Starting and Stopping Welds in the Field 6

[STrctPono]

I have some repairs that we are making to a steel plate girder bridge. We are welding new 1/4" steel plates to the outside of the girder web. We specified similar repairs to another area of this bridge last year and were told that the Contractor warped the 1/4" steel plates when they made the continuous CJP weld. Too much heat applied in one location all at once.

My question is this: Is there a difference in weld quality/strength if they were to weld continuously and completely around the web plate vs. stitch welding it 3" at a time @ 12" o.c. and then come back and weld in the areas to remain? In essence, does starting and stopping create issues at the point where you start/stop? They are most likely going to be using Shielded Metal Arc Welding but might choose to use flux cored arc welding too given the total length of the welds.

 

[david339933]

Call me stupid, but what is this "stitch welding" I see tossed around?

Definitely not stupid....just playing the part. Every year you ask this question.

 

[dik]

I was going to respond..."Hi Stupid", explaining that he wanted me to call him that... but, I thought better of it. 'gtaw' is one of the good guys...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[gtaw]

I've answered to worse.

Best regards - Al

 

[dik]

Me too... my name says it all...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[The Stick Man]

Hey. Interesting thread & more so the location of the job. 1/2in - 5/16in would probably be best for longevity under the circumstances. Mark the steel with datums every 6in against a reference that won't be in a heat affected zone. Monitor the expansion at the datums. Good tacks and staggered stitch welding every 4in, 4in long. Treat with suitable paint, preferably an epoxy type and perhaps spray with cavity wax to repel salt and water. Just a tip of course.

 

[DAVIDSTECKER]

Is "Peening" the welds allowed?
From what I understand it is a form of stress relieving which to me would seem to be a way to reduce warpage.
I've also seen vibratory stress relieving systems that can be used while welding that is supposedly to also reduce warpage.

 

[ATSE]

Following up with what Tugboat said: "...After the stitches are made, the beginnings and ends should be gouged..."
While this may be good practice and produce a better weld, is this actually a D1.1 code requirement for fillet or PJP welds? If so, please cite the code reference and learn me.
For field SMAW, the welds are of course chipped and power wire brushed, but grinding at the ends of welds before a re-start is rare.

 

vibratory stress relieving systems

is for all practical purposes voodoo marketing.

It can be done in principle, but you either need an extremely simple configuration or a very long science project to tailor it to the application.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[FacEngrPE]

There is shipyard trade straightener that does exactly what you need for the 1/4 plate, pulling the warpage out of a ship bulkhead, after it is welded on place. The task requires shrinking the center of the installed plate using heat and water. We do not attempt to describe the process, just specify the result.

I agree with the comments above - adding corrosion allowance is a good idea, but there may be other considerations. Adding 1/2 inch to both sides might be too much weight. If you need corrosion allowance on the weld, make the weld bigger.

Check the weld symbol, A weld with a 1/4" throat is unusual on a 1/4" plate.

 

[chicopee]

Looking at the extent of corrosion damage with holes thru the webs of the larger girders and by the time you sand blast and beef up the damage sections before repainting, you may be better off to replace the entire bridge.