Steel vs. Aluminum (part 1)

This week's tip has to do with tanks. As the title says Steel vs. Aluminum. We've all heard divers carry on about what is better steel tanks or aluminum. The argument can go on for hours even days.

What do we think? Well let's not talk about what we like let's just simply present the facts and you can decide for yourself. So without any further adieu...

Tank Weight:

For starters let's compare two tanks of equal size. Both tanks will be brand new 80 cubic foot tanks with a working pressure of 3000 psi. The argument is that steel is always heavier. The truth is steel is a stronger metal then aluminum so in order to hold 3000 psi we need to use more aluminum then we do steel to keep the strength of the cylinder. What does that mean? Well when you carry your tanks down to the ocean or over to the boat a steel 80 is going to weigh less then an aluminum 80.

Advantage: Steel

Corrosion:

Nobody wants to breathe bad air right? We agree so lets talk about the corroding of the two tanks. Any moisture that gets in either of these tanks can do serious damage. When moisture is introduced into an aluminum tank aluminum oxide is created. This is very dangerous to breath and any tank with even a small amount of aluminum oxide in it is condemned immediately. When moisture is introduced into a steel tank the result is ferrous oxide (commonly known as rust). Again not great to breath but not as bad as aluminum oxide. Rust particles no mater how small they are cannot get to the lung level. Aluminum oxide on the other had can easily penetrate down into the lungs. When a tank comes in for it's annual visual inspection the tank is opened and checked for impurities. If rust is found in the tank we have a few options...first we can wire whip the tank and clean it out using air to remove all the rust particles. If that does not work we can tumble the tank using porcelain chips and remove all the rust. Tumbling can take anywhere from 3 to 48 hours depending on how bad the tank is. Why can't we do these things to aluminum tanks? The reason is that the metal is weak and wire whipping it or tumbling it will dent and ding the metal and significantly weaken the tank. It's not uncommon to see steel tanks that are 30 years old because of this reason.

Advantage: Steel

Working Pressure:

As stated above these are 2 brand new 80 cubic foot tanks that have a working pressure of 3000 psi. Remember back in the day when you took Open Water Scuba and they taught you all about the tanks and the markings on the neck? Remember the hydro date? It's a number that looks like "10 02". That date says the tank was inspected in October of 2002 and is good for 5 years from that date. That's how we can tell your tank is strong enough to handle the working pressure when we fill it. On a new steel tank you will see the same number "10 02+". Wait a second what is that plus for? The "+" means we can fill that tank to 10% above its rated working pressure. So we can fill our steel tank to 3000 + 10% = 3000 + 300 or 3300 psi. Why can't you do that to aluminum? Again the weakness of the metal is the issue. Overfilling an aluminum tank will weaken the cylinder. In fact, that's what they do as a hydrostatic test. They fill the tank to 5/3 its working pressure and see if the tank expands but does not contract. So I can overfill my steel tank forever? Not exactly. Each time your tank goes in for hydro they will stamp a new date on it. If the tank can still be overfilled that date will have a "+" next to it.

Advantage: Steel

Cost:

The difference in cost of these two tanks is vast. One is twice the price of the other. A steel 80 will run you somewhere in the ballpark of 300 to 330 dollars while an Aluminum 80 is in the ballpark of 120 to 150 dollars. The aluminum tanks are designed to have a shorter lifespan than the steel tanks.

Advantage: Aluminum

Buoyancy and Water Weight:

Well we talked about how heavy your tanks are when you're lugging them down to the boat, but how heavy are they in the water? Stop back next week and we'll tell you a lot more about the differences between steel and aluminum tanks.

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