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Slide1

Title slide

Pipeline

Qra Seminar

1

Slide2

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

2

Slide3

Consequence Assessmentrelease of hydrocarbon gas

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

Q

0

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

where

Following values of CD have been recommended:

Sharp thin edged orifices: 0.62

Straight thick edged orifices: 0.82Rounded orifices: 0.96Pipe rupture: 1.00

3

Slide4

Consequence Assessmentrelease of hydrocarbon gas

For METHANE a simple approximation is as follows:

Where

D: leak area (mm

2) P: pressure (bar)

4

Slide5

Consequence Assessmentrelease of hydrocarbon gas

Typical gas leak sizes for oil and gas installations:

ItemLeak sizes in mm< 1010 <2525<5050<7575<100>=100N/AActuated 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%04%0%7%0%

5

Slide6

Consequence Assessmentrelease of hydrocarbon gas

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

PressurebargD=1 mmRelease rateD=8mmRelease rateD=37.5mmRelease rate10.000 kg/s0.011 kg/s0.234 kg/s50.000 kg/s0.032 kg/s0.699 kg/s150.001 kg/s0.085 kg/s1.861 kg/s300.003 Kg/s0.164 Kg/s3.605 kg/s450.004 kg/s0.243 kg/s5.348 kg/s600.005 kg/s0.323 kg/s7.092 kg/s

6

Slide7

Consequence Assessmentrelease of hydrocarbon gas

Decaying releasesPressure 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)

7

Slide8

Consequence Assessmentrelease of hydrocarbon gas

Releases from liquid inventories are governed by the following equation.

Q

0

: 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)

8

Slide9

Consequence Assessmentrelease of hydrocarbon gas

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.

Where:

mg: mass of gas

ml: 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

9

Slide10

Consequence Assessmentgas dispersion

Open field dispersion of gas clouds not impinging on large obstacles generally consist of threesections, 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 releases3. Gaussian dispersion of the gas cloud due to ambient turbulence

10

Slide11

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

11

Slide12

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

85.29

86.37

87.67

30.42

32.59

36.84

1.06E+01

60

67.74

70.11

71.39

23.71

26.82

30.13

7.90E+00

45

48.92

51.99

54.89

17.00

19.27

22.41

5.23E+00

30

25.83

29.96

36.37

9.61

11.58

14.36

2.65E+00

15

5.39

6.27

8.75

3.74

4.25

4.88

2.87E-01

1

37.5

6.60

7.81

11.39

1.34

4.94

6.02

4.85E-01

60

5.82

6.81

9.52

4.15

4.52

5.06

3.59E-01

45

5.19

5.71

7.82

3.13

3.61

4.43

2.38E-01

30

3.92

4.56

5.67

2.41

2.54

3.16

1.21E-01

15

1.42

1.72

2.15

0.89

0.97

1.08

1.31E-02

1

8

1.15

1.22

1.47

0.62

0.65

0.71

7.57E-03

60

1.03

1.11

1.25

0.56

0.58

0.61

5.62E-03

45

0.84

0.93

1.08

0.46

0.48

0.52

3.72E-03

30

0.58

0.61

0.72

0.29

0.30

0.32

1.88E-03

15

0.19

0.19

0.21

0.06

0.06

0.06

2.04E-04

1

1

m

m

m

m

m

m

kg/s

barg

mm

10D

6D

1.5F

10D

6D

1.5F

Release rate

Pressure

Hole size

Distance to 50 %LEL

Distance to LEL

12

Slide13

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

13

Slide14

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 temperatureRadiationToxicityH2SCombustion products (smoke)Oxygen depletionExplosionOverpressureMissilesWhole body displacementObscuration of vision

14

Slide15

Consequence AssessmentHuman vulnerability

High air temperatureHigh air temperature can cause skin burns, heat stress, and breathing difficulty. The table indicates the effects of elevated temperatures.

