Internal rust & flash rust in steel tanks
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As I said I had the same problem , its down to the dew point when filling , also where you store your tanks cold garage floors are not good either , I asked a guy in the UK who regulates this stuff, I will post a better reply tomorrow ,
Thanks for now Alban
Thanks for now Alban
Hi:
Thank you for your reply to my message DNAXdiver.
How does one make a tumbler? Is this expensive??
Another question as well: if there is rust and no pitting, is it best to leave it there and try to get the best air there is or better tumble?
Thank you
FredT
Guest
"flash rust" gives the tank a golden look inside. This usually happens during the initial drying and stops when the water is gone. Hold the valveless tank upside down over a white paper and smack it with a hammer. If nothing falls out you probably have this form. Do nothing with it but watch for it getting heavier.
A velvety brown coating could be heavy flash rust, but more likely it's due to humid air going in. If you have this find a new air source that knows how to change dryer chemicals and maintain some backpressure on the 'presor output.
Both of the above can usually be "whipped out" with an abrasive whip, then blown out with clean SCUBA air (shop tool compressors are ALWAYS "wet"!) or known dry nitrogen gas.
A phosphoric acid rinse before and after the first whipping will stop any pits starting in the metal. If doing O2 cleaning afterward it's suggested to whip again after drying the last acid rinse.
Brown "popcorn" on the otherwise clean tank wall indicates a bit of water from a fill whip or valve dunk before filling. Find a new fill monkey, then acid rinse and and tumble the tank.
As far as building a tumbler goes the rules are REALLY simple.
1. Tank should rotate between 30 and 60 RPM
2. Support shafts HAVE to be long enough to take the tank and parallel to each other or the tank walks, but with adjustable bearings the walking thing is easy to "dial in".
3. Frame has to be stiff enough to hold the shafts in place and support the tank with media without too much deflection (that amount which causes the tank to "walk" on the tumbler is too much.)
4. Drive guarding as required by your circumstance. I guard mine by running it under a table, but my kids are WAY out of the "fingers in everything" stage and know machines bite!
Buying parts and building from scratch my tumbler cost about $100 including the motor.
I you're into the "Junkyard Wars" type of thing I've seen tumblers from "scrap parts" that were built for near $0.00, but did require a couple afternoons in dumps finding a washer or dryer motor that worked and field stripping a couple other "dead" appliances for belts and drive hardware. Finding a junk roller conveyor that had a few good rollers on it for the drive rolls and frame parts just makes this thing way too easy. Boat trailer rollers also work, and a simple drive roll is a piece of 3/4" or 1" rod with a tightly fitted rubber heater hose bonded and clamped to it. This works for both rolls if doing a single place tumbler. If scrounging first find the bearings, then look for suitable shafts. Frames can be wood, metal or heavy plastic. You decide what you can lay hands on easiest. Diagonal bracing is a good idea to maintain shaft alignment.
FT
A velvety brown coating could be heavy flash rust, but more likely it's due to humid air going in. If you have this find a new air source that knows how to change dryer chemicals and maintain some backpressure on the 'presor output.
Both of the above can usually be "whipped out" with an abrasive whip, then blown out with clean SCUBA air (shop tool compressors are ALWAYS "wet"!) or known dry nitrogen gas.
A phosphoric acid rinse before and after the first whipping will stop any pits starting in the metal. If doing O2 cleaning afterward it's suggested to whip again after drying the last acid rinse.
Brown "popcorn" on the otherwise clean tank wall indicates a bit of water from a fill whip or valve dunk before filling. Find a new fill monkey, then acid rinse and and tumble the tank.
As far as building a tumbler goes the rules are REALLY simple.
1. Tank should rotate between 30 and 60 RPM
2. Support shafts HAVE to be long enough to take the tank and parallel to each other or the tank walks, but with adjustable bearings the walking thing is easy to "dial in".
3. Frame has to be stiff enough to hold the shafts in place and support the tank with media without too much deflection (that amount which causes the tank to "walk" on the tumbler is too much.)
4. Drive guarding as required by your circumstance. I guard mine by running it under a table, but my kids are WAY out of the "fingers in everything" stage and know machines bite!
Buying parts and building from scratch my tumbler cost about $100 including the motor.
