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I'd like to get some advice from experienced welders regarding welding sequence, i.e. what would be general rules for welding sequence in welding complex steel structures in order to reduce distortion and residual stresses. Do you weld first longitudinal or transverse welds, stiffeners, butt or fillet welds, etc? Please give me some hints from practical point of view, something that's been proved to work.
Without seeing pictures I think your question is going to be hard to answer.
A generic answer is, skip around, and back step any long welds. Good idea when fabricating anything is monitor the movement with a tape measure, and square. Don't just drop your helmet and weld away!
The Engineer should provide you with a Weld Map if it is needed. Otherwise just skip around as much as possible
If you want a book on it, read Masubuchi's "Analysis of Welded Structures".
Having done a great deal of reading on welding induced distortion, and being a welding engineer, I'll say this (assuming manual welding, everything changes when you go mechanized):
Bead shape (total nugget shape, not just the face) has a huge effect on distortion. Every welder is going to do something a little different in his technique/setting to affect that. Because of this, I'd be inclined to leave it up to the welder to decide the sequence of how he wants to weld it to meet the print. I'll agree with Cactus that if you're specified a document, follow it. However, if the document wasn't developed and proven on a full sized test mockup with a very experienced team of welders/techs/engineers, it's probably worthless. And that little hitch isn't really under the umbrella of what I'd consider to be the typical welder's concern.
When in doubt... Use JB weld.. It doesn't distort too bad... LOL
Hammer to fit, paint to match.
I did see a guy fill in the score marks on a hydraulic ram though then emery cloth it down flush and smooth... I thought he was full of crap but by dam it worked pretty good... He put new seals in and the darn thing quit leaking...
That's the only thing I have seen JB weld work on.. LOL
Some movement is inevitable and sometime unavoidable. John P. Stewart's book of flame straightening and distortion has several suggestions that work well. If heat straightening in not an option, then you will have to jig the weldment in a fixture and adjust the members to be welded in anticipation of how far you think they will move(previous experience required), so that when they are welded and cooled back to ambient, they are where you want them. Temporary braces can help, but be careful not to remove them until the weldment has cooled completely or it will spring right back. The pictures posted are so small that they aren't of much help. Do you have them in something other than the thumbnail size?
Would you normally start welding from the centre of the structure?
You asked a question that can be answered in the bible.
Read the Lincoln handbook of arc welding.
Because different things need different ideas.
As far as what Cactus said.
I worked on the Hanford nuclear power plant in Washington.
We followed the engineers and inspectors to the T!!!!!!!
It was refereed to as WHOOOPS!!!!!!!!!!!!!!!
Gee guess inspectors and engineers are not as smart as some people make them out to be.
Hope this helps.
Thank you for your time and consideration.
Try to think what each weld will do the structure. As the molten metal cools it will draw or shrink up a bit. Sometimes you can use that to help the situation. For instance if a joint or structure is not exactly square, weld first the weld that will pull the way things need to go or at least keep the joint from getting worse. Often skipping around is a good idea. Alternate opposing welds can be good. Sometimes it just does not matter.
Common sense, thinking about it, and experience; use at least two of the three and that will answer your question.
You are right ! However, If the Engineer gives you a Weld map and you adhere to it, and it still distorts beyond recognition. ITS HIS FAULT. Not the Welders. I also work on the STP Nuke in South Texas. it was a Giant Cluster F*^k. Guess who's fault it was............The Engineers. Not the Welders.
I have never EVER seen a comprehensive spec given on welding sequence for distortion prevention. Even in the "high tech" world of aerospace welding, often it is left up to the operators/welders to determine what will work best. There are so many variables to consider that I personally believe it would be an engineering miracle to even produce a very general document on how to pull it off. Lots of shops establish standards like 2" on 3" centers on a certain beam or structure, and even go farther like x amount of tacking then welders start opposite sides in a certain order etc. But those specs were developed by trial and error for the most part. Sheet metal has a whole different set of disciplines vs. structural members for instance. If in doubt hire a reputable consultant with confidence in your particular type of structure to give you a starting point to developing your defacto procedure. The whole working knowledge of weld distortion and applied heat distortion is something of a black art or voodoo science....personally I call it welding intuition. I am sure there are several engineering references on the subject but I highly doubt you will find any that will be specifically applied to your particular issues.
My little $.02
if needed sometimes tack in a brace to control distortion if allowed.
When inspecting some jobs with doubler plates welded into large columns it was quite a challenge to keep the WF flanges from pulling around too far and causing the member to be out of acceptable specs.
Using higher pre-heats, jacks to push flanges the opposite direction, then putting stiffeners between the flanges, stress relieving after welding and they still pulled around more than desired but stayed within standards. It all depends upon the weld size, how many passes, the location in relation to the rest of the structure, pre-heat, post-heat, and just plain lucky guess work. After a couple are finished you can get a pretty good handle on how to minimize the distortion. Don't know if you can ever eliminate the distortion. If you did it would be so time consuming and develop so much stress that it probably wouldn't be worth it.
Have a Great Day, Brent
NEVER HAVE I SEEN SO MANY SHODY ANSWERS TO ONE QUESTION IN MY LIFE.
A good steel fabricator can answer this one. Is there one out there?
Are you going to post a picture of said structure?_ or Do we have to guess at what it looks like and give welding sequencing advice based on our assumptions?
I'd like to hear from you: your thoughts and ideas regarding welding sequencing in general.
Enlighten us oh great one!
C'mon skaggydog, show us what you got. :-)
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