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Welding Forum > UKWelder > Practical Welding Questions
polyman
can anyone explain the causes of suck-back and how to distiguish the difference between suck-back and lack of penetration
3Rs

when you do your root to you look at it?

If not why not!!!!

If your putting a root in and its concaved then that will mean your not tipping enough wire in the pool.

Now say for example your roots are ok

And you put in the hot pass, If the hot pass is to hot then you will be likly to have suck back. Now suck back is basically where the weld is "Sucked Backed into the joint" which leaves it concaved. Lower your amps or you can maintain the amps that you have been using the past only tip even more wire into the pool this way you are cooling the pool down.

All so few other things. When hot passing,filling,capping. You should be using a heaver rod. 2.5 or there abouts for the root, and a 3.2 or there abouts for hot pass,fill cap.

once you have finished your fills and ready for the cap, Leave the pipe "let it cool down" for about 15-20 mins as this will further reduce suck back.
Autolupus
Pretty much as 3Rs says, it's either lack of filler deposition, too much heat or a combination of both.
On thin gauge fillets, pipe/sheet suckback will show itself as small/ not so small craters, where the weld leeches material from the parent metal if not enough filler rod is used.
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