pipeline qra seminar

1SEPTEMBER 8-12, 2014

INOGATE PIPELINE QRA SEMINAR

PIPELINE QRA SEMINAR

SEPTEMBER 8-12, 2014


2

CONSEQUENCE ASSESSMENTINTRODUCTION

• Release of material

• Release of Gas

• Release of Liquid

• Release of Two- phase

• Gas dispersion

• Human vulnerability

Fire

• Jet fire

• Pool Fire

• Flash fire

• BLEVE

• Explosion

• Escalation



3

CONSEQUENCE ASSESSMENTRELEASE OF HYDROCARBON GAS

Releases from gas inventories are governed by the following equation for the initial release rate:

ZPACQ D 00

Q0: initial release rate (kg/s) CD: discharge coefficient A: area (m²) P0: initial pressure (Pa (N/m²)) M: molecular weight of the gas (kg/kmol) g : ratio of ideal gas specific heats

(1.3 for methane) R: universal gas constant (8314 J/(kg mol∙K)) T0: initial temperature (Kelvin)

1

1

0 12

RTM

Zwhere

Following values of CD have been recommended:

• Sharp thin edged orifices: 0.62• Straight thick edged orifices: 0.82• Rounded orifices: 0.96• Pipe rupture: 1.00



4


For METHANE a simple approximation is as follows:

420 10)()( barPmmDQ

WhereD: leak area (mm2) P: pressure (bar)

http://www.chm.bris.ac.uk/motm/methane/methane.mol



5


Typical gas leak sizes for oil and gas installations:Item Leak sizes in mm

< 10 10 <25 25<50 50<75 75<100 >=100 N/A

Actuated Block Valve,D <= 3"

87% 7% 0% 0% 7% 0% 0%

Actuated Block Valve,3" < D <= 11"

68% 9% 14% 0% 0% 0% 9%

Actuated Block Valve,D> 11"

83% 17% 0% 0% 0% 0% 0%

Flanges, D <= 3" 78% 10% 8% 2% 1% 1% 0%

Flanges,3" < D <= 11"

84% 5% 4% 1% 0% 6% 0%

Flanges, D> 11" 85% 4% 0 4% 0% 7% 0%



6


Examples of release rates (CD=0.62, =1.3)

Pressurebarg

D=1 mmRelease rate

D=8mmRelease rate

D=37.5mmRelease rate

1 0.000 kg/s 0.011 kg/s 0.234 kg/s

5 0.000 kg/s 0.032 kg/s 0.699 kg/s

15 0.001 kg/s 0.085 kg/s 1.861 kg/s

30 0.003 Kg/s 0.164 Kg/s 3.605 kg/s

45 0.004 kg/s 0.243 kg/s 5.348 kg/s

60 0.005 kg/s 0.323 kg/s 7.092 kg/s



7


Decaying releases

Pressure decay as a function of leak size - including the effect of blowdown

(for 25 m³ gas inventory at a HP compressor, 63.9 barg, MW=18.3)

0.00E+00 Pa

1.00E+06 Pa

2.00E+06 Pa

3.00E+06 Pa

4.00E+06 Pa

5.00E+06 Pa

6.00E+06 Pa

7.00E+06 Pa

0 s 100 s 200 s 300 s 400 s 500 s 600 s 700 s 800 s 900 s 1000 s

Hp Gas @ 63.9 barg & 25 m3

0.00E+00 Pa

1.00E+06 Pa

2.00E+06 Pa

3.00E+06 Pa

4.00E+06 Pa

5.00E+06 Pa

6.00E+06 Pa

7.00E+06 Pa

0 s 100 s 200 s 300 s 400 s 500 s 600 s 700 s 800 s 900 s 1000 s

Small

Small with blowdown

Medium

Medium with Blowdown

Large

Large with blowdown

Limit



8

CONSEQUENCE ASSESSMENTRELEASE OF HYDROCARBON GASReleases from liquid inventories are governed by the following equation.

hgPPACQ lalD )(2 00

Q0: initial release rate (kg/s)

CD: discharge coefficient (typical values 0.62-0.8)A: area (m²) : liquid density (kg/m3)P0: initial pressure (Pa (N/m²))

Pa: atmospheric pressure (105 Pa) g: acceleration due to gravity (9.81 m/s2) h: height of the liquid surface above the hole (m)



9


Two Phase:

Release of two-phase flows will have a release rate between that for gas and that for liquid.

