Tank replacement at 15 years? You're kidding right?

[atikovi]

From the 1998-2000 GX Range? thread.

Because in 4 years, after the tank expires, they go bad?

What does that mean, as I just bought a '99? Does Honda say you must replace the tank after 15 years? Even if there is nothing wrong with it? If that is so, it seems absurd. I assume it's 100% product liability related so if someone with a 16 year old tank has a gas leak and the car blows up Honda can say we told you so. I see on many Mercedes cars a sticker in the door jamb saying you must replace the airbags after 15 years as well but I can't imagine any 1994 Mercedes owners spending $2,000 or $3,000 to replace the airbags. The tank is a piece of composite that doesn't rust and isn't exposed to the elements. I can't imagine, if it makes it to 15 years, why it shouldn't last the life of the car.

[Lakewood90712]

Re: Tank replacement at 15 years? You're kidding right?

From the 1998-2000 GX Range? thread.



What does that mean, as I just bought a '99? Does Honda say you must replace the tank after 15 years

Honda advises the owner to comply with the requirements of the U.S. D.O.T. , the requrements of the tank Maufacturer and any state/local laws for CNG motor vehicle fuel cylinders. The regulations are targeted for normal service life , and still apply to a vehicle with low miles / few cycles on the tank.

Most safety laws were " inked with the blood of a victim "

It is rare for a tank to rupture, but when it happens, (usually during refueling)massive damage, usually with loss of limbs, life ,etc. All of these incidents happen without warning.

I see from your other posts you are inquiring about selling. Why did you buy a GX in the first place

[Franz]

Re: Tank replacement at 15 years? You're kidding right?

A tank may not corrode but it is subject to cycling stresses of from roughly depleted at around 250 to 500 psig the to 3600 psig on the average of one cycle every two to three days (some more, some less).

Lakewood is entirely correct. Many of the rules and codes about tanks and safety have happened "after the fact". It takes an incident to force the rules makers to enact a code.

The entire NGV-2 cylinder standard came about because of a series of composite tank failures in the mid 1990's, most of them resulting in injuries to the operators during refueling.

Franz

[atikovi]

Re: Tank replacement at 15 years? You're kidding right?

I see from your other posts you are inquiring about selling. Why did you buy a GX in the first place

I bought and sold a bunch of '03 Crown Vic CNG's 5 years ago and did fairly well since around here there are few refueling stations. They all shipped out west. I bought the GX more out curiosity to see how they function and to flip it as well.

A tank may not corrode but it is subject to cycling stresses of from roughly depleted at around 250 to 500 psig the to 3600 psig on the average of one cycle every two to three days (some more, some less).

On a super low mileage car like my '99 with 22,000 miles the cycling stresses would be much less frequent, so by logic, shouldn't the tank have aged no more than say a 2006 model with 22,000 miles. Then ideally the tank wouldn't need replacing for 12 years. Just thinking out loud.

[Larryect]

Re: Tank replacement at 15 years? You're kidding right?

I am not an expert. But it is my understanding that many composites, such as fiberglass, also become brittle with age. I suspect pressure cycles would only be part of the issue.

[John Mitton]

Re: Tank replacement at 15 years? You're kidding right?

I understand the California explosion a few weeks ago was a 14 yr old tank:
http://www.cngchat.com/forum/showthread.php?t=4581

[freedml]

Re: Tank replacement at 15 years? You're kidding right?

I reread the thread and don't see any mention of the age of the tank. Where was that?

[Dave Fox]

Re: Tank replacement at 15 years? You're kidding right?

The nature of the resins is very simple. They are cured by adding a catalyst or removing the inhibitor. This causes the resins to cure and as such they continue to cure for the life of the part. If any of you ride motorcycles or race cars, I assume you use a Snell approved helmet. They are good for a limited number of years, used to be 4 and I have thrown away 6 perfectly good $800 helmets because with age the shell no longer performs the designed function. Ever seen a failure test on a piece of carbon, or glass material. It is not a place to be without protection.

I factored in the $3000 cost when I bought my 09 GX. As a side note, if your are fast filling that is when the tank is stressed most, kind of like hitting your thumb with a hammer. Do it enough times and your thumb gets very big. Every time you fast fill the composite strucure expands a little more until the resin bond is broken and the tank cato's.

I slow fill mine from an FMQ 2-36 and should be able to go beyond that 15 years but it is not worth the risk.

[John Mitton]

Re: Tank replacement at 15 years? You're kidding right?

I reread the thread and don't see any mention of the age of the tank. Where was that?

I learned this from a cylinder supplier who was contacted as part of the investigation.

[mickey]

Re: Tank replacement at 15 years? You're kidding right?

