Muligheter for storskala eksperimentell bistand ved risikovurdering

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1 Muligheter for storskala eksperimentell bistand ved risikovurdering Ragnar Wighus Sjefforsker SINTEF NBL as

2 Innhold Bakgrunn: "Lita tue kan velte stort lass" Hva har vi gjort tidligere? Hva er muligheten i dag? Forslag til eksperimentelle undersøkelser 2

3 Viktige spørsmål: Virkelige varmelaster ved tap av barriærer: Vet vi virkelig hva som fører til storulykker? Arbeider vi nok med storulykkespotensialet i forhold til risikoanalyse (ALARP) er vi forberedt på at en installasjon vil gå fullstendig tapt? Er barriærene som benyttes sett som en helhet, eller vurderes og optimaliseres disse innefor hver enkelt fagområde? 3

4 Piper Alpha: Riserbrudd etter mindre lekkasje 4

5 Deep Water Horizon: Hvilke barriærebrudd førte til storulykke? 5

6 Ved starten av "oljealderen" var hydrokarbonbrann et nytt tema. HC-kurven ble introdusert som erstatning for ISO-brann for typiske branner (Boliger) Etter Piper Alpha-ulykken ble det mye fokus på jet-brann 6

7 Hvilke brannscenarier er benyttet i risikoanalyser i dag? Jet fires Pool fires (on land and on the sea surface) Spray fires Running liquid fire Water content in liquid spray fires Enclosed and open fires 7

8 High temperature Jet fire SINTEF NBL experience Same Propane Jet as standard Jet fire 0,3 kg/sec propane (may be increased) 1 m from nozzle to test specimen Increased enclosure (2,5 x 2,5 x 3 m) Additional air to improve combustion Typical furnace temperatures: 1200 C 1400 C 8

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12 Temperature in furnace [ C] TIME- TEMPERATURE CURVES FOR TEST FURNACES : "RWS curve" : HC-curve ISO : Standard fire curve ISO [Time in minutes] Teknologi for et 12 bedre samfunn

13 Hva er avgjørende for om barriærer holder? (Brannfysikken i praksis) Brannlast, scenario Varmekapasitet og varmeledningsevne Varmetransport ved strømmende medier, baksiden av skiller Detaljer i områder, bolter, flenser, ventiler, instrumentering, signaloverføring Bærende konstruksjoner, understøttelse, oppheng Brudd og siging i stål 13

14 Instrumentation with thermocouples to reveal temperature of details 14

15 Horizontal low 3 kg/s Diesel spray fire

16 Horizontal high 3 kg/s Diesel spray fire

17 Varmefluks i spraybranner: Anses likt med jetbrann Lite eksperimentell erfaring med oppbrudd av stråler til dråper, og fordampning og forbrenning av dråpene 17

18 Pool fire: Burning release of liquid fuel from a pool, buoyancy driven fire plume with no initial vertical velocity Pool geometry may vary Pool substrate may vary (water, solid material, ground) Low erosive effect Gradients of heat flux densities in vertical direction 18

19 8000 litres of crude oil spreading on the sea surface. Max pool diameter 40 m, max height of flame 60 m (Spitsbergen 1996) 19

20 Steel tower floating in a basin cut in the ice. Temperatures, heat fluxes, velocities and gas composition were measured. The diameter of the oil Pool (crude oil) was 10 m. (Fire on the sea surface, Spitsbergen 1996)

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22 8000 litre crude oil spreading on the sea surface. Max diameter 40 m, max flame heighth 60 m. (Spitsbergen 1996)

23 Temperature (C) Temperatures of thermocouples in smoke/flame Svalbard Winter experiments, SINTEF Time (sec)

24 Fire on the sea surface results from experiments Spitsbergen 1996 FIRE TYPE Crude oil 8000 litre 10 m diameter pool Burning duration: ~ 15 minutes Heat flux density Lower 1/3 of flame: 0,5 minute average: 260 kw/m 2. 1 minute average: 220 kw/m 2. 24

25 Running liquid fire In open air: Little experimental evidence for droplet formation by falling liquid in fire conditions Running liquid over surfaces seems to have little experimental verification (IMO 1165 test of water-based firefighting systems includes a running liquid fire) Splashing and pool surface disturbance will influence burning behaviour 25

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27 Blast&Fire: Enclosed fire experiments 415 m 3 rig 27

28 Blast and Fire Engineering for Topside Structures

29 Enclosed fires - results from experiments with Sleipner condensate in a 415 m 3 room (Blast&Fire) FIRE TYPE Jet fire hitting an object (vertical and horizontal tube) Enclosed pool fire up to 24 m 2 Fire load Local heat flux density: kw/m 2. Typical heat flux density against walls: 200 kw/m 2. Air/fuel ratio: 0,8 of stoichiometric leads to highest evaporation rate. Local heat flux density: kw/m 2. Typical heat flux density against walls: 200 kw/m 2. 29

30 ENCLOSED FIRES RESULTS FROM EXPERIMENTS (Blast & Fire) FIRE TYPE Heat load Jet fire hitting an object Local heat loads of kw/m 2. Typical heat loads to walls 200 kw/m 2. Enclosed pool fire A ventilation ratio of 0,8 of stoichiometric mixture gives the highest evaporation rate. Local heat load values of kw/m 2 are measured in a room volume of 415 m 3 and a 24 m 2 condensate pool area. Typical heat load to walls 200 kw/m 2. 30

