CVEF -­‐ NGVs at Petroleum Terminals Natural Gas Vehicle Compatibility with Operations at Liquid Petroleum Fuel Terminals Prepared by: Clean Vehicle Education Foundation July 2013 July 2013 1 CVEF -­‐ NGVs at Petroleum Terminals Acknowledgements The authors wish to thank the following companies and organizations for their invaluable contributions to this document: Agility Fuel Systems Chart Paccar/Kenworth Mack/Volvo NGV America Clean Energy Fuels Mansfield Oil Company Mansfield Energy Partners Love’s Kwik-­‐Trip July 2013 2 CVEF -­‐ NGVs at Petroleum Terminals Executive Summary Several bulk fuel terminal operators have raised concerns regarding the safety of allowing spark-­‐ignited natural gas-­‐fueled tractors to fill “under the rack”. These concerns appear to be based on several aspects of spark-­‐ignited engines, including: 1. The potential for spark or electric arc to serve as an ignition source; 2. The temperatures of certain exhaust system components serving as an autoignition heat source for flammable or combustible liquids e.g., gasoline or diesel; 3. Uncertainty about risks from retrofit-­‐kit modifications that are not original equipment; and 4. The potential for venting of compressed natural gas (CNG) or liquefied natural gas (LNG) tanks to create a flammable or explosive environment under the racks. The Clean Vehicle Education Foundation (CVEF) in consultation with tractor and engine OEMs, fleet operators, natural gas vehicle (NGV) experts, and other expert parties, has attempted to systematically address each concern in this paper, and have carefully concluded that there is no diminished margin of safety associated with the operation of spark-­‐ignited NGVs in the terminal area, specifically including the area under terminal loading rack. In summary, CVEF has found: 1. The modern “solid state” design of natural gas engines, including coil on plug encapsulated high voltage systems mitigate the risk of stray spark or arc that may have been associated with earlier generations of spark-­‐ignited gasoline engines; 2. Current diesel engine exhaust component temperatures are and have been well above the autoignition temperature of gasoline and diesel for years, with no known incidents. The fact that certain NGV exhaust components are comparatively above this autoignition temperature poses no identifiable incremental risk, making NGVs no less safe than diesel engine technology in this regard; 3. Natural gas retrofits in the market today provide for direct injection of natural gas with diesel into compression engines, with the diesel compression ignition providing the source for natural gas ignition. Hence, they operate in a manner similar to diesel engines (i.e., no spark plugs, and similar exhaust system components and temperatures.) There are no known manufacturers of conversion kits to convert diesel engines to spark-­‐ignited natural gas engines, nor are there any clear economic incentive to do so; and July 2013 3 CVEF -­‐ NGVs at Petroleum Terminals 4. CNG cylinders and LNG tanks do not vent natural gas during operation. a. CNG cylinders are protected by a thermal relief valve that only operates if the cylinder is exposed to fire. b. LNG tanks will only vent if left standing for several days or more (typically 7-­‐10 days), and the simple act of operating the vehicle to arrive at the terminal will naturally reduce any pressure from “boil off”, making the relief extremely unlikely to actuate in the terminal area. The basis for the findings that these issues pose no significant decrease in the margin of safety is detailed within this document. July 2013 4 CVEF -­‐ NGVs at Petroleum Terminals Introduction Members of the International Liquid Terminals Association (ILTA) have expressed concerns about the use of spark-­‐ignited natural gas engine (NGV) tractors at petroleum distillate bulk fuel terminals. The concerns articulated include: 1. Do spark-­‐ignited (SI) natural gas engines pose an increased risk of ignition of flammable and combustible liquids and their vapors that may be present at the loading racks?1 2. What is the potential for auto-­‐ignition of bulk fuel spills and their associated vapors in a spark-­‐ignited NGV environment as compared to that associated with diesel tractors? 3. Are there retrofit engines or other spark-­‐ignited engines in the market and do they pose a different or greater risk of arc ignition compared to the current the coil-­‐on-­‐plug technology in use by original equipment manufacturers (OEM)? 4. Do CNG cylinders on board the vehicle pose a venting risk, or present an additional hazard of failing under pressure during an incident at the fueling rack, and will LNG tanks on the vehicle vent LNG vapor while the truck is located at the fueling rack? This document, which was prepared by the Clean Vehicle Education Foundation (CVEF2), will address each of these issues in a comprehensive and sound manner by providing the reader with a fundamental technical understanding of spark-­‐ignited natural gas fueled engines, their associated fuel storage systems, and detailed design information where appropriate CVEF wished to acknowledge the significant technical contributions by many tractor and engine manufacturers, bulk petroleum liquid fuel transportation and logistics providers, and others. Topic #1: Spark Ignited (SI) Natural Gas Engine Arc/Spark Risk Historically, stray arc or spark concerns associated with spark-­‐ignited engines were based on older generation ignition system technologies including high voltage wiring harnesses that were subject to vibration and wear due to relative motion between the engine, chassis, and ignition system high-­‐voltage wiring and other components. These ultimately could sustain wear or abrasion of the high-­‐voltage components and create a risk of an external arc. 1 Currently, only compression ignition (diesel) engines are allowed for this service by a few terminal operators. The CVEF is a non-­‐profit national organization whose mission is to assess and guide alternative fuels including NGVs. CVEF coordinates and implements a variety of public awareness, education, market research, codes and standards and technology programs at the national level. 2 July 2013 5 CVEF -­‐ NGVs at Petroleum Terminals Older designs for spark ignited (SI) gasoline powered engines involved an ignition system that was comprised of individual components located remotely from each engine cylinder. Components included, but were not limited to: 1. An exterior ignition coil 2. A single high-­‐tension rubber coated cable run from the coil to the ignition distributor. a. This single cable length could reach 12” to 18”. b. This cable was typically a press fit at each end with a simple rubber boot for moisture protection. i. This cable could wear and cause arcing to the nearest metal source on the engine or under the vehicle hood. 3. The distributor. 4. A series of high-­‐tension rubber coated cables run from the distributor to each individual cylinder spark plug. a. Each of these single cables could reach lengths of 24” to 42” for a total linear length of up to 14’. b. Each cable would be routed around various engine obstructions and (or) vehicle accessories then simply clipped in place via a press fit clamp. c. These cables were typically a press fit at each end with a simple rubber boot for moisture protection at the distributor and moisture / heat protection at the spark plug. d. These cables were the single greatest source of ignition system complaints due to chaffing, cracking and loose fitting connections, causing arcing and loss of power. 