Oxygen compatibility, materials and explosions

[KevinNM]

Doesn’t 40% or less nitrox reduce the worry about the O2 issues?

40% behaves more like the way people expect air to work. However things will burn in 40% that will not burn in air. For example, firefighter bunker gear made of Nomex. Nomex will ignite and burn merrily in 40% (iirc, at 25% or so too). But 40% is much less dangerous in general.

Legally the feds want businesses to treat 23% like 100%, but it isn’t.

 

[broncobowsher]

Dunno what kind of compressor you’re running, but most diester and triester oils have a flashpoint of 800f or so. I haven’t come across many that run much below 500f or so, on the 4th stage head.

You are confused about tempertures. Yes, the head temp might get up to 500° (which I consider scorching hot but I have nearly hit that with a single stage shop compressor in the past). That is just the head temp, not the gas temp. That is all over the place. Every compression cycle it spikes. Every intake cycle it drops. So to have a 500° head you need spike temps well above that.

Look at a diesel engine. 17:1 compression ratio. A compression test will produce ~400 PSI spikes. And this engine, cold, will generate spikes in temperature enough to light diesel fuel. That is cold. Your head temps are hundreds of degrees hotter than what a fully warmed up diesel engine will see. Even 800° isn't that much when your precompression temps are only a few hundred degrees lower.

I know some compressors have an overtemp warning/shut down system. Anyone know what the temp typically is? I have heard of old IR compressors running so hot the head could be seen glowing if the lights in the room were turned off.

Pure oxygen doesn't scare me. It is the compression ignition potential that I respect.

 

[Wookie]

I don’t understand your point. When I use an IR gun, the head temp reads 500f on a 5406 mako in an ambient temp of 110f. With chem lube 751 and worn rings it was enough to ignite while pumping 36%.

The lesson learned was to replace the piston and liner at half the recommended service interval and switch to an 800f flashpoint oil, which led to its own problems.

 

[Wookie]

And, the hottest exhaust temps I see on my MAN diesels are about 850f, far hotter than an aluminum head air compressor will take. But the point is, Diesel engines are designed for combustion in the jug. Air compressors are decidedly not.

 

[TrimixToo]

I don’t understand your point. When I use an IR gun, the head temp reads 500f on a 5406 mako in an ambient temp of 110f. With chem lube 751 and worn rings it was enough to ignite while pumping 36%.

The lesson learned was to replace the piston and liner at half the recommended service interval and switch to an 800f flashpoint oil, which led to its own problems.

I think what he was trying to explain is that the head temperature you read with your handy IR thermometer (or thermocouple, for those of you who have temperature monitoring) is something close to the the *average* gas temperature. During some parts of the cycle, the gas being compressed is markedly cooler; during other parts of the cycle, similarly warmer.

 

[rabe]

I've spent the whole weekend diving, and now I have to catch up with all the replies...

 

[DogDiver]

I have survived 2 oxygen tank (AL30) deco bottles explosions. There was a fatality in north Florida where the employee was killed, and another fire 3 years ago where the high pressure hose let loose and caught fire. These were O2 cleaned deco bottles. Bad things can just happen for no reason.

 

[rhwestfall]

Underwater? :O

Yes. Was doing deco. Cooked his esophagus/ lungs. Didn't live...

 

[Marie13]

Yes. Was doing deco. Cooked his esophagus/ lungs. Didn't live...

Dang.

 

[broncobowsher]

I think what he was trying to explain is that the head temperature you read with your handy IR thermometer (or thermocouple, for those of you who have temperature monitoring) is something close to the the *average* gas temperature. During some parts of the cycle, the gas being compressed is markedly cooler; during other parts of the cycle, similarly warmer.

Correct. The measured head temp is NOT peak temp. The compressed gas is hotter then the head temp. The peak of the compression stroke is the peak heat, the rest it is cooler. So how hot is the gas if only 10-50% of the time it is heating the head and the rest of the time it is cooling?

Average means some of the data is below that number and some is above. Lets make some very rough numbers 4th stage inlet air temp, call it 200°. It's been through 3 prior stages, and some interstage cooling. I remember that interstage coolers are still too hot to touch while running. But I will consider that a reasonable guess. Your head temp is 500°. That is a 300° rise above inlet temp. Since there is additional cooling from simple radiation and conductive cooling to the rest of the compressor the average is probably even higher, but will ignor that. So the average is 500° the low side of that average is 200°. That puts the high side at 800° in order to get that 500° average. (the average of 200 and 800 is 500). Yes, it is very crude math. But simple enough to follow (I hope).