Gas tank replacement?

[Coopspeed]

I read while doing research on a possible purchase that the gas tank needs to be replaced at 100,000 miles or the date on the tank.

Is that a good idea or mandatory? Is it enforced? By who?

How much would a new tank for a 2002 Cavalier cost?

Thanks

Jim

[cngmike]

The repalcement of CNG cylenders are on a 15 years. with visual in vehical inspections every 3 years or 36,000 miles. new tanks are rated at 20 years.

[kameron13462]

I have to ask - why 15 years? Corrosion? Metal fatigue? Gas tank manufacturer needs a new pair of shoes?

[Coopspeed]

So there is no requirement based on mileage?

I read that at 100,000 miles a tank is done.

That is false?

Jim

[Highmarker]

All tanks are certified per NGV2-2000 specification. This specification mandates a cylinder life of 20 years. An important note is that all OEM vehicles (Ford F-150, Chevy Cavalier, Ford Contour) have tanks that were certified per NGV2-1998 specification. This specification mandates a cylinder life of 15 years. There is no requirement based on mileage (only the visual inspection that cngmike talked about).
To understand the reason why they put a expiration date on the cylinders you have to understand where composite overwrapped pressure vessels have came from over the past 40 years. Even self-contained breathing appratus (SCBA) tanks have an expiration date on them after 15 years (per DOT-CFFC). These tanks have to be hydrostatic proof tested every 3 to 5 years (CNG tanks do not). Most pressure vessel specifications are spin-offs of the military specification. The life of a tank is based on the pressurization cycle testing of the cylinder. Each CNG cylinder design has to pass 11,250 pressure cycles. Do the math, that is just over 560 cycles a year for 20 years.