5. The spark plug. a. Each cylinder is furnished with a ceramic insulated spark plug, generally threaded into the cylinder head. i. Each spark plug was supplied power via a press fit high-­‐tension cable. ii. The ceramic insulator could crack and cause arcing to and around the cylinder head. Current SI technology, as described below, is vastly different. It eliminates hazards from each of the above, thus virtually eliminating the arc potential and spark risk associated with earlier generation engines. Cummins Westport Inc. (CWI) is currently the only U.S. provider of natural gas engines used in tractors for petroleum fuel tank trucks. CWI has provided the following design and layout details for its current fleet of engines: the ISL G and ISX12 G. CWI’s spark-­‐ignited engines are practically identical to Cummins diesel engines in terms of ancillary components (e.g., starter motors) and low-­‐voltage (typically 12V) wiring harnessing that connect to the engine ECM, sensors, valves, etc. Since the Cummins diesel engines share these low-­‐voltage systems, which are currently acceptable for service at petroleum fuel terminals, similar ancillary components used July 2013 6 CVEF -­‐ NGVs at Petroleum Terminals on the natural gas engine will pose no greater risk of arcing, and thus should be acceptable as well. The unique aspect of this new generation of SI NG engines (relative to diesel engines) is the spark ignition system. CWI’s engines available in North America (ISL G & ISX12 G) use “coil-­‐on-­‐plug” technology, which are individual modular cylinder ignition systems that are simpler, much more efficient and cannot cause exterior arcing. There is no longer a need for a distributor, so all high-­‐tension cables are gone. Each cylinder is equipped with a self-­‐
contained ignition coil and spark plug assembly that is mechanically secured (clamps / screws) together and then mechanically secured (bolted) to the engine. The spark plug is completely enclosed inside the coil cover and cylinder head. There is no opportunity for cables to work loose, no cables to chafe, wear and or crack eliminating any potential for engine ignition system arcing as these cables have been completely eliminated from a modern (SI) engine installation. This arrangement is shown in Figure 1 below. Ignition
Coils (6)
Cylinder
Head
Ignition Control
Module
Engine Control
Module
Figure 1. ISX12 G Engine July 2013 7 CVEF -­‐ NGVs at Petroleum Terminals A low voltage wiring harness connects the Ignition Control Module (ICM) to the ignition coils. All high voltage components are encapsulated within the engine envelope as illustrated in Figure 2 below, thus fully mitigating spark/arc concerns associated with high-­‐voltage wiring in earlier generations of spark-­‐ignited gasoline engines. Coil
Wire Harness
Connection
Valve Cover
Cylinder Head
Coil Extension
Spark Plug
Figure 2. ISX12 G Cylinder Head, Coil, Coil Extension and Spark Plug Cross Section July 2013 8 CVEF -­‐ NGVs at Petroleum Terminals On both CNG and diesel engines, the engine harness and part of ignition wiring harness will typically be operated at 13.5V DC (assuming nominal 12V operation). Expected maximum voltages will be 15.5 -­‐ 16V (due to battery overcharging). Some diesel engines are designed to run at 24V DC, and will have commensurately higher voltage ranges. Ignition wiring harness from the ignition control module to the coils can see short pulse duration (~ 40 -­‐ 50 micro-­‐seconds) of voltages, encased in the cylinder heads from 300 -­‐ 400V DC. The wires in the harnesses comply with SAE J1128 standards. CWI’s 8.9-­‐liter ISL G engine contains the same relevant features as the ISX12 G, including the use of an enclosed coil-­‐on-­‐plug ignition system. In the ISL G, the ICM is also connected to the ignition coils via a low voltage wire harness. The primary difference is that the ISL G high voltage ignition coils are rigidly mounted to the cylinder head with an external bracket, as shown in Figures 3a and 3b. The ISL G ignition coil extensions are made of a rigid thermoplastic and connect to the spark plugs, which are threaded into the cylinder head. As a result, the ISL G high voltage ignition system components form a rigid assembly that is not subject to relative motion with respect to other engine components, thus eliminating high-­‐voltage arc/spark potential. Ignition Coils & Mounting Bracket
Low Voltage Wire Harness
Ignition Control Module
Figure 3a. ISL G Ignition System July 2013 9 CVEF -­‐ NGVs at Petroleum Terminals Ignition Coil
Mountin
g Bracket
Spark Plug
Ignition Coil Extension
Ignition Control Module
Figure 3b. ISL G Ignition System Components Topic #1 Conclusion: The current OEM design of spark-­‐ignition NGV engines eliminates the potential for external spark by using an encapsulated design that does not contain external high voltage wiring that can become a source of an arc or spark. Topic #2. Exhaust System Component Temperatures and Potential as an Autoignition Source Autoignition require direct contact between the hot surface and the liquid fuel. Laboratory-­‐measured autoignition temperatures3 for gasoline and diesel are: • Gasoline 224-­‐2800C/(475-­‐5360F) • Diesel 177-­‐3300C (350-­‐6250F) The temperature data shown in Table 1 is compiled from various engine manufacturer datasheets and technical documents. Note that in all cases, the components shown below would be, during loading, situated outside of typical Class I, Division 2 areas so these temperatures are isolated from a compliance thresholds. 3 Source: Engineering Toolbox http://www.engineeringtoolbox.com/fuels-­‐ignition-­‐temperatures-­‐
d_171.html July 2013 10 CVEF -­‐ NGVs at Petroleum Terminals Table 1. Engine Exhaust Temperatures Maximum Temperature (0C/0F)a Parameter Spark Diesel c HPDI b NGV d DPF skin temperature -­‐ normal operation 350/662 350/662 N/A DPF skin temperature -­‐ active regeneration 360/680 360/680 N/A Exhaust temp at DPF outlet -­‐ active 600/1112 600/1112 N/A regeneration Exhaust temp at DFP outlet -­‐ failure mode 975/1787 975/1787 N/A SCR catalyst skin temperature -­‐ normal 368/694 368/694 N/A operation Exhaust temp at SCR catalyst outlet -­‐ normal 600/1112 600/1112 N/A operation SCR catalyst skin temp -­‐ failure mode 325/617 325/617 N/A Exhaust temp at SCR catalyst outlet -­‐ failure 800/1472 800/1472 N/A mode Catalyst skin temperature -­‐ normal operation N/A N/A 700/1292 Exhaust temperature at catalyst outlet -­‐ N/A N/A 800/1472 normal operation a – Maximum Temperatures during highest engine loading over a sustained period b – High Pressure Direct Injection -­‐ natural gas injected with diesel into the cylinder c – Diesel and HPDI engines do not have 3-­‐way catalyst d – Spark ignited natural gas engine – Does not have DPF and SCR Virtually all temperatures on the table above are above the autoignition temperature of diesel and gasoline during normal operating modes, for both spark ignited and diesel engine exhaust system components, yet we were not able to identify any instances of autoignition under normal rack loading conditions, including occurrences of product release. A study4 of temperature and pressure impacts on delay time for autoignition of methane (the primary constituent of natural gas) demonstrates that once above the autoignition temperature, higher temperatures do NOT equate to a reduced margin of safety. This raises two questions: (1) ) why have there been no such incidents even with exhaust component temperatures exceeding the autoignition temperatures of these fuels, and (2) would not an increased normal operating T for a NGV engine (800*C vs. 600*C for diesel) aggravate this situation? Temp. Finding #1: Steep Time Gradient 4 AUTOIGNITION CHARACTERISTICS OF GASEOUS FUELS AT REPRESENTATIVE GAS TURBINE