I you're into the "Junkyard Wars" type of thing I've seen tumblers from "scrap parts" that were built for near $0.00, but did require a couple afternoons in dumps finding a washer or dryer motor that worked and field stripping a couple other "dead" appliances for belts and drive hardware. Finding a junk roller conveyor that had a few good rollers on it for the drive rolls and frame parts just makes this thing way too easy. Boat trailer rollers also work, and a simple drive roll is a piece of 3/4" or 1" rod with a tightly fitted rubber heater hose bonded and clamped to it. This works for both rolls if doing a single place tumbler. If scrounging first find the bearings, then look for suitable shafts. Frames can be wood, metal or heavy plastic. You decide what you can lay hands on easiest. Diagonal bracing is a good idea to maintain shaft alignment.
FT
Hello guys
I have coppied some stuff that may be of interest :
The rust will come from the due point moisture when a clynder is pumped fast and dropped tempertuers will cause moisture in them, also Boat compressors will cause quite a lot of moisutre build up due to the location of intakes on boats,
But fast filling is the over all problem and storage over the winter on garage floors ect, the temperture in concrete over the winter months can alter quite a lot.
All air contains water vapour of varying quantities. The dew point indicates the amount of moisture in the air. The higher the dew point, the higher the moisture content of the air at a given temperature. Conversely, the dew point of humid air will be higher than the dew point of dry air.
Dew point temperature is defined as the temperature to which the air would have to cool (at constant pressure and constant water vapour content) in order to reach saturation. A state of saturation exists when the air is holding the maximum amount of water vapour possible at the existing temperature and pressure.
Condensation of water vapour begins when the temperature of air is lowered to its dew point and beyond.
Fred T you obliviously now your stuff here, have you ever come across this ? I am from the UK we mostly use steel fabers 12 lts pumped to 232 bar used in salt water , I allways try to look after my tanks like any of my kit , I have a water butt and I remove the boots and dunk them in there to remove salt deposits , so often I see people toss there tanks in the garage without washing them.
You talk here of making your own tumbler , do you guys have regs the same as us or is this something you would consider doing before you sent your tank for inspection ?
Sorry for all the questions Alban
I have coppied some stuff that may be of interest :
The rust will come from the due point moisture when a clynder is pumped fast and dropped tempertuers will cause moisture in them, also Boat compressors will cause quite a lot of moisutre build up due to the location of intakes on boats,
But fast filling is the over all problem and storage over the winter on garage floors ect, the temperture in concrete over the winter months can alter quite a lot.
All air contains water vapour of varying quantities. The dew point indicates the amount of moisture in the air. The higher the dew point, the higher the moisture content of the air at a given temperature. Conversely, the dew point of humid air will be higher than the dew point of dry air.
Dew point temperature is defined as the temperature to which the air would have to cool (at constant pressure and constant water vapour content) in order to reach saturation. A state of saturation exists when the air is holding the maximum amount of water vapour possible at the existing temperature and pressure.
Condensation of water vapour begins when the temperature of air is lowered to its dew point and beyond.
Fred T you obliviously now your stuff here, have you ever come across this ? I am from the UK we mostly use steel fabers 12 lts pumped to 232 bar used in salt water , I allways try to look after my tanks like any of my kit , I have a water butt and I remove the boots and dunk them in there to remove salt deposits , so often I see people toss there tanks in the garage without washing them.
You talk here of making your own tumbler , do you guys have regs the same as us or is this something you would consider doing before you sent your tank for inspection ?
Sorry for all the questions Alban
FredT
Guest
If you are getting tanks filled on boats expect to tumble regularly. Maritime rules generally make having a "bank" on a boat cost prohibitive. They pretty much have to fill off the 'pressor, but a bit of care can make that even much safer than it usually is.
When air is compressed _Some_ water drops out in the interstages and as the pressure rises more drops out, simply because there isn't as much room between the O2 and N2 molecules for it. Even putting 15% relative humidity air into a tank at 500psi will tend to cause condensation on the tank walls. The best bet is to "pressure dry" the air by keeping 2500 psi or better back pressure on the filter stack at all times, and changing the water absorption filter often. The pressure dry forces 95% of the water that _WILL_ come out to drop out at the coalescing filter. (Please note that air at the output of th coalescing filter ALWAYS has a RH of 100%) This not only extends the life of the dessicant secton of the filter, it allows for a much dryer air output. The output from the dessicant section should be LESS THAN 15% RH at the instantaneous output pressure. The problem here is if the air coming out of the compressor only sees 500psi, then the absolute amount of water in the mix is an order of magnitude above the portion of the gas that sees 3000psi in the filter!
