is 12992-1 (1993): safety relief valves - spring loaded, part ...safety relief valves’, issued by...

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IS 12992-1 (1993): Safety Relief Valves - Spring Loaded,Part 1: Design [MED 17: Chemical Engineering Plants andRelated Equipment]

IS 12992 ( Part 1) : 1993

wTiif9 WIT

Indiavz Standard

SAFETY RELIEF VALVES - SPRING LOADED - SPECIFICATION

PART 1 DESIGN

UDC 621.646~28

0 BIS 1993

BUREAU OF INDIAN STANDARDS MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

October 1993 Price Group 13

Chemical Engineering Plants and Related Equipment Sectional Committee, HMD 17

FOREWORD

This Indian Standard ( Part 1 ) was adopted by the Bureau of Indian Standards after the draft finalized by the Chemical Engineering Plants and Related Equipment Sectional Committee, had been approved by the Heavy Mechanical Engineering Division Council.

In the formulation of this standard assistance has been derived from API 526 : 1984 ‘Flanged steel safety relief valves’, issued by the American Petroleum Institute.

This standard is being issued in two parts, Part 1 covers design and Part 2 testing.

For the purpose of deciding whether a particular requirement of this standard is complied with, the final value, observed or calculated, expressing the result of a test or analysis, shall be rounded off in accordance with IS 2 : 1960 ‘Rules for rounding off numerical values ( revised )‘. The number of signs_ cant places retained in the rounded off value should be the same as that of the specified value in this standard.

IS 12992 ( Part 1) : 1993

Indian Standard

SAFETYRELIEFVALVES-SPRINGLOADED- SPECIFICATION

PART 1 DESIGN

1 SCOPE

1.1 This standard covers the specification for flanged steel spring loaded safety relief valves. Basic requirements are given for:

a) orifice designation and area; b) valve size and rating, inlet and outlet; c) materials, body and spring; d) pressure-temperature limits; and e) centre-to-face dimensions, inlet and outlet.

1.2 The valves regulated by IBR (Indian Boiler Regulations) are excluded from the scope of this standard. 1.3 For ihe convenience of the purchaser, a sample specification sheet is given in Annex A. 1.4 Name plate nomenclature and requirements for stamping are detailed in Annex B. 1.5 The purchaser is primarily responsible for:

a) Selection of type of valve and desired pressure- temperature ratings; and

b) Specification of materials which will satisfac- torily resist corrosion from the process fluid or environmental conditions.

1.6 Whenever the information included on the purchaser’s specification sheet or purchase order con- flicts with the provisions of this standard, the purchaser’s specification sheet or purchase order shall govern. The manufacturer shall call such conflicting requirements to the attention of the purchaser whenever possible.

2 REFERENCES

IS No.

2825 : 1969

28.56 : 1979

3038 : 1983

3233 : 1965

4899 : 1976

Tide

Code of unfired pressure vessels

Carbon steel castings for pressure containing parts suitable for high temperature service (fusion welding quality) ( second revision )

Alloy steel castings for pressure containing parts suitable for high temperature service ( second revision )

Glossary of terms for safety valves and their parts Ferritic steel castings for use at low temperatures (first revision )

7806 : 1975 Ferritic and austenitic steel cast-’ ings for high temperature service

12992 Spring loaded safety relief valves : ( Part 2) :1990 Part 2 Testing

13159 Steel pipe flanges and flanged fit- (Part 1) :1993 tings : Part 1 Dimensions

3 DEFINITiONS

For definitions ofvarious terms used in connectionwith spring loaded pressure relief valves, refer to IS 3233 : 1965.

4 DESIGN

4.1 General

Safety and safety reliefvalves discussed in this standard shall be designed and manufactured in accordance with the applicable requirements of IS 2825 : 1969.

4.2 Determination of Orifice Area

The required orifice area shall be determined in accordance with Annex C and Annex D. The standard orifice areas and the corresponding letter designations are :

Orifice Area Orifice Area

64 mm) 69 mm) D 71 L 1841

E 126 M 2323

F 198 N 2800

G 325 P 4116

H 506 Q 7129

J 830 R 10323

K ‘1186 T 16774

4.3 Valve Selection

For valves described in this standard, inlet and outlet flange sizes and pressure-temperature ratings shall con- form to the data in Tables 1 to 14. Inlet pressure limits are governed by inlet flange pressure limits or by manufacturer.‘s spring design limits, whichever is smaller. Outlet pressure limits are determined by valve design. 4.4 Dimensions

Centre-to-face dimensions shall be in accordance with Tables 1 to 34 with tolerances as follows:

Valve Inlet Size Tolerance

Up to and including 100 mm * 1.6 mm

Above 100 mm rt 3.2 mm

1

IS 12992 ( Part 1) : 1993

Flange facings and dimensicns shall be in accordance with IS 13159 (*Part 1) : 1993, the inlet flange may be modified to increase the height of the raised face.

