Rust Inside Steel Tank-Need Advice!

[realdiver7]

I just bought 2 PST 100 c.f. tanks about 3 months ago, but have only had them filled about 4 times. I always keep air in them at all times. Today I did a visual inspection because I'm going to use them for Nitrox, since they have been approved for Nitrox.

During my inspection, I noticed some very light surface rust around the sides at the very bottom, and around the inside near the valve, with other light surface rust spots throughout. Both tanks are always stored inside in environmentally controlled conditions.

When I rinse them after each dive, I leave off the DIN dust cap and rinse inside the DIN part of the valve. Before I use the tanks, I turn the air on for a split second to clear any water from the valve before I connect my first stage. I dive in salt water 99% of the time.

1. Is this light surface rust normal?

2. Do I need to do anything else before using Nitrox, given that the tanks have been cleaned for Nitrox and I have only used them for a short while, with air fills being from a reputable dealer?

3. Can I still use regular air on occasion, or do I have to dedicate the tank for Nitrox?

4. Should I use a different method to clean the salt from the valves?

Any advice would be greatly appreciated.

Thanks!

 

[joed]

I,m an old timer diver so alot of the new technology is real new to me. However in 1974 I had a steel 72 cu ft tank. The tank rusted due probably to moisture in the air that it was filled with. In those days, the dive shop traded the tank for a new one no questions asked. I would go for a new tank, if I could.

 

[wedivebc]

I just bought 2 PST 100 c.f. tanks about 3 months ago, but have only had them filled about 4 times. I always keep air in them at all times. Today I did a visual inspection because I'm going to use them for Nitrox, since they have been approved for Nitrox.

During my inspection, I noticed some very light surface rust around the sides at the very bottom, and around the inside near the valve, with other light surface rust spots throughout. Both tanks are always stored inside in environmentally controlled conditions.

When I rinse them after each dive, I leave off the DIN dust cap and rinse inside the DIN part of the valve. Before I use the tanks, I turn the air on for a split second to clear any water from the valve before I connect my first stage. I dive in salt water 99% of the time.

1. Is this light surface rust normal?

2. Do I need to do anything else before using Nitrox, given that the tanks have been cleaned for Nitrox and I have only used them for a short while, with air fills being from a reputable dealer?

3. Can I still use regular air on occasion, or do I have to dedicate the tank for Nitrox?

4. Should I use a different method to clean the salt from the valves?

Any advice would be greatly appreciated.

Thanks!

Small amounts of surface rust or "flash rust" is very common on steel tanks. Although there is a rust inhibor available to prevent it I believe it is not O2 compatable so is not a good idea for nitrox tanks. As long as the rust is not forming scale or pits it should not be a concern.

 

[msandler]

1. Is this light surface rust normal?

well its common anyway. after cleaning, an O2 safe rust inhibitor should be be used to prevent flash rusting during the drying process. To cleanout the light rust you described, you can tumble with ceramic media and avoid re-hydroing. If you using PP blended trox you should remove the rust (actually you should remove the rust anyway but...) steel in high O2 will oxidize.

2. Do I need to do anything else before using Nitrox, given that the tanks have been cleaned for Nitrox and I have only used them for a short while, with air fills being from a reputable dealer?

If pp blending then I'd say yes

3. Can I still use regular air on occasion, or do I have to dedicate the tank for Nitrox?

find a shop that pumps modified grade E

4. Should I use a different method to clean the salt from the valves?

I would crack the valve immediately after rinsing to dry the valve but, only crack it slightly (so the gas comes out slowly) and leave it open till dry. rapidly expanding gas will cause condensation on the inside of the valve which equates to moisture possibly getting in the tank even though compressed scuba air is typically very dry.

 

[msandler]

Although there is a rust inhibor available to prevent it I believe it is not O2 compatable

"compound O" from Global is.