0.97 0.97 0.98 0.99
K S – Su Sup p er erh h eat Co Corr r ec ectt i o n Fac Factt o r SET SAT. PRES. STEAM oC barg 138 1.03 121 1.00 1.38 126 1.00 2.76 142 4.14 153 5.52 162 6.90 170 8.27 177 9.65 183 11.0 188 12.4 193 13.8 198 15.2 202 16.6 206 17.9 210 19.3 213 20.7 217 24.1 225 27.6 231 31.0 238 34.5 243
[METRIC]
TOTAL STEAM TEMPERATURE, o C 149 1.00 1.00 1.00
160 1.00 1.00 1.00 1.00
171 0.99 0.99 1.00 1.00 1.00 1.00
182 0.99 0.99 0.99 0.99 1.00 1.00
193 0.98 0.98 0.99 0.99 0.99 1.00 1.00 1.00 1.00
205 0.98 0.98 0.98 0.98 0.99 0.99 0.99 1.00 1.00 1.00 1.00 1.00
216 0.97 0.97 0.97 0.97 0.98 0.98 0.98 0.99 0.99 0.99 0.99 1.00 1.00 1.00 1.00
227 0.96 0.96 0.96 0.96 0.97 0.97 0.97 0.98 0.98 0.98 0.99 0.99 0.99 0.99 1.00 1.00 1.00
238 0.95 0.95 0.95 0.95 0.96 0.96 0.96 0.96 0.97 0.97 0.97 0.98 0.98 0.98 0.99 0.99 1.00 1.00
249 0.94 0.94 0.94 0.94 0.94 0.95 0.95 0.95 0.95 0.96 0.96 0.96 0.97 0.97 0.97 0.98 0.99 0.99 1.00 1.00
260 0.93 0.93 0.93 0.93 0.93 0.94 0.94 0.94 0.94 0.95 0.95 0.95 0.95 0.96 0.96 0.96 0.97 0.98 0.99 0.99
271 0.93 0.93 0.93 0.93 0.93 0.94 0.94 0.94 0.94 0.94 0.94 0.95 0.95 0.96 0.96 0.96 0.97 0.97 0.98 0.99
K P - High Pre ressur ssure e Corre orrectio ction n Fa Factor 1.25
1.15
KP KP =
1.05
0.1906 0.1 906P P - 100 1000 0 0.2292 0.2 292P P - 106 1061 1
0.95 1500 [103.4]
1900 [131.0]
2300 [158.6]
2700 [186.2]
Pressure, psi psig g [barg] [ barg]
3100 [213.8]
3500 [241.3]
St eam Si zi n g No t es Sec. VI VIII – Use 10 10% ov ove er press p ressur ure e Sec. I – Use 3% 3% ov ove er pressu p ressure re Soni onic c Flow Flow – Use Ste tea am Equations Equations Sub ub--Son onic ic Flo low w – Use Gas/V s/Va apo porr Equ Equa ati tion ons s
Liqu Li quid id Siz izin ing g E NGLISH UNITS UNITS
A
V L G 38 KK W K V P A
P B
METRIC UNI UNITS TS
A
V L G 5.094 KK W K V P A
P B
For ormu mula la Sym ymbo bols ls SYMBOL
A P A PB VL G K KW KV
DESCRIPIPTION
Calc lcul ula ated Orifi Ori fice ce Ar Are ea Inlet Flowing Flowin g Pressu Pressure re [ P1 = Pset + Pover – Ploss] Outl utle et Flowing Flowi ng Pressu Pressure re [ P2 = Pback] Required Capacity Spe pecif cific ic Gravity [K=0. =0.90 90 x K d ] ASME A SME Coeff Coef f i c i en entt o f Di Dis s c h ar arg g e [K Back Pressu Pressure re Cor orrecti rection on Fact Factor or Visc iscosi osity ty Correction Facto Factor r
NOT OTE E: Tempera emperatu ture re is not required requi red to calcul ate or orif ific ice e are area. a.
