The Lincoln Manual of Arc Welding discusses this in pretty good detail. The instructions tremendously helped us by showing us to not overheat (not necessary) and to use a garden sprayer mist to cool it off. The basic idea is: let's say you have a block of steel made by your good friend on his mill and it is exactly one point o inch in all directions. If you put it in a decent vise and snug it, then heat it and let it cool, likely it will fall from the vise and then when you measure it - it won't be the same dimensions in all directions anymore. The principle of restraint and unrestrained is taught to welders....when to clamp, when to not clamp, what direction to clamp, sequence of welds etc. Similar block heated up without the vise will return to the same dimensions.
This is because the "temperature to strength curve" for steels that are typically used for equipment and buildings tends to weaken noticeably when heated and not necessarily that hot. Also this is exactly why steel frame buildings have fire protection and why our shops made of metal "so called it wont burn" quickly fall into a big heap when there is a contents fire.
Given this theory, the next trick is to figure out the shape of the heating pattern and also we definitely can suggest in getting a nice rosebud as opposed to the cutting torch (w/o lance LOL) for the heating. Gotta know your acetylene flows and very likely need to manifold the acetylene when using a decent rosebud; bigger gas cylinders have higher allowable flows. Check with your welding gas supplier.
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The job typically plods along and once you get setup to keep from being worried about the usual stuff like burning up wires or yourself, and you have your measuring tools or string or whatever, it is kind of interesting to be involved to plod along and see it all happen. Kind of reminds me like painting or mowing a lawn or troweling a concrete slab.
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If the steel is alloyed, then this procedure may need to be watched and the heating temperature absolutely limited to around 600 or 700F degrees - this can be checked with a temp stick which is like a wax crayon that melts at a certain temperature and is inexpensive (out two faves are ones at around 600 / 700 and a 350F for aluminum). Heating to red hot is not necessary - this I can tell you, which is what we did when we were experimenting without the knowledge. Structural steels with low carbon like A36 and A992 don't have enough carbon to make them respond to temperatures that would change the grain on an alloy steel or higher carbon steel.... for example, once carbon is increased like 1040/1050 or certainly a 4130 crmo with it's alloy components, then excessive temps which certainly include welding temps will affect the properties permanently and immensely. We generally figure if the steel spec allows welding, then some miscellaneous heating to less than 700F will be quite OK for us to use the flame. We have had to submit this procedure and its basis in writing [as some folks immediately prohibit flame heating] to get an overriding decision from The Authority Having Jurisdiction.
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A wedge shape is a common heat zone for wide flanges. We have cambered and uncambered many things using this. Tube steel and pipe we arent quite as competent - gotta refine the technique.
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I would imagine a combination of the heat and some restraint would make the job proceed in short order, to the point where the gathering and prep and cleanup would take longer than the heating. And I guess I should mention that sprayer concept from the Lincoln book seems to help greatly: I figure if the steel absorbs too much heat energy overall, then the differential is lessened. All "sages" we learned from did not mention the sprayer but we were told by quite a few "ya dont need to git er real hot if ya know what yer doin" and of course they didn't supply many details LOL.
Steel does have what some call memory which is from the internal stresses from the grain structure and the (hot and cold) forming process at the rolling mill; some beams obey readily but others are more stubborn...and the as delivered so called natural camber is not necessarily the hint that you can count on.
Hope I got the idea across; you will have to take a look at your job to see how this applies and if things like braces or clips could interfere with this etc.