Why chip your welds?

[75]

I was asked this recently by one of the new fellows at my work when I pointed out he needed to make sure all the welds got chipped. (That slag covering on the weld is the flux coating on the welding rod after it melts, combines with dirt & impurities on the pieces being joined, floats to the surface & cools. It's an essential part of the stick and fluxcore welding processes. MIG welding is a different process & doesn't produce this slag covering on the finished weld)

I could have just said "Because you have to!", but that isn't much of an answer. There are several reasons:

If the job is being done to CWB (Canadian Welding Bureau) specs, an example being structural steel fabrication, all welds must receive at least a visual inspection. You can't inspect what you can't see! An engineer or steel inspector can cite unchipped welds as a deficiency - I've seen it happen!

If the weld you are doing requires multiple passes, the slag must be chipped away before laying another pass down. Remember that dirt & impurities are contained in that slag, if you weld right over top they will be trapped in the weld. A large number of welder test plates that fail the X-ray examination do so because of "slag inclusions", tiny bits of slag that didn't get cleaned off & were trapped in the next layer of weld metal.

And, it looks a lot more professional. Rough-looking unchipped welds are NOT something I want to leave as a calling card.

[Gordon]

Another key reason for slag on the weld is that it doesn't allow air to hit the weld as quickly and allows a slower cooling time. This way the weld doesn't become brittle from quick cooling.

Gordon

[1grnlwn]

If you don't chip your weld, then you paint, eventually the slag will come off and then the joint will rust. This is why when welding vessels even a small ball will not pass.

[75]

1grnlwn, good point about the painting.

When you mentioned "small ball", are you referring to spatter? (the little tiny balls that are often seen next to a weld) If so, you're right - they should be cleaned off too.

Even when a weld isn't on a vessel, things like chipping slag & cleaning off spatter are an indication of good workmanship, IMO.

[1grnlwn]

Yes spatter. You know I'm in Fert. Cut mode right now. Fab mode is strictly winter work for me.

[eslawns]

MIG welding doesn't produce slag, but (esp. with flux core wire) it makes a lot of splatter. You can use a chipping hammer to knock most of these off your work pieces.

Just a thought.