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Up Topic Welding Industry / General Welding Discussion / Back gouging using copper back up bars
- - By mcphilly Date 08-23-2009 14:27
We are using copper backing bars on full pen joint connections with a 3/8 root opening . My question is this , the inspector said we have to do a back scarf and fill but in the past and on a lot of other jobs where it said to back gouge the inspectors have let us just run a grinder to the back side until we get clean metal and then run a few cover passes . Does back gouging have to be done with an air arc or will a grinder work as well ?

We are using 5/64 flux core wire core 8 . Some of the splice connections are only a 1/2 inch thick where it is just your root pass , and pretty much 2 more passes to fill it up . It doesnt really make sense to me to have to airarc something that small .....

Any help would be greatly appreciated..........If you could give me the pages in the book where it states it that would be very helpful as well...

Parent - - By alan domagala (**) Date 08-23-2009 15:02
Parent - - By ssbn727 (*****) Date 08-23-2009 17:19 Edited 08-23-2009 19:09
Well that sounds fine and dandy but, "ultimately" the person who decides which method to use will be the EOR... And it may have been already decided that CAC-A (Air Carbon Arc Cutting) was already specified as the process to use in the contract specification documents beforehand...

However, if CAC-A is not specified anywhere in the documentation by any method, (And you better make darn sure that it isn't specified, or the EOR may lose confidence in you with respect to your proficiency in the proper interpretation of engineering drawings - Yikes!!!) then you want to be absolutely sure that the EOR wants to use this process as a "requirement" as opposed to a "preferred" process by bringing it up to the EOR for clarification because this way, you have "CYA"  (Covered Your Arse!) as well as all the bases - so to speak which will end the confusion all together and leaving the decision & responsibility - "ultimately" resting in the hands of the EOR. ;) 

In other words, the welding inspector's responsibility is to inspect the weld(s) as well as assuring that the proper procedures are being followed by the welder(s)... And the Engineer's responsibility is to apply sound engineering judgment in designing into as well as approving the proper welding procedures through the use of calculating, and incorporating conservative as well as economically reasonable factors of safety into the design of the weldment(s) in question based on well established, empirical research and proven design methods of application. 

Therefore requiring complete co-operation between the welding inspector(s), and the Engineer Of Record in case any confusion may arise in the interpretation of the specifications by seeking clarification with each other as sometimes it is the case where an engineer may seek guidance from an inspector as well as visa-versa. ;)

Also, if there is a lack of specificity present towards achieving & applying the most optimal quality standard(s) into the fabrication, assembly,welding and any other manufacturing methods used in the construction of the product whether it be a single joint configuration, structure or components of different sized/ shaped structures, and then assembled together in a specific sequence in order to result in the efficient construction of a relatively complicated system or interacting systems that work together in achieving their intended design application... Then it is essential that total cooperation is established between the responsible parties as well as completely comprehending each others intended roles in order to implement the necessary changes properly in a timely manner to achieve without delays or re-work the design's intended goals as well as meeting the required safety considerations!!!

Bear in mind however, that the EOR  is not required to follow the guidelines & requirements set forth in whatever code to the letter per se - that is being applied in the the design of whatever it is they're designing!!! In other words, the EOR may exceed the minimum requirements & guidelines found written into any code or standard that is applicable towards their design... However, if they fail to meet at the very least - the minimum requirements & guidelines of whatever code they are applying into their design, and catastrophic failure is a result of their own proven negligence to incorporate more than enough factors of safety in to the design, then they will become legally liable for any damages as well as injuries resulting in possible civil actions as well as criminal charges imposed on them by the courts!!!

This is why it is so important for all parties involved to become totally aware of their own roles & responsibilities from the beginning to the end of any project that will be subject to such scrutiny even before one sequence of operation is started!!! So, always know ahead of time what you're getting yourself into before you find yourself in a position that you'll regret later on, and never assume responsibility for something or someone that isn't yours in the first place!!! ;)

Parent - - By alan domagala (**) Date 08-23-2009 17:41
Parent - By ssbn727 (*****) Date 08-23-2009 19:14 Edited 08-23-2009 23:00
Please read my post carefully again, so then you can thoroughly understand what I am saying  - CAPECHE??? ;)