Temperature (°C)Physiological Response127Impeded breathing1405-min tolerance limit149Oral breathing difficult, temperature limit for escape160Rapid, unbearable pain with dry skin182Irreversible injury in 30 seconds203Respiratory tolerance time less than four minutes with wet skin

15

Slide16

Consequence AssessmentHuman vulnerability

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)Effect1.2Received from the sun at noon in summer in northern Europe2Minimum to cause pain after 1 minuteLess than 5Will cause pain in 15-20 seconds and injury after 30 seconds exposureGreater than 6Pain within approximately 10 seconds, rapid escape only is possible12.5Significant 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 failure25* 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 failure35* Cellulosic material will pilot ignite within one minute’s exposure* significant chance of fatality for people exposed instantaneously

16

Slide17

Consequence Assessmentradiation design example

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

17

Slide18

Consequence Assessmentradiation Considerations

Wind Sun Crane, if present Roads and walkways Offices Working areas Muster area

18

Slide19

Consequence AssessmentHuman vulnerability

Toxicity - H2SHydrogen 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.ppmPhysical properties0.02 – 0.03Odour threshold1Weak smell 5Distinguishable smell30Sense of smell is paralysed

Acute lethal poisoning

> 2000

Lethal after 30 to 60 minutes

1000 – 1200

Immediate acute poisoning

1000

Painful eye irritation, vomiting

500 - 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, headache

150 – 200

Objection to light after 4 hours exposure

50

Conjunctivitis

20 - 30

 

Effects on humans

Conc.

ppm

19

Slide20

Consequence AssessmentHuman vulnerability

Toxicity – Combustion productsSmoke from hydrocarbon fires contains various combustion products:Carbon monoxideCarbon dioxideOxides of nitrogenAmmoniaSulphur dioxideHydrogen fluoride

0

0

0

0

O

2

9.2

8.2

11.8

10.9

CO2

3.1

3

0.08

0.04

CO

Liquid fire

Gas fire

Liquid fire

Gas fire

Under ventilated fire

Well 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

20

Slide21

Consequence AssessmentHuman vulnerability

Toxicity – Combustion products – Effects on human health

Conc.Effects1,500 ppmHeadache after 15 minutes, collapse after 30 minutes and death after 1 hour.2,000 ppmHeadache after 10minutes, collapse after 20 minutes and death after 45 minutes.3,000 ppmMaximum “safe” exposure for 5 minutes, danger of collapse in 10 minutes.6,000 ppmHeadache and dizziness in 1 to 2 minutes, danger of death in 10 to 15 minutes12,800 ppmImmediate effect, unconscious after 2 to 3 breaths, danger of death in 1 to 3 minutes.

Com-po-nentEffectsNOxStrong pulmonary irritant capable of causing immediate death as well as delayed injuryNH3Pungent, unbearable odour; irritant to eye and noseSO2A strong irritant, intolerable well below lethal concentrationsHFRespiration irritants

Conc.Effects20,000 ppm (2% v/v)50% increase in breathing rate and depth30,000 ppm (3% v/v)100% increase in breathing rate and depth50,000 ppm (5% v/v)Breathing becomes laboured and difficult

CO

CO2

NOx, NH3, SO2, HF

21

Slide22

Consequence AssessmentHuman vulnerability

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 (%)Responses11Headache, dizziness, early fatigue, tolerance time 30 minutes.9Shortness of breath quickened pulse, slight cyanosis, nausea, tolerance time 5 minutes.7Above symptoms becomes serious, stupor sets in, unconsciousness occurs, tolerance time 3 minutes 6Heart contractions stop 6 to 8 minutes after respiration stops3-2Death occurs within 45 seconds

22

Slide23

Consequence AssessmentHuman vulnerability

Explosion – OverpressureCompression 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]Consequence0.21020% probability of fatality to personnel inside0% probability of fatality to personnel in the open0.35050% probability of fatality to personnel inside15% probability of fatality to personnel in the open0.70100% 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

23

Slide24

Consequence AssessmentHuman vulnerability

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 bar90% level glass breakage peak=0.062 bar

InjuryPeak overpressure (bar)Impact velocity (m/s)Impulse (Ns/m²)Skin laceration threshold0.07-0.15 15512Serious wound threshold0.15-0.2 301024Serious wound near 50% probability0.25-0.35 551877Serious wound near 100% probability0.5-0.55 903071

Mass of glass fragments (g)Impact velocity (m/s)1%50%99%0.1781362430.6539116114682143103860118

