Soldering of copper tubes for medical gases transportation

[SamuelMoura]

Recently i've been assigned to inspect a pipeline of medical gases in a cirurgy clinic. The medical gases involved was N2O and O2. The operation pressure of the pipeline will be alway below 7 kgf/cm2 (100 psi). Researching the correspondent technical data and norms, i've found it is recomended the so called "strong bending", "strong soldering" or "silver soldering" - wich is made with a temperature above 450°C (850°F), instead of the "weak soldering", "weak bending" or "tin soldering". My question is: what would be the effect of using this last one type of soldering?

 

[MiketheEngineer]

"Tin" probably has some lead in it and is generally disliked where humans are involved. Also, lead allows for lower melting temperatures.

Silver solder is more expensive, takes much more heat, free of bad things and much stronger.

 

[unclesyd]

I jsut recently watched a Cu piping system being installed in a in a hospital expansion where they use SILFos. The contractor used the same mechanics to solder the pipng for the HVAC and the medial gas lines. I didn't ask but I would assume that it requires a little more skill to use.

http://www.silfos.com/products/catalog/Sil-Fos-orderby0-p-1-c-55.html

 

[ScottyUK]

There are plety lead-free solders available for both the electronics industry and for potable water system plumbing, so you should be able to find something chemically acceptable. I agree that silver solder is the way to go if you need strength - watch out for cadmium-bearing types though because they'll raise similar concerns as lead-bearing types. Some info here:

http://www.hse.gov.uk/pubns/eis31.pdf

Whatever you're making, make sure you can either remove the flux or ensure it is compatible with your process gases. Some of the soft-solder fluxes are water-soluble but are pretty aggressive if left behind. Hard solder (silver solder) fluxes may require pickling and/or mechanical removal.



----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[littletoes]

You are talking about Medical Gas piping!

The fluxes used for "Tin-Soldering" can and will kill if inhaled, hence the large build up of Medical Gas Code, from the NFPA code.

Most required silver-solder must have a melting point above 1000* F, and usually a silver content above 15%. This of course runs the cost up, but the higher silver content ensures a better flow rate, less failure, and a cleaner joint.

There are also several tests that must be performed before said piping can be turned over and certified for use.

The "owner" of the building is foremost responsible for end results by said code.