43 Lifting Levers

Plain lifting levers shall be provided on all safety valves for steam or air service and on safety relief valves when designated on the purchaser’s specification sheet; packed lifting levers shall be provided on hot water service and wheri specified by purchaser. Lifting levers shall be capable of relea&ng the seating force on the disc when the valve is subjected to a pressure of at least 75 percent of the set pressure of the valve. All safety relief valves shall be furnished with a threaded cap over the spring adjusting screw unless otherwise stated. 45.1 Means shall be provided in the design of all valves for sealing all adjustments which can be made without disassembly of the valve before or after it is installed.

4.6 Special Construction Features

Special construction features shall be provided as agreed upon by the manufacturer and the purchaser.

5 MArnRL4L

5.1 General

For special corrosion problems and applications beyond the pressure temperature limits of this standard, constructioh materials shall be those agreed upon by the manufacturer and the purchaser.

5.2 Body and Spring

The body and spring material shall be in accordance with Tables 1 through 14 for the required temperature range. The valve body material shall be equivalent to, or better @an, the following types and grades:

Cast carbon Steel IS 2856, Gr 2

Cast carbon molybdenum steel IS 3038, Gr 4

Cast 3; percent nickel steel IS 4899, Gr 7

Cast austenitic steel IS 7806, Gr 3 or 5

5.3 Inter& Parts

Materials for the internal parts of the valve shall be in accordance with the manufacturer’s standards for temperature and service and indicated on the purchaser’s specification sheet.

6 INSPECTION AND SHOP TESTS

6.1 Inspection

The purchaser reserves the right to witness the shop tests and inspect valves in the manufacturer’s plant according to the extent specified on the purchase order.

6.1.1. Shell Test. The primary pressure parts ofeach valve exceeding DN 25 or 21 bar set pressure where the materials used are either cast or welded shall be tested at a pressure of at least 1.5 times the design pressure of the parts. These tests shall be conducted after all machining operations have been completed. The secondary pressure zone of each closed bonnet valve exceeding DN 25 inlet size wheri such valves are designed for discharge to a closed

system shall b$ tested with air or other gas at a pressure of at least 2 bar. There shall be no visible sign of leakage.

6.2 Set P&we Test

All safety and safety relief valves shall be set and adjusted to the specified set pressure in accordance with IS 2825 : 1969, the manufacturer’s standard practice as published, or as designated by the purchaser. The set pressure adjustment shall be sealed when specified.

6.3 Seat Lea’kage Test

Safety and safety relief valves shall be subjected to a seat leakage test in accordance with IS 12992 (Part 2 ) : 1990.

7 MARKING

7.1 On the Body of the Safety Valve

The following minimum information shall be marked ou the body of all safety valves. Marking on the body may be integral with the body or on a plate securely fixed to the body. When a plate is used, it shall be separate and distinct from the identification plate referred elsewhere in this standard:

a> b) 4

4

The inlet and outlet nominal size, for example PN; The material designation of the body; The nianufacturer’s name and/or trade-mark; and An arrow showing the direction of flow where the inlet and outlet connections have the same dimensions or the same pressure rating.

7.2 Identification Plate

The following minimum information, stating units, shall be on ad identificatiou plate securely fixed to the safety valve:

a) The limiting operating temperature(s) (in “C) for which the valve has been designed;

b) The set pressure in MPa; c) The number of this standard; d) Manufacturer’s type reference; e) Coefficient or discharge or certified discharge

capacity of reference fluid, kg/b; f) Flow area in square centimetres; and g) Lift in millimetres and corresponding over

pressure expressed as a percentage.

7.3 Name Plate

Each valve shall have a corrosion-resistant name plate permaneutly attached to the body or bonnet. The name plate shall be stamped with the data specified in Annex B.

7.4 Tagging

Each valve shall be stamped with the valve number or other identificatiou data as specified on the purchase order. This data may be stamped ou the name plate or on a separate corrosion-resistant tag that is permanently attached to the valve.

