Measuring total use of a welding process gas

[Willnhorse]

Please redirect if I am in the wrong forum,
I am starting a project that I have been asked to accurately determine how much process gas (Argon/CO2 blend) we use at any given time. The scope is to be able to walk up to the meter and read a display reflecting the total usage since last read. Could you take a minute and suggest a brand name to consider or your experience in dealing with similar applications. In the short amount of time I have spent, I've learned it's not as simple as I thought and there's a great deal of things to consider.

Thank you

 

[MiketheEngineer]

Pick up that 2 ton phone and call your vendor. IF anyone knows - they should!!

 

[TD2K]

Talk also to Emerson process controls. You'll want to be able to give them an idea of the flow rates involved, pressures and accuracy you need. Is this something you want on a cylinder of gas or is this for a fab shop?

 

[TD2K]

They'll also need to have an idea of the turndown, minimum flow you want to measure and maximum flow. Hint, zero will not be an acceptable minimum.

 

[BigInch]

I'm not seeing this as a flowrate measurement process... yet. the way he said that I would guess that they want to know how much they've consumed during a certain period of time, not the instantaneous flowrate.

I'd do something like that with mass readings at T₂-T₁, as in weigh the tank, but that might get a little troublesome if the Ar is in a huge pressure tank on site, or something, so I suggest you read the pressure and temperature and convert that to a mass, or to the Standard Gas Volume contained in the tank each time you make a reading. Then subtract the latest reading from the previous to find out how much has been used. Should be pretty easy to do with a little knowledge of Ar compressibility factors. Some more details about the way this gas is stored would help.

What would you be doing, if you knew that you could not fail?

 

[BigInch]

I mean, if this was something simple like a small fab shop that had welding gas delivered in common gas pressure cylinders, I'm sure he could have figured out some way to do that, right.

What would you be doing, if you knew that you could not fail?

 

[MiketheEngineer]

If you are using tanks as delivered - this is pretty straight forward - just keep track of your change outs??

 

[berkshire]

Willnhorse,
You do not say what your application is.
Are your tanks on individual machines, or do you have a manifold system supplying the whole shop?
This could be as simple as a flowmeter in the supply line, or as Mike says you will need to keep track of your tanks.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[Willnhorse]

Sorry for the delayed response been busy on another project. This is for an entire plant and it is bulk supplied from a vertical unit outside of our facility. We bring the gas in to a blender where we blend our other process gases for the welding operation. The bulk of the blend is Argon that why I chose to go after it rather than trying to split hairs on the others involved.

 

[zdas04]

Small volume flow rates are especially difficult to measure with any precision. Doing as BigInch suggests and simply record (either in an RTU or on an old fashioned piece of paper) pressure and temperature on each tank and it is a simple calc to convert that to quantity used. If you do it in an RTU, you can record hourly "rate" by having the RTU add in any additions to the start volume and subtract this hour's volume from last hour's volume.

Doing this as a stepwise batch calc is trivial. Capturing flow rates after the gas has left the tank is borderline impossible.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.