The fraction that flashes is related to fraction of gas at atmospheric conditions compared to the overall release.

lg

gg mm

mx

Where:

mg: mass of gasml: mass of liquid

The models for calculating two-phase flows are very complex and normally calculations are performed using computer programmes.

Phase equilibrium affected by airAll methane - Butane



10

CONSEQUENCE ASSESSMENTGAS DISPERSION

Open field dispersion of gas clouds not impinging on large obstacles generally consist of three

sections, each dominated by its own mechanism.

1. This is the first section near the release point; Mixing of air into the jet, due to momentum of the release and shear forces at the edge (Cone shape)

2. The next section; Velocity of the release has been reduced and mixing of air into the cloud due to the wind velocity – Especially for cross wind releases

3. Gaussian dispersion of the gas cloud due to ambient turbulence



11

CONSEQUENCE ASSESSMENTGAS DISPERSION

Gas release from a inventory with a pressure of 45 barg through an 8 mm leak (0.36 kg/s). The release occurs

in the downwind direction and the wind speed is 1.5 m/s.

Red: concentrations above the upper flammable limit (UFL)Yellow: contractions at or below the UFLGreen: concentrations at or above lower flammable limit (LFL)Blue: concentrations at or below 50% LFL



12

CONSEQUENCE ASSESSMENTGAS DISPERSION – WIND SPEED

At high wind speeds the gas cloud will be more diluted as

more air will be entrained.

The dilutions are more pronounced for the 50% LFL conc. of gas

PHAST calculations at 1.5 m/s, 6 m/s and 10 m/s wind speeds, with stability class F, D and D respectively.

85.2986.3787.6730.4232.5936.841.06E+0160

67.7470.1171.3923.7126.8230.137.90E+0045

48.9251.9954.8917.0019.2722.415.23E+0030

25.8329.9636.379.6111.5814.362.65E+0015

5.396.278.753.744.254.882.87E-011

37.5

6.607.8111.391.344.946.024.85E-0160

5.826.819.524.154.525.063.59E-0145

5.195.717.823.133.614.432.38E-0130

3.924.565.672.412.543.161.21E-0115

1.421.722.150.890.971.081.31E-021

8

1.151.221.470.620.650.717.57E-0360

1.031.111.250.560.580.615.62E-0345

0.840.931.080.460.480.523.72E-0330

0.580.610.720.290.300.321.88E-0315

0.190.190.210.060.060.062.04E-041

1

mmmmmmkg/sbargmm10D6D1.5F10D6D1.5FRelease ratePressureHole size

Distance to 50 %LELDistance to LEL



13

CONSEQUENCE ASSESSMENTGAS DISPERSION – WIND DIRECTION

• The dispersion of the gas cloud is affected by the wind in the 2nd and 3rd section with low velocity for the gas plume.

• Accordingly the direction of the wind compared to the gas release will influence the shape of the gas cloud.

• Analyses of upwind releases computer simulations will have to be made using Computational Fluid Dynamics

Upwards vertical release, zero wind speed.

Upwards vertical release, finite wind speed.

Downwards vertical release, zero wind speed.

Upwards vertical release, finite wind speed.

Horizontal release, zero wind speed.

Horizontal release, wind speed in direction of release

Horizontal release, wind speed in direction opposed to release

Neutral buoyancy Buoyant Heavy



14

CONSEQUENCE ASSESSMENTHUMAN VULNERABILITY

Following conditions in relation to loss of hydrocarbon containment with subsequent events such as fire and

explosion can be a threat to human health

• High air temperature

• Radiation

• Toxicity

• H2S

• Combustion products (smoke)

• Oxygen depletion

• Explosion

• Overpressure

• Missiles

• Whole body displacement

• Obscuration of vision



15

CONSEQUENCE ASSESSMENTHUMAN VULNERABILITYHigh air temperature

High air temperature can cause skin burns, heat stress, and breathing difficulty.

