Back Gouging

[Ryan225]

Why does it have to be done? I was taught to do this when I practice welding pipe between each pass. I have seen it done in other places. But I do not understand why it is done.

Any ideas?

-Ryan

[irnwrkr1]

to back gouge a joint say in the pipe like you are talking about , it must be some pretty heavy walled pipe and pretty big in diameter so that someone can get in it to do it. just about every joint that ive ever done from 2" to 12" we've only ever ground out the root and hot passed and capped .never back gouged. but on platework though this is a different story. first the welded joint side is either got a back up bar or ceramic rods so that the joint can be welded properly and then after the joint has been welded up the backup bar is gouged off or the ceramic rods come off and then gouged out to the thickness set out in the blueprint specs. the whole reasoning for that is so that the weld is x ray quality and all chances of porosity,slag inclusions and stuff that you dont want in a weld are taken out.its like weld "insurance". i'm sure that CWB(canada welding bureau) and the AWS (amer.welding society) procedures are very very similar when it comes to a full penetration joint.whether it be x ray, UT ,dye,magnaflux NDT .hope i answered your question

[Ryan225]

Yes, that makes sense now. I must have had my term for "back gouging wrong. The pipe I am practicing on is a 4" ID SCH 40 pipe, which is only 1/4" thick. I would do the weld in 3 passes, root, hot, and cap. I would grind the root and hot pass. That is what I was calling back gouging. I guess the term back gouging only refers to when you use carbon arc to do your gouging.

[asad]

I guess the term back gouging only refers to when you use carbon arc to do your gouging.

I don't think that's right.

I thought that backgouging was when you grind out the backside of the root pass in order to re-weld from the back.

That's my impression from what I've read here on the forum, and that's what the post above yours seems to indicate.

Asad

[enlpck]

Yes, that makes sense now. I must have had my term for "back gouging wrong. The pipe I am practicing on is a 4" ID SCH 40 pipe, which is only 1/4" thick. I would do the weld in 3 passes, root, hot, and cap. I would grind the root and hot pass. That is what I was calling back gouging. I guess the term back gouging only refers to when you use carbon arc to do your gouging.

Back gouging referes to removing material from the root side (back) of the weld, usually so that that side can be covered wih weld, using a couging process (carbon-air arc, plasma, gouging chisel, etc). Also back grinding, back chipping.

Reasons for back prep as described by irnwkr (remove possibly contaminated material from root side and allow clean weld metal to be laid in)

What you are describing is needed for several reasons, primary ones including removing any slag that may be trapped in undercut, removing undercut deep in the groove, giving a smooth surface for the next pass (making it easier not to trap slag in the weld), and allowing you to profile the groove such that the next pass can be laid in without having the groove faces interfere with the electrode position.

Practice reduces the need for grinding by allowing you to control all of these issues. (lay the weld metal so the slag doesn;t hang up, minimize undercut, minimize rough edges and weld face, ability to manipulate the electrode around awkward bounds)