The "fast fill" bit is a red herring to divert you from the fact that the air going into your tank ain't dry anyway! A fast fill with "wet" air may cause condensation inside the tank, a fast fill with properly dried air simply will not condense at all! As the tank is starting to fill the dew point of the mix going in will be well under -120°F at that lower pressure.
Dew point is related to relative humidity at a particular temperature and pressure, not an absoute water quantity. Get the dew point to -40° at full tank pressure and internal tank condensation simply can't happen. When a shop is talking about "fast fills" and condensation what they are really telling you is to go find someone to fill your tanks that has a clue how the physics works adn what that means to their compressor operation procedures!
I do my own inspections, but that is a good thing even if you don't "certify" the tank. A pre-inspection tells you a lot about your air source, and cleaning it yourself can save a bunch of $ when getting several tanks inspected.
FT
When air is compressed _Some_ water drops out in the interstages and as the pressure rises more drops out, simply because there isn't as much room between the O2 and N2 molecules for it. Even putting 15% relative humidity air into a tank at 500psi will tend to cause condensation on the tank walls. The best bet is to "pressure dry" the air by keeping 2500 psi or better back pressure on the filter stack at all times, and changing the water absorption filter often. The pressure dry forces 95% of the water that _WILL_ come out to drop out at the coalescing filter. (Please note that air at the output of th coalescing filter ALWAYS has a RH of 100%) This not only extends the life of the dessicant secton of the filter, it allows for a much dryer air output. The output from the dessicant section should be LESS THAN 15% RH at the instantaneous output pressure. The problem here is if the air coming out of the compressor only sees 500psi, then the absolute amount of water in the mix is an order of magnitude above the portion of the gas that sees 3000psi in the filter!
The "fast fill" bit is a red herring to divert you from the fact that the air going into your tank ain't dry anyway! A fast fill with "wet" air may cause condensation inside the tank, a fast fill with properly dried air simply will not condense at all! As the tank is starting to fill the dew point of the mix going in will be well under -120°F at that lower pressure.
Dew point is related to relative humidity at a particular temperature and pressure, not an absoute water quantity. Get the dew point to -40° at full tank pressure and internal tank condensation simply can't happen. When a shop is talking about "fast fills" and condensation what they are really telling you is to go find someone to fill your tanks that has a clue how the physics works adn what that means to their compressor operation procedures!
I do my own inspections, but that is a good thing even if you don't "certify" the tank. A pre-inspection tells you a lot about your air source, and cleaning it yourself can save a bunch of $ when getting several tanks inspected.
FT
MrSquid
Guest
Anyone know where I can pick up an abrasive whip? I have some flash rust in one of my tanks that I would like to try and remove myself.
Thanks,
The Squid
Thanks,
The Squid
FredT
Guest
Easiest way I know of is to contact chris and tell him what you want. His e-mail is :
covci@covci.com
FT
covci@covci.com
FT
So FredT,
Any suggestions on the right questions to ask a dive shop/fill station to make sure they are doing the right thing with the compressor and fill procedure.
I understand the physics but don't know the finer points of compressor operation... I'm the proud owner of new Faber steel tanks and I want to keep them happy.
Thanks,
Mer
Thanks FredT
I accepted what I was told in good faith and it seemed to make sense at the time, the B.S. Limit is 0.5 g /cubic meter water vapour, a new Bauer would be less than 25mg. Perhaps I should build that tumbler system changing where I get my fills would be more expensive ( we know how to charge for petrol here )
;-0
Good point from Mer I would like to ask a few questions too.
thanks for the reply Alban
I accepted what I was told in good faith and it seemed to make sense at the time, the B.S. Limit is 0.5 g /cubic meter water vapour, a new Bauer would be less than 25mg. Perhaps I should build that tumbler system changing where I get my fills would be more expensive ( we know how to charge for petrol here )
;-0
Good point from Mer I would like to ask a few questions too.
thanks for the reply Alban
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