CONDITIONS C.J. Goy, A.J. Moran, Rolls-Royce, PLC, Ansty, Coventry CV7 9JR, United Kingdom and G.O. Thomas,
Department of Physics, University of Wales, Aberystwyth, Ceredigion SY23 3BZ United Kingdome
http://ddtexperts.com/ref89.pdf July 2013 11 CVEF -­‐ NGVs at Petroleum Terminals The maximum temperatures shown in Table 1 and Figure 5 are based on the engines operating at maximum loading for a sustained period of time (e.g., high interstate speeds with full loads, climbing steep mountainous terrain). It is highly unlikely that a truck entering the terminal area will have been recently operating under these conditions, thus leading to the expectation lower surface temperatures. Moreover, the International Fire Code 5706.6.1.3 (See Appendix B) requires that all engines of tank vehicles or tractors be shut down during the making or breaking of hose connection and during the loading operation. The temperatures of both the diesel and natural gas exhaust systems will decrease before and during the fueling operations. This is supported by Figure 45, which illustrates the speed at which exhaust gas and surface temperatures drop following the completion of a regeneration cycle on a 12-­‐liter diesel engine. Figure 4. International 7500 Exhaust Temperatures after Regeneration From these data, it is shown that the temperature at the venturi6, drops from 800F to 400F in 5 min (80 degrees/min). The temperature on the outside of the tailpipe drops 5 Diesel Exhaust Emission System Temperature Test, U.S. Department of Agriculture, Forest Service National Technology & Development Program, 5100—Fire Management, 0851 1816—SDTDC, December 2008 6A venturi is a short tube with a tapering constriction in the middle that causes an increase in the velocity of flow of a fluid and a corresponding decrease in fluid pressure and that is used especially in measuring fluid flow or for creating a suction. July 2013 12 CVEF -­‐ NGVs at Petroleum Terminals from 500F to 200F in just 4.2 min (72 degrees/min). Assuming a conservative cool down rate of 70F/min (it will actually be higher at higher temperatures), at an initial catalyst skin maximum temperature of 1292F, it would only take 12.7 minutes to get below a 400F threshold. Given the amount of time it takes a tractor to throttle down from highway speeds, drive to and enter the terminal area and pull under the rack and get connected, coupled with the low likelihood of the exhaust actually being at the highest temperature, it’s a reasonable assumption that the exhaust system will be well below any reasonable autoignition temperature before connecting to the rack. Temp. Finding #2: Steep Temperature Gradient Based on Cummins Engineering Bulletin AEB21.10, Figure 5 below shows the temperatures at various points on the natural gas engine catalyst system, which corresponds with the data on Table 1 above. It is notable that while the maximum temperature on the catalyst exhaust surface can be 7000C (12920F), the maximum temperature just 3 inches from the outer skin is only 2000C (3920F). There is a design specification (see Appendix A) that is required to protect thermal sensor wiring which results in a maximum temperature of 1250C 10 inches from the catalyst skin. Thus, only inches away from the catalyst, the temperatures, even under maximum design conditions, are below the autoignition temperatures. Figure 5. Natural Gas Engine Catalyst Maximum Temperatures While the outlet exhaust can be up to 8000C at the point it exits from the pipe, most tractor OEMs install additional pipes or diffusers which promote cooling. Moreover, Cummins recommends that the exhaust stack is mounted vertically, thus directing these exhaust gas up and away from the loading rack and Class I, Division 2 area. July 2013 13 CVEF -­‐ NGVs at Petroleum Terminals The National Electrical Code (NFPA 70) Table 515.3 (See Appendix B) states that during loading through a bottom connection, the Class 1 Division 2 classified area extends 900 mm (3 Feet) in all directions from the point of connection, 3 meters horizontally from the point of connection and 450 mm above grade, as illustrated in Figures 6& 7. Figure 6. Class I, Division 2 Loading Area Diagram The exhaust system components of natural gas tractors are located well beyond this classified area as shown in Figure 7. The scully system is the closest connection point on the trailer to the heat source on the tractor. July 2013 14 CVEF -­‐ NGVs at Petroleum Terminals Figure 7. Tractor Exhaust components relative to Class I, Division 2 Areas The 3 foot cube or sphere from the connection point is depicted on Figure 8, but for purposes of potential ignition one should consider the requirement to be within 3 meters horizontally from the point of connection. As noted in Figure 8, the scully system is roughly 21 inches from the ground. Taking the scully system as the center point and extending 3 meters or roughly 10 feet in all directions (a circle) the clearance from the closest point of the circle to the exhaust stack on the tractor is roughly 17 feet. If the unit was fitted with a horizontal exhaust the distance would be approximately the same or perhaps 1 to 2 feet less. The wheelbase on the tractor depicted is 185 inches, which is fairly standard for petroleum haulers. Most CNG or LNG configurations are going to employ a slightly longer rail frame due to tank requirements (191 to 205 inches) but we are not aware of any that would shorten the rail frame. Thus the engine exhaust components are well outside of the Class I, Division 2 area. Temp. Finding #3: Observed Flash points are lower in Controlled Lab Environments Another consideration is that flash points measured in laboratory environments are typically significantly lower than those experienced in real world conditions. For July 2013 15 CVEF -­‐ NGVs at Petroleum Terminals example, a study conducted by University of Washington7 evaluated actual autoignition temperatures of diesel in vehicular environments, with the results shown in Tables 2 and 3 below. Table 2. Diesel Autoignition Temperatures Material
Autoignition
Temperature oF
Diesel
350-625
Diesel
>1200
Diesel
Notes
Source
Laboratory - ASTM
Heated catalytic converter. No
ignition, test stopped at 1200
degrees F
[3]
950-1000
Heated pipe
[10]
Diesel
1010-1125
Recessed stainless steel plate
[4]
B100
(Biodiesel)
705-840
B20 (Biodiesel)
980-1300
Recessed stainless steel plate
and fluid spray
[15]
E-diesel
(Ethanol blend)
1265-1400
3.
Arndt, S., et al., “The Motor Vehicle in the Post-Crash Environment, an Understanding of
Ignition Properties of Spilled Fuels,” SAE 1999-01-0086, 1999.
4.
Colwell, J. D., et al., “Hot Surface Ignition of Automotive and Aviation Fluids,” Fire
Technology, 41, pages 105-123, 2005.
7 http://depts.washington.edu/vehfire/fuels/detailedresults.html July 2013 16 CVEF -­‐ NGVs at Petroleum Terminals Table 3. Gasoline Autoignition Temperatures Material
50-100 Octane
Autoignition
Temperature oF
495-853
Unleaded
1350-1550
87 Octane
>1200
89 Octane
>1200
91 Octane
>1200
Unleaded, 89
Octane
1100
Unleaded, 87
Octane
87 Octane and
92 Octane
Notes
Source
Laboratory - ASTM
Full-scale vehicle tests
[1]
Heated catalytic converter.