The table indicates the effects of elevated temperatures.Temperature (°C) Physiological Response

127 Impeded breathing

140 5-min tolerance limit

149 Oral breathing difficult, temperature limit for escape

160 Rapid, unbearable pain with dry skin

182 Irreversible injury in 30 seconds

203 Respiratory tolerance time less than four minutes with wet skin



16


Radiation

• The pathological effects of thermal radiation on humans are progressively:

Pain First degree burns Second degree burns Third degree burns Fatality

• The combination of effect and time of exposure can be summed up in “Thermal Dose”:

I: intensity (kW/m2)t: time (s)

Thermal Radiation (kW/m²)

Effect

1.2 Received from the sun at noon in summer in northern Europe

2 Minimum to cause pain after 1 minute

Less than 5 Will cause pain in 15-20 seconds and injury after 30 seconds exposure

Greater than 6

Pain within approximately 10 seconds, rapid escape only is possible

12.5 Significant chance of fatality for medium duration exposure.* Thin steel with insulation on side away from the fire may reach thermal stress level high enough to cause structural failure

25 * Likely fatality for extended exposure and significant chance of fatality for instantaneous exposure* Spontaneous ignition of wood after long exposure* Unprotected steel will reach thermal stress temperature that can cause failure

35 * Cellulosic material will pilot ignite within one minute’s exposure* significant chance of fatality for people exposed instantaneously



17

CONSEQUENCE ASSESSMENTRADIATION DESIGN EXAMPLE

The height of the flare stack is determined based on requirements to radiation at various locations as per API 521.



18

CONSEQUENCE ASSESSMENTRADIATION CONSIDERATIONS• Wind

• Sun

• Crane, if present

• Roads and walkways

• Offices

• Working areas

• Muster area



19


Toxicity - H2S

Hydrogen Sulphide is considered a broad-spectrum poison mostly affecting the nervous

system.

Hydrogen Sulphide has a very distinctive smell of rotten eggs, but at higher concentrations

the sense of smell is paralysed. Conc.ppm

Physical properties

0.02 – 0.03 Odour threshold

1 Weak smell

5 Distinguishable smell

30 Sense of smell is paralysed

Acute lethal poisoning> 2000

Lethal after 30 to 60 minutes1000 – 1200

Immediate acute poisoning1000

Painful eye irritation, vomiting500 - 1000

Pulmonary oedema and bronchial pneumonia after prolonged exposure

250 - 600

Slight symptoms of poisoning after several hours 200 – 400

Objection to light, irritation of mucous membranes, headache150 – 200

Objection to light after 4 hours exposure50

Conjunctivitis20 - 30

Effects on humans Conc. ppm



20


Toxicity – Combustion products

Smoke from hydrocarbon fires contains various combustion products:

• Carbon monoxide

• Carbon dioxide

• Oxides of nitrogen

• Ammonia

• Sulphur dioxide

• Hydrogen fluoride

0000O2

9.28.211.810.9CO2

3.130.080.04CO

Liquid fireGas fireLiquid fireGas fire

Under ventilated fireWell ventilated fire

Concentration in smoke (%)Gas

The concentration of the various components depends on the material being burnt, the amount of oxygen present and the combustion temperature



21


Toxicity – Combustion products – Effects on human health

Conc. Effects

1,500 ppm

Headache after 15 minutes, collapse after 30 minutes and death after 1 hour.

2,000 ppm

Headache after 10minutes, collapse after 20 minutes and death after 45 minutes.

3,000 ppm

Maximum “safe” exposure for 5 minutes, danger of collapse in 10 minutes.

6,000 ppm

Headache and dizziness in 1 to 2 minutes, danger of death in 10 to 15 minutes

12,800 ppm

Immediate effect, unconscious after 2 to 3 breaths, danger of death in 1 to 3 minutes.

