How To Calculate The Size Of An Lng Tanker Hull Leakage

Transcription

1 Scientific Journals Maritime University of Szczecin Zeszyty Naukowe Akademia Morska w Szczecinie 2011, 25(97) pp , 25(97) s Estimation of the consequences of LNG vessel tank leakage in the port of Świnoujście Szacowanie skutków rozszczelnienia zbiorników tankowca LNG w porcie Świnoujście Wojciech Ślączka Maritime University of Szczecin, Faculty of Navigation, Institute of Marine Traffic Engineering Akademia Morska w Szczecinie, Wydział Nawigacyjny, Instytut Inżynierii Ruchu Morskiego Szczecin, ul. Wały Chrobrego 1 2, w.slaczka@am.szczecin.pl Key words: accident risk, LNG terminal, thermal effect, accident consequences, LNG tanker operations, the port of Świnoujście Abstract The safe operations of LNG terminal in Świnoujście mainly depends on safe operations of LNG tankers. Manoeuvring the LNG tanker at the terminal entrance and basin is always connected with a risk of accident. Areas where the risk of accident is the greatest are those in the vicinity of entrance heads and the turning basin. Accidents within these areas are burdened with the most serious consequences. This article presents possible scenarios of LNG tanker accident consequences in the LNG Terminal in Świnoujście. Słowa kluczowe: ryzyko awarii, terminal LNG, oddziaływanie termiczne, skutki awarii, eksploatacja tankowców LNG, port Świnoujście Abstrakt Bezpieczna eksploatacja terminalu LNG w Świnoujściu w głównej mierze uzależniona jest od bezpiecznej eksploatacji gazowców LNG. Manewrowanie statkiem na wejściu do terminalu i w jego obszarze zagrożone jest możliwością wystąpienia awarii. Obszarami potencjalnie najbardziej narażonymi na awarie są główki wejściowe do terminalu oraz obrotnica. Wystąpienie awarii w tych obszarach obarczone jest największymi skutkami. W artykule zostały zaprezentowane możliwe warianty wystąpienia skutków awarii tankowca LNG na terminalu w Świnoujściu. Introduction The LNG Terminal in Świnoujście is being built as a completely new investment project. To this end, a new outer port was designed, located east of the existing eastern shelter breakwater. Besides, a new approach channel was designed, a branch of the existing approach channel leading to Świnoujście seaport. Before the construction of new infrastructure and waterways, attempts have to be made to estimate associated operational risks and, consequently, procedures have to be established with the aim od minimizing the risk level and potential consequences of an accident. The safety of Świnoujscie LNG terminal operations principally depends on: safe technical operation and manoeuvring of LNG tankers on new waterways (entrance heads and the turning basin), safe technical operation of the land-based cargo handling facilities. Part of a relevant analysis presented below refers to safe LNG tanker operation and the prediction of consequences of LNG tanker collision with an element of port infrastructure. The estimated data related with the consequences of vessel damage are based on simulation models of ship 70 Scientific Journals 25(97)

2 Hole size [m 2 Estimation of the consequences of LNG vessel tank leakage in the port of Świnoujście movement created by using a dedicated simulator of the LNG Terminal in Świnoujście (Fig. 1) and research results of other centres [1, 2. Outer hull Inner hull Collision speed [knots Fig. 1. Simulated model of an LNG terminal, Maritime University of Szczecin Rys. 1. Model symulacyjny terminalu LNG w Akademii Morskiej w Szczecinie This article aims at presenting a method for estimating the size of LNG tanker hull leakage due to a collision with a port structure and potential consequences of such accident. The consequences were brought down to the determination of the density of thermal radiation due to ignition of LNG. The affected areas were marked on the port map. Identification of potential threats The basic method used for the identification of threats is the simulation method for determining the amount of LNG leaking from a damaged vessel. The size of the leak depends on the surface area of the hole the liquid gas escapes through. For this purpose analyses were made, based on experiments conducted in the world in real conditions and based on the simulation method. The research was conducted on tankers with the plating and double bottom, size and construction resembling LNG gas carriers. One of the main experimental tests was a rectangular collision of a large container