Btw, "fine and dandy" is an expression I like to use in the place of: "If it were only so straightforward." Do you see the comparison in the amount of words used??? In other words, three words for "fine and dandy." Yet for "If it were only so straightforward" one ends up with using six, or actually seven if one separates the word "straightforward" so, it's just a matter of economy!!! ;) ;) ;) So what do you think Al??? ;) Moore Jr. - that is!!! :) :) :)

Parent - By jrw159 (*****) Date 08-23-2009 20:13
Basically if the contract specs and the EOR do not call out for a specific means of removal, be it grinding, air arc, or beating it out with a hammer, then the method of removal is open to the described methods in the code, NOT, what the inspector prefers to see. To take the stance of calling out the method of removal as mandatory based only upon the inspectors preference is out of the realm of the inspectors responsibility thus asking for trouble.

jrw159 :-)
Parent - - By alan domagala (**) Date 08-23-2009 21:57
Parent - - By jrw159 (*****) Date 08-23-2009 22:22
  This is where inspectors must heed caution.

"I know first hand that with grinding, sometimes you may not go "deep enough" and thats probably why the inspector insists on air arcing."

"I was assuming in my response that the welding inspector knows what the engineer wants and was relaying that information to the welders."

Parent - - By alan domagala (**) Date 08-24-2009 00:16
Parent - - By ssbn727 (*****) Date 08-24-2009 06:52 Edited 08-24-2009 07:12
Hello there Alan Domagala!

Like I'm sorry to have disappointed you with my rather "long winded answer" to your post on this thread... Would you have preferred single sentence catch phrases??? I mean, if you think my response was long winded, then you ought to look at some of the ones I have put up over the years that were meant to be "in depth"

Furthermore, I'm not the only one in here that gives, and has given what you want to describe as "some long winded answer" so, prepare to read on with responses that may have exponentially more paragraphs than you insist on being willing to accept for what may or may not constitute an answer that "YOU" may have been looking for.

Is that short enough for you??? I mean I used only two paragraphs for your consideration!!! ;) Okay, all right all ready - it was three if you include this one but, err, but, who's counting anyway??? whoops!!!;) I forgot... It is you that's doing all of that detailed analysis, and all by yourself, without assistance from anyone else!!! How impressive (loud cheer in the background)!!! About as impressive as a - okay, okay Ross! I'll behave - this time!!! :) :) :) Ba-da-bing, Ba-da-boom, Ba-da-bang!!! ;) ;) ;)
BTW, "Weldcome" to the "World's Greatest Welding forum!!!" And more importantly, "Have a Nice Day!!!"

Respectfully, (if only tentatively! :) )
Parent - - By alan domagala (**) Date 08-24-2009 20:37 Edited 08-24-2009 21:07
WHATEVER HENRY!! I'll delete all my posts for ya, happy?...HAVE A NICE DAY!
Parent - By ssbn727 (*****) Date 08-24-2009 22:44 Edited 08-25-2009 01:39
Now why would you want to go ahead and do something like that??? I wasn't trying to ridicule you at first... I only responded to your remark of me being so long winded after wards... All I was trying to do was to mention the importance of knowing one's roles and responsibilities!!! :(  Imagine that!!! Why can't we be Friends? Why can't we be Friends/ Why can't we be Friends?? Why can't we be Friends??? :) :) :)

Parent - By mightymoe (**) Date 08-26-2009 20:47
I thought your reply was long. It's your reply, heck, you could make it 8 pages long. Your reply made sense and I agree with it, I just have a short attention span.
Parent - By phaux (***) Date 08-23-2009 15:40
I'd choose gouging over grinding any day. A lot faster, and fun.
Parent - - By Iron Head 49 (***) Date 08-24-2009 11:32
One thing to keep in mind, sometimes grinding will mask / cover up imperfections, where as an “Air Arc” done properly will open up any defects in the weld or base material. 
Parent - - By 803056 (*****) Date 08-25-2009 00:12 Edited 08-25-2009 00:20
As is often the case, we are not provided with the particulars of the job or project. In most circumstances, I would not expect the welder on the production floor to be privy to those documents. As a matter of fact, I often had a difficult time getting a copy of the project specifications to read.