Com-po-nent

Effects

NOx Strong pulmonary irritant capable of causing immediate death as well as delayed injury

NH3 Pungent, unbearable odour; irritant to eye and nose

SO2 A strong irritant, intolerable well below lethal concentrations

HF Respiration irritants

Conc. Effects

20,000 ppm (2% v/v)

50% increase in breathing rate and depth

30,000 ppm (3% v/v)

100% increase in breathing rate and depth

50,000 ppm (5% v/v)

Breathing becomes laboured and difficult

CO CO2 NOx, NH3, SO2, HF



22


Toxicity – Oxygen depletion

• Normal air contains 21% oxygen, however during fire, part of or all the oxygen is used for combustion.

• At oxygen concentrations below 15 %, oxygen starvation effects such as increased breathing, faulty

judgement, and rapid onset of fatigue will occur.

Concentration of oxygen in air

(%)Responses

11 Headache, dizziness, early fatigue, tolerance time 30 minutes.

9 Shortness of breath quickened pulse, slight cyanosis, nausea, tolerance time 5 minutes.

7 Above symptoms becomes serious, stupor sets in, unconsciousness occurs, tolerance time 3 minutes

6 Heart contractions stop 6 to 8 minutes after respiration stops

3-2 Death occurs within 45 seconds

http://images.google.dk/imgres?imgurl=http://www.ct.gov/dcf/lib/dcf/wmv/images/fire.jpg&imgrefurl=http://www.ct.gov/dcf/cwp/view.asp?Q%3D332996%26a%3D2869&h=378&w=504&sz=31&hl=en&start=2&sig2=_wAsIEjrJ33tUwE3PeNqEQ&um=1&usg=__-TYkZkhk5-5r_9mMXlXPmkyYMJ4=&tbnid=GJCJxxeT6cVuAM:&tbnh=98&tbnw=130&ei=3ZgBSd2WApqOwQH22K33Cw&prev=/images?q%3Dfire%2Bimages%26um%3D1%26hl%3Den%26sa%3DX



23


Explosion – Overpressure

• Compression and decompression of a blast

wave on the human body results in

transmissions of pressure waves through

the tissues.

• Damage occurs primarily at junctions

between tissues at different densities;

bone, muscle and air cavities.

• Lungs and ear drums are especially

susceptible to the damaging effects of

overpressure.

Overpressure [barg]

Consequence

0.210 20% probability of fatality to personnel inside0% probability of fatality to personnel in the open

0.350 50% probability of fatality to personnel inside15% probability of fatality to personnel in the open

0.70 100% probability of fatality to personnel inside or in unprotected structures

Relatively high pressures are required for fatalities, and these are often related to missiles, collapse of buildings or drag force effects, and knock over of personnel



24


Explosion – Missiles

• Missiles in terms of fragments can be loose items

or items that are broken loose by the blast and

conveyed by the drag forces.

• Broken glass can generates sharp missiles and

glass breaks at relative low pressures:

• 1% level glass breakage peak=0.017 bar

• 90% level glass breakage peak=0.062

bar

InjuryPeak

overpressure (bar)

Impact velocity

(m/s)

Impulse (Ns/m²)

Skin laceration threshold 0.07-0.15 15 512

Serious wound threshold 0.15-0.2 30 1024

Serious wound near 50% probability

0.25-0.35 55 1877

Serious wound near 100% probability

0.5-0.55 90 3071

Mass of glass fragments (g)

Impact velocity (m/s)

1% 50% 99%

0.1 78 136 243

0.6 53 91 161

1 46 82 143

10 38 60 118



25


Explosion – Whole body displacement

The blast overpressure and the impulse can knock personnel over or literally pick personnel up and translate

them in the direction of the blast wave.

The head is the most vulnerable part of the body from the effects of the translation and subsequent impact

with a solid surface.