ship ( DWT) with a tanker ( DWT) by means of which the size of the hole in the plating was determined as the function of the striking vessel s speed (Fig. 2). Operational threats connected with the risk of vessel manoeuvring The basic threats resulting from the risk of manoeuvring LNG gas carriers while approaching the LNG terminal in Świnoujście are grounding on a shoal and the ship s collision with a hydrotechnical structure. During the vessel s grounding on the approach fairway the following effects will occur: Fig. 2. Graph of the size of vessel hull as the function of speed [1 Rys. 2. Wykres wielkości rozszczelnienia kadłuba w funkcji prędkości [1 denting of the external hull (no hole) resulting from the inclination angle of the fairway slope and also the kind of ground (sand), temporary blocking of the fairway, operation of bringing the LNG carrier off the shoal. A collision with a hydrotechnical structure, such as the outer breakwater heads of the port of Świnoujście, may result in puncturing the ship s hull plating. The above diagram may serve as the basis for estimating the size of a hole in LNG tanker hull caused by a collision with another vessel or running aground on the rocky bottom. It follows from an analysis of the characteristics presented in figure 2 that: no hole in the outer plating was observed for a speed up to 2.2 knots and in the inner plating for a speed up to 4.8 knots, a hole of the size of 5 m 2 in the outer plating is possible when the vessel moves at speed of 4.2 knots, a hole of 5 m 2 area in the inner plating is possible when the vessel moves at a speed of 6.2 knots. In order for environmental pollution to take place the inner plating has to be punctured, and, consequently, a leakage of LNG gas will occur. LNG vessels passing the outer breakwater heads were moving at a speed not exceeding 5.5 knots, which in case of a rectangular collision with the bow of another vessel may cause a hole not larger than 3 m 2. On approach to the outer port of Świnoujście such an event should not take place because two-way traffic is not permitted when an LNG Zeszyty Naukowe 25(97) 71

3 Wojciech Ślączka carrier is towed in. Nevertheless, assuming a possible collision with a hydrotechnical structure, e.g. breakwater heads, the following assumptions were made: an LNG carrier at the moment of collision proceeds at 5 knots (as a matter of fact, the gas carrier is not able to strike at such speed against the breakwater head as it will not move perpendicularly to it); the size of the hole in the inner hull plating is not larger than 2 m 2. Threats connected with cargo handling technology Among the main threats coming from cargohandling operations resulting in environmental pollution are as follows: leakage due to operator error may occur in the system of pipelines and valves, elements of LNG cargo-handling facilities, either on the side of the ship or on the side of the terminal; damage to cargo pipeline due to vessel s motion along the quay, e.g. as a result of the breaking of vessel s ropes; another vessel hitting the gas carrier on which cargo-handling operations are carried out; deliberate action, such as a terrorist attack (from land, water or air). Estimation of threats to LNG carriage and handling Due to the specific nature of cargo carried, an LNG tanker is exposed during its operation to gas leakage as a result of: unintentional damage to the LNG containment system, e.g. as a result of collision with another vessel, grounding, collision with a stationary object, purposeful action, e.g. terrorist attack (from water or air), possible tank failure or the vessel s cargohandling installation damage, human error in handling LNG transfer installation. The gas leakage may result in: fire due to ignition of LNG vapours; a) b) Thermal intensity do 55 kw/m Rys. Strefy rażenia będące wynikiem kolizji masowca zbiornikowca LNG 200 podczas cumowania do Rys. Strefy rażenia będące wynikiem kolizji zbiornikowca LNG 200 podczas cumowania do terminalu LNG Fig. 3. Zones of fire resulting from a collision of a bulk carrier with an LNG tanker 200 while mooring at the LNG in terminalu LNG Świnoujście: a) hole 1 m 2 w Świnoujściu, otwór, b) hole 2 m 2 przebicia 1 m 2. w Świnoujściu, otwór przebicia 2 m 2. Rys. 3. Strefy gęstości oddziaływania termicznego powstałe w wyniku kolizji tankowca LNG 200 podczas cumowania w terminalu LNG w Świnoujściu: a) rozszczelnienie kadłuba 1 m 2, b) rozszczelnienie kadłuba 2 m 2 72 Scientific Journals 25(97)