No ignition, test stopped at
1200 degrees F
[3]
Heated pipe
[10]
1135-1225
Recessed stainless steel
plate
[4]
1460-1520
Nodular iron exhaust manifold
1395
1325-1350
89 Octane
1240-1445
89 Octane
1425-1485
E85
1300-1325
Stainless steel heat shield
[5]
Stainless steel exhaust
manifold
Recessed stainless steel plate
and fluid spray
[15]
3.
Arndt, S., et al., “The Motor Vehicle in the Post-Crash Environment, an Understanding of Ignition
Properties of Spilled Fuels,” SAE 1999-01-0086, 1999
5.
LaPointe, N., et al., “Hot Surface Ignition of Gasoline on Engine Materials,” SAE
2006-01-1013, 2006.
The principal conclusion of these studies is that the real world autoignition temperatures of gasoline and diesel on a catalytic converter (the unique component of the spark ignited natural gas tractor’s exhaust stream) are well over 1200 F and thus highly unlikely to provide a risk of fuel ignition at the temperatures one can expect exhaust systems to be once under the rack.. Temp. Finding #4: Contribution of Excess Heat Above Autoignition Temperature is Statistically Insignificant. As shown in Figure 8 below, higher temperatures do results in some reduction in autoignition delay time; however, the delay reduction is measured in milliseconds. For example, an increase of 3000F results in a shortening of time delay of 8 milliseconds (0.008 seconds), which is statistically insignificant relative to human reaction time. Said another way, if the component is 3000F hotter, autoignition will occur only 0.008 seconds faster than if at the lower temperature. July 2013 17 CVEF -­‐ NGVs at Petroleum Terminals Figure 8. Methane Autoignition Time Delay as a Function of Temperature and Pressure July 2013 18 CVEF -­‐ NGVs at Petroleum Terminals Topic #2 Conclusion: 1. While certain NGV exhaust system components can have a maximum temperature of 100-­‐2000C above comparable diesel exhaust components, as highlighted on Table1, this potential hazard is mitigated for several reasons. 2. While the auto ignition temperatures of gasoline and diesel may seem comparatively low under laboratory conditions, they are significantly higher in real world conditions (For example, gasoline has an autoignition temperature range of 495-­‐8530F in the lab, yet in practice it is well over 12000F when exposed to a catalytic converter skin) 3. Once above the autoignition temperature, higher temperatures provide no meaningful difference in the time to autoignition. (Pregnant is pregnant) As an example, the difference between autoignition at 6000C (highest diesel temperature under normal operations) and 8000C (highest NGV temperature under normal conditions.) would be about 10 milliseconds, far below any human reaction time. 4. Both engines are well outside of the Class 1 Division 2 area, both diesel and NGV tractors are compliant with NFPA requirements. 5. Exhaust components cool down very quickly (70-­‐800F/minute), and are well below maximum temperatures prior to filling under the rack. 6. While catalyst skin temperatures can be as high as 7000C, Cummins design specification results in temperatures of a maximum of 2000C, just 3 inches from the catalyst skin Taken together, these facts yield the reasonable conclusion that natural gas engines are no less safe than their diesel counterparts in this regard. Topic #3 Retrofit Engine Technology for Class 8 Tractors At this time the only spark-­‐ignited natural gas engines available in the market with OEM first-­‐fit design for Class 8 tractors are the two CWI engines described above. The only type of retrofit available on the market converts diesel engines to duel fuel diesel/natural gas engines (also known as High Pressure Direct Injection – “HPDI”) maintaining the diesel cycle. These engines start on diesel and only partially substitute natural gas under increased loading. The operation of the engine and exhaust system is otherwise identical to that of diesel engines. There are no known manufacturers of conversion kits to convert diesel engines to spark-­‐ignited natural gas engines, nor would there likely be any economic incentive to do so due to the cost and complexity of conversion and certification July 2013 19 CVEF -­‐ NGVs at Petroleum Terminals Topic #3 Conclusion: Retrofits of diesel engines to natural gas are only available to allow the use of natural gas to be injected along with diesel, but otherwise operate in a manner nearly identical to conventional diesel engines. Due to the lack of spark ignition and virtually identical exhaust system design temperatures, there is no quantifiable reduction in safety margins associated with these retrofits as compared to diesel-­‐only engines. Topic #4 Potential for CNG and LNG release while under the rack Due to the nature of their designs, neither CNG nor LNG tanks are designed to vent during normal operation under the rack. (See Appendix A for more detailed information) CNG tank are built with a substantial operating pressure design margin. Once filled, the pressure will only decrease as the vehicle is operated and the relief is designed to release natural gas in the event the tank is consumed by fire. LNG tanks have normal operating pressure well below the relief set point, and “boil-­‐off” would have to be occurring for more than 7 days before the pressure would cause the relief to lift. The simple act of driving the vehicle to the loading rack would cause this pressure to drop as the engine inducts the natural gas vapors. Additional information on each is provided below: 4.A Compressed Natural Gas (CNG) Cylinder Design and Operation The design, testing and certification of CNG cylinders provides for a very high margin of safety and an extremely remote chance of venting during fueling operations. Every CNG cylinder must meet all of the requirements of Title 49 CFR 571.304. These requirements include life cycle testing, hydrostatic burst test at 2.25 times the service pressure and a bonfire test. These tests ensure an appropriate cylinder engineering design margin that will not fail due to pressure or fire exposure under expected operating conditions including collisions. CNG cylinders designed to the ANSI/NGV2 national standard8 meet the 571.304 requirements plus the fourteen additional test requirements imposed by ANSI/NGV29. 8 This standard is copyright protected and cannot be excerpted in this document. A copy can be obtained for a fee from CSA Group at http://webstore.ansi.org/RecordDetail.aspx?sku=ANSI+NGV2-­‐
2007&keyword=_inurl:webstore.ansi.org%23inurl:sku%3Dansi&source=google&adgroup=ANSI-­‐
Standards&gclid=CLSKh-­‐3StLgCFSdk7AodSF0Aaw 9 Out of the more than 100 incidents involving NGVs all vehicle fires were caused by the non-­‐CNG or LNG fuel systems. Most vehicles fires are electrical, tire, break or hydraulic line failures. The fire exposure test done under FMVSS 304 and NGV 2 are to make sure that the CNG cylinder will not fail from exposure to the fire. July 2013 20 CVEF -­‐ NGVs at Petroleum Terminals At the fueling station, the natural gas dispenser controls the fill pressure in the CNG cylinder. The dispenser is temperature compensated which ensures that the settled pressure in the cylinder will be equal to (or less than) the design working pressure. The maximum stress that the cylinder sees in service is at the time of fueling and it is less than 50% of the design stress. Once the vehicle leaves the station the pressure falls gradually over time as fuel is consumed thereby reducing the stress on the cylinder. Each CNG cylinder is protected by a thermal pressure relief device (PRD). PRDs are certified in accordance with ANSI PRD110, a performance standard developed specifically for PRDs used on natural gas vehicles cylinders by including extensive durability testing in simulated vehicle service