What's stich weld?
If you mean intermittent fillet weld, I know what that is. I believe you are looking for the unwelded spaces between the weld segments. The length of the unwelded space is simply the pitch minus the weld segment length. So, if you have 3-8 to the right of the fillet weld symbol, it means that the minimum weld length of each segment is 3 inches and the maximum unwelded space between the adjacent fillet weld is 5 inches. Notice I said minimum weld length and maximum unwelded space between welded segments.
There is no need to lay out the pitch (cneter to center) distance and then weld 1 1/2 inches to the left and right of centerline of the pitch.
As an example, you could have the following: given the 3-5 requirement; from the end of the joint, skip 2 1/2 inches, weld 3 1/4 inches, skip 4 inches, ............................... weld 3 1/2 inch, skip 4 1/2 inches, weld 4 inches, skip 3 inches, weld 4 inches, skip 2 inches upon reaching the opposite end of the joint. The point being that the length of each welded segment can be more than 3 inches as long as no unwelded space between adjacent welds is more than 5 inches. Any tolerance for the maximum length of the weld, location of the centerline of each weld segment, the minimum length of unwelded spacing between welds, the need to start with a weld segment at the end of the joint, etc., are workmanship issues addressed by the appropriate fabrication standard or the manufacturer's in-house quality standard.
Al
Yeah I do mean intermitten welds not stitch welds. Everyone I work with calls them stitch welds. That does help slightly. But I mean if I have a 49.5 inch of welding needed with a 1-3 then hwo would I figure the number of welds and where to start to have equal weld spacing from start to finish. I was wondering if there was a calculation instead of laying out multiple combinations of intermitten welds and finally getting a combination that has equal start and end spacing along with the correct weld sequence ex. 1-3 in 49.5 inches. Hopefully this makes sense what I am asking.
Stitch weld is a method of hand welding large diameter items, such as the penstock of a hydroelectric power plant or a column of an oil refinery. The weld is transversal to the piece, i.e., it's done on the circular perimeter.
The method was devised with the intention of prevent distortion of the piece (or at least reduce it to the minimum possible).
The method is as follows:
Two welders in two positions 180° apart apply a long tack weld (say 4 to 6 inches long) at the same time. When the weld has cooled down, they move to a position 90° degrees apart from the first one and apply a similar tack weld.
When it has cooled down, they move to a position 45° apart and apply a similar weld.
The work proceeds until the whole periphery has been welded. That's the first pass. Of course, the welders must be qualified, as well as the procedure. Subsequent passes are given in the usual way.
Back in my days of erector engineer I used to follow that method for welding oil refinery columns and large
diameter steel stacks that arrived to the job site in two or three pieces and had to be joined at field.
Giovanni S. Crisi
Sao Paulo - Brazil
That is very good information, but I still would like to know if there is a calculation for intermitten welds not stitch welds.
Is what You are asking "How do I get the same spacing at each end" or must You have the skips and the end spacings all equal? If You lay out If You want equal end spacing that can be different from the rest of the skips, start in the center with the center of a bead or a skip, and divide the remaining length by the pitch and see if the end spacing is acceptable, if not use the center of the other [if the center of the bead didn't work out, use the center of the skip. If You want ALL the skips including the end spacings equal, well that is too hard for Me to describe on the net.
I am speaking about structural steel on this but we don't actually "calculate" intermittant fillet welds (stitch welds). The weld length is a minimum length; it is OK to make the fillet longer if that suits your pitch, or "spacing", better. You could make your first and/or last fillets longer if that will suit your welding better. We like to have a weld at each end of the joint, mostly so there is no argument about it.
An example of how we layout our stitch welds - assuming 3" on 8", you need 3 inches of weld, 5 inches of no weld, 3 inches of weld...and so on. That is equivalent to laying out weld centerlines every 8 inches, then measuring 1.5" each side of each centerline, but 3-5-3-5.... is easier to do.
If you had a weld joint 27" long, everything would work out nice and evenly (3-5-3-5-3-5-3). That doesn't happen often though.
Lets say the joint is 30" long. We might layout longer welds (4.5") at each end, then use the 3-5 spacing between (4.5-5-3-5-3-5-4.5). Or you could layout some shorter spaces, (3-4-3-4-3-4-3-3-3). You can arrive at many possibilities but the key is the welds should not be shorter then specified and the spacing should not be larger.
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