4 Estimation of the consequences of LNG vessel tank leakage in the port of Świnoujście if there is no combustion, the spreading of LNG vapours in the form of a cloud over a distance dependent on external factors; sudden explosion of LNG vapours in the form of a cloud with flames, accompanied by a shock wave, with force likely to injure crew members and to cause damage to the gas carrier hull and, possibly, to vessels in the immediate vicinity; direct contact of the vessel s crew member with low-temperature liquid, likely to cause frostbite or burning; accumulation in the air of large LNG amounts changing into the gaseous phase; unless those vapours are ignited and burnt, they may lead to people s suffocation; accumulation of leaking LNG between the vessel s structural elements may, because of the very large difference in temperatures of the cargo and the hull s structure, lead to steel brittleness and destructively affect the welds. Consequently, the size of damage will be much larger, which in turn will cause larger cargo leakage producing the domino effect with disastrous results for the vessel. Estimation of navigational risk of an LNG carrier entering or leaving the outer port of Świnoujście The probable effects of LNG cargo spillage into the water or evaporation are identical with the ones described above, where leakage takes place in the open sea. The effects, however, may influence the vessel and its crew as well as other vessels berthing in the port. Elements of the surrounding infrastructure, such as bridges or tunnels as well as the LNG terminal itself, port or surrounding buildings may also be damaged or destroyed. In case of LNG leakage in the port all persons staying in the area affected by a vapour cloud (tug, pilot boat, terminal personnel etc.) are exposed to the related risk. Based on assumptions previously made concerning the likelihood of collision of an LNG carrier entering a port, LNG leakage endangered zones and fire intensity zones (thermal intensity) were identified. Figures 3 present threat zones created after a collision of the gas carrier with the eastern head of the outer breakwater and the inner head of the outer port. The collision, although not very likely to happen as the vessel enters assisted by tugs, if it did occur in windless weather, it would have the following effects: for a 1 m 2 hole in the inner plating (Fig. 3a): the diameter of LNG spill range will amount to ca 150 m, the radius of thermal radiation intensity (see figure 3a) of 37.5 kw/m 2 be ca 180 m, the radius of thermal intensity radiation of not more than 5 kw/m 2 will be ca 550 m; for a 2 m 2 hole in the inner plating (Fig. 3b): the diameter of LNG spill will be ca 210 m, the radius of thermal radiation intensity (see figure 3b) of 37.5 kw/m 2 will be ca 250 m, the radius of thermal intensity radiation of not more than 5 kw/m 2 will be ca 780 m. Figure 4 presents zones of fire resulting from leakage of LNG due to a hole of 5 m 2 in area. Such a large hole may be made after a terrorist attack or any unintentional action that may cause such results. Because such event does not result from a collision with a hydrotechnical structure, the zones have been designated for a vessel approaching the heads and manoeuvring inside the port basin. It follows from an analysis of figure 4 that: the diameter of LNG spill will be ca 330 m, the radius of thermal radiation intensity of 37.5 kw/m 2 will be ca 390 m, the radius of thermal radiation intensity not more than 5 kw/m 2 will be ca 1300 m. The results of thermal radiation effect on the environment have been presented in the table 1 [1, 2. Table 1. Results of thermal radiation effect on the environment Tabela 1. Skutki oddziaływania promieniowania termicznego na środowisko Intensity of thermal Kind of damage radiation Admissible level for people and environment, 1.6 one can be exposed to radiation without time limitation Admissible level in areas where the rescue action was continued for a few minutes. It is 4.7 permitted for a person to stay without a thermal screen, but in adequate clothing. Admissible level in areas where the rescue action was continued for one minute. It is permitted for a person to stay without thermal 6.3 screen, but in adequate clothing. Admissible level in areas where person s exposure to radiation must not exceed a few seconds, 9.5 sufficient to escape from the danger zone Level at which plants undergo combustion. Minimum radiation energy indispensable for 12.5 combustion of wood in combination with open fire, causes melting of plastic Minimal radiation energy indispensable for 25 combustion of wood subjected to radiation for a longer time without access of open fire Sufficient energy causing destruction of fixed 37.5 objects (e.g. steel structures, cargo-handling devices etc.) Zeszyty Naukowe 25(97) 73

