PSV Connection in Caesar II

Stress Analysis Analysis of PSV connected Piping systems using Caesar II PSV or pressure safety valves are very common to any process industry. To protect any equipment from overpressure PSV systems are used in lines. Two types of PSVs are extensively used in process industries: a !pen disc"arge PSV and # Closed disc"arge PSV. $ue to any uncertain event if pressure of any equipment #ecomes "ig"er t"an t"e set pressure of t"e installed PSV s t"en t"ey pop up and reduce t"e system pressure. $uring popong up activity t"e PSVs exert "uge reaction force over t"e system. $uring analysis of PSv connected stress systems we "ave to consider t"is reaction force. T"is is t"e main reason t"at PSV connected systems #ecome stress critical. T"e following write up will try to explain t"e met"ods used during analysis of suc" systems using Caesar II. Required Documents for analysis:

T"e following documents are required w"ile inputting in Caesar II. •

Stress isometrics

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P%I$ and line list

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PSV datas"eet wit" reaction force and PSV weig"ts.

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&quipment 'A and datas"eet if equipment is part of t"e stress system.

Reaction force Application philosophy: (eforee we star (efor startt t"e actu actual al analy analysis sis we s"ould first )now t"e reaction force. *ormal *ormal pract practice ice is to o#tain t"e reaction force from PSV vendor or manufacturer. +owever if during preliminary stage of analysis data is not availa#le t"en t"e reaction force for open disc"arge PSVs can #e calculated using t"e #elow mentioned formula ,from API -P /0. (ut later it must #e corrected for forces received from vendor.

1ig.2: Typical !pen disc"arge PSV connection -eaction force at t"e point of disc"arge in l#f3 145,67899 ;<=T7,=>2?@>AP +ere3 64flow of any gas or vapour in l#m7"r  =4ratio of specific "eats ,Cp7Cv at t"e outlet condition T4temperature at t"e outlet in o?4molecular weig"t of t"e process fluid A4area of t"e outlet at t"e point of disc"arge in inc"B/ P4Static pressure wit"in t"e outlet at t"e point of disc"arge in psig. Cp and Cv4Specific "eat at t"e constant pressure and at constant volume respectively. 1or closed disc"arge PSV systems t"ere is no specific met"od to calculate t"e reaction force. Complex time "istory analysis can #e used to exactly calculate t"e reaction force for closed disc"arge PSV systems. T"e reaction force application p"ilosop"y for open disc"arge PSV ,PSV output disc"arges into atmosp"ere connected systems is same t"roug"out t"e process industries. (ut for closed disc"arge PSV connected system t"e force application p"ilosop"y varies from organisation to organisation. 1ew organisation applies t"e reaction force for closed disc"are PSVs #ut few organisations does not consider  it. So user to follow t"e company specific proect guidelines is suc" cases.

Where to apply the reaction force:

T"e following figure ,1ig. / s"ows t"e points w"ere t"e reaction force is required to #e applied for open disc"arge PSVs.

1ig./: -eaction force Application point for open disc"arge PSV connected systems. 1ig. 8 s"ows t"e application point ,If required of reaction forces for closed disc"arge PSV connected systems.

1ig.8: -eaction force Application point for Closed disc"arge PSV connected systems. Caesar II load cases for PSV connected systems: PSV forces are considered as occassional forces. So occasional Stress due to PSV reaction force "as to #e calculated and to #e limited wit"in 2.88 times S" ,As per code AS?& ( 82.8. +ere S"4(asic allowa#le stress at "ot condition. (ased on company practise PSV reaction force is added eit"er wit" $esign temperature case or wit" operating temperature case. Also some organisations "ave t"e practise of ma)ing !ne PSV popping up and ot"er stand #y load cases. Accordingly ma)e t"e load cases as s"own #elow:

1ig.: Caesar II simple load cases for analysis PSV connected system T"e following load cases assumes two temperatures ,T24!perating temp3 T/4design temp alongwit" 6ind and Seismic load cases: D2.

66>+P

+E$

D/.

6>T2>P2

!P& F!perating temperature case

D8.

6>T/>P2

!P&FG$esign temperature case

DH.

