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gunsmith
11-18-2004, 08:09 PM
For years I have watched this happened and never wondered why. Now I wonder. When I pre heat steel to weld, stress relieve or for any reason, I always see moisture form on the surface and then evaporate. My question is, does it form on the surface during the heating process or is leaving from within the steel molicule?

pgmrdan
11-18-2004, 08:13 PM
If you're heating with OxyAcetylene or Propane I have a guess.

A product of burning OxyAcetylene and Propane is water. I would assume that the high concentration of water vapor hitting cooler metal would cause condensation on the not yet warmed metal. Then it evaporates off as the metal warms.

Sound reasonable?

SGW
11-18-2004, 08:33 PM
That's what I've always been led to believe,too. (Condenstion of the products of combustion, i.e. water vapor.)

hollister
11-18-2004, 10:28 PM
Like water dripping out a tailpipe .

Ries
11-19-2004, 01:34 AM
The way to test this would be to preheat in an oven, rather than with a torch. I would be willing to bet that there is no moisture when you do it that way. Moisture is coming from the combustion from the torch- it just looks like its coming from the steel.

Evan
11-19-2004, 01:45 AM
Yes, of course. The combustion byproducts of a neutral flame are water and CO2.

gunsmith
11-19-2004, 08:40 PM
Of course thats the answer. Propane contains about 14% moisture. The reason I asked was because I usualy paint what I am making or repairing. It is seldom I had to heat it though. I was wondering if I should heat everything I paint to avoid having that trapping moisture in the steel molicule? I guess this means it's not necessary!