Question on plus (+) sign on Steel Tanks

[Magicdiver]

I am a Dive-Con student and my instructor has given me a question that i cannot find the answer to so i am turning it over to scuba board.

Stamped on Steel tanks is the normal markings (manufactur cerial number, max fill rateing, hydrostatic testing date ect...) but on steel tanks only can there be a plus sign. The (+) sign indicates that the steel tank can be overfilled by 10% without causing damage to the tank or blowing a disk. The plus sign indicates this but where did the plus sign origonaly come from ? I have narrowed it down to the DOT haveing a part in it. I hope im on track. Can anyone tell me the orgian of the plus (+) sign?

Thanks in advance
Magicdiver

 

[Scott L]

I am a Dive-Con student and my instructor has given me a question that i cannot find the answer to so i am turning it over to scuba board.

Stamped on Steel tanks is the normal markings (manufactur cerial number, max fill rateing, hydrostatic testing date ect...) but on steel tanks only can there be a plus sign. The (+) sign indicates that the steel tank can be overfilled by 10% without causing damage to the tank or blowing a disk. The plus sign indicates this but where did the plus sign origonaly come from ? I have narrowed it down to the DOT haveing a part in it. I hope im on track. Can anyone tell me the orgian of the plus (+) sign?

Thanks in advance
Magicdiver

If you want an immediate answer PM DA Aquamaster for answer. I can tell you the burst disk is not in play with regard to the + marking and 10% overfills...

 

[Magicdiver]

As i am new to this how do i PM DA Aquamaster?

 

[HowardE]

Could this be the answer you're looking for?

http://www.scubaboard.com/forums/tanks-valves-bands/195649-increasing-tank-psi.html

 

[Magicdiver]

Thank you! you are awsome

 

[Scott L]

I have had great difficulty getting a LDS to test for the + rating. It's my opinion they purposely avoid beleiving it is best not to overfill regardless of the rating. The extra step does further stress the cylinder as compared to the normal hydro giving them some arguement. If you want the + rating bypass the LDS and go straight to a hydro facility...

 

[HowardE]

I find it interesting in this thread:
http://www.scubaboard.com/forums/ta...6-10-overfill-plus-rating-steel-lp-tanks.html

Post # 10

Today I called DOT's Hazmat hotline 800-467-4922 and spoke with Kurt Eichenlaub.

After being put on hold a long time so he could research my question and confer with others, he emphatically answered my question.

49 CFR section 173.302a(b) allows for tanks stamped with the "+" to be overfilled 10% EVEN IF THE TANK DID NOT GET A "+" STAMP ON SUBSEQUENT HYDROSTATIC TESTING. If the "+" was originally stamped on the tank, it can be overfilled by 10% so long as the tank's vis and hydro are current.

Obviously, DOT considers the service pressure for a tank stamped 2400+ to be 2640 psi. If the tank was originally stamped "+," subsequent "+" stamping is redundant. After all, nobody expects the hydro tester to stamp "2400."

Mr. Eichenlaub also confirmed what you said earlier, that filling at your LSD and then driving to a dive location is not putting the tank into interstate transport, and therefore the DOT has no regulations on fill limits, albeit state negligence laws apply

 

[captain]

The + rating came about during World War Two as a way of transporting more gas in fewer cylinders and saving steel for other war needs.

 

[Scott L]

I find it interesting in this thread:
http://www.scubaboard.com/forums/ta...6-10-overfill-plus-rating-steel-lp-tanks.html

Post # 10

Great post. Thanks! In real life I do not find the + marking to be a difference maker. Most LDS's that overfill will continue to do so provided they perform their own visual inspection. They have really tightened the practice in my area such that I have switched most of my clylinders to HP. I could beg to get a nice fill but I could see they really did not want to do so...

 

[captain]

I have had great difficulty getting a LDS to test for the + rating. It's my opinion they purposely avoid beleiving it is best not to overfill regardless of the rating. The extra step does further stress the cylinder as compared to the normal hydro giving them some arguement. If you want the + rating bypass the LDS and go straight to a hydro facility...

There is no extra step that stresses the cylinder. It is tested to the exact same pressure as any hydro. The plus is derived from simply a mathamtical calculation that the shops don't have the ability to do because they do not have the magic number, the the REE limit (residual elastic expansion limit), or simply refuse to do it.

Newer steel cylinders sometimes has the REE stamped on the cylinders, older ones do not. If the REE is stamped on the cylinder there is no good reason not to + rate the cylinder if it qualifies.