2

IS 12992 ( Part 1) : 1993

8 SHIPMENT b) Threaded opeklgs shall be plugged with a

8.1 Preparation for Shipment suitable protective device. Temporary plugs should be readily distinguishable from per-

a) After test and inspection, all exterior sur- manent metal plugs. faces except flange facings shall be painted. Corrosion-resistant materials need not be

c) To prevent damage to the faces during shipment’ and foreign material from entering, inlet and

painted. outlet flanges shall be protected.

Table 1 Flanged Steel Safety Relief Valves - ‘D’ Orifiie

( Clauses 4.3 and 4.4 )

P

Materials V&W ~omioal EYange Mdmum Pressure &ding Bar Cetlll+tO-F8_ Sizes Rating(Clas3) Conventional Balanced Bellows and Balanced Piston Valves Conven- Balanced Dim&

tiOMl Below (mm)

Valves Valves

Inlet by Inlet Outlet

Body Spring Orifice by Inlet Outlet - 267oc -60°C to - 29°C to - 28OC to 232°C 427% 540°C 38’C 38OC Inlet outlet outlet to - 102°C - 101°C - 59OC 38°C

Temperature Range - 28°C to 23Z’C

25D50 150 150 20 13 20 105 114

25D50 300 150 20 20 20 105 114

Cast Carbon 25D50 300 150 52 43 20 105 114 carbon steel steel 25D50 600 150 104 87 20 105 114

4OD50 900 ux) 156 130 42 105 140

40D50 1500 300 266 217 42 105 140

4oD65 2500 300 422 361 52 140 165

. .

Cast carbon steel

High

temperature alloy

steel

25D50 150 150

25D50 300 150

25D50 300 150

25D50 600 150

4OD50 900 300

4OD50 1500 300

4OD65 2500 300

233’% to 42PC TmpFaturr Range

13

- 20

43

87

130

217

361

Temperature Range 428°C te 540%

* . 6 20 ios 114

20 20 105 114

29 20 - 105 114

58 20 105 114

87 42 105 140

145 42 105 140

241 52 - 140 165

Cast

carbon molybdenum

steel

High 23D50 300 150 36 16 20 105 114

temper- 25D50 600 150 71 31 20 105 114 ature

40D50 YOO 300 107 47 52 105 140 alloy . . . steel 4OD50 1500 300 179 78 52 105 140

40D65 2500 300 297 131 52 140 165

Materials Valve Sizes

Table 2 Flanged Steel Safety Relief Valves - ‘E’ Or&e t:

( Clauses 4.3 and 4.4 ) G

z! NominallFlange Maximum Pressure Rating Bar Ceotr&o-Face

Rating ( C&s ) Conventional Balanced Bellows and Balanced Piston Valves Convett- Balanced Dimensions

tionaI BdOW 64

Body

Valves Valves

Inlet by Inlet Outlet

Spring Orifice by Inlet Outlet - 267°C -60°C to - 29OC to - zw to 232’C 427°C 540°C 38“C 38°C Inlet Outlet outlet to - 102°C - 101°C - 59OC 38OC

h

2 3 c

V

. .

c

s Temperature Ram : - 2@C to 232%

I 20 105 114

20 105 114

20 105 114

20 105 114

42 105 140

42 105 140

52 140 165

20 13

20 20

52 43

104 87

156 130

260 217

422 361

2SE!50 150 150

25E30 300 150

25E50 300 150

25E50 600 150

4OE50 900 300

4Ol30 1500 300

4OE65 2500 300

Cast carbon steel

Carbon steel

Temperature Range 233°C to 427“C

6

20

29

58

87

145

241

- I 105 114

105 114

105 114

105 114

i

105 140

105 140

140 165

20

20

20

20

42

42

52

Temperature Range 428OC to 540% I +

Cast carbon molybdenum Steel

300 150

660 150

900 300

1500 300

2500 300

36 16 20 105 114

71 31 20 105 114

107 41 52 105 140

179 78 52 105 140

297 131 52 140 165

High 2.X50

temper- 2SE50 ature alloy

4oF.50

steel 4OE50

4OE65

W

Temperature Rauge -29°C to -59°C

4OF50 150 15g u) 20 16 124 121

Cast 4OF50 300 150 20 20 16 124 121

3; Carbon 4OF50 300 150 52 .- 20 16 124 152

percent steel 4OF50 600 150 104 nickel

20 16 124 152

steel 4OF65 900 300 156 52 35 124 152

4OF65 1500 300 260 - 52 35 124 152

4OF65 2500 300 352 52 35 140 165

Temperature Range -60°C to - 101°C

4OF.50 150 150 ?9. 20 16 124 121

Cast 4OF50 300 150 19 1 20 16 124

3;