conditions. The PRD is designed to operate when the cylinder is exposed in a fire and reach a temperature of 2190F. A “bonfire test” ensures the cylinder/PRD system operates as designed by the cylinder manufacturer. The PRD is designed to open and relieve the pressure in the cylinder well before there is any risk of cylinder failure. Note that the PRD is quite different than a traditional mechanical relief valve, in that it is not pressure sensitive, it is temperature sensitive; and once it opens it will not reseal. (It is more like a fuse that blows, than a resettable circuit breaker). Figure 9 below shows an external view of a red manual cylinder valve with an inline PRD installed in the tube going down and under the cylinder and then vented a safe location for discharge The National Fire Protection Association (NFPA) Code 52 requires that each PRD be piped away from the cylinder to a safe location on the vehicle. Since the PRD only operates when the vehicle/cylinder is in a fully involved fire the natural gas that is vented may ignite but it is normally at a point above the vehicle so not to impinge on adjacent equipment or personnel, and is well outside the Class I, Division 2 area as depicted in Figures 6 and 7. 10 ANSI PRD 1 -­‐2013 can be obtained as noted in footnote #4 for a fee July 2013 21 CVEF -­‐ NGVs at Petroleum Terminals Manual Valve PRD – In line Relief Piping Figure 9. CNG Cylinder Valve with PRD Natural gas is lighter than air and will quickly dissipate if released. It will not pool on the ground, as do liquid fuels, which would allow vapors to accumulate. Natural gas has a much higher ignition temperature than diesel or gasoline (greater than 5800C/10760F) and a narrow flammability range (between 5% and 15%). By contrast, diesel has lower flammability limit11 (0.6%-­‐0.75%), making it more likely to ignite both at lower concentrations and lower autoignition temperature 4.B Liquefied Natural Gas (LNG) Fuel System Design and Operation An LNG tank is a stainless steel double wall super insulated cryogenic dewar, as shown in Figure 10. When filled at the LNG fueling station the pressure in the LNG tank ranges between 50 psig and 120 psig. The colder and denser the LNG, the lower the pressure. Even with the cryogenic design of the LNG tank some amount of heat is transferred from the ambient environment to the LNG, slightly increasing the internal pressure between 10 psig and 15 psig per day. A LNG fuel tank system that normally operates at 11 Diesel Upper Flammability Limit: 7.5%. Source: http://www.engineeringtoolbox.com/explosive-­‐concentration-­‐limits-­‐d_423.html July 2013 22 CVEF -­‐ NGVs at Petroleum Terminals 120 psig would hold the LNG for 7 to 10 days before the pressure relief valve would open to relieve the internal pressure. As seen below in Figure 10, the primary relief valve in a LNG fuel tank system is set at 230 psig and resets at 207 psig. If the LNG tank were allowed to sit unused for over 7 days until the relief valve operated, the approximate amount of natural gas released would be 1.7% of the total volume of the tank. For a 120-­‐gallon LNG tank this release would be equal in energy to about 1 gallon of diesel fuel. Unlike a liquid spill the gas would quickly dissipate to below the flammability limit. Such a small amount would not accumulate under canopy as an ignitable vapor. Even if a LNG vehicle sat unused for a period of time allowing the pressure to build before driving up to the liquid petroleum terminal, the simple act of operating the vehicle would reduce the pressure in the LNG tank back to the normal operating pressure. In the diagram above, the economizer regulator opens when the engine is started to provide natural gas directly to the engine. This action reduces the LNG tank pressure back down to the normal operating pressure. The only way a LNG tank would vent natural gas at a terminal facility would be if the LNG vehicle were parked for more than seven days at the terminal rack without operating the engine. Under normal loading conditions, this LNG tank would not be left idle and thus would not be expected to vent. Figure 10. LNG Tank Arrangement July 2013 23 CVEF -­‐ NGVs at Petroleum Terminals Issue #4 Conclusions: Neither LNG nor CNG tanks are designed to vent under normal operations at the loading rack. The CNG tank would have to be involved in a fire before the PRD would operate, and the LNG truck would have to be parked at the rack for 7-­‐10 days for the pressure to build up enough to lift. Thus, the venting of natural gas should not happen under normal operations, implying no additional risk. Should there be a small leak, it would be detectied by an onboard methane detection system for LNG, and it would produce a noticeable smell for the CNG. Topic #5. Other CNG/LNG Tank Considerations CNG Cylinder Life Like all other stressed components in vehicles, CNG cylinders are assumed to have a limited safe life but unlike other components, that life is explicitly determined and shown on each cylinder label as a “Do not use after…” date required by the federal regulations FMVSS 304. Two mechanisms that could cause a failure in a cylinder used for an infinite time are identified and controlled by both design qualification tests and recurring tests of batches during production. These failure modes are fatigue cracking of metals and stress rupture of fiber reinforced composites. Virtually all of the operating loads on a cylinder are carried by metals and/or composites. Fatigue cracking results from alternating or varying stresses on a metal structure. Each design and each batch of NGV2 cylinders must be tested to pressure cycles representing 750 worst-­‐case refueling pressure cycles per year of design life and not fail. Each cycle assumes that the cylinder contains only 360 psi before the fill and that every fill occurs on a hot day and results in a full pressure of 4,500 psi, the maximum allowable under service conditions. All of these values are conservative for actual vehicle use where low fuel warnings are commonly triggered above 360 psi, not all days of filling are hot and vehicles actually do not experience 15,000 full fuel fills during a 20-­‐year life. In addition to this triply conservative batch test requirement there is another design test requirement for a low-­‐hazard leak-­‐before-­‐burst (LBB) failure mode if a cylinder is somehow used until it fails in fatigue. In this test cylinders must fail by developing a small fuel leak unless they demonstrate a fatigue life of 45,000 cycles to 5,400 psi. This is the most demanding LBB test requirement in any major cylinder standard and the combination of the two requirements has been effective in preventing metal fatigue crack failures in NGV2 cylinders. The life-­‐limiting composite failure mode is stress rupture, sometimes called static fatigue. Fibers used in composites have a characteristic life in stress rupture in which the probability of failure increase with the time under load and inversely with the ratio July 2013 24 CVEF -­‐ NGVs at Petroleum Terminals of the short-­‐term tensile strength of the fiber to the operating stress, called stress ratio. The more highly stressed the fiber is the more likely it is fail in stress rupture with increasing time. Composite cylinders must be designed with limited minimum stress ratios for each fiber type to provide a predicted failure rate in stress rupture of 1: 1,000,000 cylinders that are kept full at 100% service pressure for its entire lifetime. This is obviously conservative for a fuel tank but there is additional conservatism by making verification of the stress ration a batch requirement by bursting a cylinder. The statistical effect of requiring a manufacturer to demonstrate the stress ratio at the minimum