2nd try, my cut & paste got munged.



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Posted by roakey on August 15, 2001 at 04:57:16:

In Reply to: O2 cleaning posted by Maciek on August 15, 2001 at 03:24:23:

>>I search and search and can't find the clear answer. What exactly it is?

I’ll give you the straight party line here, and I’m sure the discussion on if it’s really necessary will follow :-)

Actually what I think you’re asking about is “ready/suitable for oxygen service.” This consists of two steps: Making sure no hydrocarbons are available for combustion (the O2 cleaning part) and only using “O2 compatible materials” (read: they won’t burst into flames in a pure O2 environment) in assembly of the parts.

So O2 cleaning is only half the equation.

Note that equipment need only be “ready for O2 service” if its exposed to a mix that has greater than 40% O2 (unless you follow the CGA guidelines, which no one does, where it’s something like 23.5% O2)

A careful distinction here. There are two ways to get Nitrox. One way is partial pressure blending. Using this method you introduce pure O2 into the cylinder and then blow hyperfiltered air (air with no hydrocarbons in it) on top of the O2. Because the cylinder “sees” O2 in concentrations greater than 40% using the partial pressure blending method, it must be ready for oxygen service (O2 clean AND O2 compatible materials are used). The second way to deliver Nitrox is if the shop has pre-blended Nitrox in their cascade and fills your cylinder with the correct mix WITHOUT ever putting pure O2 in your cylinder. In this case your cylinder DOES NOT have to be ready for oxygen service because it never “sees” O2 in any concentration greater than 40% (I’m assuming recreational Nitrox here). So if a shop does Nitrox fills via the second method (usually referred to as a “membrane system” though that’s only one method to get pre-blended Nitrox), you can use any ‘ol air cylinder for your pre-blended Nitrox, but usually only after the shop sells you an expensive sticker and tells you all sorts of BS.

So your questions can be answered in two contexts: A cylinder ready for oxygen service (partial pressure blending) or one that’s only used for pre-blended Nitrox. Because the latter is any ‘ol air cylinder, it only makes sense to answer your questions for a cylinder used for partial pressure blending, so here goes:

>>1) can O2 cleaned tank be used for air?

A cylinder that’s ready for oxygen service can be filled with air if it’s hyperfiltered air. In other words the same air the shop uses for partial pressure blending. If you’re buying air at “Fred’s Filldirt and SCUBA shop” and they don’t offer partial-pressure blended Nitrox, no, you can’t use their air because it contains (in theory) hydrocarbons that will deposit on the walls of your cylinder. Upon the next partial pressure fill as you’re filling with pure oxygen these hydrocarbons may ignite, causing complete and rapid disassembly of the cylinder and valve.

>>2) if O2 cleaned tank is used for air is it still O2 clean?

I think this question is answered above.

>>3) typically what is the price for O2 cleaning of reg and tank? how long does it take?
>>who does that? Does it need to be repeated?

First off for recreational Nitrox (O2 >4) Does O2 cleaning impose any restrictions onto tank?
>>For example that I can't depresurise it and take a valve out?

The only special consideration is not to contaminate the cylinder. So simply depressurizing the cylinder and removing the valve won’t cause any problem unless you pour motor oil in there. :-). However, most shops upon receiving a cylinder that’s ready for oxygen service that has no pressure in it will see a great revenue opportunity and spread much FUD (fear, uncertainty and doubt) about the cleanliness of your cylinder and want to charge you for another cleaning.

>>5) any differences between O2 cleaning for alu/steel tanks?

No.

Roak

Now let the “is O2 cleaning really necessary?” debate begin! :-)



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