121

Auste- ,4OF50 300 150 51 - nitic . 20 16 124 .152 percent

steel 4OF50 600 150 101 nickel 20 16 124 152

steel 4OF65

I I :z , ;;i, i, !, if, !, ! ] r, !, ! ;; ] ;;, ;i, if

Temperature Range - 102°C to - 267‘%

4OF.50 150 150 19 20 16 124 121

cast 4OF.50 300 150 19 20 16 124 121

autenit- Auste- 4OF50 300 150 43 its

nitic 2n 16 124 152

steel steel 4OF50 600 150 87 20 16 124 152

4OF65 900 300 130 52 35 124 152

4OF65 1500 300 155 52 35 124 152

4OF65 2500 300 239 52 35 140 165

_~...r____~_ -.-____ -. - __ -. -

4OH80 150 1.50 20 20 16 130 124 Cast 3; 4OH80 300 150 20 20 16 130 124 Carbon

50H80 300 150 52 .- 20 16 130 124 percent steel

nickal SOH80 600 150 104 20 16 1.54 162

steel 50H80 900 150 1.56 . - 20 16 154 162

I , 5OH80 , 1500, 300, - I - I 193 ( - I - I - I - I 52 , 29 , 154 ( 162

Temperature Range - 60% to - 101°C

4OH80 150 150 19 20 16 130 124 Cast 3; Auteni- 4oH80 3M) 150 19 20 16 130 124

tic 50H80 300 150 51 20 16 130 124 percent

nickel steel 50H80 600 150 101 20 16 154 162

steel 50H80 900 150 104 20 16 154 162

1 5OH80 1 1500 1 3m I - I 112 l -I -I -I -I -I 52 I 29 I 154 1 162

Temperature Range -1Ot’C to -2@C

4OH80 150 150 19 20 16 130 124

Cast Auste- 4oH80 300 150 19 20 16 130 124

austen- nitic 5OH80 300 150 43 i 20 16 itic

130 124

steel steel 5oH80 600 150 87 20 16 154 162

50H80 900. 150 104 - . 20 16 154 162

5OH80 1500 300 112 52 29 154 162

Table 6 Flanged Steel Safety Relief Valves - ‘J’ Orifice

( czuuses 4.3 and 4:4 )

Nontioal Flange Rating ( Class )

MaxImum Pressure Rating Bar

Conventional Balanced Bellows and EIaIanced Piston Valves Conven- BaIanced tionaI Below Valves Valves

Css~tre-to-Face DimCnSioOS

(mm)

Inlet

Inlet Outlet

Outlet - 26pC -60oC to - 29OC to -28Yto 232% 427oc 54ooc 38OC 38OC InIet Outkt to - 1wc - 10l°C - 59°C 38OC 1

1 :-WCtC 12°C

20 13

20 20

52 43

104 87

156 130

190 190

-&Ire Ral

.-

6

20

29

58

87

145

High 65JlOO 300 150 36 temper- 65JlOO 600 150 71

ature alloy 655100 900 150 107

steel 8OJlOO 1500 300 143

5OJ80 150

5OJ80 300

65JlOO 300

i

65Jloo 600

805100 900

8OJloo 1500

5OJ80

5OJ80

653100

653100

65JlOO

655100

1.50

300

308

600

900

1500

L

I

137

137

137

156

184

184

124

124

143

171

181

181

20

20

20

20

20

42

20

20

30

20

20

42

16

16

16

16

16

16

16

16

16

16

16

16

150

150

150

150

150

300

150

150

150

150

150

300

Cast carbon steel

Carbon steel

-I-

I I

Temperatuure Rat c 233’C to 427‘%

124

124

143

171

181

181

13

20

43

87

130

190

High

temperature alloy stqel

cast C@OIl

steel

Temperature Range 428’C to 540°C

Cast carbon Molyb- denum

steel

Temperature Range -29OC to -59°C

Cast

3+

percent

nickel steel

Carbon steel

5OJ80 150 150 20 20 16 137 124

5oJ80 300 150 20 20 16 137 124

655100 300 150 - 52 20 16 I37 143

655100 600 150 104 20 16 156 171

8OJloO 900 150 104 2 20 16 184 181

Cast

3;

