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Up Topic Welding Industry / Welding Safety / Acetylene draw rates
- - By DaveBoyer (*****) Date 11-26-2009 05:38
The following was posted on another forum by an industrial safety guy, as the topic had come up there:

For those interested in Acetylene draw rates.
Just got an "OSHA Quicktakes" today of interest.
Mentions that the rules for Acetylene had been changed and became final. Mentions that the new rule is based on the now out of date CGA G-1 rule of 2003. Current CGA G-1 is 2009. At any rate the 1966 rule called for 1/7th of tank capacity draw rate. The 2003 rule calls for 1/10th draw for intermittant use, and 1/15th draw rate for continuous use.
Interesting.
Reference 29CFR1910.102, 1910.102(a), and 1910.253

Pretty hard to use a rosebud without exceding these draw rates. Comments?
Parent - - By Lawrence (*****) Date 11-26-2009 13:25
I wonder if it's not the typical liberal/democrat style of controling something to the point it is no longer viable in order to push the majority over to Propylene.

Really... They are doing it for our own good.

For the children.
Parent - - By Superflux (****) Date 11-26-2009 17:41 Edited 11-26-2009 17:48
"By the BOOK" to "safely" use a rosebud one must manifold multiple acetylene bottles together. And then there is the cupric acetylide issue, so you can't use copper for the manifold piping.
Parent - - By Superflux (****) Date 11-26-2009 17:45
Then there is another volume issue of using too small of supply hose for rosebuds. The 15 psi (maximum) pressure is there on any sized hose, but this is why large rosebuds are always popping like an M60 machine.
Parent - - By 803056 (*****) Date 11-30-2009 03:40
I've addressed the draw on acetylene tanks in my courses for years. It is interesting to note how few welders are aware of the issue of withdraw rates for acetylene from a given tank size.

Superflux hits the nail on the head with his comments regarding the multi-orifice torch tips back firing when connected to a tank that is undersize for the demand placed on it. The work around is to use propane or a different gas provided the flame is hot enough for the work being performed. Oxy-propane is hot enough for cutting or brazing, but it is not the best choice for torch welding. Then again, how often is that an issue when using multi-orifice tips?

This is a subject that needs to be discussed, so "Thank You" Dave for bring it up and for including the applicable the references that can be cited.

Best regards - Al 
Parent - - By Superflux (****) Date 11-30-2009 06:47 Edited 11-30-2009 07:14
803056,
"It is interesting to note how few welders are aware of the issue of withdraw rates for acetylene from a given tank size. "
In response to this. It is not only the welders, but Foremen, shop managers and their purchasing agents are also to blame for this potentialy serious safety issue.
The backfiring of rosebuds can melt a torch mixing barrel. Fortunately most places install check valves these days, so it's been quite a while since I've seen the hoses blow up (which is something that definately gets the blood flowing).
I was in a shop a couple of years back and they had just purchased 6 brand new rosebuds. I don't recall what size they were, but were of such large of orifi that the smoke would not even begin to clear when opened all the way. Not a single person could use them with out backfiring.

Since I mentioned in my previous post about cupric acetylide, though I ought to elaborate a bit. It is a very unstable and shock sensitive explosive compound that is made by the passing of actylene through copper (under certain conditions)...rare, yes but it can happen. I was touring XXXXXX solid rocket motor plant and test site and shown some impressive holes in the ground where some of these type compounds in test-tube quantities got away from them. NASA and the military have all the FUN TOYS! 

http://www2.itap.purdue.edu/MSDS/detail.cfm?MSDSID=7218

Moral of the story is...If buying your own supplies, get the small rosebud! Yes, you might think it takes longer, maybe it does, but so does relighting a torch that's always popping out. Charge by the hour!
Anyway, I've found propane weed burners to be far cheaper and efficient for most preheat applications.
Parent - By DaveBoyer (*****) Date 12-01-2009 04:55
Make that REALLY SMALL rosebud. I have a Purox 100A multi flame tip, it is only about 5/8 " in diameter with 8 pretty large holes. I looked it up and found it is supposed to be used at 100 CFH. That would take (3) 12" diameter cylinders for intirmitent use by the new rules.

Even the Harris #2 rosebud with (8) .040" holes takes from 30-50 CFH. I have run this one for small jobs from a 75 CuFt cylinder without problems, but by these rules I should be using one of those 12" diameter cylinder as a minimum. My largest ones are 145 CuFt and I don't have a way or plan to manifold them.

I am looking into propane or propalene for cutting & heating fuel.
Parent - By magodley (**) Date 01-11-2010 19:23
I believe that flow rate is considered "advisory" and not mandatory. Have any mfg. started putting the 1/10th rate in thier owner's manuals?
Up Topic Welding Industry / Welding Safety / Acetylene draw rates

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