Nitrox tank service life

[Antosh]

G'day everybody.

I recently got my nitrox certificate and I've got two tanks that are currently on air. I took in my newer tank to get cleaned and converted to nitrox (3 years old, 3 hydrostatic tests). The service guy told me that since its not brand new, it might only last a few years on nitrox, then it'll have to be switched to air only. He said this is due to possible existing rust becoming an issue with the higher air content. He also said that after its been nitroxed I'd have to rumble (de-rust it) it a lot more often (possibly as much as every year in his words) than if I just left it air.

Now I've talked to a few dive shops about tanks and the like, but that issue has never come up with converting a used tank into nitrox. I look after my tanks and leave pressure in it and I know that higher O2 concentration will mean faster corrosion, but I dont see it turning it into a pile of rust he envisioned.
Either he was just trying to scare me into buying a new tank, or he's just giving me the worst case scenario with converting a used tank into nitrox. It's pretty much academic cos I got it done anyway, just wanting to know anybodys thoughts or experiences on this topic.

Thanks guys
Antosh

 

[Wayward Son]

it's a steamy pile of bull squeeze.

the tank gets serviced annually. if you see any rust, it gets tumbled & cleaned. just like any other tank.

 

[Couv]

Hello Antos-Welcome to Scuba Board,

It may be time to find another service guy, but before you do anything drastic, lets get a few terms sorted out.

A hydrostatic test is done to check the elasticity of the cylinder. (Google hydrostatic testing) In the US, hydrostatic testing is usually done every 5 years, so I will hazard to assume you meant a Visual Inspection was done 3 times in 3 years.

A Visual inspection is usually done annually. It is an internal and external inspection looking for defects such as corrosion, thread damage, pits, dents etc. See this link for more info:
http://www.luxfercylinders.com/downloads/docs/scubaguide.pdf

As to the cleaning/rust part of your question, you might find this thread helpful.
http://www.scubaboard.com/forums/tanks-valves-bands/289548-oxygen-tank-cleaning-how-do.html

Cheers,

Couv

 

[DevonDiver]

Every tank, whether Nitrox or not, has a Visual Inspection annually and a Hydro-static Inspection every 5 years (unless governed by other local laws). As long as the tank passes those inspections it can remain in use.

If using the tank for nitrox... and it may be filled using Partial Pressure Blending, then the tank will have to be cleaned for O2 Service alongside the visual inspection each year (or more often if something occurs to contaminate the tank). That would deal with an rust issues.

Likewise, if any excessive rust was noted during the visual inspection, the tank would need to be cleaned (tumbled) to remove it. It isn't a big deal.

As a nitrox tank is only filled with nitrox-clean air (double filtered) it should be nice and dry anyway.... so the potential of greater rust due to the O2 content is off-set by the cleaner, more guaranteed air in the bottle.

 

[Wayward Son]

the OP is in Perth. As I understand it, in Oz tanks get a hydro every year, unlike our 5 year schedule.

 

[DevonDiver]

ouch!

 

[Wayward Son]

Yeah, I have 13 tanks for my family. If they had to be hydro'd annually that would hurt

 

[DevonDiver]

Tank testing on Oz must be the most lucrative and profitable job in the diving industry!

 

[Jim Lapenta]

Does not change the fact that the guy's source of info is full of crap. I have two 72's that are O2 clean and set up as doubles. Use nitrox, O2 compatible air, and helitrox in them. One is from 71 the other from 70. Sounds like they are trying to get him to buy new tanks. Shameful.

 

[JahJahwarrior]

G'day everybody.

I recently got my nitrox certificate and I've got two tanks that are currently on air. I took in my newer tank to get cleaned and converted to nitrox Tanks aren't so much "converted" as they are cleaned, and they only need to be cleaned if the shop is partial pressure blending. (3 years old, 3 hydrostatic tests). The service guy told me that since its not brand new, it might only last a few years on nitrox, then it'll have to be switched to air only. BS if I ever heard it! He said this is due to possible existing rust Any existing rust should be cleaned! becoming an issue with the higher air content. O2 content... He also said that after its been nitroxed I actually really like this word and will have to start using it! I'd have to rumble "tumble" not rumble (de-rust it) it a lot more often (possibly as much as every year in his words) than if I just left it air. BS if I ever heard it.

The guy who told you all that was either pulling your leg, trying to sell you a new tank because he thought you were an idiot, or he himself is an idiot. I've got tanks from the 70s that have been Nitroxed and are doing just fine, regardless of what that tank monkey says or thinks. You seem more intelligent than him, perhaps you should talk to the shop owner and mention how stupid their service man is? Just do it politely, I've found shop owners don't always like to be told that they have hired an idiot. Best of luck with you and your nitroxed tanks, and I'm real sorry to hear about how often they have to be hydroed!