Potential cause of HP seat failure

[happy-diver]

Something, like relax, does that work for you.

he believes it is a defective part and that he'll see to it that it gets fixed

The fellow that did the viz said it was fine

 

[Geo7]

@Kendall Raine So, now knowing this, I'm gonna get it tumbled before using it again. The thing that kills me is, I did get it viz'ed, and the guy at the shop said the powder wasn't coming off, he didn't know what it was, and he was just concerned it be leaching CO or something. No mention of aluminum oxide, no mention of pulmonary fibrosis, not even a suggestion of getting it tumbled. My question now is, I've breathed off that tank for about 6 hours in total. Is there anything I should do (other than getting it tumbled), like, say, see a doctor or something?

I would just check the sinter filter in addition to changing the seat (add another 5 mins labour and another 3$ part...).

 

[Kendall Raine]

@Kendall Raine So, now knowing this, I'm gonna get it tumbled before using it again. The thing that kills me is, I did get it viz'ed, and the guy at the shop said the powder wasn't coming off, he didn't know what it was, and he was just concerned it be leaching CO or something. No mention of aluminum oxide, no mention of pulmonary fibrosis, not even a suggestion of getting it tumbled. My question now is, I've breathed off that tank for about 6 hours in total. Is there anything I should do (other than getting it tumbled), like, say, see a doctor or something?

Don't sweat it. Just get the tank cleaned by someone who knows what they're doing and make sure the valve is clear of sea water when filling going forward. The boats I go on always open the valve for a quick blast before attaching the fill whip. I've never heard of "CO leaching" and don't know why CO in an aluminum tank would leave a white residue or any other tell tale. A doctor might give you a pulmonary function test but, absent symptoms, I doubt they'll go past that. If you don't see white residue on the filter or in the second stage you probably didn't get any significant quantity. Besides, any white residue in the reg-particularly the filter-can simply be a few drops of sea water. If the reg is functioning OK (holding its IP) the seat is probably just fine.

Live long and prosper.

 

[Johnsonsa93]

so if it were aluminum oxide, I would see it in the filter?

For those interested here is what an extreme case of aluminum oxide in your filter would look like. This had clogged a customers regulator so badly that it was causing his SPG needle to drop significantly upon inhale and restricting breathing at depth. Due to it being an AquaLung DIN regulator with an ACD the filter was not visible so it wasn't until I took it apart that it could be diagnosed.

What's insane is he only uses steel tanks at home, he said he was on a liveaboard for a little over a week using their aluminum tanks. so in just a week it completely clogged his 1st stage.

 

[SouthernSharktoothDiver]

@Kendall Raine Good advice. I checked with the company that I go to for Hydros (local fire equipment company), and they say they also do roller treatments, so I think I'll take care of that soon.
@Johnsonsa93 That's a good reference pic. I saw nothing like that in my regset, sinter filter or elsewhere. I did see quite a lot of that changing a carburetor on a lawn mower, so perhaps I'll need to be more careful with those going forward lol.

 

[halocline]

There’s a common misconception that high supply pressure causes more wear in the HP seat. That’s not the way regulators work; it’s IP that forces the HP poppet (seat) against the orifice and closes the valve. In your case, if your 1st stage is the same as the SP MK11, that’s an upstream valve so the higher the supply pressure, the lower IP is. The seating force on your HP seat is essentially unaffected by HP fills.

So your creep has nothing to do with the overfills. It’s a little discouraging that a dive shop owner/regulator technician doesn’t seem to understand this. But not too surprising. Of course, other components in the 1st stage are affected by hihg supply pressure; the yoke/DIN fittings, and some o-rings that are subjected to supply pressure.

Regardless, you need a rebuild on this 1st stage.

 

[Tanks A Lot]

[...]
Alumaprep33 will dissolve all the white oxide and stop at clean aluminum. Dump out the acid wash and rinse well with clean water. Use a cut off garden hose and hang the tank upside down to rinse. After it’s rinsed check it to see if all the oxide is gone. Repeat if necessary, you can’t overdo it.
[...]

I'm not entirely sure that this is the best way to go, for a few very specific reasons. The main ingredients in Aluminaprep33, according to Henkel, are:

• 10% to 30% Phosphoric acid as an active ingredient.
• 10% to 30% 2-Butoxyethanol as a surfactant.

Phosphoric acid is caustic to aluminum. There are acids with a higher dissolution rate of aluminum like hydrochloric or sulfuric acids, but phosphoric acid nevertheless dissolves aluminum at a substantial rate. It by no means only removes the white powdery aluminum oxide Al₂O₃ that is sticking to the walls and lies loosely inside the cylinder. The alloy itself is protected by a layer of Al₂O₃, which the phosphoric acid will remove just the same. But the protective layer quickly forms again, just to be removed by the acid, just to form quickly... you get the picture. The reason you see "clean" aluminium, is that you removed enough material to lay bare the base alloy.

Now, the main concern is not that you'd remove too much material to have the walls too thin to withstand the pressure. This would indeed take quite some time. However, the acid treatment greatly increases the chances of stress corrosion cracking (SCC), not to be confused with SLC in 6351 cylinders. The acid may very well attack the grain boundary in the alloy, and if residual manufacturing tensile stresses are present, which they always are, especially in the neck area, these can act as crack initiators.
This is the main reason why manufacturers strongly discourage the use of caustic substances on or in cylinders. It has nothing to do with thinning the walls by any meaningful amount but the increased risk of SCC.

I'm not saying you will ruin your cylinders quickly by using this approach, but you can almost certainly overdo it, and just because it worked up until now does not mean it will continue to do so. All cylinders have slightly different characteristics in the alloy composition, homogeneity of the alloy, residual tensile stresses from manufacturing, and so on. Tank A may be indifferent to caustic substances, up to a certain degree, but tank B may develop SCC quickly.


Furthermore, I'm not entirely sure that a product with 2-Butoxyethanol is the best choice for preparing equipment for oxygen use. While it is a great surfactant and will certainly remove any residual oils, it itself can be a problem. With the chemical formula BuOC₂H₄OH, it becomes clear that it is a hydrocarbon, something we are trying to keep away from our oxygen-clear equipment.
It is also a rather non-volatile member of the glycol ethers. Non-volatility is undesirable in these circumstances, as a volatile chemical evaporates faster, making it easier to remove from the inside of the cylinder. A volatile chemical will be expelled faster from the inside of the cylinder with the usage of compressed air than a comparable non-volatile medium.
Coupling this with the fact that 2-Butoxyethanol is a known respiratory irritant, makes it a rather poor choice for the intended job in my opinion.

I have always been rather suspect of chemical-only cleaning methods. There is almost always a trade-off to be made, like in this case. Again, you are not putting yourself in immediate danger by doing what you are doing, but I believe the chemical properties warrant at least a second thought about the product's proposed usage here.