Shielding Gas Dew Point

Date 06-08-2012 11:26

While researching dew point meters for checking our shielding gases, a thought came to mind. Many times in the past when I would bring out the dew point meter or have a supplier bring one in, I remember some of the senior welders talk about how they always seen dry ice used to check the gases when they suspected purity problems. I never heard any details so I began searching the net but haven’t had any luck. Anyone else heard of this? I am beginning to think it may be similar to miracle oil or sky hooks.
Regards
Scott

By fschweighardt (***)

Date 06-08-2012 13:47

if you cool the gas down to dry ice temps, you may be able to condense any moisture. however, DI is -109 deg F. The theory is to flow the gas through a tube that is externally cooled with the ice, and then you inspect the tube. I have heard of using Pyrex tubing and then you can look inside the tube to see if anything condensed. Not a very precise method, as you have to keep atmosphere out of the sample area, and if you go long enough, -109 could show a condensing dewpoint of ~.7PPM. Then there is the difficulty of determining what temp the gas was when you started to see moisture, etc. etc.

We use a Meeco Waterboy II for our on-site analysis, and it seems pretty good. Pricey though ~$6K 8 years ago

By G.S.Crisi (****)

Date 06-12-2012 19:15

fsch is right. Dry ice didn' measure dew point, it just gave a rough idea on whether the shielding gas contained any moisture or not. The method was used in old times (that's why the old welders remember it and the young ones don't even know that it existed) when dew point meters were not invented still or they were complicated laboratory instruments too expensive to be used on job sites or welding shops.
Giovanni S. Crisi
Sao Paulo - Brazil