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Question
Posted : January 28, 2009
Dear Sir,
Thank you for your response on the paint scheme of the diving cylinders. may I request another pice of information. what is the recommended reagent for chemical cleaning of diving cylinders from inside for prevention of corrosion


Answer
Posted : January 28, 2009
First question to stump me !! well done.

I have seen lots of information on this across my desk over the last decade as some of these reagents are very unsuitable given the pressures, gases used and importantly the fact that the Inspired PPM of those that leach airborne esters and other molecular components.

I will do scientific search as the main companies producing cylinders will have had to prove these are totally chemically inert at both atmospheric and also to the limits of commercial and recreational diving.... which I understand the qualifications will yield 750msw and 150msw respecively.

My website www.admdiving.co.uk has extensive information in the library on oxygen cleaning reagents for the conditioning and cleaning of the cylinders. It does not have the information you ask...

Note: every dive gas facility in the UK should now be following the much tougher DVIS9 standard for air purity which has reduced the level of water vapour to a very low level 35mg/m3 for 200BAR+ sample - our last spectral analysis showed we deliver air at 12.8mg/m3 - but then we use special filters that contain military/commercial diving mediums which readily meet this standard. (the test was done nearing the end of life of the main 1st stage filter - at 85% of life).

Why all the above - this new standard is to ensure that cylinders do not rust or more to the point flash rust, hence this perhaps obfuscates the need for such chemical inhibitors to be used... Note also the change in specification of the steel earlier this decade too.

May I ask why do you want the information... are you entering the market as a cylinder manufacturer as the use of such reagents you state are not generally for test stations of cylinders....

I'll post an update when I have he answer, unless above sorts out the needs...
Answer provided by ADM Diving

Andrew Dawson-Maddocks
Additional Comment

Posted : January 31, 2009 by - ADM Diving
Ah yes this is as I thought a real can of issues.

The main manufacturers use a phosphatized approach which is done as a final phase to the successive oil heat treatments to anneal and sort out stresses within the melecular structure of the metal.

The process used phosphoric acid and this acts as an effective rust inhibitor.

Many of the old products that used Amines as there base and other such genotoxic and carcinogenic substances have gone out of use.

Many now contain food grade Sodium Nitrite which is an effective rust inhibitor albeit it too has a Material Safety Data Sheet that would make you wince at its use in your cylinders !!

The proceedures for the use of these inhibitors as part of the chemicals for O2 cleaning cylinders or for use after a Periodic Inspection and Test need to be followed very carefully to ensure the residue is totoally removed 'thereby mitigating the any MSDS issues with the alcaline base (or similar).

I guess the key point as always is ensure you get your kit serviced at a really good facility - don't just look at price and do make sure you understand what they do and what solutions they use for such servicing...

Thanks for this question. It reminded me when I was looking in to the answer as to all the issues I found (some to my horror) about actually how compressor filter cartridges work and behave as a function of time in use, time idle and type of contaminents that they are meant to physically filter out (i.e. 100% absorb and chemically bind to prevent release).

Hope the answers helped. Best regards Andrew.
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