Titanium myths

[canuckton]

I've seen a lot of posts lately that say that Titanium Regulators shouldn't be used with enriched air.

I'm fairly sure that isn't true.

First of all, yes, Titanium is a Class 2, Group E combustible metal. What this means is that in dust concentrations, in air or enriched environments, a particle content of >8% is considered dangerously combustible. Fair enough. But aluminum, marine brass, stainless steel and copper are also Class 2 Group E metals, and all are used in regulators, and even oxygen service equipment............... BTW: flour, grain dust, polyurethane dust, and nylon are also Class 2 materials.

Second, the classification is for pure titanium, not the alloys used in most manufacturing. I believe that Scubapro uses 6.5V 3Al spec titanium...which is inherently stronger and has a higher specific heat capacity than pure titanium. I'm not sure if that is relevant to dust-explosions, though.

Third, titanium fittings and valves are used in many pure O2 service facilities. Because Titanium does not get as brittle as some metals in cold applications, and is stronger for fittings than brass, it is used in Liquid O2 applications. it is also used in aviation O2 applications. Even Ti needle and gate valves are used in supersonic oxygen environments with little fear of fire.

This is because the sparking index of Titanium is lower than that of marine brass, aluminum, stainless steel, and invar. Inconel sparks even less easily, thus making it the preference in high-volume O2 production. Copper is also hard to spark.

I find it hard to believe that a titanium orifice (really, the part in question) would reach sufficient temperature to begin any type of oxygen fire in the environment provided by a first stage regulator. Certainly not in a Scubapro, where the piston orifice is *rounded* to begin with, thus depriving the regulator of a thin, easily heated edge for friction heating. Furthermore, the very design of a Flow-through piston regulator nullifies the danger of friction sparking.

It is my contention that titanium regulators are perfectly ok with enriched air service, provided they are oxygen cleaned and oxygen ready.

C

 

[roakey]

Originally posted by canuckton
I find it hard to believe that a titanium orifice (really, the part in question) would reach sufficient temperature to begin any type of oxygen fire in the environment provided by a first stage regulator. Certainly not in a Scubapro, where the piston orifice is *rounded* to begin with, thus depriving the regulator of a thin, easily heated edge for friction heating. Furthermore, the very design of a Flow-through piston regulator nullifies the danger of friction sparking.

Friction? What does frictions have to do with it? You've got the basic cause of combustion all wrong.

Look up the word "adiabatic."

Roak

 

[jonnythan]

Adiabatic refers to a process at a constant temperature, or amount of heat.

What does it have to do with this? Can titanium dust combust at room temperature?

What's different about titanium than the other metals listed that makes it dangerous for oxygen service?

(I just bumped into this discussion, I'm just playing devil's advocate to feed my curiosity )

 

[Rick Murchison]

Let's not get off track here - whether the heat of combustion is generated by friction or adiabatic heating from sudden pressure increases or both or neither isn't the question. The real question is whether titanium in regulator first stages is more risky than brass or steel - and from the original post the contention is that it is not. From personal experience I know that steel will burn readily under the right conditions, even in air. So will titanium. Never seen brass do it.
I for one do not know for sure - but I'd like to. Any real metalurgists out there?
Rick

 

[rcohn]

I did a little research online a couple of years ago http://www.scubadiving.com/talk/read.php?f=1&i=142825&t=142346 that shows Ti can easily ignite in a high pressure O2 environment. Remember that in a regulator we are dealing with moving parts, which could scrape off a protective oxidized coating exposing bare Ti or create fine dust particles. Ignition of any trace contaminates could trigger a serious Ti fire. Personally, I would not be inclined to experiment with a Ti regulator and high percent O2 mixes. I believe the manufacturers now state that the regulators should not be used with high percent O2 mixes. Anyone know what the manufacturers warning states?

Also, why would anyone want to use an expensive Ti regulator on a deco stage bottle? The only justification I can imagine for a Ti regulator is international travel to remote destinations where weight savings are critical.

Ralph

 

[Spectre]

Originally posted by rcohn
Anyone know what the manufacturers warning states?

Mares
Titanium is incompatible with oxygen-rich environments, and, therefore the Ti-Planet regulator should not be used with Nitrox breathing mixes.

Atomic
NITROX (EAN USE)
IMPORTANT NOTICE -READ BEFORE YOU USE THIS REGULATOR

This regulator was assembled, cleaned and tested with components compatible for enriched air NITROX (EAN) to a maximum 40% oxygen concentration at a maxium pressure of 3500 psi. It does not require additional cleaning or servicing.
At time of purchase, you must decide if this regulator is to be used with EAN or standard compressed air. If you desire to use EAN, this product should be dedicated for use with EAN only and identified as such. Do not switch between EAN and standard compressed air, as compressed air may contain traces of hydrocarbons which could contaminate your regulator system eith potentially flammable residues incompatible with EAN. If you use or test this regulator with compressed air, it must be re-cleaned before EAN use.