strength of his design and not the mean strength is to add approximately three orders of magnitude conservatism to the stress rupture life making it 1,000 to 2,000 years for a predicted 1:1,000,000 failures. These types of requirements have been used for composite gas cylinders for almost 40 years and for NGV2 cylinders since about 1993. CVEF has no record of a CNG cylinder or any other similar cylinder failing due to exceeding its actual safe life. LNG Tank Life LNG tanks are specifically designed for vehicular fuels systems and are intended to serve for the life of the vehicle with no restrictions. The LNG tank is a stainless steel double wall pressure vessel with the inner tank wrapped with super insulation. The space between the inner and outer tank is also evacuated to provide a superior insulation system. All materials used are compatible for cryogenic service. The inner tank contains the LNG. The outer tank and its support system are specifically designed to withstand the stresses associated with over-­‐the road-­‐vehicles. The LNG tank operates a relatively low pressure (less than 230 psig) and the design of a stainless steel pressure vessel at these stress levels are well known and has nearly an unlimited life. LNG tanks must pass a number of severe abuse tests similar to CNG cylinders including a fire test, impact test and pressure test. Minor Leaks In the unlikely event of a small leak (e.g., due to a loose fitting), there are separate alert mechanisms for CNG and LNG. CNG is odorized with mercaptan, which emits a rotten egg smell to alert people of the presence of a natural gas leak. For LNG, there is an onboard methane detection system (required by NFPA 52-­‐2013 section 9.13.3) to alert the driver of the presence of any natural gas leakage. Leaks can be visually detected due to the formation of a small vapor cloud that would be visible at the source of the leak. The systems are also inspected for potential leaks during routine maintenance visits. July 2013 25 CVEF -­‐ NGVs at Petroleum Terminals Conclusions Based on the current state of design of natural gas engines and both LNG and CNG fuel tanks, there is no identifiable reduction in safety or increased risk to bulk fuel terminals associated with the operation of NGVs under the rack when compared to diesel engine tractors. 1. Modern natural gas engines are no more a risk as a source of spark or arc ignition than a diesel engine due to the integrated and encapsulated design; 2. The exhaust system components of both diesel and natural gas engines both have surfaces well above the laboratory measured autoignition temperature of diesel and gasoline, providing for a similar risk profile and no identifiable history of autoignition due to diesel exhaust system temperatures; 3. The only available retrofits of diesel engines to natural gas involve the use of direct injection of natural gas along with the diesel (“dual fuel”). These designs use compression ignition and exhaust systems identical to other diesel engines, thus providing no change in safety margins as compared to a diesel-­‐only engine. 4. A CNG cylinder is not at risk of failure and will only release natural gas when exposed to fire. The release would be to a safe location above the vehicle; a. LNG tanks in normal operation will not vent natural gas while at the liquid fuel terminal. b. CNG cylinders and LNG tanks have stringent design margins and testing/certification standards to ensure safe use over their design life. July 2013 26 CVEF -­‐ NGVs at Petroleum Terminals Appendix A Engine Technical Specifications Pressure Relief Valve (PRV) and Thermal Pressure Relieve Device (PRD) spec sheets – Separate PDF files • PRD-­‐ 8100 Series • PRD -­‐OMB -­‐ York Spec Sheet • PRV-­‐ Cryo LNG Spec Sheet Other Cummins and Cummins-­‐Westport Specifications to be provided to ILTA directly by Cummins. July 2013 27 CVEF -­‐ NGVs at Petroleum Terminals Agility Systems CNG/LNG Tank Systems Typical CNG System
1. CNG Cylinders
2. Solenoid Valve
3. Pressure Relief
Device (PRD)
4. Ball Valve
5. Manifold
6. Pressure Transducer
7. Bleed Valve
8. Needle Valve
9. Defuel Port
10.Filter
11.Fill Manifold
12.Fill Receptacle
13.Fill Receptacle
14.Low Pressure Gauge
15.High Pressure Gauge
16.Filter
17.Solenoid
18.Regulator
19.UV Protected Blue
Cap
20.Tubing
21.Pressure Relief
Device
Plumbing and Major
Components
Basic CNG Block Diagram
1. Tank
Superstructure
Stores the CNG under
pressure. Various
configurations
accommodate a multitude
of vehicles. Integral PRD
activates at approximately
219 Deg. F to protect fuel
storage system from
catastrophic damage during
fire.
2. Ball Valve
A ball valve, also called the
emergency shutoff valve,
is used to direct the gas
flow. This valve is normally
OPEN.
3. High Pressure
Filter
4. Solenoid
Valve
Removes impurities from the
fuel to maximize system life.
Key-on/Key-off controls
the flow of CNG from
the cylinders to the
engine. This valve is
normally CLOSED
. . . High Pressure up to 4,500 psi . . .
6. Low Pressure Filter
Further removes impurities and
moisture from the CNG before
delivering fuel to the engine.
5. Pressure Regulator
Reduces and maintains fuel
pressure to useable levels for the
engine. Integrated PRV activates at
200 psi to protect downstream
components.
. . . Low Pressure up to 200 psi . . .
July 2013 28 CVEF -­‐ NGVs at Petroleum Terminals Typical Truck Back of Cab CNG System
Tank
System
FMM (under
tank
system,
opposite
side)
Typical Truck CNG Rail Mount
Tank
System
FMM
(between
tank system
and rear
wheel)
July 2013 29 CVEF -­‐ NGVs at Petroleum Terminals 6
Driver warnings:
Low temp warning
Methane detection system
1
2
4
3
5
Typical LNG System Schematic - Major Components of the Agility/Chart Fuel System
1 Over Pressure Regulation. Ensures that the vaporized fuel pressure does not exceed the
pressure specified by the engine manufacturer
2 Fuel Shutoff Valve – automatically stops fuel flow from the tank to the engine when the ignition
key is in the off position
3 Heat Exchanger. Uses the coolant fluid from the engine to vaporize LNG to a gaseous phase
4 Tank – Stores cryogenic fuel onboard the vehicle and includes fill valve, pressure relief valve,
excess flow valve, fuel flow and vent flow isolation valves, and economizer regulator
5 Fuel Gauge – displays liquid level of tank to vehicle operator
6 Driver Warnings – low temp and methane detection warnings notify driver of system
malfunctions.
17
Typical LNG System Pressures and Temperatures
100-230 PSI (-169F to -200F bi-phase)
Requirement: 70150 PSI
(-40F to 200F)
Vapor
pr
Economizer
Liquid
100-150 PSI (40F to 200F gas)
100-230 PSI (40F to 200F gas)
Heat Exchanger
July 2013 Solenoid
Overpressure Regulator
Engine Filter
Confidential – Agility Fuel Systems
30 CVEF -­‐ NGVs at Petroleum Terminals Dual Fuel Aftermarket System12 The American Power Group (APG) Dual-Fuel system is a patented aftermarket upgrade
system which seamlessly meters Compressed Natural Gas (CNG) from CNG fuel tanks into
the induction system of a diesel engine.
The Dual-Fuel configuration does not change any of the OEM diesel engine components
and monitors compliance with OEM system parameters like oil pressure, coolant temp,
exhaust gas temp, manifold air pressure, diesel fuel pressure, etc., either through the
Communication Area Network (CAN) system or installed sensors.
The Dual-Fuel controller will not allow CNG to flow unless the base engine parameters are
within standard operating range (i.e., the CNG does not flow until the engine coolant temp
and exhaust gas temps are at “normal” operating values, therefore “cold” engine start-up is
on 100% diesel fuel). The conventional diesel engine governor controller acts to reduce
diesel fuel flow as CNG is introduced to maintain requested engine speed/load.
