CNG Cylinder (tank) inspection

[Gaz Guy]

How many of you are aware of the Federally mandated CNG Cylinder (tank) inspection requirements of NGV2-2000 and FMVSS 304?
Every 3 years or 36,000 miles, whichever comes first. Did the folks you bought your vehicle from happen to mention this?

[echamberlain]

If your vehicle was manufactured after 1996, the CNG tank external visual inspections should be listed in your vehicle maintenance schedule.

Ford's TSB 05-5-6 (http://www.ford-trucks.com/tsb/fulltext/show_article.php?tsb=05-5-6) has more information about the tank inspections.

[sixpak]

How many of you are aware of the Federally mandated CNG Cylinder (tank) inspection requirements of NGV2-2000 and FMVSS 304?
Every 3 years or 36,000 miles, whichever comes first. Did the folks you bought your vehicle from happen to mention this?


It was in the manual for my GX. I just paid Norm Reeves about $148 and it seemed a little high.

[malibu]

How much does it cost to replace if it does not pass inspection?

[afvman]

Depends...

Type 1 (all steel/aluminum) cylinders in my van cost $200 ea. Type 4 (all composite) can go up to $1000-1500.

Each (Type 1, 2, 3 and 4) have advantages and disadvantages. It's interesting that as the number/type goes up, so does the price.

afvman

[Surfdancer]

Silly question, but if one ignores the requirement to have their cylinders inspected (or runs them beyond their life expiration date), AND an event occured AND the owner survives the event, would they be liable for their neglect?

It would seem to me that these records would be at the top of the list if / when an insurance company or some lawyer became involved in an incident investigation.

I shut down our company vehicles when I learned the tank inspections were overdue. I had people very upset, but I could not take a chance having perfectly safe, yet uninspected, vehicled on the road. Fortunately, I was able to get the cylinders inspected in short order (not easy to do in a rural area on the East coast), and all issues were resolved.

[afvman]

Gaz Guy et al,

The cylinder inspection agency is currently CSA-America (the old AGA Labs) in Cleveland, OH. They've been working on a whole new exam and training program for inspectors. It's being released as we speak.

They're the best bet for qualified cylinder inspections. See:
http://www.csa-america.org/advisory_services/cng_certification/

If I can help, let me know.

afvman/Bill
Lancaster, OH

[altfuelsguy]

Depends...

Type 1 (all steel/aluminum) cylinders in my van cost $200 ea. Type 4 (all composite) can go up to $1000-1500.

Each (Type 1, 2, 3 and 4) have advantages and disadvantages. It's interesting that as the number/type goes up, so does the price.

afvman

Where can I get type 1 tanks?
I'm in CA.
What is good mfg. to look for.
thanks.

[johnnjerri]

Can anyone tell me what the service life is on the tank in a new Honda 09 GX? Is it 15 years from manufacture date or??
Thanks!!

[snakeskinner]

Class 1 is an all Steel or Aluminum tank, Class 2 is a Hoop wrapped steel or aluminum tank which means the center is wrapped in composite and the ends are exposed. Class 3 is aluminum or steel and completely wrapped in composite. class 4 is a total composite tank. Prices will vary depending on material, size, manufacturer and quality. I have heard of some very poor quality tanks available overseas (not sure they have been imported to the US) that are having high failure rates. We are installing Lincoln Composite Class 4 tanks in the trucks we are building. I believe they are a 12-15 gallon equivelant tank and are much more expensive than a lower class tank. I have not personally priced them myself but I have heard they can cost upwards of 6-7 thousand for a high quality class 4 of this size. Of course the smaller tanks wouldn't cost as much.

Regulations will vary from state to state. Oklahoma requires anyone that touches a CNG system to be state certified. The NGV 2 tanks typically are a 15 year lifespan although the latest tanks we received from Lincoln are 20 year tanks. I have no idea what the new honda is but it should be listed on a label nearby the filler or under the hood (or both).

