Which brand of steel cylinder / tank should I buy?

[Mario S Caner]

Rainreg,
I was just talking to Don via ICQ and we got into a discussion about Steel Cylinders. It turns out that many of his friends prefer Pressed Steel's cylinders while many of mine prefer OMS's cylinders. What does the NAVY say about steel cylinders, if not what are your personal views on the subject?

Thanks,
Mario

 

[Warhammer]

Glad you asked that question...

I'm pondering the 2 myself.

Just what exactly is Chrome Moly?

Painted?

 

[Iguana Don]

Mario,

I thought we had run out,but I see you found another one on the shelf, can of worms.

Warhammer,

Chrome Moly refers to the kind of steel the take is made out of. The rest we'll have to wait until the Guru comes online.

 

[Warhammer]

Ok, and the Press Steel are galvanized correct?

I heard mixed reviews on OMS's valves.

What's the deal there?

 

[Iguana Don]

Warhammer,

Not exactly, galvanized is what both tanks are coated with to stop corrosion. An electrolital process where the tank is put in a vat of some chemical that is negative charged and a wire to the tank that makes it positive charge, the an electrical current is shot through the chemical and the chemical sticks to the tank.

Or something like that.

Don

 

[Dee]

We currently own 3 Pressed Steel HP tanks...120cf, 100cf and 65cf. I want a HP80 and I've been told that PSI lost it's distributor (AquaLung?) in the States. Can't find out whether that's true ot not, but several shops have told me PSI tanks are on backorder.

So if I can't find PSI tanks I'll have to go with another brand and I don't know which.

I'll be watching this thread.

 

[Mario S Caner]

Dee,

This whole thing started when I told Ma(Don)na that I had a PS cylinder but wanted to pick up some OMS LP cylinders and double them up using an OMS manifold.

We have plenty of shops in this area that continue to get stocked up with PS-HP80's. They even started getting in the 65's again, which they weren't supposedly going to make anymore.

I'm still waiting on the DOT and the CTC to approve composite cylinder use by scuba divers. Tell me that won't be the best!

Oh by the way us City Folk don't get all the barnyard stuff... LOL!


Mario

 

[Dee]

You just have to remember 3 things.

1. Wait till the herd leaves the pond before you get in.

2. Dive on the opposite side of the pond from the herd.

3. Be careful of 'floaties' and water mocassins.

 

[Kevin]

Don's description of galvanising was quite accurate. The coating does stick to the cylinder better than paint because of the electrical charge which is used and therefore gives a longer lasting corrosion protection.

Chrome and molybdenum are two elements which are added to the steel at the production stage and they give the steel more inherent corrosion protection so that should the galvanised coating be scratched off the steel will still have a resistance to rust.

The amount of chromium which is added can vary between 0 and 18%. The more added the better the resistance to rust.

18% will give you the best quality stainless steel and is used in applications such as hospital instruments.

Hope this answers the question.

 

[rcohn]

I just thought I 'd point out that the zinc in the coating acts as a sacrificial anode protecting the steel better than paint does. What this means is that the steel, zinc, and water form a battery.

The steel is the cathode where the hydrogen ions are reduced and the zinc is the anode where zinc is oxidized, slowly corroding away. As long as sufficient zinc remains the steel will be protected.

Paints merely cover up the steel preventing the water from contacting it and causing corrosion. A scratch in the paint may lead to rapid corrosion in the underlying steel, particularly if it is in contact with a metal that is more electropositive such as brass (a Cu-Zn alloy).

Here the steel would form the anode and the brass the cathode leading to rapid corrosion at the small surface area of the scratch.

In this case a bare cylinder, with its large surface area, would corrode more slowly. Note the practice of painting a zinc coated cylinder is questionable.

You reduce the effectiveness of the sacrificial anode by covering it up and preventing it from properly doing its job.


Ralph