jet fire pressure vessel

7/28/2019 Jet Fire Pressure Vessel

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Jet Fire Pressure Vessel

2007 12 7


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1. Objectives

[Objectives]

Hydrocarbon Jet Fire Pressure Vessel

1) New Design Requirements:

Safety-based design

Pressure vessel failure analysis

Application of passive fire protection (PFP) on pressure vessels

2) Recommended Practice (API)

3) New Perspective

4) Acceptance Criteria

5) Example


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2. Fire Protection of Equipment

[Heat Exposure of Process Equipment]

[Fire Protection of Process System]

Emergency Shutdown (ESD), Depressurization SDVs, BDVs Active Fire Protection (AFP) Deluge, Hydrant/Hose Reel, etc.

Passive Fire Protection (PFP) Fire Wall, PFP on Vessel/Piping

JetFire


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3. Recommended Practice

[Recommended Practice]

Standards: API 520 and 521.

[Background]

The recommended Heat Load is based on experiments performed beforelast world war and consider only pool fire load.

Some experiments were originally for use by the rubber industry.

The standard is widely used in areas where jet fire can occur.

Emergency response time is not considered.


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4. API Requirements

[API Fire Load]

0

100200

300

400

500

600

700

800

900

0 10 20 30 40

Wetted area [m2]

Absorbedeffect[kW]

0

5

10

15

20

25

30

35

40

45

50

Heatfluxtowetteda

rea

[kW/m2]

Q q

18.02.43 = FAq82.02.43 FAQ =

[kW/m2], average unit heat absorption

[kW], total heat absorption to wetted surface

F: environment factor, A: total wetted area


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4. API Requirements

[API Acceptance Criteria]

An alternative is to provide depressuring on all equipment that processeslight hydrocarbons and set the depressured rate to achieve 100 psig (6.9barg) or 50 percent of the vessel Design Pressure, whichever is lower, in 15minutes.

Time History of Internal Pressur e and Average Temperature of Vessel Shell

0

500

1 000

1 500

2 000

2 500

3 000

0 2 4 6 8 10 12 14

Time [min]

Pressure[kPa]

0

200

400

600

800

1000

1200

1400

Temperature[C

]

Pressure in vessel Max. averagesteel temperature

API 520

Criteria


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4. API Requirements

[API Acceptance Criteria - coverage]

Time History of Yield Stress, Applied Stress and Average Temperature of Vessel Shell

0

10

20

30

40

50

60

70

80

90100

0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0

Time [min]

Stress[N/mm2]

0

200

400

600

800

1000

1200

1400

Tempe

rature[

]

UTS Calculatedstress of shell

Max. averagesteel temperature

API criteria


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5. New Perspective

[Features]

New fire loads heating both gas and liquid zone.

Each segment is considered as a whole.

Depressurization time must coincide with strength of material in segment-objects.

Process integrity is linked to time for evacuation.

Inventory composition is important.

[Reference]

Guidance for the Design and Analysis of Fire Response of Pressurized Systems,Statoil, Hydro, Scandpower

Guidelines for the Design and Protection of Pressure Systems to withstand SevereFires, Institute of Petroleum, London

Technical Safety, S-001, NORSOK

VessFire User Manual, Petrell AS


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5. New Perspective

[Design of Depressurization] System and scenarioinformation

Estimate size ofdepressurization orifice

Calculate P(t) for theprocess segment and

T(t) for the steel

Is flarecapacityutilized?

Will equipt/pipe rupture?

OK

Are the

consequenceof the ruptureacceptable?

Improve Design /apply PFP

Increase orifice

size

Failure criteria

No

No

Yes

Yes

No


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6. Acceptance Criteria

[Acceptance Criteria (principles)]

The main strategy is to avoid escalation of accidents.

A small fire leading to a big fire is not acceptable.

A big fire leading to a minor additional leakage can be acceptable. This iscalled a secondary leakage.