I would be interested in knowing if the inspector in question is a third party inspector or the fabricator's QC/QA inspector. It does make a difference. If the project specification does not address the issue of back gouging, and I would be surprised if it did, the fabricator has several options available. Depending on the specifics of the job, there are choices to be made. Back gouging can be done in any number of ways; there is air carbon arc gouging (CAC-A), grinding, chipping and grinding, machining, oxy-fuel gouging, plasma gouging, etc. The choice is typically left to the fabricator unless there are specifics that would favor one method above the rest. Codes, in general, have no preference of one method over another  except in special cases such as back gouging quenched and tempered steels.

In any event, the last person to weigh in should be the third party inspector. The third party inspector, except for rare occasions, should not be advising the fabricator on the ways and means of accomplishing any work. The TPI is not the fabricator's consultant and should not be asked to participate in such matters unless the owner/EOR is doing the asking. Once the TPI weighs in with a suggestion on how something should be done, he is no longer a disinterested unbiased party. He naturally has a vested interest in seeing his suggestion work. The impartiality is gone. This is not as easy as it sounds. There is nothing more difficult for an inspector to do than to stand on the sidelines and watch the fabricator make stupid mistakes, but I've seen more than one inspector asked to leave a project for interfering with the fabricator's operations by interjecting his opinion on matters where his help wasn't appreciated. Trust me, there are few fabricators that will not stick up the inspector's butt if one of the inspector's suggestions doesn't pan out the way it was expected to.

In this case, the use of copper backing with a 3/8 inch root opening is suspect. There is a potential problem of picking up copper in the root pass. Copper doesn't play well with many metals and can its use  can result in cracking problems. Any back gouge operation, regardless of the method employed, should include NDT specifically to look for cracks caused by the copper. The extent of BG may go well beyond simply looking (visually) for sound metal.

Henry makes some very good points with regards to good communication and understanding what each party's responsibilities are. The EOR and TPI work for the owner. They are retained by the owner to protect the owner's interest. When a problem arises the three entities have to communicate to achieve the objectives, i.e., a structure that will fulfill the owner's needs and code requirements. Relationships can sour very quickly when one party or another oversteps the boundaries without an invitation.

Best regards - Al
Parent - By DaveBoyer (*****) Date 08-25-2009 02:32
I have read of copper backing bars being nickel plated to prevent copper contamination of the weld. Is this done in field work, or is it only used on fixturing for shop work?
Parent - By Iron Head 49 (***) Date 08-25-2009 11:30
Hi 803056, (Al)
I was going to mention, (lost my train of thought) that copper would not be my first choice in this situation. I would much rather have ceramic backing with a gap this big. Copper is a great backing and heat sink on thinner material, with smaller gaps. 
Parent - - By mcphilly Date 08-25-2009 02:28 Edited 08-25-2009 05:17
thanks for all your input fellas . The prints did not say anything about using air arc for back gouging it was just something the inspector wanted so I brought up the use of grinders on some of the connections and he said that was fine . The reason I was kinda big dealing the scarfing on all the connections was due to the fact that it was not in are contract or bid and basically that almost doubles you weld time due to set up and hassle . We are not shop welders we are union steel erectors and as most of you know it is a lot different out in the field than it is in a shop ..... We are currently building a 220 foot sky bridge at the airport and it would be a pain in the ass to drag an air arc around to every connection when I could just run a grinder on it for a minute and then burn all that **** out of there with a few passes with the core 8 ...

Thanks again
Parent - - By ssbn727 (*****) Date 08-25-2009 07:32
Hi McPhilly!

First off, let me "Weldcome" you into the World's Greatest Welding Forum!!! ;) I also have a few questions for you if you don't mind...

Is the inspector going to perform NDT on the back gouged grooves prior to welding the backside of these CJP weld connections? Also, is this 220 foot Sky bridge being welded to the AWS D1.5 Bridge welding code? You also mentioned in your initial post that some of the splice connections are only one half inch in thickness... Are some of the CJP connections of greater thickness?? Finally, what is the grade(s) of steel being used for these connections???

I ask this because as Al mentioned previously... Quote: "the use of copper backing with a 3/8 inch root opening is suspect. There is a potential problem of picking up copper in the root pass. Copper doesn't play well with many metals and its use can result in cracking problems. Any back gouge operation, regardless of the method employed, should include NDT specifically to look for cracks caused by the copper. The extent of BG may go well beyond simply looking (visually) for sound metal."