31 Upside-down horizontal test furnace 31

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33 Benchmarking two cases Watercut: Some oilfields produce oil and gas containing large portions of water Searching the critical watercut that causes extinguishment and to quantify the fire load reduction as a function of water content in the mixture Deluge and monitors: Optimization of water-based firefighting systems using CFD modelling Large scale tests with oil and gas releases into complex geometry, including the effect of deluge systems Comparison and CFD modelling of two fire suppression systems

34 Large-scale oil and gas fires A new test rig is constructed at an outdoor test facility, at SINTEF NBLs laboratories in Trondheim. The test rig is located on a concrete plate collecting all spill water from the tests. The test rig dimensions is 10 m high, 10 m wide and 15 m long. The concrete plate is be 30 m x 40 m, with a collection capacity of litres of water. A water supply and pumping station with a capacity of min litres/min is constructed The rig can facilitate fires of at least 3 kg/s oil and/or gas fires (120 MW) The test rig can also supply a mixture of water/oil/gas to study the effect of water content in the release 34

35 Test set up - overview 35

36 Test set up the mixing unit Crude oil and propane were premixed in a pressurized tank. Water and hydrocarbons were mixed in the mixing unit. Typical pressure in the mixing unit was 5-8 bar. Typical spray length was m. 3 kg oil and gas pr second. 36

37 Critical watercut with free jet The watercut was increased gradually during the tests. The gas to oil ratio 2 in the mixture was 100m³/m³. Extinguishment was observed several times for WC=250% (WC*=71%). Hankinson et.al. reported extinguishment when WC*=55%. The gas to oil ratio seemed to influence on the critical watercut. 2. At standard conditions 37

38 Critical watercut with a flame stabilizer obstructing the jet An obstruction stabilizes the jet. When the jet was obstructed the spray kept burning even at a higher WC than 250% (WC*=71%). 38

39 Passive and/or active fire protection? In oil- and gas industry, passive and active fire protection are used independently or in combination Most knowledge is based on independent performance, little is known about interaction 39

40 What is a jet fire? 40

41 JET FIRES RESULTS FROM EXPERIMENTS FIRE TYPE Free jet, gas or liquid (Spadeadam) Jet fire test for passive fire protection materials (SINTEF, Shell) Enhanced jet fire test (SINTEF) Heat load Rate 8 kg/s, hitting a 900 mm diameter horizontal pipe: Maximum 300 kw/m 2 over less than 1 m 2 surface, 250 kw/m 2 over 4 m 2 surface. Rate 0,3 kg/s, into a box construction, (1,5 m x 1,5 m, 0,5 m deep): Local spots of 300 kw/m 2, average over rear box surface 200 kw/m 2. Rate 0,5-0,9 kg/s kw/m 2 onto large objects pressurised and filled with combustible gas or liquid. Tests can be carried out until collapse. 41

42 Summary: Open fires Type Pool fire on sea surface Free jet, gas Free jet, liquid Test method for jet fire hitting an object Heat load In the lower 1/3 of the flames is the averaged value in half a minute 260 kw/m 2, while 1 minute s average is 220 kw/m 2. Rate 8 kg/s, hitting a 900 mm horizontal pipe: Maximum 300 kw/ m 2 over less than 1 m 2 surface, above 250 kw/m 2 over less than 4 m 2 of the pipe. Liquid mixed in the same jet: The same heat flux density. Propane leakage of 0,3 kg/s in a box construction (1.5 x 1.5) gives local heat loads of 300 kw/m 2 and an average of 200 kw/m 2 against the backwall of the box.

43 Offshore standard heat loads Fire loads used in oil-and gas industry in Norway are described in NORSOK S-001: The global average heat load represents the average heat load that expose a significant part of the process segment or structure. The global average heat load provides the major part of the heat input to the process segment and, hence, affects the pressure in the segment. The local peak heat load exposes a small (local) area of the process segment or of the structure to the peak heat flux. The local peak heat load, with the highest heat flux, determines the rupture temperature of different equipment and piping within the process segment. The local peak heat load has marginal influence on the pressure profile within the process segment. 43 Ragnar Wighus 6th International Seminar on Fire and Explosion Hazards Leeds 2010

44 Forslag til eksperimentelle undersøkelser Mer realistiske eksperimenter med delvis innelukkede eller helt innelukkede branner Flere undersøkelser av virkningen av vannbaserte brannbekjempelsessystemer, også i vind Eksperimenter med realistiske strukturer og prosessutstyr, inkludert detaljer som kan være årsak til barriæretap Hvor store er design-brannene i forhold til de branntestene som utføres 44

45 Hva kan utføre av tester? SINTEF NBL utfører standard branntester, i standard ovner og standard jetbrannrigg Spesialiteten er skreddersydde tester når standard ikke finnes eller ikke dekker: Utvidet jetbranntest Opp-ned-ovn Spraybranner Reelle pool-branner of rennende væske Storskala branner i realistiske omgivelser Trykksatt utstyr Utstyr med hydrokarboner inni Utstyr påvirket av aktive brannbekjempelesanlegg Termokamera 45

46 Hva kan SINTEF NBL tilby? Storskala eksperimenter i den største branntesthallen i Europa, spesialbygget for oljeog gassbranner og brannbekjempelsessytemer Eget utendørs testområde for store olje-og gassbranner og brannbekjempelsessytemer Kort mobliseringstid og rask levering av resultater Robuste resultater: Reelle branner, realistiske grensebetingelser, pålitelige målinger Verifikasjon av beregningmodeller 46

47 ØNSKE: Ingeniørene som jobber i drift og ved skrivebord må komme til brannlaboratoriet, oppleve brann og bli skremt Brannforskerne må ut på plattformer og inn i beslutningsprosessene for å få til mer realistiske eksperimenter 47

48 Ragnar Wighus Sjefforsker, SINTEF NBL as Tel