Butt welded piping fitting to fitting make-up weld gap
Butt welded piping fitting to fitting make-up weld gap
(OP)
Folks,
In my neck of the woods this has been an age old question that rears its ugly head on occasion. When you have two fittings being welded together, (for this discussion a 6" LR 90 Ell and a 6" 300# RFWN) should the dimension include the required weld gap? Example: 6" LR 90 = 9" + weld gap of 1/8" + 6" 300# RFWN thru hub of 3 7/8" = 13" dimension. The argument is made that the gap "disappears" during welding but some measurable gap remains. As an engineering contractor we have clients that prefer it one way or the other. Just wanted to see what other thoughts were on the matter. I'm doubting this is the first thread of this nature so the simple solution may be to direct me to a previous thread. Thanks in advance for your comments!
In my neck of the woods this has been an age old question that rears its ugly head on occasion. When you have two fittings being welded together, (for this discussion a 6" LR 90 Ell and a 6" 300# RFWN) should the dimension include the required weld gap? Example: 6" LR 90 = 9" + weld gap of 1/8" + 6" 300# RFWN thru hub of 3 7/8" = 13" dimension. The argument is made that the gap "disappears" during welding but some measurable gap remains. As an engineering contractor we have clients that prefer it one way or the other. Just wanted to see what other thoughts were on the matter. I'm doubting this is the first thread of this nature so the simple solution may be to direct me to a previous thread. Thanks in advance for your comments!





RE: Butt welded piping fitting to fitting make-up weld gap
RE: Butt welded piping fitting to fitting make-up weld gap
RE: Butt welded piping fitting to fitting make-up weld gap
My experience includes many years in the design room and a few years as the Engineering Manager in a Pipe Fabrication Shop. That said I stand with Robin Handy. Do not show the gap and do not add the gap dimension in the overall dimension.
The accumulative error you referred is a different problem and must be taken care of in a different way.
prognosis: Lead or Lag
RE: Butt welded piping fitting to fitting make-up weld gap
Weld gap is an item that varies according to the personal habits of the welder, and can vary even by the temperature of the day. Sometimes the gap will close while welding ,othertimes not.
It is far more important to have the welder properly certified for the type of weld, than to tell him/her how to do his/her job.
Robin Handy has it right.
B.E.
"A free people ought not only be armed and disciplined, but they should have sufficient arms and ammunition to maintain a status of independence from any who might attempt to abuse them, which would include their own government."
-George Washington, President of the United States----
RE: Butt welded piping fitting to fitting make-up weld gap
RE: Butt welded piping fitting to fitting make-up weld gap
RE: Butt welded piping fitting to fitting make-up weld gap
Having spent many years as a pipewelder and/or pipefitter before I moved into quality control I agree with all the comments listed above.
Gasket measurements should be included as they are a constant measurement whereas weld gap can change markedly based on welding process, shrinkage rate,shrinkage rate based on material (c/s versus s/s)etc etc.
Hypothetically we have an isometric showing a pipe spool that has two x 300 nb 90 degree elbows, two x 300 nb RFWN flanges, two x 300 nb pipe pieces and 1 x 300 nb Ball valve.
The isometric should show the measurement from the centre of one elbow to the flange face, then the valve length should be shown which includes 6 mm (2 x gaskets)and then the measurement from the flange face to the centre of the remaining elbow.
It should also show the critical measurement of centre to centre of the two elbows (which should be the same as the sub totals combined).
Now the onus is on the contractor to calculate the pipe lengths required based on welding process, initial root gap, calculated weld shrinkage etc and these lengths are then given to the cutting team and hopefully when everything is fabricated it is within allowable tolerances for length,
Regards,
Kiwi
RE: Butt welded piping fitting to fitting make-up weld gap