Whose moronic idea was it to stamp the cylinder crown?

[Pavao]

Cool
That begs the question - does it pass because it's not in use?

This reminds me…
In more recent years, say within the last 10 years, I have observed divers started asking in for sale ads of used scuba tanks, “hOw MaNy DiVeS oN iT?”

Likewise, ads recently started adding the “OnLy DoVe In FrEsH wAtEr”

So irrelevant!

 

[Belzelbub]

This reminds me…
In more recent years, say within the last 10 years, I have observed divers started asking in for sale ads of used scuba tanks, “hOw MaNy DiVeS oN iT?”

Likewise, ads recently started adding the “OnLy DoVe In FrEsH wAtEr”

That's just dumb. I honestly wouldn't be able to answer for any of my tanks. Currently I have 2 AL80s, 2 HP120s, and 4 HP100s. I might be closest on the 120s as I've only had them for a year. The rest have been used by several divers and have no clue on how many dives. And, yeah, it's completely irrelevant.

My favorite is the ads for dive computers stating that the computer was only used as a backup. My Garmin has around 70 dives on it. Most of those as a backup. 70 dives is 70 dives. And even that wouldn't concern me depending on after dive care.

 

[boulderjohn]

So in fact, any marking to determine a cylinder has been inspected and tested can be attached to the cylinder?

There are two kinds of inspections--visual and hydrostatic. Rules differ from country to country. In the USA, visual inspections are done every year, and hydrostatic inspections are done every 5 years. The visual inspection is noted by a sticker, and the hydrostatic inspection is stamped.

In reality, though, in the USA only the hydrostatic is required by law, and that is only for transportation. The visual inspection requirement is a scuba industry agreement. The people who do the inspections are supposed to be trained and certified, but when you take a tank in to have it inspected, you have no control over who is doing the testing.

 

[OMyMyOHellYes]

The people who do the inspections are supposed to be trained and certified, but when you take a tank in to have it inspected, you have no control over who is doing the testing.

When I was getting started in the sport (and I'm an admitted gear guy), I found that if I asked the same tank question of the same employees at three different scuba shops here, I would get six different answers.

That told me that despite my early impression that the LDS guys were all-knowing scuba gods, none of them really spoke with authority on some (a lot) of things scuba related. There was a lot of "tribal knowledge" and isolated pockets of "religious dogma" sprinkled around that had no relationship to reality. Huge amounts of ignorance; old, outdated info; ignorance; undeserved arrogance; and ignorance in the LDS (and sometimes even the DOT licensed hydro retesters). 'tis why almost all local shops tell folks that their pre-1990 bottles cannot be hydro'ed as if it's a law when in reality, the fire extinguisher shop they all outsource hydros to can't keep the rules straight. I've seen some perfectly good bottles in the condemned stack because of this ignorance.

That's when I went and got training to roll my own and went and got the training...

 

[Tracy]

This reminds me…
In more recent years, say within the last 10 years, I have observed divers started asking in for sale ads of used scuba tanks, “hOw MaNy DiVeS oN iT?”

Likewise, ads recently started adding the “OnLy DoVe In FrEsH wAtEr”

So irrelevant!

The fresh water only thing is quite relevent. Fresh water tanks generally look like new regardless of age and number of dives. Galvanized tanks dove in saltwater look like crap. It doesn't hurt them, but it a major appearance difference. Saltwater valves are also generally pitted, not in freshwater.

 

[Pavao]

The fresh water only thing is quite relevent. Fresh water tanks generally look like new regardless of age and number of dives. Galvanized tanks dove in saltwater look like crap. It doesn't hurt them, but it a major appearance difference.

I honestly do not know what you mean, I’m searching my memory to try and find a single galvanized tank in an ocean of a gazillion tanks belonging to shops, costumers, friends, personals, etc…that looks as bad as you making it sound like, and the sample of tanks gone in saltwater is quite big.

Saltwater valves are also generally pitted, not in freshwater.

Again, not sure what you mean here, or admittedly I may not know what “pitted” means. I thought it meant corrosion causing “holes” eating away the material, if that’s what you mean, I’m again having a hard time thinking of actually a single instance where I’ve been able to observe that.