percent

nickel steel

, 8OJloO , 1500, 300, -, -, -, 190 , - I - I - I 42 I 16 , 184 , 181

Temperature Range -6O’C to -101°C

5oJ80 150 150 19 20 16 137 124

Auste- 5oJ80 300 150 19 20 16 137 124

nitic 655100 300 150 35 20 16 137 143

steel 655100 600 150 44 20 16 156 171

8OJlOO 900 150 56 20 16 184 181

, 8CUlOLI , 1500, 300, - I 56 I - I - I - I - I - I 42 I 16 1 184 I 181

Temperature Range -102°C to -267?Z

Cast austen-

itic

steel

50580 150 150 19 20 16 137 124

Auste- 50580 3cNl 150 19 20 16 137 124

nitic 655100 300 150 36 20 16 137 143

steel 65JlOO , 600 150 44 - . .-. 20 16 156 171,

8OJlOO 900 150 56 20 16 184 181

8OJlOO 1500 300 56 - 42 16 184 181

Table 7 Flanged Steel Safety Relief Valves - ‘K’ Oritice


Conventional Balanced Bellows and Balanced Piston Valves

Temperature Range -W’C to 232“C

’ 80KlCHII 150 150 20 13 20 11 156 162

Cast 80Klal 300 150 20 20 - 20 11 156 162

carbon Carbon

‘steel 8OKlcQ 300 150 52 43 20 11 156 162

steel 80K100 600 150 104 87 20 14 184 181

80K150 900 150 156 130 20 14 198 216

80K150 1500 300 156 156 42 14 197 216 I

Temperature Ranee 233O to 427°C

1 80KlOO High

80KlOO temper-

ature 80KlOO

alloy steel

80KlOO

80K150

80K150

150 150 13 6 20 11 156 162

300 150 20 20 20 11 156 162

300 150 43 29 20 11 156 162

600 150 87 58 20 14 184 181

900 150 130 87 20 14 198 216

1500 300 156 145 42 14 197 216

300

600

900

1500

150.

150 T 150

300

Temperature Range 428OC to HO’%

156

156

184

197

162

162

181.

216

e -29OC to Tern

52

T!IIIDW&II-C RN

Cast

3;

percent nickel

steel

cast 3;

percent

nickel steel

I :

178

178

lOOM150

lOOMl5P

lOOM150

lOOM150

150

300

300

600

150

300

300

600

150

150

150

150

150

150

150

150

150

150

150

150

Carbon steel

178 184

-T- 178 184 i9

42 42

1OOM150

Austen- lOOM150

itic steel . lOOM150

lOOM150

20 . 6

20 6

20 _ 11

20 11 \

178 184

178 I

203

Temperature Range -102“C to -267°C

lOOM150 150 19

19

37

42

20

20

20

20

cast austen-

itic steel

Auste- loOM150 300

IlitiC

steel lOOMl50 300

lOOMl50 600

.

Table 11 Flanged Steel Safety Relief Valves - ‘P’ Orifiie

( czauses 4.3 and 414 )

Ccntrc-to-Faa Dimensions

(mm)

Nominal Flange Maximum Pressure Rating Bar Matekials Valve sizes Rating ( class ) Conventional Balanced Bellows and Balanced Piston VaIves Qaven- Balanced

IionaI Below

Valves Valves

Ti ‘tisy Inlet 1 Outlet t;:zCI lyzO; 1 -_29Jc1 1 - zto 1 232’C 1 427’C 1 540°C 38“Cou~3SoC Inlet 1 Outlet

Temperature Range -28°C to 232°C

Cast carbon Carbml

steel steel

lOOP150 150 150 20 13 20 6 181 229

. lOOPl50 300 150 - 20 20 20 6 181 229

looP150 300 150 37 37 - 20 11 225 254

lOOP150 600 150 70 70 .- 20 11 225 254

Temperature Range 233“C to 427°C

High 150

150

150

150

150

20

20

20

20

20

13 6

20 20

37 29

70 58

70 70

lOOP150 150

100P150 ,300

looPl50 300

lOOP150 600

h00P150 900

181 229

181 229

225 254

225 254

225 254

temper- atme alloy steel

cast carbon steel

Temperature Range 428°C to 540°C

1

cast High carbon temper- molyb- ature denum alloy steel steel

lOOP150

lcOP150

~lOOP150

36

70

70

254

254

254

Temperature Range -29°C to -59°C

150 20 .- 20 6

150 20 20 6

150 37 ‘- 20 11

150 - 70 20 11

150

300 L 300

cast 1 lOoP150

lalP150

looP150

lOoP150

3: Carbon.

