cold temps

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I was wondering about if the weather plays a big role in welding. Being form south Louisiana we dont have to worry about that stuff down here. It doesn't get cold enough to matter. When welding thick stuff that requires multiple passes do you have to preheat. What about the thin stuff.  Do you need to take into concideration that the metal will expand when it warms up.63' Lincoln SA200 2008 miller trailblazer 302fibre-metal pipelinermiller camo BWEand all the guns and ammo a growin boy needs
Reply:Yes, weather and temperature play a big part. Most times I will take my material or job, to be welded, from outside to inside and allow it to climatize to the temperature (during the winter).John -  fabricator extraordinaire, car nut!-  bleeding Miller blue! http://www.weldfabzone.com
Reply:Most of our procedures require us to preheat to 70 degrees. I usually warm it until its just warm to the touch.
Reply:Working in the blizzard conditions of colorado required some metals to be preheated and postheated.
Reply:Most welding codes have a minimum ambient temperature below which you must preheat.  The preheat is not to prepare the metal to receive the welding heat but to prepare the metal so that it will not cool too rapidly AFTER the welding has been done.  An example of this problem is magnified when an arc track is left on the side of a pressure vessel or bridge structure.  Often this is cause by someone carelessly dragging a hot welding lead across the work.  At the location that the stray arc has touched the surface of the steel it is superheated very suddenly then the adjacent material acts as a heat sink to cool the location very rapidly.  This creates a hard and brittle spot on the metal.  This small formation of martensite will be the future location of a failure.   I have seen a brittle fracture cause by such an arc track   If you talk to any pipeline welder I am sure he will tell you tales of woe over doing repairs on an arc track.  Often it involves grinding out the defect to a set depth then repairing followed by some some sort of expensive inspection such as X-ray.   In cold weather preheat.  It does not have to be a great amount... just enough so that the area is warm to the touch.  On thick material you must preheat.
Reply:thanks for all the info fellas63' Lincoln SA200 2008 miller trailblazer 302fibre-metal pipelinermiller camo BWEand all the guns and ammo a growin boy needs
Reply:Originally Posted by lotechman  If you talk to any pipeline welder I am sure he will tell you tales of woe over doing repairs on an arc track.  Often it involves grinding out the defect to a set depth then repairing followed by some some sort of expensive inspection such as X-ray.
Reply:The pre-heat is to sweat the weld area before striking an arc. You can watch the moisture peel away from the heat. Hence the "warm to the touch" rule, if it's comfortable to the hand then the heat has removed the moisture. Naturally the amount of heat varies with the thickness of the work-piece. Post weld is to allow the weld to cool naturally so it varies with the climate and work-piece.
Reply:Originally Posted by JTMcCThere isn't a gas company in America that would allow an arc burn to be repaired, they are cut outs.JTMcC.