Units SYMBOL
ENGLISH
METRIC
A P A PB VL G K KW KV
in2 psig psig gpm ---------
cm2 barg barg m 3/h /hr r ---------
Liqu Li quid id The herm rma al Exp Expa ans nsio ion n Re Reli lie ef V L VL = B= H= G= C=
BH B H
500G C
Li quid Liqu id Flow Rate, Rate, gp gpm m Cubi ubicl cle e Exp xpa ans nsio ion n Coeffi Coeffici cie ent pe p er °F °F To t al Heat Heat Tr ans ansff er Rate, BTU/h BTU/h r Spe pecif cific ic Gravity Speci pecifi fic c He Hea at, BTU BTU/lb°F /lb°F
Perr API Pe A PI 521 521,, Sec Sec t i o n 3. 3.14 14
Fi r e Si zi n g The Pro roc c edu dure re Us ed In Fir ire e Siz izin ing g Depe pend nds s On The Co de des s An A n d En Eng g i n eer eerii n g Pr Prac actt i c es A p p l i ed A t Eac Each h In Ins s t al alll at atii o n . Som ome e Pro roce cedu dure res s Tha hatt May B e Use sed d For Fir ire e Siz izin ing: g: API A PI RP 521 Re Reco comm mmended ended Pract Practic ices es For For The Desi Design gn An A n d In Ins s t al alll at atii o n Of Pr Pres ess s u r e Reliev Reli evii n g Systems In Refineries. (SET 15 ps psig ig [1.0 [1.03 3 barg]) barg] ) API A PI 2000 Venting Atmosp Atmospheric heric And Low Pressure Storage Stor age Tanks Tanks (S (SET ET < 15 ps psig ig [1.0 [1.03 3 barg]) barg ]) API A PI 2510 Design Of Lp L p Gas Gas Installations Installation s NFPA 58 Stor torage age And Ha Handli ndling ng Liq Liquefied uefied Pe Petro troleum leum Gasse asses s (Natio (National nal Fire Protection A ssoc ssociation) iation) CGA S-1.3 Sta Stati tion onary ary Storage Sto rage Tanks Tanks
API A PI 521 (Fir (Fi r e) – Un Unw w et ettt ed Ves Vess s el els s A
F ' AS P1
A = Ca Calc lcul ula ated PSV Ori Orifi fice ce Ar Are ea, in 2 F’ = Rel Rel ates to t o Bare Vessel Vessel Me Metal tal unkn know own, n, F’=0.0 F’=0.042 42)) Temper emperatu aturr e at at Re Rell i ef (if un A S = Exp xpos ose ed Sur urface face Ar Are ea of Vess sse el , ft 2 P1 = Reli lie evin ving g pressur pressure e, psia [ P1 = Pset + Pover – Ploss + Patm ]
Perr API Pe A PI 521 521,, Sec Sec t i o n 3. 3.15 15
API A PI 521 (Fir (Fi r e) – Un Unw w et ettt ed Ves Vess s el els s F’ Opera perati ting ng Fac to tor r 700
F '
600
0.1406 T wall T 1
1.25
0.6506
CKT 1
k = 1.001 500
s a G F º
400
k = 1.4 1.4 300 200
Conservative
Minimum
100 0 0.005
0.015
0.025
0.035
0.045
Operati Ope rating ng Fact ctor, or, F
0.055
Twall , °R T1, °R
Step 1
API A PI 521 (Fir (Fi r e) – Wet Wettt ed Ves Vess s el els s Prom rompt pt Fire-F Fire-Fight ighting ing Effo fforts rts & Ad A d eq equ u at ate e Drai Dr ain n ag age e Exists
Q
21,000 F Awe wet t
0.82
Prom rompt pt Fire-F Fire-Figh ightin ting g Efforts & Ad A d eq equ u at ate e Drai Dr ain n ag age e Does Not Exists Exist s
Q
34,500 F Awe wet t
0.82
Q = Tot otal al Heat Heat Input Inp ut t o Wet Wet t ed Sur Surff ace, BTU/ BTU/hr hr F = Environ nvi ronme mental ntal Facto ctor r A w et = Tot otal al We Wett t ed Surf Sur f ace Ar Area ea,, ft 2
Perr API Pe A PI 521 521,, Sec Sec t i o n 3. 3.15 15
API A PI 521 (Fir (Fi r e) – Wet Wettt ed Ves Vess s el els s Tot otal al Vessel Vessel Wetted Sur face Area, ft2, Up Up to t o 25 ft. ft . Ab Abov ove e Ground Groun d Leve L evell or, o r, (in the th e Case Case of a Sph Sphere) ere) to th the e Elevation Ele vation of Largest Diamete Diameterr - Whic hicheve heverr Is Greate Greater. r. Sphere
Vertical Vessel Horizontal Vessel
Max. Dia.