5 Wojciech Ślączka Fig. 4. Fire zones resulting from an event other than a collision of LNG 200 tanker during mooring operations at the LNG terminal in Świnoujście, hole 5 m 2 Rys. 4. Strefy gęstości oddziaływania termicznego powstałe w wyniku kolizji tankowca LNG 200 podczas cumowania w terminalu LNG w Świnoujściu, rozszczelnienie kadłuba 5 m 2 Rys. Strefy rażenia będące skutkiem działania innego niż kolizja dla zbiornikowca LNG 200 podczas cumowania do terminalu LNG w Świnoujściu, otwór przebicia 5 m 2. a) b) Isobath m m Thermal intensity kw/m2kw/m Fig. Rys. Strefy 5. rażenia Zones będące of wynikiem fire resulting kolizji zbiornikowca from LNG a collision 200 podczas cumowania of LNG do terminalu 200 tanker LNG w during Rys. Strefy mooring rażenia będące at wynikiem the LNG kolizji zbiornikowca terminal LNG in 200 Świnoujście: podczas cumowania a) do terminalu hole 1 LNG m 2 w, b) hole 2 m 2 Świnoujściu, otwór przebicia 1 m 2. Świnoujściu, otwór przebicia 2 m 2. Rys. 5. Strefy gęstości oddziaływania termicznego powstałe w wyniku kolizji tankowca LNG 200 podczas cumowania w terminalu LNG w Świnoujściu: a) rozszczelnienie kadłuba 1 m 2, b) rozszczelnienie kadłuba 2 m 2 74 Scientific Journals 25(97)

6 Estimation of the consequences of LNG vessel tank leakage in the port of Świnoujście Risk assessment for LNG handling Assumptions for the risk assessment: there is a risk of damage to an LNG carrier by another manoeuvring vessel in the turning basin, there is a risk of damage to pipeline, there will be more serious consequences for the environment when the gas carrier is damaged by another vessel than because of pipeline damage. Figures 5 present zones of thermal radiation intensity for the surface area of a leakage hole equal to, respectively, 1 m 2 and 2 m 2. The ranges are similar to those estimated for a collision with breakwater heads. Risk management during an LNG leakage Risk management during the operation of LNG carriers starts with the designation of danger zones. Mostly, three zones are designated, with essentially different danger conditions, and, consequently, varying level of safety. The zones can be designated by the previously presented method through an analysis of thermal radiation intensity and its effect on the surroundings and the environment. Guidelines concerning risk management in various situations of unintentional LNG leakage will be presented below (prepared on the basis of ABS Consulting documents, contract number FERC04C40196). Guidelines concerning risk management in the case of unintentional LNG leakage Zone 1 These are areas where LNG transport takes place in narrow ports or canals, under major bridges or above tunnels, or it takes place at a distance shorter than ca 250 m to residential buildings or other important infrastructure elements, e.g. military objects, densely populated areas or industrial plants. In this zone the risk and the consequences of accidental LNG leakage can be considerable and may have very serious results. Thermal radiation creates serious threat to public safety and may cause serious damage to local infrastructure. The strategy of risk management should cover threat caused both by spreading of vapours and by appearance of fire, which is why the most rigorous preventive measures such as safety zones around ships and establishing control over the ships are elements of risk management if an emergency situation is likely. It is very important to coordinate the activities of all port security services. The method of management and response in case of accident should be analysed in detail so as to ensure the availability of various kinds of measures (fire fighting, rescue services etc.) in order to minimize threat and the consequences of accident. Zone 2 These are areas where LNG transport takes place in wider canals or larger outer ports or at distances from m to 750 m from major infrastructure elements, such as industrial centres and populated areas. Thermal radiation constitutes smaller danger for public safety and buildings. In zone 2 the consequences of accidental LNG leakage are less