Total body impact tolerance Related velocity (m/s)

Most “safe” 3.05

Lethality threshold 6.40

Lethality 50% 16.46

Lethality near 100% 42.06

http://images.google.dk/imgres?imgurl=http://www.ourfunlife.com/health/xray.jpg&imgrefurl=http://www.ourfunlife.com/health/funny.html&h=768&w=637&sz=61&hl=en&start=11&sig2=S5mzYFO8Sq6j_boXw25Zcg&um=1&usg=__4JP6_Rk48C8LOekCnUxTejp8HEk=&tbnid=PD81iLBFo1gbqM:&tbnh=142&tbnw=118&ei=JocASb2zI42SxAGOs-mRDA&prev=/images?q%3DX-ray%2Bhead%26ndsp%3D21%26um%3D1%26hl%3Den%26sa%3DN



26

CONSEQUENCE ASSESSMENTFIRE

Chemical reaction

A hydrocarbon fire is a chemical reaction between the oxygen in the air and the hydrocarbon molecules which requires energy to initiate the reaction (ignition).

1 CH4 + 2 O2 CO2 + 2 H2O + 809 KJ/mole

Convection

Conduction

RadiationCOSoot

IncompleteCombustion



27


• Jet fire

• Pool fire

• Flash fire

• Fireball/BLEVE

• Explosion

Different types of fire:

http://www.nascoinc.com/standards/flash_fire/flash_fire.jpg



28


Radiation

The fraction of energy radiated from a fire depends on the type of fire, jet fire or pool fire and the size of the fire.

Gas Burner diameter (cm)

Fraction of heat radiated

Methane 0.51 0.103

1.90 0.160

4.10 0.161

Butane 0.51 0.215

1.91 0.253

4.10 0.285

20.30 0.280

Natural gas (95% Methane)

20.3 0.192

40.60 0.232

Fractions of radiation for diffusion flames. Fractions of radiation for jet fire



29

CONSEQUENCE ASSESSMENTJET FIRE

Multiphase jet fire test at SpadeAdam

Rule of thumb

Flame size: Fl=18.5∙Q0.41

Fl: flame length (m)Q: release rate (kg/s)

Ignited high momentum and continuous release of flammable gas or liquid. These fires are extremely violent with the formation of large turbulent flames, emitting high levels of radiation.

Jet fire in terms of an ignited gas blowout in Algeria



30

CONSEQUENCE ASSESSMENTJET FIREJet fire – Radiation

Jet fires have a very high heat output and the surface emissive power of the flame can be as high as 300 to 400 kW/m².

Jet fire

For leaks m > 2 kg/s

For leaks m > 0.1 kg/s

Local peak heat load

350 kW/m² 250 kW/m²

Global average heat load

100 kW/m² 0 kW/m²

Radiation contours for 45 barg release through a 37.5 mm hole simulated in PHAST



31

CONSEQUENCE ASSESSMENTPOOL FIRE

Pool fire test at SpadeAdam

Release of flammable liquid, a two phase jet with rain out of oil or low pressure two phase releases can lead to formation of an oil pool.

If ignited fumes evaporating from the oil pool will burn (low momentum).

The heat from the fire will cause more evaporation and cause the fire to accelerate.



32


Flame sizeThe diameter of an unobstructed pool fire on an even surface fed by a continuous release:

D: diameter (m)Q: release rate (kg/s)b: mass burning rate (kg/(s∙m²))

bQ

D

4

Once the diameter of the pool has been established the flame length can be derived from the following:

L: flame length (m)D: pool diameter (m)b: masburning rate (kg/(m²∙s))ρa: density of ambient air (kg/m³)g: acceleration due to gravity (m/s²)

61.0

5.0)(42/

Dgb

DLa

Substance Mass burning rate Kg/(s∙m²)

Gasoline 0.05

Kerosene 0.06

Hexane 0.08

Butane 0.08

LNG 0.09

LPG 0.11

Crude oil 0.035 – 0.05



33


Pool fire radiation

Pool fires have a lower radiation than jet fires,

typically between 100 to 200 kW/m².