If you don't have your tank inspected every 3yrs/36k miles, it likely depends on your state laws. Oklahoma does not have a policing agency so it's up to the owner to obey the regulations. Granted, there is nobody going to stop someone because they don't have the tank inspected but do you really want that liability? In the case that you might get in an accident, if a police officer were educated in CNG and noticed your tank was out of date or hadn't been inspected, your state may have fines or worse. Every issue I've heard from CNG was due to improper handling of the tank. You're dealing with 3600 psi in most cases, not worth the gamble. The "tank inspection" should actually include a total inspection of the system. From what I have seen, the industry standard to perform this thorough inspection is 3 hours.

Kyle

[sjseng]

If it is an internal tank inspection, does the vehicle need to come in with a nearly empty tank? Does the inspecting agency (say Honda) fill your tank back up if you happen to bring it in nearly full? How does that work.

Thanks

[karlhafen]

Tanks are only visually inspected on the outside. The only time you would drain a good tank would be to replace a pressure relief device or tank valve

[sjseng]

Thank you.

[cowboy]

I dont understand this is not safety all it takes is a little water presto you have rust inside weakning the tank not checking the inside like going to the canser doctor and not looking up your butt just stand there with your clothes on my you look good today as your insides are ate up I dont do tank certs but I own a scope and do check the inside of the tanks I buy before I send them off for hydro saves cash and time I have never had a tank fail hydro that looked good inside now im am dealing with strait steel not on road just storage still makes sense to check all tanks inside no mater what kind as and is not hard to do I bought my scope for229.oo with light as a tank failure is a very bad thing as i saw a air compresser tank set at 150 psi blow a cinder block wall down in a friends shop lucky no one was there when it happend cant fatham what 3600 psi whould do blow down a city block or two ?

[Franz]

Cowboy, I have had two cylinders fail while I was there. Both were new installs, one with a CNG brand, the other a PST cylinder. Both split mid way between the straps. Neither of them showed any signs of damage that might indicate failure, and one wouldnt expect a failure on a new cylinder with a factory installed service valve.

Both splits were about 4 inches long at about 3000 psig pressure, on the first full fill, after a series of step up preliminary fills with leak checks. The tanks did not rupture full open, just one loud snap then VERY loud hissing.

In the cases where the tank was weakened by external impact or corrosion, a decompressive release can be exciting. These well publicized cases:
The Super Shuttle van recently;
Crown Plumbing in House (bent a chassis up about 6 inches)
Two GMC Sierra trucks of the early 90's;

One primary reason for internal failure on CNG tanks is a product found in natural gas if it is not fully scrubbed at the gas plant, Sulfur Dioxide. If any moisture is present in the fuel, it will react with the SO2 and cause a corrosion line which can weaken a type 1, type 2 or a type 3 cylinder. A type 4 cylinder is not as effected.

The method of hydrostatically testing cylinders to two times their maximum working pressure is required by law but technically archaic, plus there can be an argument that this process can initiate a weakening effect as well. There are plenty of non destructive processes that are gaining recognition in the industry. Some states already recognize acoustical testing for example.

Franz

[Highmarker]

The method of hydrostatically testing cylinders to two times their maximum working pressure is required by law but technically archaic, plus there can be an argument that this process can initiate a weakening effect as well. There are plenty of non destructive processes that are gaining recognition in the industry. Some states already recognize acoustical testing for example.

Franz

Franz,

According to NGV2 (The CNG Tank Specification), the hydrostatic test pressure is 1.5 times service pressure (5,400 psi for a 3,600 psi tank). The hydrostatic test procedure is ONLY a ONE TIME process on CNG tanks. Hence the need for the tank inspection every 36,000 miles or 3 years. Going back to the hydrostatic test...For type II and type III tanks, there is a process called autofrettage. This process occurs before hydrostatic testing. During this process, the manufacturer pressurizes the cylinder up to about 2+ times service pressure and holds it for 2 minutes, then relieves the pressure. This allows the metallic liner (usually aluminum) to be in a compressive state at zero pressure. Then when the cylinder is pressurized up to 3,600 psi (or even 4,500 psi - according to the spec), the aluminum liner stays predominately in compression, but it does see some tension forces. This makes it hard for any crack to start and propagate, which would cause leaking. It is a fatigue issue with the metallic liner. For a type IV tank, this autofrettage is not used, because plastic liners don't fatigue like metallic liners do. The autofrettage process does not damage the cylinder in any way. Carbon fibers don't creep to failure like other materials. They are very stiff fibers and have only about a 2% elongation at failure.

