1230 - Ewan - Study of Pressure Safety Valve Response Times Under Transient Overpressures

8/10/2019 1230 - Ewan - Study of Pressure Safety Valve Response Times Under Transient Overpressures

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A Study of Pressure Safety Valve Response Times

under Transient Overpressures

B C R Ewan, C Weil, M Scanlon

HAZ 716


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BACKGROUND TO THE WORK

2000 HSE funds parallel programme to investigate relief device opening times

under transient pulse loadings for discs and relief valves (sizes H-L)

2000 Institute of Petroleum undertakes experimental programme to

investigate effects of tube rupture in STHE - publishes guidelines on

design and safe operation

Experience over 20 years indicates :

possibility of accidental rupture of bursting discs, e.g. reverse rupture in

flare systems, discharge of cooling water into relief systems

failure rate of bursting discs more frequent than genuine tube rupture

- introduces its own hazard rate

Problem under consideration is the hazard of working with shell and tube

heat exchangers with high pressure gas in tubes and low pressure

liquid-filled shell

Question arises - how feasible is the use of relief valves for this scenario ?


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gas

bubblehydraulic

wave

SCHEMATIC OF EVENT IMMEDIATELY FOLLOWING A TUBE RUPTURE


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REPRESENTATION OF TUBE RUPTURE SCENARIO


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PREVIOUS WORK


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EXAMPLE 2" AND 4" RUPTURE DISCS

UPSTREAM SIDE BEFORE OPERATION

DOWNSTREAM SIDE AFTER OPERATION


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-1 0 1 2 3 4 5 6 7 8 9 10 11 12

0

10

20

30

40

50

Pressure-barg

msec

3" SS reverse buckling disc

disc burst pressure = 14.5 barg

incident pulse

pressure

pressure recorded

at disc location

PRESSURE BEHAVIOUR AT DISC DURING RUPTURE EVENT - 3" DISC


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-1 0 1 2 3 4 5 6 7 8 9 10 11 12

0

20

40

60

80

100

120

Pressure

-barg

msec

4" SS reverse buckling disc

disc burst pressure = 14.5 barg

incident pulsepressure

pressure recorded

at disc location

PRESSURE BEHAVIOUR AT DISC DURING RUPTURE EVENT - 4" DISC


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Valve

letter

Discharge

area (in2)

Valve

letter

Discharge

area (in2)

D 0.110 L 2.853

E 0.196 M 3.600

F 0.307 N 4.340

G 0.503 P 6.38H 0.785 Q 11.05

J 1.287 R 16.0

K 1.838 T 26.0

Bursting disks Relief valves

Number Size Number Size

1 1" 9 D

6 2" 4 E

3 3" 1 F

8 4" 3 G

16 6" 3 H3 6.4" 3 J

15 8" 7 L

1 8.3" 2 M

3 10" 2 N

2 10.4" 9 P

Typical distribution of sizes

and numbers of a sample of

relief valves and burstingdisks in current use

Valve discharge areas

by letter code


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EXAMPLE BEHAVIOUR OF L SIZE VALVE WITH 60 BAR PULSE LOAD


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Valve type Test condition

Overpressure

(%)

Opening time

(msec)

Conventional

spring loaded

SRV(2H3, 15 barg)

high pressure 400 4

mediumpressure

200 5

Conventional

spring loaded

SRV(4L6, 10 barg)

high pressure 520 4

medium

pressure230 5

low pressure 70 10

SUMMARY OF PREVIOUS FINDINGS


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To establish pressure/flow characteristics for safety valvesprior to dynamic testing for comparison with post-dynamic

test behaviour.

Main objective

Requirements

Provide water reservoir of sufficient volume

Provide some pressure control

Monitor pressure and flowrate over sufficient duration

pressures 11 - 14 barg

flowrates in range 60 - 150 kg/sec

STATIC TESTING OF VALVES

Method


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PT

water tank

(4 m3

)

25 bar airreservoir

3m3

3" gate valve

3" pipe

4" pipe

SCHEMATIC OF GEOMETRY USED FOR STATIC VALVE TESTING


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WATER RESERVOIR WITH VALVE MOUNTED


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70 80 90 100 110 120 130 140

