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Breaking of Tack Weld During Preheating for Welding

07/27/2017 2:58 AM

It was observed that during preheating(150deg.C) (Before welding) time, the tack weld was getting cracked.Tacking was done by ER80S-G.(fillet weld)

What is the reason for getting cracked.Tack weld length is 50mm

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#1

Re: Breaking of Tack weld during preheating for welding

07/27/2017 3:01 AM

The stresses in the material at the moment of fracture exceeded the material's ability to withstand them.

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#2

Re: Breaking of Tack weld during preheating for welding

07/27/2017 4:18 AM

<...It was observed...> So, what did the observer actually see and under what circumstances? Surely this is the best avenue of enquiry?

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#3

Re: Breaking of Tack weld during preheating for welding

07/27/2017 5:14 AM

What material do you try to weld?

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#4

Re: Breaking of Tack Weld During Preheating for Welding

07/27/2017 6:29 AM

As the learned PWSlack has already explained the cause, no more need be said.

If you were looking for a solution, which apparently you are not, I'd look into increasing the length, or frequency, of the tack welds.

My time has expired.

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#5

Re: Breaking of Tack Weld During Preheating for Welding

07/27/2017 6:51 AM

Cracks on the tacks weld are frequent and must be removed before welding

ASME B31-3 sets:

(c) Tack welds at the root of the joint shall be made

with filler metal equivalent to that used in the root pass.

Tack welds shall be made by a qualified welder or welding

operator. Tack welds shall be fused with the root

pass weld, except that those which have cracked shall

be removed. Bridge tacks (above the weld) shall be removed

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#6

Re: Breaking of Tack Weld During Preheating for Welding

07/27/2017 11:11 AM

As PWSLack stated, the thermal expansion stress was too much in regards to the length and placement of tack welds, and the cracked tack welds must be removed.

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#7

Re: Breaking of Tack Weld During Preheating for Welding

07/27/2017 10:22 PM

You weren't planning on only preheating some of the welds, were you?

Preheat needs to be applied to all welds kept. If you did not preheat 50mm tack welds then these need to be ground out regardless of whether or not cracking is evident.

Align

Preheat

Tack

Weld

Post weld treatment

.

Yes, they will bitch, but 50mm tack welding is welding. If preheat is required then either preheat for tacking or grind out the tacks.

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#8

Re: Breaking of Tack Weld During Preheating for Welding

07/28/2017 12:06 AM

Preheat the piece at a much slower rate. That should help to minimize thermal stresses.

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#9

Re: Breaking of Tack Weld During Preheating for Welding

08/02/2017 10:39 PM

Preheating before tacking is as critical as the welding.

Even if the tack weld is fully removed, the damage to the HAZ from tacking without the prescribed preheat will remain.

Tacking without preheat can also increase the risk of Hydrogen inclusions

Solution is as above - preheat prior to tacking, ensure tacking is of sufficient size to allow for the thermal and structural stresses applied during the welding of the root run. Ensure tack is visually examined and then tapered to allow for the successful welding of the root run.

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Users who posted comments:

Anonymous Poster (1); Chris Wylie (1); James Stewart (1); lyn (1); PWSlack (2); truth is not a compromise (1); Whitephone (2)

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