WARNING
DO NOT UNDER ANY CIRCUMSTANCES USE THIS REGULATOR WITH PURE OXYGEN OR ANY GAS MIXTURE EXCEEDING 40% OXYGEN. FAILURE TO COMPLY WITH THE ABOVE WARNINGS COULD CAUSE SERIOUS PERSONAL INJURY OR DEATH FROM FIRE OR EXPLOSION.


Zeagle

What about titanium regulators- are you going to make one?

We've looked at titanium quite a bit recently. On the surface it would seem to be an excellent material for regulator parts, as it is quite non corrosive and light in weight. It is, however expensive and difficult to machine. Some serious concerns have been raised recently in the engineering community regarding the suitability of titanium (and aluminum alloys as well) for use in high pressure applications, particularly with enriched air or nitrox. Engineers associated with the NASA White Sands Testing Facility have suggested that under some circumstances, particularly if there are small particles of metal in the air supply, there is risk of ignition and burning of the metal in titanium high pressure systems. No material is perfect, but copper alloys, such as brass and bronze, have excellent resistance to ignition in a pressurized environment. We are continuing to look at titanium, but until questions concerning its suitability are resolved we will continue to make our regulator bodies from proven brass alloys. If you are interested in this you can check the ASTM web site www.astm.org and search for committee G04 on sensitivity of materials in Oxygen enriched atmospheres.


There are a number that state they are O2 cleaned to 40%, but none that say they are ok for higher O2 mixes.

 

[jetblast00]

the fear isn't that the titanium will catch on fire and light the O2, rather it's the other way around... adiabatic heating, with regards to this discussion, has to do with the gas (air, EAN, O2, etc...) becomming compressed and having to make sharp bends as it does so (ie, going through the valve when filling a tank). This causes the temp of the gas to rise. basic physics...

but, if there are hydrocarbons (the big worry) or other contaminants present, the heat generated may be enough to ignite them. These little ignited hydrocarbons act as kindling that in turn ignites the O2 if the O2 concentration is high enough (through by the industry to be high enough if over 40%... that's why you see that number so often).

Accually, the O2 doesn't ignite... anything else present will rapidly oxidize in the presence of the O2 and give off considerable amounts of heat in the process (ie, burn). basic chemistry...

If another material will oxidize (burn) or not is determained by its flashpoint, or temperature at which it will burn. Titanium, compared to other metals, has a VERY low flashpoint . I don't have the numbers in front of me right now though, sorry... But it's much much less than brass.

This is the reason that Titanium isn't recomended in high ppO2 environments.

 

[padiscubapro]

jetblast00 once bubbled...
the fear isn't that the titanium will catch on fire and light the O2, rather it's the other way around... adiabatic heating, with regards to this discussion, has to do with the gas (air, EAN, O2, etc...) becomming compressed and having to make sharp bends as it does so (ie, going through the valve when filling a tank). This causes the temp of the gas to rise. basic physics...

but, if there are hydrocarbons (the big worry) or other contaminants present, the heat generated may be enough to ignite them. These little ignited hydrocarbons act as kindling that in turn ignites the O2 if the O2 concentration is high enough (through by the industry to be high enough if over 40%... that's why you see that number so often).

Accually, the O2 doesn't ignite... anything else present will rapidly oxidize in the presence of the O2 and give off considerable amounts of heat in the process (ie, burn). basic chemistry...

If another material will oxidize (burn) or not is determained by its flashpoint, or temperature at which it will burn. Titanium, compared to other metals, has a VERY low flashpoint . I don't have the numbers in front of me right now though, sorry... But it's much much less than brass.

This is the reason that Titanium isn't recomended in high ppO2 environments.

I dont have the numbers handy but there was a test run by nasa testing various metals, by inducing a spark in a 100% o2 on a ver thin piece of metal at various pressures, the titanium ignited at pressures not much above normal ambient pressure, brass was well over 100 times higher with stainless below the brass and copper at the top.. a metal that performed very well and is very strong and corrosion resistant is MONEL, Atomic now makes a Monel reg!


There has been 1 documented ignition of a titanium reg in california, I think it was an atomic reg but I'm not sure.. The reg was used several times at 80% and when it iginited it had just over 70%

 

[scubatexastony]

Just a misconseption so many have. But add it to any material at it's flash point and you a really nice fire.

jm2cw

tony

 

[CincyBengalsFan]

Just curious about a few things. They made the SR-71 out of Titanium and the space shuttle. I'm sure they use O2 all over both these machines. How can they do it but the Scuba industry can not? Also, How many flashfires, etc. etc. have been documented in standard brass or any other metal regs. or valves?