steel

L

percent nickel

St4

lable 12 Flanged Steel Safety Relief Valves - ‘Q’ Orifice


-

Materials Valve Nomi naNlange Maximum Pressure Rating Bar Ckutre-to-Face Sizes Rating ( Class ) Conventional Balanced Bellows and Balanced Piston Valves Conven- Balanced Dimensions

tional Below (mm>

Valves Valves

Ir?et by Inlet ’ Outlet

Body Spring Orifice by outlet

Inlet Outlet - 26% -60°C to - 29°C to - 28’=C to 540°C 38T to - 102T - 101°C - 59°C 38OC

Temperature Range -28°C to 232°C

15OQ200 150 1.50 12 12 8 5 240 241

Cast

rrbon steel

Carbon steel

15oQ2Oo 300 150 12 12 - . 8 5 240 241

15oQ200 300 150 21 21 8 8 240 241

15oQ200 600 150 42 42 . - 8 8 240 241

Temperature Range 233’C to 427?Z

1500200 150 150 12 6 8 5 240 241

High Cast temper- 15oQ200 300 150 12 12 8 5 240 241

nrboo ature steei alloy 15ocEoo 300 150 21 21 8 8 240 241

steel

15OQ200 600 150 42 42 8 8 240 241

Temperature Rauge 428% to 544Y’C

Cast High 15OQ200 300 150 12 12 8 8 240 241 arbon temper- nolyb- ature lenum 15oQ200 600 alloy 150 42 31 8 8 240 241 s

steel steel

c

C:ap Screwed/Bolted Lever Plain/Packed GAG Yes/No

Screwed/Bolted Plain/Packed

Yes/No

Screwed/Bolted Plain/Packed

Yes/No

Screwed/Bolted

Plain/Packed Yes/No

28 2 Others I I

29 30 31 32 33 34 35 36 37

41 42 43

Body Disc Nozzle Spindle Resilient Seat Seal Guide

47 q 48 ’

Spring Bonnet

49 Bellows m 50 F3 51 5

h

Code

Fire Calculated area, cm2 Selected area, cm2 Orifice letter Manufacturer’s model No. Valve capacity Internal valve code Malve rated capacity

Size Inlet/outlet Screwed socket Type facing

52 . Inspection agency 53 g Form of certificate

E 54 Mounting details D. No.

IS 12992 (Part 1) : 1993

ANNEX B

(Clause 1.4)

SAFETY RELIEF VALVE NAMEPLATE NOMENCLATURE

Nomenclature

Size

Type, style,model or figure No.

Orifice

Capacity at x percent overpressure

Serial No. or Shop NO.

Set pressure bar

Back pressure bar

Cold differential test pressure bar

Description

Nominal pipe size, inlet by outlet

Manufacturer’s designation

Valve orifice size, tan- dardized letter designation

kg/h of saturated steam, normal cubic metre per hour of air or litres per minute of water at 21°C Manufacturer’s identification number

Valve inlet pressure at which the pressure relief valve is adjusted to open under service conditions (see Note)

Constant (Example: 7 bar) Variable (Example : 0 to 7 Bar) Valve inlet opeing (see below) pressure on an air test stand at am- bient temperature against atmospheric back pressure. Cold differential test pressure includes applicable temperature correction.

Example 1 Conventional Valve Set pressure bar 14

Back pressure bar Atmoshperic (or zero)

Temperature, deg C 200

Cold differential test pressure, 14 + manufacturer’s bar recommended

temperature correction

Example 2 - Balanced Bellows Valve Set pressure, bar 14

Back pressure, bar 3.5 or 0 to 3.5


Cold differential test pressure, 14 t manufacturer’s bar recommended


Example 3 - Conventional Valve

Set pressure, bar 14

Back pressure, bar 3.5


Cold differential test pressure, 10.5 t manufacturer’s bar recommended


NOTE- Popping pressure on vapours and gases - When constant back pressure is present on conventional valves: Set pressure = Differential test pressure + Back pressure (Depending upon the service fluid temperature, an addi- tional correction factor may be required to obtain thecold differential test pressure for adjusting the valve on the test stand.)

