Will my tank blow up in an accident?

[Curtis]

One of the most frequently asked questions I hear. Conservatively I would say that a CNG tank is probably 3 times less likely to explode, or catch fire, than a gasoline tank. The testing that a tank must pass is unbelievable. Drop tests, bonfires, being shot at, blown up... I will attempt to get this video to work here. It is an older piece, but I think you'll get the point.



Here's the link to it. Tank testing video

Fixed: Timon

[Highmarker]

Curtis,

Let me shed some light on the testing that a certified CNG cylinder design goes through before the cylinder is allowed to be manufactured. All these tests are per NGV2-2000 specification (the most common CNG specification).

For simplicity I have used a Type III (aluminum lined carbon fiber full wrapped) 3,600 psi cylinder as an example.

Ambient Cycling Test - Pressure cycle from 0 psi to 4,500 psi at a rate not greater than 10 cycles per minute. The cylinder must achieve at least 11,250 cycles and must fail by leakage (not rupture).

Environmental Test - This test includes five solutions for exposure along with a pendulum impact. The five solutions are: Sulfuric Acid, Sodium Hydroxide, Methanol/Gasoline, Ammonium Nitrate, and Windshield Washer Fluid. The pendulum impact shall have the shape of a pyramid and the impact energy shall not be less than 22.1 ft-lb. The solutions shall remain on the cylinder during the following pressure cycle test. Pressure cycle from 0 psi to 4,500 psi for a total of 3,000 cycles. At the end of the cycling, the cylinder shall be pressurized to 4,500 psi and held for 48 hours. The cylinder cannot leak nor rupture during the test.

Extreme Temperature Cycle Test - Start at 0 psi and 180°F and pressure cycle from 0 psi to 4,500 psi for 4,000 cycles. Stabilize the cylinder at 0 psi and ambient temperature, then stabilize the cylinder at 0 psi and -40°F and pressure cycle from 0 psi to 4,500 psi for 4,000 cycles. The cylinder must not leak nor rupture.

Hydrostatic Burst Test – A cylinder shall be hydrostatically (with water) pressurized until failure. The ultimate pressure shall be greater than 8,100 psi.

Composite Flaw Tolerance Test – Cylinder shall have two flaws in the longitudinal direction: One flaw shall be 1 inch long and 0.05 inch deep and one flaw shall be 8 inches long and 0.03 inch deep. The cylinder shall be pressure cycle tested from 0 psi to 4,500 psi for 11,250 cycles. The cylinder may leak after 3,000 cycles, but must not rupture.

Drop Test – Three drop tests shall be performed. One with the cylinder horizontal dropped from 6 feet onto a concrete floor. One with the cylinder vertical dropped onto a concrete floor to achieve 360 ft-lbs. One with the cylinder at a 45° angle dropped onto the dome of the cylinder onto a concrete floor from 2 feet. After drop testing, the cylinder shall be pressure cycled from 0 psi to 4,500 psi for 11,250 cycles. The cylinder may leak after 3,000 cycles, but must not rupture.

Bonfire Test – The cylinder shall be placed over a bonfire that within 5 minutes of ignition the temperature is 800°F. The cylinder shall vent through a pressure relief device without bursting. Oh, did I mention that the cylinder shall be pressurized to 3,600 psi with natural gas?

Accelerated Stress Rupture Test – Cylinder shall be pressurized to 4,500 psi at 140°F and held for 1,000 hours. The cylinder shall then be pressurized until failure. The burst pressure shall be at least 6,075 psi.

Penetration Test – Cylinder shall be pressurized with air to 3,600 psi and be penetrated with a .30 caliber armor piercing bullet. The cylinder shall not rupture.

As you can see, these tests are very rigorous. The cylinders are design to leak before rupture or have the pressure relief device vent before rupture. I don't know of any specifications that a gasoline tank has.

Once these tests are completed, the cylinder design is allowed to be used to manufacture and sell CNG cylinders.

[jetboatjohnny]

No wonder why they are so expensive.

[1996crownvicman]

that is a terrific video how could i share that with some friends of mine is it available on you-tube?

Thanks

[CraziFuzzy]

that is a terrific video how could i share that with some friends of mine is it available on you-tube?

Thanks

Close, it's on google video. YouTube wouldn.t let me post it (too big or somerthing), so that is why it's on google instead.

Just bring your friends here to watch it if you like.

[Tax Counsel]

I knew that the tanks were subject to rigorous testing. But it wasn't until I watched that video--and read Highmarker's additional comments--that I learned just how much abuse CNG tanks receive before they are certified.

It's clear that these extreme measures provide a major return on investment. With only two major recent incidents being reported on this board, I'm convinced that my CrownVic is at less risk of a fuel fire in an accident than my wife's gasoline-powered Swedish car.

Thanks, again
TC

[Green GX]

...I'm convinced that my CrownVic is at less risk of a fuel fire in an accident than my wife's gasoline-powered Swedish car.

Thanks, again
TC

TC,

And certainly at far less of a risk than a gasoline powered Crown Vic. There have been stories in the news in the past couple of years where city councils have been sueing Ford over exploding gasoline tanks when Crown Vic police cars have been rearended.

Bill