By ssbn727
Date 02-20-2010 00:08
Edited 02-20-2010 00:11
BWWWWAAAAAHHHHHHHHAAHHHAAHHAAHHAAHHAAHH!!!!!!!!!! :) :) :) :) :)
Al! You definitely have a
propensity (Not in A 3.0 either ;) ) to make me at the very least, laugh as hard as I possibly can with some of your comments and observations, especially so much so in the past few days (Including the pic with the rebar bending which was priceless! ;) ) that I am starting to feel much better today from my own self-imposed down in the dumps like attitude I've been experiencing lately, and this is mainly because of the untimely death of one my very best childhood friends to lung cancer which is brutal to watch & listen someone you know go through it, especially someone whom you care so much about...
You have managed to cheer me up without even trying to do so, and I am grateful for that Al!!! :) :) :) Thank You my friend!!! ;) Do you you think he's talking about an intermittent fillet weld of some sort??? ;)
Respectfully,
Henry
Al,
suppose an oil refinery tower that arrives to the job site split into two pieces due to transportation limitations. The tower is 150 feet tall and 10 feet diameter. The two pieces could be joined and welded on the ground, but in this case my explanation on what "stitch welding" consist of would be more complicated. So, let's assume that due to lifting equipment limitations the tower has to be erected in two steps: first, erect the 80 feet tall lower piece, and afterwards the 70 feet tall upper piece.
Let's suppose that the two pieces have already been erected, their plumbness checked, the clearance between welding ends is OK (buttering has been done where necessary) and everything is ready to start welding. In my personal experience, welding at 80 feet heigth is better carried out using the good old coverd (or stick) electrode method than MIG, but this isn't that important for what I'm going to explain.
OK, welding begins. The plate thickness is 1/2 inch so the welding ends have a V shape. Two welders, one at the 12 o'clock position and the other one at the 6 o'clock position WORKING AT THE SAME TIME, apply a weld, say, one foot long. After they've cooled down, the welders move to the 3 o'clock and the 9 o'clock position, and working at the same time apply two welds one foot long. After they've cooled down, the welders move again, one at the 1:30 and the other one to the 7:30 position and again, they apply a weld one foot long, working at the same time. Now they move to the 4:30 and 10:30 positions and etc. etc. etc.
This job goes on until the first pass is completed. As welding was in progress, the tower plumbness was continuosly checked and found OK.
This welding technique, or method, or procedure, is called "stich welding". Why was it used? To prevent the two pieces of the tower to go off plumbness and straightness. Where did I learn the expression from? From an old Marmaduke Surfaceblow story that appeared on POWER magazine some 40 years ago. Marmaduke used the stitch welding technique to weld a 140 inches diameter flange to the penstock of a hydraulic power plant. And who's Marmaduke Surfaceblow? He's the second greatest engineer human kind has ever produced, second only to Leonardo da Vinci. So, if he called that method "stitch welding", IT IS stitch welding, no matter what AWS and IIW may say.
Actually, Marmaduke Surfaceblow never existed, he was a fictional character created by Stephen Michael Elonka (whom I had the honor to meet back in 1977), whose stories were published on POWER magazine until 1983, when he passed away. Marmaduke was a fictional character but his stories were not.
They were actual puzzling and intrincate engineering problems that were solved in an incredible simple manner. The stories were based on real case histories that Steve received from readers all around the world. I myself have contributed to three Marmaduke stories (a demineralized water whose silica content was too high, a natural gas compressing station that was too noisy and a stainless steel weld that insisted in showing cracks at X ray examination).
I consider those three Marmaduke Surfaceblow stories as my best contributions to the engineering profession, so proud I'm of them.
Giovanni S. Crisi
PS. By the way, the oil refinery tower I was speaking of, is not fictional. That's how we welded the crude oil distillation tower of the Lujan de Cuyo refinery in Argentina.
Hello Giovanni, not to detract from the meaning or description that you have described, I have heard that method described as "back-step welding". To me, it follows the same logic used when torqueing heads on an engine, however, in this case, it allows for an even and consistent method for dealing with weld shrinkage and stresses. Enjoyed your story immensely and definitely followed it's intent. Best regards, Allan
Allan,
No, the method I described, or at least tried to describe (English is not my mother language), is not the backstep welding.
I've got a drawing from Lincoln that shows clearly what backstep welding is and would like to attach it to a post, but I don't know how it is done.
If you explain it to me, I'll attach the drawing and you'll see.
Giovanni S. Crisi