34

IS 12992 (Part I ) : 1993

ANNEX C

(Clause 4.2) DETERMINATION OF ORIFICE AREA

Kb = Capacity correction factor due to back pressure[constant or variable]. This can be obtained horn Fig. 2 which is applied to balanced bellows valves. For conventional safety reliefvalves& = 1. Molecular weight of the gas or vapour. Various handbooks carry tables of molecular weights of materials,but the composition ofthe flowing gas or vapour is seldom the same as that listed in the tables. This value should be obtained from the process data.

a) For Vapour

A = CKP,K,,B m . . . . . . . . . . (1)

M= b) For Sat Steam

A= W

51.45 P,KK&, B . . . . . . . . . . (2)

For P c 105.5. Bar, Kc = 1

For P 2 105.5 Bar, ii =2.7103P-1000 T =

’ 3.2592P- 1061

c) For Superheated Steam z = W

A=51.45P,KKcKbKshB

d) For Liquid P=

A= v?T v,

84.09K 41.25P - Pb K, K, Kp . . . . . . . . . . (3) Pb =

G = [ 25% Over Pressure ]

where Ksh = A =

w=

c =

K=

NOTE - For liquid service ifK is unknown, a conserva- tive value of 0.62 is recommended. VI. =

P, =

B =

Upstream relieving pressure, in bars. This is the k-= set pressure plus the allowable overpressure plus the atmospheric pressure in bar. Capacity correction factor due to constant back pressure. This can be obtained from Fig. 1 which applies to conventional safety relief valves.

Required effective discharge area of the valve in square centimetres. This is a nominal or corn- puted area of flow through a pressure-relief

K, =

valve, differing from the actual discharge area, for use in recognized flow formulae to deter- mine the capacity of a pressure relief valve. (see 4.2 for values). Required flow through valve, in kilograms per hour. K, = Coefficient determined by ratio of specific heats of the gas or vapour at standard conditions. This can be obtained from Table 15. Effective coefficient of discharge for use in

Kp =

fonnula (1) and for formula (2) value assigned by manufacturer.

Absolute temperature of the inlet vapour, in degrees centigrade t 273. Compressibility factor for the deviation of the actual gas from A perfect gas, a ratio evaluated at inlet conditions.

Set pressure at which relief valve is to begin opening, in bar. Back pressure, in bar.

Specific gravity of the liquid at the flowing temperature referred to water = 1.00 at 21’C.

Superheat correction factor. This can be obtained from Table 16. Capacity correction factor due to back pressure. If the back pressure is atmospheric, the factor can be disregarded, or Kw = 1.00 conventional valves in back pressure service require no special correction Kw = 1.00 . Balanced bellows valves in back pressure service will require the correction factor as determined from Fig. 3. Capacity correction factor due to viscosity. For most applications, viscosity may not be sig- nificant, in which case K, = 1.00.

Capacity correction factor due to over pressure. k, ny relief valves in liquid service are sized on the basis of 25 percent over pressure, in which case Kp = 1.00. The factor for other percentages of overpressure can be obtained from Fig. 4. Liquid discharge capacity , I/m.

C&, the ratio ofspecitic heats of any ideal gas or the ratio of specific heats of a diatomic acutal gas that expands in accordance with the perfect gas laws, values of K can be determined from the properties of gases as presented in any acceptable reference work.

35

IS 12992 ( Part 1) : 1993

0.6

n I1 I I I III I I I I ‘0 10 20 30 40 50 60 70 60 90 100

% ABSOLUTE BACK PRESSURE = BACK PRESS”RE’ ber SET PRESSlJRE.OVERPRESSURE,bar

* 100

5 YxlOO

Example

Set pressure [MAWP] =7bar Superimposed back pressure = 5 bar Spring set =2bar Built up back pressure = 0.7 bar

Percent absolute back pressure = +$$+ (loo) = 77.1 percent

Follow dotted line 8 = 0.89 [From curve] Capacity with back pressure = (0.89) (Rated capacity without back pressure)

NOTE - This chart is typical and suitable for use only when the make of valve or the actual critical flow pressure point for the vapour or gas is unknown; otherwise, the valve manufacturer should be consulted for specific data.