Now you already mentioned that you were going to use copper back up bars in your initial post... Plus the fact that the advice is based on years of sound Iron working experience from Al also... So I would if I were you, take Al's advice in order to avoid any chance of experiencing a situation whereby taking a short cut turns around after-wards, and ends up biting you big time in the "wallet" with more expensive re-work as a result of trying to save time as well as costs without taking into consideration a proven method of in process quality control in order to make sure the CJP weld connections pass NDT after completion... Btw, I'm not trying to be critical here, I'm just trying to be helpful. :) :) :) LOL!

Parent - - By mcphilly Date 08-26-2009 03:52
The inspector just took a visual peek at are back gouges and then gave us the go ahead . I do not know  what an NDT is but if it involves any type of instrument or tool none was used. As far as I know we are using D1.1 but I could be wrong that is something I will check into . As for the main I beams they are all between 1.25 and 1.50 inches thick . The smaller half inch beams are all the transverse beams . I do not know what grade of steel it is but I will check into it as well . I am not the foreman I am just a 4th year apprentice trying to gain knowledge and understanding of this stuff  . I have been welding for around 15 years but I am only in my 4th year as a Union Iron worker .....Our welding foreman has quite a bit of experience and knowledge but I think he was a little gun shy about going head to head with the inspector when he wasnt 100% sure . I told him about this forum and said that it was full of answers, right or wrong lol...
He asked me to shoot a post up and see what other people had to say.
Thanks again and I will get back to you on the Code we are using and grade of Steel

Oh as for the copper back up bars , I have done over a 150 full pens using the copper and have never had a reject... Is the problem you were talking about something that comes down the road later on or in the UT?  Correct me if I am wrong but the copper is just used to keep your root and hot pass from falling out . After those first two passes I take it off and then fill it up . Then we gouge the back out until we get sound metal . If I follow that procedure I should be correct ?
Parent - - By HgTX (***) Date 08-26-2009 18:04
NDT:  nondestructive testing.  Ultrasound, radiography, magnetic particle, liquid dye penetrant, etc.

Parent - By 803056 (*****) Date 08-27-2009 21:34
Copper isn't tolerated by iron very well, i.e., it does not go into solution to form either a substitution solid solution or an interstitial solid solution unless the weight volume is very, very low. It segregates to the grain boundaries as a low melting point constituent, much like sulfur or lead.

The typical problem occurs when the welding arc momentarily impinges on the copper backing and causes a minute amount of the copper to melt. The copper mixes with the molten steel and is rejected (solute rejection) as the steel solidifies and grains are formed. The higher melting point constituents freeze first along the bottom and edges of the weld bead where heat is disipated by the thermal mass and thermal conductivity of the "cold" base metal. The low melting point constituents freeze last. In the case of the weld, the last region to freeze is the centerline of the weld, toward the top of the bead (remember, gases are insulators). Steels typically solidify between 2700 and 2800 degrees (round numbers), whereas the copper solidifies around 1981, and lead (another bad actor) around 460 degrees F.  The low melting point constituents as they are called are pushed toward the last regions of the weld to solidify. Being weak along the grain boundaries where the LMPC are located, cracks form when the welds cool to ambient temperatures and the residual stresses (tensile stresses) rear their ugliness. 

The cracks can be very small and very difficult to see with the naked eye. Visual examination alone may not be capable of detecting the problem. That why I suggest addition NDT, such as magnetic particle or preferably contrast dye penetrant testing be employed to verify the excavated root is free of cracks. If VT alone is employed, I would hope the inspector is using magnefication as an aid to seeing the small cracks.

If the welded joints are subject to UT, I’m sure the cracks will be easily detected and rejected by a responsible UT technician.  The repair will be considerably more expensive and involved at that point.

I make crack samples for training purposes by placing a single strand of copper wire (the size of a hair) from a welding lead, measuring only ¼ inch or so in length, on the joint to be fillet welded. Cracking is guaranteed. They are so small the inspectors in training rarely see them until they perform the penetrant test or magnetic particle test.

I don’t consider myself to be an expert in these matters. I’ve only been a member of Ironworkers Local 15, Hartford, CT for 40 years. I served my apprenticeship in the late "60's" and still consider myself to be learning the trade.

Good luck in your new career.

Best regards – Al
Up Topic Welding Industry / General Welding Discussion / Back gouging using copper back up bars

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