My Steel HP100's have surface rust, WTH?

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Reef

Contributor
Messages
968
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Location
Tampa, FL and Washington, NC
# of dives
1000 - 2499
On the way home from the office I stopped to get the annual inspection on 2 of my tanks.

The LDS pointed out a flash rust on the inside of both tanks. He told me next year they would need to be blasted, and said whomever was filling them was letting in water. He also said breathing them down to under 500psi could cause this.

My wife and I have never let a tank get below 500psi, and this LDS has done all of our fills with the exception of some trips. The tanks have 100 dives each on them. We do a lot of beach dives which I wondered somehow could cause this?

This LDS always does hot fills, but I was told that would not affect the integrity of the tank. Tomorrow I'm taking my other tanks to him for Viz. Any recommendations? Thank you...
 
On the way home from the office I stopped to get the annual inspection on 2 of my tanks.

The LDS pointed out a flash rust on the inside of both tanks. He told me next year they would need to be blasted, and said whomever was filling them was letting in water. He also said breathing them down to under 500psi could cause this.

My wife and I have never let a tank get below 500psi, and this LDS has done all of our fills with the exception of some trips. The tanks have 100 dives each on them. We do a lot of beach dives which I wondered somehow could cause this?

This LDS always does hot fills, but I was told that would not affect the integrity of the tank. Tomorrow I'm taking my other tanks to him for Viz. Any recommendations? Thank you...

Well hot fills and moisture will cause that... but it only takes a couple of times to get flash rust....I would be suspect of the shop you are using.
 
Personaly I prefer wet filling for reasons of a full fill and less stress on the cylinder. LDS's are moving in the other direction which I object. If fill stations are properly configured with whip holders and good staff the introduction of water should not be a concern...
 
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...not sure I would immediately blame your LDS....the OP says he's had some fills done away from the LDS on some trips....so who really knows where the problem lies.
 
...not sure I would immediately blame your LDS....the OP says he's had some fills done away from the LDS on some trips....so who really knows where the problem lies.

Quite true. Check out this resource for the argument for and against wet filling/dry filling. Fill Express in Ft Lauderdale, FL is an industry leader in technical scuba tank filling.


Fill Express -- FAQ About Filling SCUBA Cylinders
 
He also said breathing them down to under 500psi could cause this.

I'm not an expert but that doesn't sound right. So 400 PSI will let the wet in but 500 keeps it out?!? I could see if you drained the tank but...

If this is correct could someone verify/explain or call it BS.
 
On the way home from the office I stopped to get the annual inspection on 2 of my tanks.

The LDS pointed out a flash rust on the inside of both tanks. He told me next year they would need to be blasted, and said whomever was filling them was letting in water. He also said breathing them down to under 500psi could cause this.

My wife and I have never let a tank get below 500psi, and this LDS has done all of our fills with the exception of some trips. The tanks have 100 dives each on them. We do a lot of beach dives which I wondered somehow could cause this?

This LDS always does hot fills, but I was told that would not affect the integrity of the tank. Tomorrow I'm taking my other tanks to him for Viz. Any recommendations? Thank you...

If you have rust in your cylinder it is almost certainly the result of a filtration failure.

Compressed air contains moisture and if a oil lubed compressor is used it also contains oils and and other hydrocarbons.

Compressor filtration is done in stages. The hot wet gas leaving the compressor first is passed through a desiccant material to remove the moisture, then it passes through Activated Charcoal (AC) which will absorb the nasty oils and other Hydrocarbons.

AC will only remove hydrocarbons if the gas is dry.

If wet gas reaches the AC portion of the filtration it will "washout" the Hydrocarbons.

How does wet gas reach the AC beds? The desiccant portion of the filter is filled beyond capacity with moisture.

What does this all mean?

If you are getting "Wetfills" i.e. wet inside the tank, you are getting water and other nasty crap in your tank.


BTW, you'd need to breath you tanks down to zero pressure before you could get any water into it.

Tobin
 
There is no need to wet fill cylinders. The industry would do better by slow filling, eliminating the heat issue. Minor flash rust is a nuisance not a hazard, don't go crazy chasing it until next hydro.
 
If the air is dry and you maintain positive pressure I would not put much stock in the 500 PSI threshold. Reasonable positive pressure should do the trick.

As for the hot fill I don't follow that one. Hot has will keep moisture away from he dew point at the time of filling. Even that is inconsequential since if there is moisture it will condense when you dive the tank in cold water. Finally there should not be enough moisture in there for anything to condense in the first place.

If a wet fill were done OR you brought a wet valve to the fill station and the water was not blown clear then some water could get pushed into the cylinder despite a good air source and dry whip handling. Good fill technique should always include blasting the valve clear by cracking the valve and eyeballing it for wetness in the connection area. I try to always do this personally as I unload my cylinders at the dive shop. They should be doing a similar purging of the whip if water is anywhere to be found. Do you by any chance hose your cylinders down at the dive shop just before presenting them for fills?

You mentioned a few fills done elsewhere, obviously it only takes one bad round of air to set you up for corrosion.

I don't see beach dives as a risk. The cylinders are still always pressurized so nothing gets in.

Over what period were the 100 dives made? Over time most steel cylinders will develop some flash rust that can eventually be of concern to the inspector. Spinning a tank whip, blasting or tumbling are not all that uncommon with cylinders that actually get to go diving frequently. To some extent it's expected maintenance. If it were a yearly need I would raise a red flag.

Pete
 
Tobin hit the nail on the head. Moisture in a tank comes from poor filtration.

Remember from your open water class that ambient pressure in psi underwater is roughly equal to half your depth in feet (0.43 psi per foot in sea water). For water to enter your tank when it has 500 psi in it would require you to be at about 1000 ft depth.

Some flash rust will not cause it to fail a visual inspection, although if you listen to some LDS's, any flash rust requires a tumble.

There are various ways to remove flash rust without tumbling, whipping or sandblasting.
 
https://www.shearwater.com/products/swift/

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