Hydro for CNG tank

[smokey73]

I can't get a scuba shop to agree to hydro my CNG tank. I have found a welding gas supply place that ships their tanks to Jacksonville FL for hydro but they need (or want) a "code" to put on the paperwork before shipping and hydro and can't seem to find the right one. They deal in all kinds of gases including a lot of welding gases but I'm in limbo trying to figure out what code they need to use.

Has anyone had their thank hydro'd and if so either how did you convince a scuba place to hydro it or what code did they use at whatever other place who did your hydro use? I'd sure appreciate the help in getting past this hurdle. By the way, the top valve can be removed and thus the tank is open and I could use some air to make sure there is no residual gas in the thank. Without the "Compressed Natural Gas" sticker on the top of the tank what is the difference between a scuba tank and a CNG tank? I know the valve at the top of the tank is different since the CNG tank valve threads are left handed but is the tank itself different?

 

[dLj]

Never mind- I thought I had it - still looking...

dj

 

[dLj]

OK - several sources now tell me the same thing - "CNG tanks cannot be recertified after they reach their expiration date, so they must be replaced. "

I was originally directing you to 49 CFR 571.304 - Standard No. 304 Compressed natural gas fuel container integrity. But then I was reading that standard and realized it is pretty much only for initial certification...

dj

 

[smokey73]

@dLj I believe that the "expiration date" issue applies to non-steel type tanks that are commonly used in CNG vehicles. CNG tanks like we usually have in boats are heavy walled steel tanks rated at 2000 psi to 2200 psi, not the 3000 or 3600 psi large tanks used in Vehicle applications. Any references to the "several sources" would be appreciated. Thanks

 

[JamesG161]

what is the difference between a scuba tank and a CNG tank?

Depends on the material of construction of the your CNG tank.

Compressed Air or Scuba has moisture with the air

CNG not much moisture.

Scuba moved to Aluminum tanks for this reason

Try asking the local Propane suppliers.

Jim...

 

[dLj]

@dLj I believe that the "expiration date" issue applies to non-steel type tanks that are commonly used in CNG vehicles. CNG tanks like we usually have in boats are heavy walled steel tanks rated at 2000 psi to 2200 psi, not the 3000 or 3600 psi large tanks used in Vehicle applications. Any references to the "several sources" would be appreciated. Thanks

The first reference would be:

Alternative Fuels Data Center: CNG Fuel System and Tank Maintenance

.

However, if you read the standard I did post - that standard applies to all materials including steel and aluminum tanks.

dj

 

[jssailem]

Hi Smokie. I am not a CNG user so this may not be helpful.
I found these websites talking about Hydrostatic testing services in South Carolina. No idea if they will test your tank as there may be a contamination question between CNG and air in their testing procedures. They may be able to provide a resource for you.

• Palmetto Hydro
• Tank Inspection South Carolina | AST Industrial Certified Inspectors
• Hydro Test of Cylinders
• Contact Us

 

[RitSim]

Following. I tried all over CT to get my 5# propane tank from '99. i could change the valve to current but no one to test and stamp. New alum tank is >$300. steel tank is $53 on Amazon. The original tank is in pristine condition.

 

[dLj]

Following. I tried all over CT to get my 5# propane tank from '99. i could change the valve to current but no one to test and stamp. New alum tank is >$300. steel tank is $53 on Amazon. The original tank is in pristine condition.

Propane tanks are not the same as CNG tanks.

Here's a simple link:

https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/docs/propane_en_v3.pdf

dj

 

[Richard19068]

I can't get a scuba shop to agree to hydro my CNG tank. I have found a welding gas supply place that ships their tanks to Jacksonville FL for hydro but they need (or want) a "code" to put on the paperwork before shipping and hydro and can't seem to find the right one. They deal in all kinds of gases including a lot of welding gases but I'm in limbo trying to figure out what code they need to use.

Has anyone had their thank hydro'd and if so either how did you convince a scuba place to hydro it or what code did they use at whatever other place who did your hydro use? I'd sure appreciate the help in getting past this hurdle. By the way, the top valve can be removed and thus the tank is open and I could use some air to make sure there is no residual gas in the thank. Without the "Compressed Natural Gas" sticker on the top of the tank what is the difference between a scuba tank and a CNG tank? I know the valve at the top of the tank is different since the CNG tank valve threads are left handed but is the tank itself different?

Have they said or given you an example or type of "code" they are looking for?

What kind of cylinder is it, e.g. DOT 3AA 2250? That's the ubiquitous cylinder used around here for marine CNG stoves. The type should be plainly stamped on the neck area. That's a common scuba cylinder and I believe there is no specified end of life. It just needs to pass hydrostatic testing.

The scuba shop that does my hydros just asks me to make sure it is completely empty. Since, as you mentioned, the valves are different, they take off my valve and use their own for the test. Have you tried asking the scuba shop if you brought in your cylinder without the valve can they put on their own valve to do the test?

My cylinders are from 1978 (yes, 45 years old) and no one has said they are too old. I used to take them to an industrial gas place (since out of business) and a guy there said they were in great shape. He attributed that to the fact that they have been cycled a comparatively very few times compared to "working" cylinders and that its the number of cycles that really count.

 

[smokey73]

Thanks for all the responses. I believe I have resolved the issues. The shops that I took the tank to (one industrial gas and two scuba shops) all send their tanks out to third parties for hydro and I think it is that fact that was causing the angst in accepting them for hydro. The scuba shop suggested I call a marine supply shop that performs their own hydro's rather than shipping them to a third party.

@Richard19068 the tank is a DOT 3AA2400 steel tank and in good condition and is, as you said, just a scuba tank with a different valve. The shop (River Supply, in Thunderbolt GA) just said to remove the valve, put in a plastic plug to keep the moisture and air out (which they supplied) and they would do the inspection and hydro. If this works out, I have three more tanks to take to them and get them certified.

 

[smokey73]

So one lesson her for consideration is if you are looking for a CNG tank you can buy a good used DOT3A or DOT3AA steel tank with the correct neck size (some old tanks have smaller diameter necks so be careful it will fit your valve) and install the proper valve for a CNG application. Not sure where you would find those valves but the tank is just a steel scuba tank. Don't get the 3000 psi or above tanks because your regulator will probably not work for that higher pressure (but that is just an assumption)

 

[Terry Cox]

CNG tanks cannot be recertified after they reach their expiration date, so they must be replaced. "

Not so. In Seattle Fire King hydro re-certifies tanks including CNG steel tanks, which have no expiration date as long as they have no deep corrosion pits or damage according to their statement. My tanks have been re-certified many times by the appearance of previous date stamps.

 

[dLj]

Not so. In Seattle Fire King hydro re-certifies tanks including CNG steel tanks, which have no expiration date as long as they have no deep corrosion pits or damage according to their statement. My tanks have been re-certified many times by the appearance of previous date stamps.

Gotta say - I love being wrong on that one... seriously...

But you are actually quoting a quote I took from a document which I referenced.

dj

 

[MikeHoncho]

49 CFR 180.205 (j) Cylinder Condemnation....Take a look at it. It matters what the cylinders actually categorizes as regarding life span. Steel doesn't have a "drop dead" life span like composites and alloys that fail out with inspection and hydros.

 

[Terry Cox]

But you are actually quoting a quote I took from a document which I referenced.

Yes, dj. Knew that going in. Anecdotal, eh?