severe, therefore the means and methods applied for decreasing danger can be less strict. In this zone the strategy of risk management during LNG operations shall cover threat caused both by spreading of vapours and appearance of fire. Methods of action shall cover managing and responding in case of accident and ensure the availability of shelters (e.g. closed areas, buildings), familiarization with warning signals and educational programmes for the residents. Zone 3 This zone covers areas where LNG transport takes place at a distance longer than ca 750 metres from important infrastructure elements, residential areas, industrial complexes, in large bays or in open waters, where the threat and consequences of LNG leakage for people and buildings is minimal. In zone 3 measures taken to minimize danger are less complicated and less strict. Methods of responding to threats should include a procedure to follow if a gas cloud starts spreading. Places of shelter should be designated and an educational programme for local inhabitants should be implemented. Guidelines concerning risk management in the case of intentional LNG leakage Zone 1 This is an area where LNG transport takes place in narrow ports or canals, under important bridges or above tunnels, or at distances shorter than ca 500 m from important infrastructure elements, such as military objects, densely populated or industrial areas. In this zone threat and consequences of a large LNG leakage can be considerable and have serious consequences for public safety and may cause damage to local infrastructure. Risk management should cover threat due to vapour spreading and fire, which is why the most rigorous preventive measures, such as safety zones around the ship, management of vessel traffic and establishing control over vessels are elements of management process in crisis situations. It is very important to coordinate actions of all port security Zeszyty Naukowe 25(97) 75

7 Wojciech Ślączka services. The method of management and response in case of accident should be analysed in detail so as to ensure the availability of various kinds of measures (fire fighting, rescue services etc.) in order to minimize threat and the consequences of accident. Zone 2 These are areas where LNG transport takes place in wider canals or larger outer ports or at distances from 500 to 1600 m from important infrastructure elements, such as industrial centres or residential areas. In zone 2 the consequences of a serious LNG leakage are less severe. Thermal radiation constitutes a smaller threat to public safety and buildings. In this zone the strategy of risk management during LNG operations shall cover threat caused by spreading of vapours and appearance of fire. Methods of action shall cover managing and responding in case of accident and ensure the availability of shelters (e.g. closed areas, buildings), familiarization with warning signals and educational programmes for the residents. Zone 3 This area covers areas where LNG transport takes place at distances longer than ca 1600 m from major infrastructure elements, residential areas, in large bays or open waters, where the threat and consequences of LNG leakage for people and buildings is minimal. Measures taken to restrict threat are less severe and than in zones 1 and 2. Methods of action in emergency situations should concern procedures to follow when a gas cloud spreads. Places of shelter should be designated and an educational programme for the residents should be implemented. Conclusions The operation of the LNG terminal in Świnoujście will call for emergency scenarios including the consequences of a technical failure or human error. Carefully developed emergency procedures going in line with possible scenarios will significantly contribute to the minimization of the consequences. The analysis of thermal radiation effects enables the determination of the radii of thermal wave density from potential locations of accidents. The presented maps may be used for the determination of areas of limited personnel stay and specification of technical equipment for the protection of terminal personnel. References 1. ABSG Consulting Inc, Consequence Assessment Methods for Incidents Involving Releases from Liquefied Natural Gas Carriers, PARFOMAK P.W.: Liquefied Natural Gas (LNG) Infrastructure Security: Background and Issues for Congress, Recenzent: dr hab. inż. Zbigniew Barciu, prof. AM Akademia Morska w Gdyni 76 Scientific Journals 25(97)