25 ft ft..
Ground
API A PI 521 (Fir (Fi r e) – Wet Wettt ed Ves Vess s el els s VESSEL B ar e (Un -In s u l at ed )
F 1.0
Insulated Cond onduct ucta ance Va Value: 4 btu btu//hr/ft 2/°F 2 1
0.3 0.15 0.075
Ear t h Co v er ed , A b o v e Gr ad e
0.03
B ar e Wi t h Wat er Sp r ay
1.0
Un d er g r o u n d
0.0
API A PI 521 (Fir (Fi r e) – Wet Wettt ed Ves Vess s el els s W
Step 2
Q
H vap
W = Requ Requii r ed Valv Valve e Ca Capaci pacitt y, l b/h b/hr r Q = Tot otal al Heat Heat Input Inp ut t o Wet Wet t ed Sur Surfac face, e, BTU/ BTU/hr hr Hv ap = Latent Heat of o f Vapo pori riz zati tion on,, BTU/lb BTU/lb EXA MPL ES:
A MMONIA B ENZENE B UTA NE CO2 ETHA NE ETHYL ENE METHA NE PROPA NE WATER
589 169 166 150 210 208 219 183 970
API A PI 521 (Fir (Fi r e) – Wet Wettt ed Ves Vess s el els s ENGL ISH
A
W TZ
CKP CK P1 K b K c M
Step 3
METRIC
A
1.316W TZ
CKP CK P1 K b K c M
Use Va Vapo porr Equ qua ati tion ons s to Calc lcul ula ate Re Requ quir ire ed Ori rifi fice ce Ar Are ea. Use the Boili Boi ling ng Temp mpe erature of th the e Li Liqu quid id (Fla lash sh to t o Va Vapor por)) for “ T” . If unkno unk nown, wn, we w e suggest sugg est usin u sing g 200 00°F °F [93 [93°C °C]]
Use Re Reli lie evi ving ng Temp mpe eratur rature e for or orif ific ice e sizing. Use Opera Operati ting ng Temp mpe eratur rature e for so soft ft go good od selection.
API A PI 2000 (Fir (Fi r e) Sett Pressur Se Press ure e < 15 ps psig ig [1.0 [1.03 3 barg]
V 1107 FA
0.82
V = Vent ntin ing g Requ quir ire ement ment,, ft 3/h /hr, r, ai ai r (6 (60° 0°F) F) F = Env nvir iron onmental mental Fact Factor or (if un unkn know own, n, F= F=1.0) A = Exp xpos ose ed Sur urface face Ar Are ea of Vess sse el, ft ft2
API A PI 2000 (Fir (Fi r e) - Su Surr f ac ace e Ar A r ea A,, A
ft2 ft
20 30 40 50 60 70 80 90 100 120 140 160 180 200 250 300
SCFM AIR A IR 352 527 702 878 1053 1228 1403 1580 1780 2100 2450 2800 3167 3517 2983 4417
A,, A
ft2 ft
2800 28 00 ft ft2
SCFM AIR A IR
350 4800 400 5200 500 5900 600 6533 700 7133 800 7700 900 8217 1000 8733 1200 9283 1400 9783 1600 10,233 1800 10,650 2000 11,033 2400 11,733 2800 12,367 over ov er 2800 2800 use formula
Using t he calculated, calculated, required, relief valve capacit capacity y and s et pressur e, use air capacity tables (10% (10% overpr ov erpressur essur e) in catalogs c atalogs to select select orifice ori fice area and valve size. For set pr essur es 15 psig and below, be sure to u se the actu actua al K D A SME “ K ” K D = ASME 0.90
Reference: Referenc e: API 2000, 2000, Secti Section on s 1.5.2 and 2.3