Proposed incident heat fluxes [Scandpower]

Pool fires

Local peak heat load 150 kW/m²

Global average heat load 100 kW/m²

Release rate

Pool diameter

Flame length

Tilt angle Surface emissive power

Distance to 12.5

kW/ m2

Distance to 5

kW/ m2

kg/s m m ° kW/m2 m m0.4 2.5 8 58 109 6.3 121.7 5 13 53 86 9.4 19

7 10 21 48 56 11 2842 25 39 39 26 13.2 3060 30 44 37 23 15.6 32

167 50 63 29 20 25.2 43427 80 88 19 20 40.2 64699 100 102 11 20 50 77

These pool sizes, flame sizes and radiation distances have been calculated by DNV programme: Flare [Guide].

The calculations are based on heptane (C7) as the medium burning.



34

CONSEQUENCE ASSESSMENTFLASH FIRE

• Flash fires are slow burning gas clouds, where the flame front does not

accelerate to detonation (non-explosive combustion of a gas cloud)

• The ignition point is typically at the edge of the cloud as the combustion zone

moves through the cloud away from the ignition point.

• The flame front of the flash fire is relatively slow (10 m/s), and the duration of

flash fires are relatively short (10 to 15s) depending on gas cloud size

• Combustion of the gas within the gas cloud will cause the cloud to expand up to

8 times it original size.

• Heat flux experiments indicates that the maximum radiation from flash fires is

in the range of 160 to 300 kW/m².

http://www.nascoinc.com/standards/flash_fire/flash_fire.jpg



35

CONSEQUENCE ASSESSMENTFIREBALL / BLEVE

• A fireball is rapid

turbulent combustion of

fuel in an expanding and

usually rising ball of fire.

• Fireballs are often related

to the sudden release of

hydrocarbons due to

failure of a pressure

vessel - Boiling Liquid

Expanding Vapour

Explosion (BLEVE)



36


Flame size

The release material will be ignited by the external fire and a fireball with intense radiation will occur. Moreover shock waves and overpressure can be generated as a result.

The maximum diameter of the fireball can be estimated by:

Dc: maximum diameter (m)mf: mass of fuel (kg)

3/18.5 fc mD

The duration of the fireball can be estimated by:

for mf < 30,000 kg

for mf > 30,000 kg

tc: duration of combustion in seconds.

3/145.0 fc mt 6/16.2 fc mt



37


Radiation

The radiation from a fireball is very intense, experiments have shown radiation levels between 320 kW/m² and 375 kW/m².

Reference FuelFuel Mass

[kg]

Fireball duration

[s]

Fireball diameter[m]

Emissive power[kW/m²]

Johnson et al. PropaneButane

1000 4.5 56 320

Johnson et al. PropaneButane

2000 9.2 88 375



38

CONSEQUENCE ASSESSMENTEXPLOSION DEFINITION

An explosion is the sudden, catastrophic, release of energy, causing a pressure wave (blast wave).

• Explosion can occur without fire e.g. failure through overpressure.

• Explosion of flamable mixture is divided into deflagration and detonation.

• Detonation: Reaction zone propagates at supersonic velocity and the main heating mechanism is shock compression.

• Deflagration: Reaction zone propagates at subsonic velocity but significant overpressure can still be generated.



39

CONSEQUENCE ASSESSMENTEXPLOSION

A gas explosion is a rapid burning gas cloud where the flame front is accelerated generating shock waves

and overpressure.

In order for a vapour cloud explosion to occur in a hydrocarbon facility, four conditions have to be present:

1. There has to be a significant release of flammable material

2. The flammable material has to be sufficiently mixed with the surrounding air

3. There has to be an ignition source

4. There has to be sufficient confinement, congestion or turbulence in the released area

In explosions the (gas cloud) flame front will expand 8 to 9 times due to the heat of combustion.



40

CONSEQUENCE ASSESSMENTRULES OF THUMB APPLIED TO NINOTSMINDA

P bargLeak D= 10 mm Leak D= 30 mm

Flame m Fireball-D Flame m Fireball-D

54 14 26 34 54

100 18 32 44 66

250 26 43 64 90

Fireball size assuming a 3 min. HC-release at the given pressures and leak sizes.



41


The effects of explosions can cause significant damage.