I'm calling BS on the "expansion-contraction" theory. If that was the issue the replacement interval would be based on mileage, not years. Obviously somebody (like me) who drives 50,000 miles a year is going to cycle the tank a whole lot more, in 15 years, than somebody who drives the U.S. average 12,500 miles a year.

12,500 x 15 = 187,500 miles. Assuming 35 mpg and 5 gallons per "top up", that's 1071 tank cycles.

At 50K per year I will have traveled 750,000 miles (yeah, right) and topped up the tank 4285 times. Four times the number of cycles as the "average" car.

Either they've erred on the side of caution to take extreme cases like me into account, in which case Joe Average could go SIXTY YEARS without a problem, or the issue has nothing to do with pressure cycles. (Or maybe Honda just doesn't care if I blow up in 4 or 5 years.)

My understanding is that the tank can simply be "inspected" for damage and remain in service after it "expires."

If the rigors of refilling ARE the reason then Honda screwed up big time. One size definitely does not fit all in this matter.

[Highmarker]

Re: Tank replacement at 15 years? You're kidding right?

The 15 year service life is not coming from Honda at all. It is coming from DOT FMVSS 304 and from ANSI NGV2. Actually NVG2-2007 now allows up to a 25 year service life. Here is the theory behind it all:

One cylinder out of each lot of cylinders made by the manufacturer must be cycle pressure tested to 1.25 times service pressure (4,500 psi for a 3,600 psi cylinder). The minimum number of cycles that cylinder must complete before leaking is equal to 750 times the service life in years (15 year service life = 11,250 cycles and 20 year service life = 15,000 cycles). The number 750 comes from filling your tank twice a day every day for a year. That is being conservative as nobody will drive/fill that much. These tanks are designed to NOT fail.

Look at every pressure vessel in use today (i.e. oxygen tanks, firefighter tanks, paintball tanks, CNG tanks). They all have expiration dates. Sure some of them are required to be hydrostatic tested every 3 - 5 years (CNG tanks are visually inspected every 3 years or 36,000 miles). But all these tank have a 15 - 20 year service life. Even infant car seats have a 5 - 6 year service life. Regardless of the condition of the car seat, the manufacturer requires that the car seat be thrown away. The same thing goes for oxygen, SCBA, paintball, and CNG tanks. It is virtually impossible to count the exact number of fills each tank recieves. Especially if the vehicle is sold and then resold again and again. And especially if the tank if removed from one vehicle and put on another vehicle.

This does not mean that if your tank expires June of 2009 that on July 1, 2009, the tank will fail. But, you don't know the history of that tank. You were not there when the tank was installed for the first time (unless you are the certified CNG installer). If filled and refilled over and over again and again, all tanks will eventually fail. When you fill your tank, the stresses in the tank are NOT ZERO. If you bend a paper clip back and forth and back and forth, eventually it will break. The same thing applies to oxygen, SCBA, paintball, and CNG tanks. If you fill it up again and again and again, it will FAIL. Yes a 15 year life is conservative, but if you play with danger it will bite you. Better be safe then dead.

Oh, and don't think that the standard Sn curves for metal fatigue apply. They don't when the metal (i.e. aluminum) has carbon fiber wrapped around it. It is a totally different ballgame.

[cowboy]

Re: Tank replacement at 15 years? You're kidding right?

I have gotting many tanks from the welding supply that the first hydro date was in the fiftys. I am starting to think that the plastic tanks are not as safe as steel ones. they may weigh a lot less but at what cost in safety? has anyone heard of a steel one blowing up that had a good hydro date and was not over filled ?

[jetboatjohnny]

Re: Tank replacement at 15 years? You're kidding right?

Does anyone know if the 2009 GX tanks are 15 years or 20 years?

[bruin]

Re: Tank replacement at 15 years? You're kidding right?

I won't show my disdain with code for expletives or any such thing, but the DOT testing was so obviously geared for vehicles which were intended for heavy fleet use that they are laughable when applied to some of the scenarios we are looking at. It is a waste of my typing since I know there are other cases out there far more extreme, but I have a 1997 CV with 61,000 actual miles on it and it does not take much in the way of math skills to know that these tanks have been pressurized fully over the years on average approx. once a month.

I will give you this that, yes, I don't have any way to know absolutely that these tanks are original from the factory, but nevertheless since the DOT regulations were very narrow and conservative it will require me or someone to replace these with potentially exceedingly expensive replacements after the upcoming expiration where some sort of testing might prove they could have a high probability of lasting several more years with only a very statistically remote chance of trouble. All hail another Federal Gov. entity which provides us with such short-sighted and inflexible regulation.
END RANT

[atikovi]

Re: Tank replacement at 15 years? You're kidding right?

So why not just equip every 15 year old vehicle with a gas detector? Just keep driving it and THEN if the tank gets a leak, it will be detected before an explosion and you can replace it, or retire the vehicle