The OEM diesel engine control system remains unchanged in APG systems. If for any
reason, the engine parameters are not within standard operating range or the CNG fuel
storage pressure falls below 150 PSI, the Dual-Fuel system turns off the CNG flow and
seamlessly returns the engine back to 100% diesel fuel operation. Also if the CNG fuel
supply is depleted, the system automatically returns to 100% diesel fuel.
12 http://www.americanpowergroupinc.com/about-­‐dual-­‐fuel/how-­‐apg-­‐works-­‐for-­‐you July 2013 31 CVEF -­‐ NGVs at Petroleum Terminals Source: The Hardstaff Group, Dual Fuel Training Level 2, 11/2012 July 2013 32 CVEF -­‐ NGVs at Petroleum Terminals Appendix B Fire Code and NFPA Citations 1. National Electrical Code NFPA 70 Table
515.3
Continued
Location
Loading through bottom connections with
atmospheric venting Office and rest rooms
NEC Class I Division
112
Loading through closed dome with
atmospheric venting Loading through
closed dome with vapor control
122
122
Bottom loading with vapor control or any
bottom unloading
2
2
Storage and repair garage for tank vehicles
Garages for other than tank vehicles
12
12
Zone
012
Unclassified
Unclassified
Outdoor drum storage Inside rooms or
storage lockers used for the storage of
Class I liquids
Indoor warehousing where there is no
flammable liquid transfer
July 2013 All pits or spaces below floor level Area up
to 450 mm (18 in.) above floor or grade
level for entire storage or repair garage If
there is any opening to these rooms within
the extent of an outdoor classified location,
the entire room shall be classified the same
as the area classification at the point of the
opening.
Unclassified
2
Unclassified
Piers and wharves
Extent of Classified Area
Area inside of the tank Within 900 mm (3
ft) of point of venting to atmosphere,
extending in all directions Area between
900 mm and 4.5 m (3 ft and 15 ft) from
point of venting to atmosphere, extending
in all directions; also, up to 450 mm (18
in.) above grade within a horizontal radius
of 3.0 m (10 ft) from point of loading
connection If there is any opening to these
rooms within the extent of an indoor
classified location, the room shall be
classified the same as if the wall, curb, or
partition did not exist.
Within 900 mm (3 ft) of open end of vent,
extending in all directions Area between
900 mm and 4.5 m (3 ft and 15 ft) from
open end of vent, extending in all
directions; also, within 900 mm (3 ft) of
edge of dome, extending in all directions
Within 900 mm (3 ft) of point of
connection of both fill and vapor lines
extending in all directions
Within 900 mm (3 ft) of point of
connections, extending in all directions;
also up to 450 mm (18 in.) above grade
within a horizontal radius of 3.0 m (10 ft)
from point of connections
2
Entire room
If there is any opening to these rooms
within the extent of an indoor classified
location, the room shall be classified the
same as if the wall, curb, or partition did
not exist.
See Figure 515.3.
33 CVEF -­‐ NGVs at Petroleum Terminals 2. International Fire Code 2012 Edition 5706.6.1.3 Vehicle motor shutdown. Motors of tank vehicles or tractors shall be shut down during the making or breaking of hose connections. If loading or unloading is performed without the use of a power pump, the tank vehicle or tractor motor shall be shut down throughout such operations. July 2013 34 CVEF -­‐ NGVs at Petroleum Terminals Appendix C CNG and LNG Storage Tank Standards 49 CFR 571.304 Title 49 -­‐ Transportation Volume: 6Date: 2011-­‐10-­‐01Original Date: 2011-­‐10-­‐01Title: Section 571.304 -­‐ Standard No. 304; Compressed natural gas fuel container integrity. Context: Title 49 -­‐ Transportation. Subtitle B -­‐ Other Regulations Relating to Transportation (Continued). CHAPTER V -­‐ NATIONAL HIGHWAY TRAFFIC SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION. PART 571 -­‐ FEDERAL MOTOR VEHICLE SAFETY STANDARDS. Subpart B -­‐ Federal Motor Vehicle Safety Standards. § 571.304 Standard No. 304; Compressed natural gas fuel container integrity. S1. Scope. This standard specifies requirements for the integrity of compressed natural gas (CNG), motor vehicle fuel containers. S2. Purpose. The purpose of this standard is to reduce deaths and injuries occurring from fires that result from fuel leakage during and after motor vehicle crashes. S3. Application. This standard applies to each passenger car, multipurpose passenger vehicle, truck, and bus that uses CNG as a motor fuel and to each container designed to store CNG as motor fuel on-­‐board any motor vehicle. S4. Definitions. Brazing means a group of welding processes wherein coalescence is produced by heating to a suitable temperature above 800 °F and by using a nonferrous filler metal, having a melting point below that to the base metals. The filler metal is distributed between the closely fitted surfaces of the joint by capillary attraction. Burst pressure means the highest internal pressure reached in a CNG fuel container during a burst test at a temperature of 21 °C (70 °F). CNG fuel container means a container designed to store CNG as motor fuel on-­‐board a motor vehicle. Fill pressure means the internal pressure of a CNG fuel container attained at the time of filling. Fill pressure varies according to the gas temperature in the container which is dependent on the charging parameters and the ambient conditions. Full wrapped means applying the reinforcement of a filament or resin system over the entire liner, including the domes. Hoop wrapped means winding of filament in a substantially circumferential pattern over the cylindrical portion of the liner so that the filament does not transmit any significant stresses in a direction parallel to the cylinder longitudinal axis. Hydrostatic pressure means the internal pressure to which a CNG fuel container is taken during testing set forth in S5.4.1. Liner means the inner gas tight container or gas cylinder to which the overwrap is applied. Service pressure means the internal settled pressure of a CNG fuel container at a uniform gas temperature of 21 °C (70 °F) and full gas content. It is the pressure for which the container has been constructed under normal conditions. S5Container and material requirements. S5.1Container designations. Container designations are as follows: S5.1.1Type 1—Non-­‐composite metallic container means a metal container. S5.1.2Type 2—Composite metallic hoop wrapped container means a metal liner reinforced with resin impregnated continuous filament that is “hoop wrapped.” S5.1.3Type 3—Composite metallic full wrapped container means a metal liner July 2013 35 CVEF -­‐ NGVs at Petroleum Terminals reinforced with resin impregnated continuous filament that is “full wrapped.” S5.1.4Type 4—Composite non-­‐metallic full wrapped container means resin impregnated continuous filament with a non-­‐metallic liner “full wrapped.” S6General requirements. S6.1Each passenger car, multipurpose passenger vehicle, truck, and bus that uses CNG as a motor fuel shall be equipped with a CNG fuel container that meets the requirements of S7 through S7.4. S6.2Each CNG fuel container manufactured on or after March 27, 1995 shall meet the requirements of S7 through S7.4. S7Test requirements. Each CNG fuel container shall meet the applicable requirements of S7 through S7.4. S7.1Pressure cycling test at ambient temperature. Each CNG fuel container shall not leak when tested in accordance with S8.1. S7.2Hydrostatic burst test. S7.2.1Each Type 1 CNG fuel container shall not leak when subjected to burst pressure and tested in accordance with S8.2. Burst