Pipeline Qra Seminar

1. Pipeline Qra Seminar Title slide

2. Consequence Assessmentintroduction • Fire • Jet fire • Pool Fire • Flash fire • BLEVE • Explosion • Escalation • Release of material • Release of Gas • Release of Liquid • Release of Two- phase • Gas dispersion • Human vulnerability

3. Consequence Assessmentrelease of hydrocarbon gas Releases from gas inventories are governed by the following equation for the initial release rate: where • 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) • : ratio of ideal gas specific heats (1.3 for methane) R: universal gas constant (8314J/(kg mol∙K)) T0: initial temperature (Kelvin) • 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. Consequence Assessmentrelease of hydrocarbon gas For METHANE a simple approximation is as follows: Where D: leak area (mm2) P: pressure (bar)

5. Consequence Assessmentrelease of hydrocarbon gas Typical gas leak sizes for oil and gas installations:

6. Consequence Assessmentrelease of hydrocarbon gas Examples of release rates (CD=0.62, =1.3)

7. Consequence Assessmentrelease of hydrocarbon gas 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)

8. Consequence Assessmentrelease of hydrocarbon gas Releases from liquid inventories are governed by the following equation. 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. 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 air All 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 UFL Green: concentrations at or above lower flammable limit (LFL) Blue: concentrations at or below 50% LFL

12. Distance to LEL Distance to 50 %LEL Hole size Pressure Release rate 1.5F 6D 10D 1.5F 6D 10D mm barg kg/s m m m m m m 1 1 2.04E-04 0.06 0.06 0.06 0.21 0.19 0.19 15 1.88E-03 0.32 0.30 0.29 0.72 0.61 0.58 30 3.72E-03 0.52 0.48 0.46 1.08 0.93 0.84 45 5.62E-03 0.61 0.58 0.56 1.25 1.11 1.03 60 7.57E-03 0.71 0.65 0.62 1.47 1.22 1.15 8 1 1.31E-02 1.08 0.97 0.89 2.15 1.72 1.42 15 1.21E-01 3.16 2.54 2.41 5.67 4.56 3.92 30 2.38E-01 4.43 3.61 3.13 7.82 5.71 5.19 45 3.59E-01 5.06 4.52 4.15 9.52 6.81 5.82 60 4.85E-01 6.02 4.94 1.34 11.39 7.81 6.60 37.5 1 2.87E-01 4.88 4.25 3.74 8.75 6.27 5.39 15 2.65E+00 14.36 11.58 9.61 36.37 29.96 25.83 30 5.23E+00 22.41 19.27 17.00 54.89 51.99 48.92 45 7.90E+00 30.13 26.82 23.71 71.39 70.11 67.74 60 1.06E+01 36.84 32.59 30.42 87.67 86.37 85.29 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.

13. Consequence Assessmentgas dispersion – wind direction Neutral buoyancy Buoyant Heavy Upwards vertical release, zero wind speed. • 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, 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

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

16. 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)

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. Conc. ppm Effects on humans 20 - 30 Conjunctivitis 50 Objection to light after 4 hours exposure 150 – 200 Objection to light, irritation of mucous membranes, headache 200 – 400 Slight symptoms of poisoning after several hours 250 - 600 Pulmonary oedema and bronchial pneumonia after prolonged exposure 500 - 1000 Painful eye irritation, vomiting 1000 Immediate acute poisoning 1000 – 1200 Lethal after 30 to 60 minutes > 2000 Acute lethal poisoning Consequence AssessmentHuman vulnerability 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.

20. The concentration of the various components depends on the material being burnt, the amount of oxygen present and the combustion temperature Gas Concentration in smoke (%) Well ventilated fire Under ventilated fire Gas fire Liquid fire Gas fire Liquid fire CO 0.04 0.08 3 3.1 CO2 10.9 11.8 8.2 9.2 O2 0 0 0 0 Consequence AssessmentHuman vulnerability Toxicity – Combustion products Smoke from hydrocarbon fires contains various combustion products: • Carbon monoxide • Carbon dioxide • Oxides of nitrogen • Ammonia • Sulphur dioxide • Hydrogen fluoride

21. Consequence AssessmentHuman vulnerability Toxicity – Combustion products – Effects on human health CO2 CO NOx, NH3, SO2, HF

22. 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.

23. Consequence AssessmentHuman vulnerability 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. 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. 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 bar • 90% level glass breakage peak=0.062 bar

25. Consequence AssessmentHuman vulnerability 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.

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 Radiation CO Soot Incomplete Combustion

27. Consequence Assessmentfire Different types of fire: • Jet fire • Pool fire • Flash fire • Fireball/BLEVE • Explosion

28. Consequence Assessmentfire 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. Fractions of radiation for diffusion flames. Fractions of radiation for jet fire

29. Consequence Assessmentjet fire 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. Multiphase jet fire test at SpadeAdam Jet fire in terms of an ignited gas blowout in Algeria Rule of thumb Flame size: Fl=18.5∙Q0.41 Fl: flame length (m) Q: release rate (kg/s)

30. Consequence Assessmentjet fire Jet 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. Radiation contours for 45 barg release through a 37.5 mm hole simulated in PHAST

31. Consequence Assessmentpool fire 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. Pool fire test at SpadeAdam

32. 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) 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)) Consequence Assessmentpool fire Flame size

33. Consequence Assessmentpool fire Pool fire radiation Pool fires have a lower radiation than jet fires, typically between 100 to 200 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.

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.

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. 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 kg tc: duration of combustion in seconds. Consequence Assessmentfireball / bleve 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.

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

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: • There has to be a significant release of flammable material • The flammable material has to be sufficiently mixed with the surrounding air • There has to be an ignition source • 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 Fireball size assuming a 3 min. HC-release at the given pressures and leak sizes.

41. Consequence Assessmentexplosion The effects of explosions can cause significant damage.

42. 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 (m3) 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).

43. Consequence Assessmentexplosion 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. 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:

45. Consequence Assessmentexplosion 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 Confinement The more confined, the less area to relieve the pressure

46. Consequence Assessmentescalation Temperature Yield stress Time BLEVE Ignited gas blow out Escalation to platform leading to loss of both rig and platform GSF Adriatic at the Temsah platform of the coast of Egypt

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.

49. Consequence Assessment Pipeline Safety Zones 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. Typical safety zoning ROW typically varies between 18 m and 36 m

50. Consequence AssessmentEXAMPLE FROM RINGSTED, DENMARK (WEST-EAST Pipeline) Pipeline D = 30”, Pipeline pressure P = 80 barg