0

25 0

50 0

75 0

1000

1250

1500

1750

2000

2250

2500

2750

3000

3250

3500

3750

4000

4250

4500

4750

5000

0

1

2

3

4

5

6

7

8

9

10

11

12

Watertan

kpressure-barg

W

atertankmass-k

g

Time - seconds

flowrate

= 83.3 kg/sec

valve

opens

Valve M

(M = 3.6 sq in)

TYPICAL VARIATION OF TANK MASS AND APPLIED PRESSURE

DURING DISCHARGE TEST


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SCHEMATIC OF TUBE GEOMETRY USED FOR PRESENT WORK


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WATER FILLED TUBE END WITH VALVE MOUNTED


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K3 locationK2 location

MAIN BODY OF WATER FILLED TUBE


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bursting diaphragm

locationK1 location

tube water

fill

water

column

air

reservoir

AIR DISCHARGE END SHOWING LOCATION OF BURSTING DIAPHRAGM


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Valve typeSet pressure

(barg)

Incident

pressure pulse

(barg)

Target

pressure

identifier

M 10

12

15

25

40

M 1.2

M 1.5

M 2.5

M 4.0

N 10

12

15

25

40

N 1.2

N 1.5

N 2.5

N 4.0

P 12.5

1520

30

50

P 1.2P 1.5

P 2.5

P 4.0

PSV TEST SCHEDULE FOR SHOCK TUBE OPERATION


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Time - msec

Pressure

-barg

set pressure

level

rise and fall

time (RFT)

K4 pressure trace

TIME RESPONSE DATA EXTRACTED FROM PRESSURE TRACES


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EXAMPLE BEHAVIOUR OF SAFETY VALVE WITH 30 BAR PULSE LOAD

Set pressure = 10 bar


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Valve Test ID Before dynamic test Test ID After dynamic test

Valve

opening

pressure

(barg)

Flow

rate

(kg/s)

Average

applied

pressure

(barg)

Valve

opening

pressure

(barg)

Flow

rate

(kg/s)

Average

applied

pressure

(barg)

M

run a 10.1 67.4 10.1 run a2 10.1 85.9 11.3

run b 10.2 83.3 11.1 run b2 10.1 86.7 11.1

run c 10.1 82.1 11.0

N

run a 10.5 108.7 11.5 run a2 10.3 100.7 10.7

run b 10.7 100.9 11.3 run b2 10.4 100.6 10.7

run c 10.4 101.1 11.2

P

run a 12.8 98.2 13.2 run a2 12.8 91.2 13.1

run b 12.8 127.0 13.5 run b2 12.8 100.6 13.1

run c 12.7 110.0 13.4

STATIC VALVE TEST RESULTS BEFORE AND AFTER DYNAMIC PULSE LOADS


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Valve test

identifier

Average peak

reflected pressure

(barg)

Average RFT

(msec)

M 1.2 27.8 6.2

M 1.5 36.8 6.5

M 2.5 58.3 7.5

M 4.0 70.5 7.1N 1.2 29.8 6.6

N 1.5 35.7 6.5

N 2.5 51.6 7.6

N 4.0 64.0 7.1

P 1.2 35.3 6.7

P 1.5 41.3 6.5

P 2.5 52.0 6.8

P 4.0 80.0 7.8

SUMMARY OF TIME RESPONSE DATA EXTRACTED FROM VALVE TESTS


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CONCLUSIONS

The University of Sheffield would like to acknowledge the support provided by the

Energy Institute during the course of this work.

Previous work has shown that bursting discs will operate in the

range 0.2 - 0.5 msec

Reflected pressure pulses are less likely with bursting discs but

pressure doubling can still occur

Pressure safety valves react more slowly and generate a pressure reflection

Current work shows that the larger safety valves (M, N P) react quickly

to large overpressures and can relieve pulse pressures on a

timescale of 6 - 8 msec.

Static flow testing has shown valve performance appears unaffected

by the large transient pressures following tube rupture


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FURTHER INFORMATION

The University of Sheffield would like to acknowledge the support provided by the

Energy Institute during the course of this work.

Additional work carried out within the project includes :

Dynamic performance of pin valve

Modelling of pressure wave generation and valve lift dynamics to

investigate other STHE factors

Production of final deliverable on updated design guidelines

See www.energyinst.org/stheto find out more.
http://www.energyinst.org/sthehttp://www.energyinst.org/sthe

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1230 - Ewan - Study of Pressure Safety Valve Response Times Under Transient Overpressures

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