pressure shall not be less than 2.25 times the service pressure for non-­‐welded containers and shall not be less than 3.5 times the service pressure for welded containers. S7.2.2Each Type 2, Type 3, or Type 4 CNG fuel container shall not leak when subjected to burst pressure and tested in accordance with S8.2. Burst pressure shall be not less than 2.25 times the service pressure. S7.3Bonfire test. Each CNG fuel container shall be equipped with a pressure relief device. Each CNG fuel container shall completely vent its contents through a pressure relief device or shall not burst while retaining its entire contents when tested in accordance with S8.3. S7.4 Labeling. Each CNG fuel container shall be permanently labeled with the information specified in paragraphs (a) through (h) of this section. Any label affixed to the container in compliance with this section shall remain in place and be legible for the manufacturer's recommended service life of the container. The information shall be in English and in letters and numbers that are at least 6.35 mm (1/4 inch) high. (a) The statement: “If there is a question about the proper use, installation, or maintenance of this container, contact__________,” inserting the CNG fuel container manufacturer's name, address, and telephone number. (b) The statement: “Manufactured in ______,” inserting the month and year of manufacture of the CNG fuel container. (c) The statement: “Service pressure ______ kPa, (______ psig).” (d) The symbol DOT, constituting a certification by the CNG container manufacturer that the container complies with all requirements of this standard. (e) The container designation (e.g., Type 1, 2, 3, 4). (f) The statement: “CNG Only.” (g) The statement: “This container should be visually inspected after a motor vehicle accident or fire and at least every 36 months or 36,000 miles, whichever comes first, for damage and deterioration. (h) The statement: “Do Not Use After ______” inserting the month and year that mark the end of the manufacturer's recommended service life for the container. S8Test conditions: fuel container integrity. S8.1Pressure cycling test. The requirements of S7.1 shall be met under the conditions of S8.1.1 through S8.1.4. S8.1.1Hydrostatically pressurize the CNG container to the service pressure, then to not more than 10 percent of the service pressure, for 13,000 cycles. S8.1.2After being pressurized as specified in S8.1.1, hydrostatically pressurize the CNG container to 125 percent of the service pressure, then to not more than 10 percent of the service pressure, for 5,000 cycles. S8.1.3The cycling rate for S8.1.1 and S8.1.2 shall be any value up to and including 10 cycles per minute. S8.1.4The cycling is conducted at ambient temperature. S8.2Hydrostatic burst test. The requirements of July 2013 36 CVEF -­‐ NGVs at Petroleum Terminals S7.2 shall be met under the conditions of S8.2.1 through S8.2.2. S8.2.1Hydrostatically pressurize the CNG fuel container, as follows: The pressure is increased up to the minimum prescribed burst pressure determined in S7.2.1 or S7.2.2, and held constant at the minimum burst pressure for 10 seconds. S8.2.2The pressurization rate throughout the test shall be any value up to and including 1,379 kPa (200 psi) per second. S8.3Bonfire test. The requirements of S7.3 shall be met under the conditions of S8.3.1 through S8.3.7. S8.3.1Fill the CNG fuel container with compressed natural gas and test it at: (a) 100 percent of service pressure; and (b) 25 percent of service pressure. S8.3.2Container positioning. (a) Position the CNG fuel container in accordance with paragraphs (b) and (c) of S8.3.2. (b) Position the CNG fuel container so that its longitudinal axis is horizontal and its bottom is 100 mm (4 inches) above the fire source. (c)(1) Position a CNG fuel container that is 1.65 meters (65 inches) in length or less and is fitted with one pressure relief device so that the center of the container is over the center of the fire source. (2) Position a CNG fuel container that is greater than 1.65 meters (65 inches) in length and is fitted with one pressure relief device at one end of the container so that the center of the fire source is 0.825 meters (32.5 inches) from the other end of the container, measured horizontally along a line parallel to the longitudinal axis of the container. (3) Position a CNG fuel container that is fitted with pressure relief devices at more than one location along its length so that the portion of container over the center of the fire source is the portion midway between the two pressure relief devices that are separated by the greatest distance, measured horizontally along a line parallel to the longitudinal axis of the container. (4) Test a CNG fuel container that is greater than 1.65 meters (65 inches) in length, is protected by thermal insulation, and does not have pressure relief devices, twice at 100 percent of service pressure. In one test, position the center of the container over the center of the fire source. In another test, position one end of the container so that the fire source is centered 0.825 meters (32.5 inches) from one end of the container, measured horizontally along a line parallel to the longitudinal axis of the container. S8.3.3Number and placement of thermocouples. To monitor flame temperature, place three thermocouples so that they are suspended 25 mm (one inch) below the bottom of the CNG fuel container. Position thermocouples so that they are equally spaced over the length of the fire source or length of the container, whichever is shorter. S8.3.4Shielding. (a) Use shielding to prevent the flame from directly contacting the CNG fuel container valves, fittings, or pressure relief devices. (b) To provide the shielding, use steel with 0.6 mm (.025 in) minimum nominal thickness. (c) Position the shielding so that it does not directly contact the CNG fuel container valves, fittings, or pressure relief devices. S8.3.5Fire source. Use a uniform fire source that is 1.65 meters long (65 inches). Beginning five minutes after the fire is ignited, maintain an average flame temperature of not less than 430 degrees Celsius (800 degrees Fahrenheit) as determined by the average of the two thermocouples recording the highest temperatures over a 60 second interval: [Please see PDF for Formula: ER30OC00.009] If the pressure relief device releases before the end of the fifth minute after ignition, then the minimum temperature requirement does not apply. S8.3.6Recording data. Record time, temperature, and pressure readings at 30 second intervals, beginning when the fire is ignited and continuing until the pressure release device releases. S8.3.7Duration of exposure to fire July 2013 37 CVEF -­‐ NGVs at Petroleum Terminals source. The CNG fuel container is exposed to the fire source for 20 minutes after ignition or until the pressure release device releases, whichever period is shorter. S8.3.8Number of tests per container. A single CNG fuel container is not subjected to more than one bonfire test. S8.3.9Wind velocity. The average ambient wind velocity at the CNG fuel container during the period specified in S8.3.6 of this standard is not to exceed 2.24 meters/second (5 mph). S8.3.10The average wind velocity at the container is any velocity up to and including 2.24 meters/second (5 mph). [59 FR 49021, Sept. 26, 1994; 59 FR 66776, Dec. 28, 1994; 60 FR 37843, July 24, 1995; 60 FR 57948, Nov. 24, 1995; 61 FR 19204, May 1, 1996; 61 FR 47089, Sept. 6, 1996; 63 FR 66765, Dec. 3, 1998; 65 FR 51772, Aug. 25, 2000; 65 FR 64626, Oct. 30, 2000] July 2013 38