24

Slide25

Consequence AssessmentHuman vulnerability

Explosion – Whole body displacementThe 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 toleranceRelated velocity (m/s)Most “safe”3.05Lethality threshold6.40Lethality 50%16.46Lethality near 100%42.06

25

Slide26

Consequence Assessmentfire

Chemical reactionA 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

ConvectionConductionRadiation

CO

Soot

Incomplete

Combustion

26

Slide27

Consequence Assessmentfire

Jet firePool fireFlash fireFireball/BLEVEExplosion

Different types of fire:

27

Slide28

Consequence Assessmentfire

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

GasBurner diameter (cm)Fraction of heat radiatedMethane0.510.1031.900.1604.100.161Butane0.510.2151.910.2534.100.28520.300.280Natural gas (95% Methane)20.30.19240.600.232

Fractions of radiation for diffusion flames.

Fractions of radiation for jet fire

28

Slide29

Consequence Assessmentjet fire

Multiphase jet fire test at

SpadeAdam

Rule of thumbFlame size: Fl=18.5∙Q0.41Fl: 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

29

Slide30

Consequence Assessmentjet fire

Jet fire – RadiationJet 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 fireFor leaks m > 2 kg/sFor leaks m > 0.1 kg/sLocal peak heat load350 kW/m²250 kW/m²Global average heat load100 kW/m²0 kW/m²

Radiation contours for 45

barg release through a 37.5 mm hole simulated in PHAST

30

Slide31

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.

31

Slide32

Consequence Assessmentpool fire

Flame size

The 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))

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)

Substance

Mass burning rate Kg/(s∙m²)

Gasoline0.05Kerosene0.06Hexane0.08Butane0.08LNG0.09LPG0.11Crude oil0.035 – 0.05

32

Slide33

Consequence Assessmentpool fire

Pool fire radiationPool fires have a lower radiation than jet fires, typically between 100 to 200 kW/m².

Proposed incident heat fluxes [Scandpower] Pool firesLocal peak heat load150 kW/m²Global average heat load100 kW/m²

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.

33

Slide34

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 sizeCombustion 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.

34

Slide35

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)

35

Slide36

Consequence Assessmentfireball / bleve

Flame sizeThe 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)

The duration of the fireball can be estimated by:

for mf < 30,000 kg

for mf > 30,000 kgtc: duration of combustion in seconds.

36

Slide37

Consequence Assessmentfireball / bleve

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

ReferenceFuelFuel Mass[kg]Fireball duration[s]Fireball diameter[m]Emissive power[kW/m²]Johnson et al.PropaneButane10004.556320Johnson et al.PropaneButane20009.288375

37

Slide38

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.

38

Slide39

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:

There has to be a significant release of flammable materialThe flammable material has to be sufficiently mixed with the surrounding airThere has to be an ignition sourceThere 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.

39

Slide40

Consequence AssessmentRULES OF THUMb APPLIED TO NINOTSMINDA

P bargLeak D= 10 mm Leak D= 30 mmFlame mFireball-D Flame mFireball-D541426 34541001832 44662502643 6490

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

40

Slide41

Consequence Assessmentexplosion

The effects of explosions can cause significant damage.

41

Slide42

Consequence Assessmentexplosion

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

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 (m

3

)

42

Slide43

Consequence Assessmentexplosion

Type of gasThe 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

43

Slide44

Consequence Assessmentexplosion

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:

44

Slide45

Consequence Assessmentexplosion

CongestionTurbulence 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 torelieve the pressure

45

Slide46

Consequence Assessmentescalation

Ignited gas blow out

Escalation to platform leading to loss of both rig and platform

BLEVE

Time

Yield stress

GSF Adriatic at the

Temsah

platform of the coast of Egypt

Temperature

46

Slide47

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.

47

Slide48

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.

48

Slide49

Consequence Assessment Pipeline Safety Zones

Typical safety zoning

ROW 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.

Slide50

Consequence AssessmentEXAMPLE FROM RINGSTED, DENMARK (WEST-EAST Pipeline)

Pipeline D = 30”, Pipeline pressure P = 80

barg

Slide51

Consequence Assessment

neighbouring distances from pipeline (Ringsted, DK)

Slide52

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.

Slide53

End of Consequence Assessment

Endslide.

53


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