Backgouge

By pipewelder_1999 (****)

Date 02-09-2004 14:32

A Definition is the removal of weld metal and base metal from the weld root side of a welded joint to facilitate complete fusion and complete joint penetration upon subsequent welding from that side.

This can be done with a grinder, Air Carbon Arc, or other methods. The backside of the joint is taken down to sound metal and then welded up. I prefer the air carbon arc process.

You can lookup some other terms and definitions at
http://weldinginspectionsvcs.com/welding_terms_and_definitions_lo.asp . These are from ASME Sec IX (With Permission).

AWS A3.0 is the ANSI Standard for welding terms and definitions and is VERY extensive.

Have a nice day

Gerald Austin

By ADKstorm Date 02-09-2004 15:00

I have a scenario: We have duct work for a waste gas system. The duct work is in either 60" or 78" ID made with 3/8" thk plate. There are portions of the duct that will be field welded to expansion joints. The expansion joint end does not have a prep. The duct work will have a prep. Currently on the drawing we have the weld as: single beveled weld and the term backgouge in the tail of the weld symbol.

Is this something that is done or is there another type of weld done.

A weld will be able to gain access inside to make the best weld possible.

Thanks for any help.

By thirdeye (***)

Date 02-09-2004 15:37

From your description you have a standard bevel groove weld (since only one of the joining members has the bevel. This is opposed to a V groove or a square groove). This type of joint is typical. As was stated above several backgouge methods may be used and I also prefer an air arc. At any rate, once properly gouged the root side of the joint will be more of a U shape and ready for a back weld.

By jwright650 (*****)

Date 02-09-2004 16:28

I guess the use of a backing bar is out of the question?

I was just in question as to whether the other side (root) of this weld is accessible. If your design allows for the change to a backing bar vs the backgouge, it would make it easier to weld without the welder being in a confined space, which brings up a whole new set of rules per OSHA.
just a thought to consider,
John Wright

By ADKstorm Date 02-09-2004 17:58

The backing bar is acceptable ....we are going to use that instead of backgouge. I assume, for the welder, the backing bar is easier than backgouging? ...and the time that it takes to weld with a backing bar is quicker backgouging is quite different? [time for welding a 78" ID duct].

By ssbn727 (*****)

Date 02-10-2004 16:55

Hi ADKstorm!
What about using ceramic backing tape instead of a backing bar which would require you to tack weld the backing bar and therefore require you to do more work?

Respectfully,
SSBN727 Run Silent... Run Deep!!!

By CHGuilford (****)

Date 02-09-2004 17:41

Just to add to the good counsel you've already gotten, I usually like to weld inside the duct work first and backgouge the outside. Air arc is very loud, smoky, and sparks can come around and "hit you in the back of the head".

To clarify the definition of backgouge, A3.0 does not say how the metal is to be removed, so air-arc, grinder, milling machine, hand file,... whatever works without causing problems, is acceptable. I added that because I have had some people tell me that 'backgouge' means air-arc only.

Also, whenever I see 'backgouge' on a welding symbol, I know the designer wants full penetration welds, and that usually the designer is open to alternative grooves as long as we can assure full-pen.
Chet Guilford

By ADKstorm Date 02-09-2004 18:03

Thanks for the information. We always try to make it easier for others to build what we design ...whether it is fabrication, erection, demolition or field welding. In business today, time is of the essence.

By - Date 02-10-2004 01:15

I do not agree that a backing bar will make the process faster, especially on a tubular of that size. The placement of the backing bar will take quite a bit of time, if done properly. Fitup conditions become somewhat more critical with a backing bar - with backgouging you can make a CJP weld with zero root gap. You probably would not be able to make a CJP weld with backing and a zero root gap.
With the use of a backing bar you also introduce inspection difficulties if any sort of volumetric NDE is required (i.e. RT or UT).
I agree with Mr. Guilford. Weld the inside first, backgouge to sound metal from the outside by whatever method is quickest, and weld it up.
Mankenberg

By jwright650 (*****)

Date 02-10-2004 02:21

ADKstorm,
I mentioned the backing bar only as another choice, if getting to the inside of this joint was difficult. I take it that this is a new installation rather than a repair or modification to an existing duct. Some of my welders prefer to use a backing bar and others don't mind using a carbon arc gouger. Use which ever method gives you the confidence that you can achieve the full pen joint you are after. I agree that if you use the gouger(or what ever means available), bevel your material so it can be filled from the inside and gouged from the outside. Fit-up of a backing bar can take some time to achieve a really tight fit-up and proper aligning of the two pieces with the correct root opening to where your welder can fill it up evenly. However there are some tricks of the trade that the fitter/welder can use to speed up the alignment and achieve the correct root opening all at the same time. Tack the backing bar to one side of the joint and then slide the other half in place. If the root opening needs to be 1/4", use several 1/4 shims at several locations around the joint to maintain the correct root opening until the other half is tacked into place. If the joint must be UT'd after welding, the UT'er may spend more time evaluating a joint with a backing bar vs one that is backgouged as has been mentioned already.
Keep us posted as to how your project turns out.
John Wright