42


Gas cloud

The size of the gas cloud has a large effect on the peak pressure from an explosion.

The size of the cloud is dependent on several factors such as leak rate, ventilation rate etc. (section 2.2 in

notes).

The original TNT equivalent of a gas cloud can be approximated by the following formula:

wTNT: weight of TNT (kg)wHC: weight of hydrocarbon released (kg)η: yield factor (3-5% [GexCon])

This model does not account for the geometrical congestions such as congestion and confinement

HCTNT w10w

Harrison and Wickers revised the TNT model to account for severe congestion:

V: the smaller of either total volume of the congested area or the volume of the gas cloud (m3)

)(V16.0w kgTNT



43


Type of gas

The composition of the gas cloud affects the strength of the explosion as methane is less reactive than propane and ethane.

Explosion pressure for natural gas depending on methane concentration



44


Gas concentration

Hydrocarbon gasses can burn in an interval from LEL to UEL, below or above the gas is too lean and too rich

to actually burn. The optimal concentration for combustion is where the gas balances the available oxygen in

the air (stoichiometric concentration).

Explosion pressure as function of concentration of the gas cloud [Design].

The Equivalence Ratio (ER) is defined as follows:

tricStoichiome

Actual

OxygenFuel

OxygenFuelER

)/(

)/(



45


Congestion

Turbulence is a key factor in accelerating the flame front travelling through the gas cloud during an explosion.

Obstacles in the gas cloud will generate turbulence as the cloud expands due to the combustion, and the

more obstacles the more turbulence and hence higher explosion pressures

ConfinementThe more confined, the less area to

relieve the pressure



46

CONSEQUENCE ASSESSMENTESCALATION

Ignited gas blow out Escalation to platform leading to loss of both rig and platform

BLEVETime

Yield stress

GSF Adriatic at the Temsah platform of the coast of Egypt

Temperature



47

CONSEQUENCE ASSESSMENTESCALATION EXAMPLES

• Small fire spreads into a large fire

• Jet fire causes BLEVE or major pool fire

• Jet fire causes loss of structural integrity or prevent escape.

• Explosion leading to loss of integrity in neighbouring areas or loss of safety functions.

• Ship collision or dropped object leads to HC release.

• Etc.



48

CONSEQUENCE ASSESSMENTESCALATION PREVENTION

The main thing in process safety design is to prevent hydrocarbon release and if released to prevent ignition. However if this occurs anyway escalation shall be prevented.

• Fire zoning

• Blast walls

• PFP and AFP

• Blowdown and ESD segregation

• Layout

• Etc.



CONSEQUENCE ASSESSMENT PIPELINE SAFETY ZONES

Typical safety zoningROW typically varies between 18 m and 36 m

Governed by local legislation.

Local legislation and guidelines typically rely on the guidelines issued by GPTC (Gas Piping Technology Committee), API and ASME.

A risk assessment will always have to be part of the safety zoning.



CONSEQUENCE ASSESSMENTEXAMPLE FROM RINGSTED, DENMARK (WEST-EAST PIPELINE)

Pipeline D = 30”, Pipeline pressure P = 80 barg



CONSEQUENCE ASSESSMENTNEIGHBOURING DISTANCES FROM PIPELINE (RINGSTED, DK)



CONSEQUENCE ASSESSMENTPOSSIBLE CATASTROPHIC SCENARIO AND CONSEQUENCES

With an Ø 75 mm breach, rule of thumb calculation gives:Jet Flame Size = 100 m (impinging on all nearby residences).

If release lasts for 3 minutes and ignites, the resulting fireball will have a diameter of 133 m (intolerable to closest residents). Legally, Ringsted pipeline complies with technical and legal requirements.

QRA is a tool to evaluate and support what in the end are POLITICAL DECISIONS to proceed with construction within questionable, high-risk and/or consequence areas.

53SEPTEMBER 8-12, 2014


END OF CONSEQUENCE ASSESSMENT

pipeline qra seminar

Documents

gas kgkmol

gas installations

gas inventories

danger of death

immediate death

universal gas constant

initial release rate

combustion temperature