Tuesday, March 03, 2015

Preheat in Welding and Similar Situations

I have written about this earlier but when I was in the engineering school, taking my first, I would call them technical courses, I was a bit terrified of the possible mistake I could do and mess up the whole production line mid-through the course. This fear later on went away. I don’t know how but maybe I didn't pay enough attention to the courses and failed a few! I really don’t remember and it doesn't matter now.
 Then starting work in the industry, I soon realized that most of the nonsense we studies in those years were only theory. No one, literally no one ever or barely utilizes them in the work and they were only good to pass hours in the classroom, pass the examinations and get the damn bachelor’s degree. Of course high-tech industry uses them but how many companies we have around the world and how many educated people we have in those companies who are really in to that.
 With that in mind I was reading the newly issued CSA Standard W59-13, that part about preheating of weld. This section has a big table (called Table 5.3) which tells you for what welding process and what thickness of base metal, what the pre-heat temperature should be.
For instance if you have between 20 and 40 mm of thickness using SMAW process and your consumables of Hydrogen Designation of less than H4, you need to apply 50° C heat prior to commence welding. This temperature should remain the same during the course welding, when the base metal is below the temperature listed the surface of the parts on which the weld metal is being deposited are at or above the minimum stated temperature for distance equal to the thickness of the thickness of the part being welded but not less than 75 mm, both laterally and in advance of welding.
 This more sounds like a stupid joke to me that if I told, no one would laugh at it. First of all who is going to check that temperature? The welder wouldn't do it because all he or rarely she wants to do is to finish the damn weld and get to his favorite bar for his beer. Welding inspector for sure wouldn’t do it. Welding inspectors are mostly a damn fool who wait until the welding is finished and then start their inspection! Unlike what is said that quality control should be proactive, not reactive, the majority of quality control actions are reactive in the industry. How about the welding supervisor? He is probably busy somewhere in a filthy office by the phone and even if he was not and really wanted to check the temperature, how would he do it? Does he have a thermometer on him?! Never!
 Even theoretically an inspection package available in the market for the inspectors does not contain a thermometer of any kind. So this is another reason as why most of the things we read in the standards, textbooks and specifications are all silly nonsense! I have a few photos of popular weld inspection sets for welding. None of them includes a thermometer of any kind. I guess I made my point. 
(Photo: A modern Welding Inspection Kit comprises of different tools but no thermometer of any kind. I have a gauge given to me by The Cheapskate, never used it so far unless for practice)

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