Concerns of PFP application:

Increase corrosion of material

Reduce possibilities of inspection and maintenance of equipment

Increase weight

Increase need for space

Increase need for maintenance of the PFP

Increase cost


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6. Acceptance Criteria

[Acceptance Criteria (detailed)]

1. If either of the following is exceeded, rupture is considered unacceptable:

Released quantity of HC (Gas + Liquid) > 4 tons,

Released quantity of the sum of Gas > 1 ton, Pressure at time of rupture of Pressure Vessel > 4.5 barg (Note 1),

Pressure at time of rupture of Piping > 20 barg (Note 2),

Rupture prior to 3 minutes after the onset of the fire (Note 3).

2. The time criterion is based on time to evacuate the area in the vicinity of the fire.

3. For flare system rupture should not occur (need for improved support of flarepiping and header systems, e.g. application of PFP).

4. For small bore gas piping, ruptures causing gas release rates > 2 kg/s areconsidered unacceptable.

NOTE:1) Segments containing < 100 kg gas at time of rupture are allowed to rupture irrespective of

pressure in the system.

2) Max allowable pressure in vessels and pipes differ due to high risk of missile effects followinga vessel rupture.

3) Time criterion is based on time to evacuate area in vicinity of fire.


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7. Heat Load

[Net Heat Transfer to Object]

qnet: net heat transfer to object, W/m2

s: emissivity of the surface material (0.85)

s: absorptivity of the surface material (0.85)

f

: emissivity of flame (1.0)

: Stefan-Boltsman constant, 5.6710-8 W/m2K4

Tr: radiation temperature of flame, K

Tf: flame gas temperature, K

Ts(t): surface temperature of the material, K

h: convective heat transfer coefficient, kW/m2K

hjet fire = 100 kW/m2K

hpool fire / diffusive fire = 30 kW/m2K

44 )())(( tTtTThTq sssfrfsnet +=


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7. Heat Load

[Heat Load and Exposure Time for Jet Fire]

NOTE:

1) NORSOK S-001: Peak & Average Heat Load = 250 kW/m2

2) For jet fires, two (2) different Scenarios shall be analyzed separately, but not be combined:

For the time period t, mleak> 2.0 kg/s, use 350 kW/m2

For the time period t, mleak> 0.1 kg/s, use 250 kW/m2 ,

where, t is the time from start of the fire until the leak rate is reduced below mleak=2 kg/s

t is the time from start of the fire until the leak rate is reduced below mleak=0.1 kg/s

3) This calculation is for an object located close to the leak source. The heat flux will vary duringthe fire duration, and 250 kW/m2 is used as the average incident heat flux.

100 kW/m20 kW/m2100 kW/m2Global average heat load (forpressure calc. in the system)

150 kW/m2250 kW/m2350 kW/m2Local peak heat load (for steeltemperature calc.)

For leak rates

m > 0.1 kg/s3)

For leak rates

m > 2 kg/s

Pool Fire

Jet Fire 1),2)

Heat Load


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8. Example - Input

[Properties for Vessel]

[Fluid Composition]

[Others]

Water Level: 673 mm, HC Level: 1,814 mm

Jet Fire Heat flux for Max. point/average load: 250 kW/m2

Manual field depressurisation sequence is considered initiated after 3minutes from detection of initial fire or gas.

Software: VessFire Ver.1.2 (Petrell AS)

Liquid

& Gas

PhaseCS 360

LT

ShellMatl68.1

mm

R.OSize

37 C62 barg

161.3

m3

3,700

mm

15,000

mm55 mmSeparator

Oper.Temp.

Oper.Press.ol.ia.ength

allthick.essel

2.373

C3H81.580

Butane1.014

Pentane40.3887.9634.85237.8890.1912.6471.103

H2Others2H6H42O22S


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8. Example - Result

[Calculation Results]


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8. Example - Conclusion

[Conclusion]

The temperature of shell reaches about 900 C after 40 minutes.

The vessel can be failed after 32 minutes.

If emergency response (evacuation) time when fired requires more than32 minutes, Passive Fire Protection (PFP) for the separator isrecommended.

[Additional Issues]

Application of PFP on Flare Header is recommended in most offshoreprojects. How to minimize the application of PFP.

The integrity of the connected piping, flanges, etc. from vessels to SDVsshall be analyzed.

jet fire pressure vessel

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