The main reason for having the hydrostatic test is to measure the expansion of the cylinder. The manufacturer can measure the water displacement (expansion) of the cylinder during the hydrostatic test and then compare this expansion to the known and proven expansion of the design. If the expansion is too much or not enough, then it tells the manufacturer that the cylinder was not fabricated properly. It is a NDT for the manufacturer to assure that the cylinder is made per the design.

[afvman]

Greetings all,

I've just posted two documents in the Chat Library that, hopefully, will shed some light on this question. See: ISO 19078 Appendix E and the CVEF Tech. Bulletin 01 re. Visual Inspections.

Having come from the Scuba Diving community, I've looked inside a lot of cylinders both breathing air and CNG. I've never seen internal corrosion from a CNG cylinder. Granted, natural gas is clean a relatively dry, but compressors aren't. There's always some oil carryover (sometimes a lot) that ends up inside the cylinders. This acts to coat and protect the ones I've inspected.

Also having been involved with the development of the visual inspection protocol, I'd hate to go backwards. The United States has led the world in the implementation of this method of inspection.

Now, having said that, there is still an argument for hydro testing Type 1's in many developing countries, but the argument is that it's harder to fudge the results from a hydro than a visual inspection. Hopefully that won't be an issue in this country.

Best regards,


afvman/Bill

[cngmike]

At the Technology exchange last week it was announced that recertification for type I tanks is being worked on. The phrase used was getting your nose in the tent.

[afvman]

Mike,

Keep us posted! As California goes, so goes the country.

Best regards,

afvman/Bill

[cowboy]

I still the inside inspection should be done I have found crorosion in cng tanks that I would not want them anywhere near me with 3600 in them I drilled a hole in them and scraped them safe than sorry oh you dont get to be sorry if you goof this as for compresser oil put new rings in it as oil will contamanate the dehydrater tower and it will not get the water out now let it mix with sulfer compounds presto you have sulfuric acid H2SO4 if I remember chem 101 not good to have in your tank you say no water in your gas go unhook you water from your hp regulator than take a drive freeze up?gas will not freeze it is the water in the gas that freezes and plugs the flow of gas almost all gas has some water so if we are going to mandate inspection of tanks lets look inside this is to be done by pros we should not have a problem with cross theaded fittings valves straps and rubbers much less a used o ring on the valve I am the king of cheap skates and I have never thought of putting a used o ring on a valve they cost less than 1 doller more like pennys the tanks are the dangerous part of a cng car the rest is no more dangerous than the stove or heater in your house might be safer as most of us dont sleep in our cars so if there is a leak we are awake to do something about it

[cowboy]

Cowboy, I have had two cylinders fail while I was there. Both were new installs, one with a CNG brand, the other a PST cylinder. Both split mid way between the straps. Neither of them showed any signs of damage that might indicate failure, and one wouldnt expect a failure on a new cylinder with a factory installed service valve.

Both splits were about 4 inches long at about 3000 psig pressure, on the first full fill, after a series of step up preliminary fills with leak checks. The tanks did not rupture full open, just one loud snap then VERY loud hissing.

In the cases where the tank was weakened by external impact or corrosion, a decompressive release can be exciting. These well publicized cases:
The Super Shuttle van recently;
Crown Plumbing in House (bent a chassis up about 6 inches)
Two GMC Sierra trucks of the early 90's;

One primary reason for internal failure on CNG tanks is a product found in natural gas if it is not fully scrubbed at the gas plant, Sulfur Dioxide. If any moisture is present in the fuel, it will react with the SO2 and cause a corrosion line which can weaken a type 1, type 2 or a type 3 cylinder. A type 4 cylinder is not as effected.

The method of hydrostatically testing cylinders to two times their maximum working pressure is required by law but technically archaic, plus there can be an argument that this process can initiate a weakening effect as well. There are plenty of non destructive processes that are gaining recognition in the industry. Some states already recognize acoustical testing for example.

