Distortion when welding Slip On Flanges
Distortion when welding Slip On Flanges
(OP)
Hi Guys,
I was wondering what novel ways you guys use to reduce angular weld distortion from welding a slip on flange. I have attached a pretty crappy sketch but hopefully it will give you a rough idea of what I am talking about.
The problem is mainly when welding Stainless Steel flanges that have a reasonably thick pipe.
http://files.engineering.com/getfile.aspx?folder=f...
Thanks
I was wondering what novel ways you guys use to reduce angular weld distortion from welding a slip on flange. I have attached a pretty crappy sketch but hopefully it will give you a rough idea of what I am talking about.
The problem is mainly when welding Stainless Steel flanges that have a reasonably thick pipe.
http://files.engineering.com/getfile.aspx?folder=f...
Thanks





RE: Distortion when welding Slip On Flanges
Best regards - Al
RE: Distortion when welding Slip On Flanges
Secondly: why are you using slip-on flanges with heavy wall pipe? If the heavy wall is required for pressure/temperature resistance, you probably do really want a weld neck.
The exterior fillet weld will just plain NOT distort the flange in any meaningful way. If the wall thickness of the pipe requires a massive interior fillet, as long as you do not attempt to do it in a single pass and allow the correct interpass temperatures, you should be fine.
RE: Distortion when welding Slip On Flanges
What you can do is weld the inside first and then before welding the outside bolt the flange to another flange.
Leave fully tightened until after cooling and then see if it has made any difference.
Cheers,
Shane
RE: Distortion when welding Slip On Flanges
RE: Distortion when welding Slip On Flanges
As per the sketch provided, welding the inside diameter first causes the weld to act as a fulcrum point. The second weld contracts once it is completed and causes the flange to rotate on the initial weld (the fulcrum point), thus the outer edge of the flange is "rotated" toward the fillet deposited against the hub.
The proposed sequence uses the strength of the flange to resist rotation around the initial fillet weld deposited against the hub. The second weld the fillet on the ID is going to contract as it cools and pull "inward". However, the mass of the flange will resist. The weak link is the relatively thin pipe wall. The pipe wall should be distorted rather than the flange. While there will be some distortion, there always is, it should be within tolerable limits.
Some times a sketch or two tells the story better than words alone. Let us know what your findings are.
Best regards - Al
RE: Distortion when welding Slip On Flanges
RE: Distortion when welding Slip On Flanges
Welding the inside of the flange first is not only standard practice it is the most logical way.
Spirit level on the flange face vertically.
Tack top and bottom on the outside once flange is level with the pipe.
Rotate flange / pipe 90 degrees.
Spirit level on the flange face vertically.
Tack top and bottom on the outside once flange is level with the pipe.
You now have 4 x tacks on the outside and the flange is (hopefully) square in both planes.
Weld the inside first and then remove all four tacks on the outside.
Fully weld the outside without interruption.
The welder wants to weld bottom to top without interruption (stopping midway at a tack) or running over an incompletely removed tack that will leave a pronounced hump.
The other thing is if you are removing tacks whilst welding the outside first will it be affecting the squareness of the flange ?
In my experience distortion comes from the pipefitter being too lazy to "centre" the pipe inside the flange.
Easier to let the flange "hang" on the pipe which when tacked up leaves a big gap on the bottom (between the pipe OD and flange ID) and no gap on top.
You are then faced with unequal amounts of weld being applied.
Regards,
Shane
RE: Distortion when welding Slip On Flanges
I've seen RFSOs warped before, but it really takes some serious heat input on the ID weld to do it. Never seen one of our own welders do it, and our subs are pretty good too- but I have seen some over the years so it's definitely possible.