Tank Moisture

[Scuba_Dad]

I dropped one of my tanks off to get VIP'd yesterday, and last night they called me to let me know there was some moisture in the tank, and it was kind of a white milky substance. I stopped by the shop to look at the tank today, and inside was white granular substance. The LDS owner said it was moist last night. Odd...

What bothers me is how did it get there? From a bad compressor? I don't know. The compressor theory was my first thought, especially since he said it was milky looking. So today, I bled down my two other tanks that are due VIP this month, and they were clean. So, I thought maybe it was from the dive shop where I filled a few of my tanks this weekend, so I drained one of those tanks... but... it was clean, too.

I'm extremely AR when it comes to keeping air in my tanks... One of my LDS's like to fill nitrox tanks from empty tanks. I always bleed them down to just under 500 psi... they fuss at me, but I keep telling them that it's a bad practice to completely drain a tank. Plus... I'm always in the water, so the air in my tanks don't get a chance to even start getting stale...

Al

 

[COVCI]

I dropped one of my tanks off to get VIP'd yesterday, and last night they called me to let me know there was some moisture in the tank, and it was kind of a white milky substance. I stopped by the shop to look at the tank today, and inside was white granular substance. The LDS owner said it was moist last night. Odd...

What bothers me is how did it get there? From a bad compressor? I don't know. The compressor theory was my first thought, especially since he said it was milky looking. So today, I bled down my two other tanks that are due VIP this month, and they were clean. So, I thought maybe it was from the dive shop where I filled a few of my tanks this weekend, so I drained one of those tanks... but... it was clean, too.

I'm extremely AR when it comes to keeping air in my tanks... One of my LDS's like to fill nitrox tanks from empty tanks. I always bleed them down to just under 500 psi... they fuss at me, but I keep telling them that it's a bad practice to completely drain a tank. Plus... I'm always in the water, so the air in my tanks don't get a chance to even start getting stale...

Al

If it is fair to make a couple of assumptions, I would start by saying that what the LDS found in your cylinder is most likely Aluminum Hydroxide.

The assumption is that your cylinder is, of course, made of aluminum.

While Aluminum cylinders will not "rust", they will oxidize. The direct result of water, oxygen, and aluminum alloy is Aluminum Oxide--white powdery substance. Add some moisture (read as water) to the mix and you have Aluminum Hydroxide--a gooey, gelatinous substance that can stick to the sides of the cylinder.

Fortunately, oxidation in aluminum cylinders is "normally" not progressive...which means that when Aluminum Oxide is discovered during a proper Visual Cylinder Inspection, it can be removed and the cylinder will not continue to oxidize unless water is reintroduced.

What removes Aluminum Oxide/Aluminum Hydroxide you may ask...?

A quick tumble with some warm, soapy water with some tumbling media--glass beads, or ironically enough, Aluminum Oxide chips--will get it out and clean up the cylinder.

Make sure that the cylinder is rinsed thoroughly and then dried by blowing compressed SCUBA air into the cylinder.

These instructions are for cylinders that are in service for SCUBA Air. If cylinders are used for partial pressure blending of Nitrox, please use proper techniques to prepare the cylinder for oxygen service/use.

I hope this helps to answer your question.

This question, along with MANY more can be answered by taking a Visual Cylinder Inspector course from any PSI Visual Cylinder Inspector Instructor, or by taking one of many classes offered by training agencies specializing in Gas Blending/Oxygen Preparation.

Take care,
Chris

 

[wedivebc]

What bothers me is how did it get there? From a bad compressor? I don't know.

More likely bad filter. Moisture is always present in compressed air. It just needs to be removed before allowing it into a scuba tank

I'm extremely AR when it comes to keeping air in my tanks... One of my LDS's like to fill nitrox tanks from empty tanks. I always bleed them down to just under 500 psi... they fuss at me, but I keep telling them that it's a bad practice to completely drain a tank. Plus... I'm always in the water, so the air in my tanks don't get a chance to even start getting stale...

Al

It is no big deal to drain the tanks for filling. The amount of moisture introduced from draining then refilling a tank is negligible. It is when a tank is left empty/open that moisture can become a problem

 

[Scuba_Dad]

The assumption is that your cylinder is, of course, made of aluminum.

Thanks for the explanation, Chris. You hit the nail on the head.. yes, it was a gelatenous white stuff stuck to the sides of the tank.

Unfortunately, I'll never figure out which LDS induced the water into my tank. Even though I got 99% of my fills at one LDS... It's always possible the water was induced from another LDS.

Al