Franz
I think I would find a new suplyer of tanks if these tanks had been hydroed at the mfg they would have busted there and avoided any chance of hurting someone what if there had been a sorce of ign when the 4 inch crack and loud hiss could had a fire to It dont sound like these nondestructive processes are getting the job done of keeping bad tanks off the road

[Blake Harve]

What is the difference between LPG & CNG,ifeel both r in liquid form.Can we use LPG in CNG kit,i wan a ans pls..Dont tell me the full form of LPG & CNG.what i wana know is can we use lpg in a cng kit for runin a car if yes i want to know all the details how can i fill lpg into cng kit(cylinder)

[Panini]

What is the difference between LPG & CNG,ifeel both r in liquid form.Can we use LPG in CNG kit,i wan a ans pls..Dont tell me the full form of LPG & CNG.what i wana know is can we use lpg in a cng kit for runin a car if yes i want to know all the details how can i fill lpg into cng kit(cylinder)

LPG and CNG, both r not in liquid form. LPG is in Liquid and CNG is in gaseous form. The pressure of CNG is 200 Bar and LPG is 10 Bar. Don't think to mix the things, there is lot of difference in Word "L" and Word "C". Take care

[larrycng]

Working backward. The old air valve mixers don't care what runs through them. You have to change the final stage regulator pressure to get volume of gas necessary to get the proper air/fuel mixture to make the engine run. OHG and Dick Baverstock (Impco) proved that concept. I would assume that the same would hold true with venturi type mixers.

Looking at the low pressure regulator, most regulators will also handle the gas. As I remember there was some difference in the diffence in the diaphram materal, but I can't remember why. The other difference might be in regulator operation. LPG uses a negative pressure regulator and CNG uses a positive pressure regulator. Of course this is applicable to mixer type systems because the they requires lower pressure than injection types systems.

Since LPG is stored at lower pressure, you can use the old 2 stage regulators and don't need the high pressure regulator that is required of CNG. Aside from the higher storage pressure of CNG, the pressures in both sytems are somewhat similar.

Because of the difference in BTU content of the fuels you either have to chance the size of the delivery orfice and use the same pressure or vary the pressure and use the same orfice to achieve the proper air/fuel ratio.

I hope this helps

Larrycng

[Wellarmed]

I agree with Larrys assesment. But to comment on the cylinder failures, they generally occur during a fast fill. I personally agree with CSA recomendations that Hydro is not necessarily the best method of inspection, as I do not feel that any form of testing that needs to hyperextend the base material should be considered NDT. En situ is probably the best method of inspection, but in the event of an overpressurization I feel that AE methods may be warranted. I had heard rumor of engineers in the past that created a sensor based system that continually measured the expansion of the cylinder during the filling procedure. It would have been interesting, if it had been developed further to be an on board system that could interface with the fueling station to shut things down in the event of sensed overpressurization. I have only heard of very few situations of vehicle overpressurization occurring, and do not recall any of them leading to tank failure. I have seen photos from one of my professors that showed a catastrophic failure in a transit bus, but again it was in a fast fill situation. My biggest concern with most mass transit systems is the fact that they generally have personel on board the vehicle when (fast) fill is taking place. I am not a big advocate of fast fill for a number of reasons, unless time is unavailable for slow fill. Such as when one is on the Interstate. As far as Franz tank failures are concerned. I am quite certain they brought the system up to pressure first with Nitrogen, before using actual NG. All fresh NG conversions or tank replacements should be purged with Nitrogen first to eliminate ANY chance that a combustible mixture could be present during the Phil procedure. Also people must remember that there also is a provision for mandatory inspection when an accident over 5 mph has occured, or vehicle fire, or potential chemical degredation has occured. Wether people head these warnings, who knows?

[CNGCARS]

If anyone needs there CNG cylinders inspected contact me to set up an appointment. I have done several CNG cylinder inpsections for guys here on the forum and just recently signed a deal with United States Post Office and started inspecting the cylinders on their vehicles. Locally they have 150 vehicles and they are keeping me very busy :) no complaints here...