Will neglecting a tank used in salt water cause problems? Yes. More than the ones neglected in fresh water? Also yes.
Neglect is the issue, and it’ll be quite apparent for the potential buyer, thus asking a question of what kind of water the tanks were used in is a moot point, either the tank is in good shape or it isn’t. Same for your aesthetics concern, either it pleases you visually or it doesn’t, let’s be honest, how many sale ads are you seeing without pictures, and especially in the case of tanks where shipping is seldom an option? You either gonna see detailed pictures or in person.

One last bit, I know of many shops with large tank rental fleets, of all kinds, Al, steel galvanized, coated, virtually from all manufacturers sold in US last several decades, here in SFL, none of them washes their tanks with fresh water after salt water use, not ever, think these tanks and valves are full of corrosion and pitting? Think again.

 

[Tanks A Lot]

[...]none of them washes their tanks with fresh water after salt water use, not ever[...]

Not washing cylinders, especially after use in saltwater, is a surefire way of damaging both the cylinder as well as the valves.

The first thing that will be damaged are the G5/8" (DIN) threads on a valve if it has some. Deposit built-up on the threads and subsequent insertion and removal of regulators will wear the threads down over time.

The next thing that gets damaged is the area right where the valve and an aluminium cylinder meet. Galvanic corrosion will cause pitting on the face of the cylinder, eventually eating into the O-Ring seating surface. I have had to re-cut the face on 100s of cylinders to make them usable again.

The next in line is the boot area on steel cylinders. Sand and debris accumulate here, making it nearly impossible for the water to drain, leaving the area permanently wet.

The neck on steel cylinders is not immune to rusting either, but it usually takes a lot longer to manifest. If it does and saltwater is left on there, the corrosion is greatly accelerated.

If you just think about the cylinder and it's wall itself, you are absolutely right that there won't be any pits developing. Unfortunately we can't just look at the cylinder in isolation, but also must take into account the "accessories" attached to make it usable, such as valves or boots on steel cylinders.
Galvanic corrosion in saltwater can be up to 10 times worse than freshwater.¹ I have seen stark differences between dive centres that wash their cylinders after use and ones that don't. None of the above effects are fast, it always takes several years, sometimes a decade or more to manifest itself. All of this occurs in freshwater, as it does in saltwater. But the damage is a lot more rapid in saltwater than it is in freshwater (Still many years!). That is simply due to the nature of saltwater and it's higher electrical conductivity.

Take for example the neck on an aluminium cylinder in saltwater. If not washed, salt will build up between the neck and valve, damaging the layer of aluminium-oxide AL₂O₃. The layer will "flake" off, exposing a a fresh layer of alloy to oxidize, which then flakes off, which then...
This happens in freshwater as well, but a lot less quick, due to freshwater's lower electrical conductivity.

The G5/8" threads on a valve exclusively used in freshwater also get damaged over time. But again, the presence of salts which have not been removed make this process much faster.

Suggesting that there is no difference between saltwater and freshwater with regards to damage of a cylinder is not quite the full story in my experience, especially if the cylinder used in saltwater never gets washed. The process is slow in both cases, but is nevertheless much faster in saltwater than freshwater.

¹ X. G. ZHANG - Galvanic Corrosion (2011)

 

[Pavao]

Suggesting that there is no difference between saltwater and freshwater with regards to damage of a cylinder is not quite the full story in my experience, especially if the cylinder used in saltwater never gets washed. The process is slow in both cases, but is nevertheless much faster in saltwater than freshwater.

¹ X. G. ZHANG - Galvanic Corrosion (2011)

Will neglecting a tank used in salt water cause problems? Yes. More than the ones neglected in fresh water? Also yes.
Neglect is the issue, and it’ll be quite apparent for the potential buyer, thus asking a question of what kind of water the tanks were used in is a moot point, either the tank is in good shape or it isn’t. Same for your aesthetics concern, either it pleases you visually or it doesn’t, let’s be honest, how many sale ads are you seeing without pictures, and especially in the case of tanks where shipping is seldom an option? You either gonna see detailed pictures or in person.

The discussion was never about which medium causes more damage to cylinders.

And besides, didn’t I already say in much fewer words what you finally concluded after all that I had to filter out on your quote?

 

[Learner Diver]

I like the idea of QR codes. I've seen QR codes lasered into Aluminium.

 

[BoltSnap]

These markings have been used for decades and there were no issues with the way they are done over these decades. You are trying to make an issue out of a totally non-issue.