6>T2>P2>12

!P&F!perating temp>PSV reaction , PSV 2 poppoing up

D.

6>T2>P2>1/

!P&F!perating temp>PSV reaction , PSV / poppoing up

D9.

6>T2>P2>6I*2

!P&F!perating temp>6ind from *ort"

D.

6>T2>P2>6I*/

!P&F!perating temp>6ind from Sout"

DJ.

6>T2>P2>6I*8

!P&F!perating temp>6ind from &ast

DK.

6>T2>P2>6I*H

!P&F!perating temp>6ind from 6est

D20.

6>T2>P2>L2

!P&F!perating temp>Seismic from *ort"

D22.

6>T2>P2GL2

!P&F!perating temp>Seismic from Sout"

D2/.

6>T2>P2>L2

!P&F!perating temp>Seismic from &ast

D28.

6>T2>P2GL2

!P&F!perating temp>Seismic from 6est

D2H.

6>P2

SLSFSustained case

D2.

DHGD/

!CCFPure PSV -eaction

D29.

DGD/

!CCFPure PSV -eaction

D2.

D9GD/

!CCFPure 6ind

D2J.

DGD/

!CCFPure 6ind

D2K.

DJGD/

!CCFPure 6ind

D/0.

DKGD/

!CCFPure 6ind

D/2.

D20GD/

!CCFPure Seismic

D//.

D22GD/

!CCFPure Seismic

D/8.

D2/GD/

!CCFPure Seismic

D/H.

D28GD/

!CCFPure Seismic

D/.

D2>D2H

!CCFPure !ccasional>Sustained

D/9.

D29>D2H

!CCFPure !ccasional>Sustained

D/.

D2>D2H

!CCFPure !ccasional>Sustained

D/J.

D2J>D2H

!CCFPure !ccasional>Sustained

D/K.

D2K>D2H

!CCFPure !ccasional>Sustained

D80.

D/0>D2H

!CCFPure !ccasional>Sustained

D82.

D/2>D2H

!CCFPure !ccasional>Sustained

D8/.

D//>D2H

!CCFPure !ccasional>Sustained

D88.

D/8>D2H

!CCFPure !ccasional>Sustained

D8H.

D/H>D2H

!CCFPure !ccasional>Sustained

D8.

D/GD2H

&MPFPure &xpansion

D89.

D8GD2H

&MPFPure &xpansion

Output Study: •

C"ec) Code stresses for load cases D23 D2H and from D/ to D89. It is #etter to )eep stresses for  D2 and D2H #elow 90N and for t"e rest wit"in J0N.

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C"ec) forces for load cases from D2 to D2H.

Fe points to !eep in mind:

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It is a #etter practice to use 8 way restraints in #ot" inlet and outlet piping of PSV connected systems if feasi#le ,As s"own in figure / and 8 a#ove. +owever if not possi#le t"en try to provide 8 way restraint in outlet only #y layout modification.

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In normal operating case Safety valve inlet line temperature will #e operating temperature up to inlet of safety valve and Safety valve outlet line will #e in am#ient temperature up to t"e "eader.

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Sometimes a $ynamic Doad 1actor ,$D1 of / is used for calculating PSV reaction force.

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If any stress failure or a#normal routing c"anges are required3 t"en certain local area from "eader  can #e used average temperature for / meters or $ w"ic" is "ig"er ,Safety valve outlet oining at "eader unction point and also s"all #e ta)en process engineerOs approval.

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If required stress engineer s"all provide -.1 pad for t"e trunnion type support.

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If connection of psv closed system is emerging from "eader wit" H put SI1 for t"is tapping. If  required tapping point of t"e outlet line and outlet "eader s"all #e reinforced to reduce SI1.

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In case of any safety valve assem#ly is placed on top platform of any vessel3 Support can #e ta)en eit"er from top platform or support can #e arranged from t"e top portion of vessel ta)ing clip from t"e vessel. In #ot" t"e cases t"e load and locations of support or clip equipment vendor  must #e informed t"oug" t"e mec"anical group along wit" t"e clip information.

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$o not provide spring #elow safety valve inlet line

*ote: Please reply in comments in case of any confusion or if you want to add somet"ing.