FIG. 1 CONSTANT BACK-PRESSURE SIZING FACWR B FOR CONVENTIONAL SAFER’ RELIEF VALVES (VAPOURS AND GASES ONLY)

Table 15 Valves of Co-eftkient ‘C’

k : C

1.00 234.3

1.02 236.7

1.04 238.3

1.06 239.9

1.08 241.4

1.10 243.8

1.12 245.4

1.14 246.9

k( c k C k c

1.32 259.5 1.48 270.4

1.34 260.2 1 so 271.2

1.36 261.8 1.52 272.1

1.38 263.4 1.54 274.3

1.40 264.9 1.56 275.2

1.42 266.5 1$8 276.6

1.44 267.3 1.60 277.5

1.46 268.8 1.62 279.1

k c

1.64 280.6

1.66 281.4

1.68 282.9

1.70 283.8

2.00 297.9

2.20 307.3

36

IS 12992 ( Part 1) : 1993

0.60

0.50 0 5 10 15 20 25 30 35 40 15 50

% GAUGE BACK PRESSURE: BACK PRESSURE, bar x ,oo

SET PRESSURE, bar

NOTE -The above curves represent a compromise of the values recommended by a number of relief valve manufacturers and may be used when the make of valve or the actual critical flow pressure point for the vapour or gas is unknown. When the make is known, the manufacturer should be consulted for the correction factor.

These curves are for set pressures of 3.5 bar and above. They are limited to back pressure below critical flow pressure for a given set pressure. For subcritical flow back pressures below 3.5 bar, the manufacturer must be consulted for the values of&

FIG. 2 VARLULE OR CONSTANT BACK-PRESSURE SIZING FACTOR ‘K,,’ FOR BALANCED BELLOWS SAFEIT RELIEF VALVES (VAPOURS AND GASES)

37

IS 12992 ( Part 1) : 1993

1.00

0.95

0.90

0.65

0.60

0.75

0.70

0.65

0.60

0.55

0.50 0 10 20 30 10 50

BACK PRESSURE, bar ‘1. GAUGE BACK PRESSURE: x 100

SET PRESSURE, bar

NOTE-The above curve represents a compromise of rbcvalues recommended by a number of relief valve manufacturers. This curve may be used when the make of the valve is not known. When the make is known, the manufacturers should be consulted for the correction factor.

,

FIG. 3 VARIABLE OR CONSTANT BACK-PRESSURE SKLNG FACIDR ‘I&’ FOR 2.5 PERCENT OVER PRESSURE ON BALANCED BELLOWS [SAITTY RELIEF VALVES (LIQUIDS O~Y)]

38

IS 12992 ( Part 1) : 1993

0.90

0.60 z.2 “0 0.70

E f 0.60

z 2 0.50

tt g 0.40

00 0.30

0.20

0 0 5 to 15 20 25 30 35 40 45 50

PERCENT OVERPRESSURE

,

NOTE-The above curve shows that up to and including 25 percent overpressure, capacity is affected by the change in lift, the change in orifice discharge co-efficient, and the change in overpressure. Above 25 percent, capacity is affected only by the change in overpressure. Valves operating at low overpressures tend to chatter; therefore, overpressures of less than JO percent should be avoided.

FIG. 4 CAPACITY CORRECTION FACKIRS DUE M OVER-PRESSURE FOR REUEFAND Sm RELIEF VALVES IN LIQUID Smvm

39

As in the Original Standard, this Page is Intentionally Left Blank

IS 12992 ( Part 1) : 1993

ANNEX D

(Clause 4.2) SIZING FOR GAS EXPANSION DUE TO EXTERNAL FIRE

The discharge areas for safety and safety relief valves F’ = on gas containing vessels exposed to open fires can be determined by the use of the following formula : A. =

where A =

F’A A= +x 18.86

0

P, =

Effective discharge area of the valve, in square centimetres.

An operating factor determined from Figure 5.

Exposed surface area of the vessel, in square metres; and

Upstream pressure, in bar. This is the set pressure multiplied by 1.10 or 1.20 ( Depending on the over pressure permissible) plus the at mospberic pressure, in bar.

i.005 0.015 0.025 0.035 0.045 0.055

RELIEF VALVE FACTOR F1

NOTE - F’ = Factors for noninsulated carbon steel vessels in gas service exposed to open fires.

FIG. 5 SIZING FOR GAS EWANSION DUE TO EXTERNAL FIRE

43

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I obtained from the Bureau of Indian Standards.

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Dot No. HMD 17 ( 5119)

Amendments Issued Since Publication ‘1

Amend No. Date of Issue Text Affected

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