using a welding rod that requires backing 1

[carbonear59]

i need some guidance .every one knows it's common practice in tank building/vessel manufacture to weld from one side ,backgouge then weld from the other side (following Section IX welder and welding procedure requirements ) .
my question is this ; if the procedure being used calls for the SAW portion to HAVE backing ,is it permissible to use SAW to actually MAKE the backing with weld metal on one side ,then gouge from the other side and fill the joint up ? it seems like a logical approach but i dont know if it is acceptable according to Section IX. (using an electrode that calls for backing to MAKE the backing ,chicken and egg kinda stuff )
any help and applicable code references would be appreciated .

 

[QAFitz]

My experience with the local Authorized Inspectors is that the procedure that you explained would have to be qualified. Once qualified - welded without backing, gouged out from opposite side, welded with backing - and accepted by the powers-to-be, you won't have a problem.

 

[carbonear59]

Thanks QAFitz , i kind of think its skirting around Section IX myself but i just don't know if its an ' indictable ' offence .

 

[unclesyd]

It is not unusual to weld a single V from on side and then back gouge and weld from the other side. The trick is to present your proposal as a single V. We do this quite regularly with thick SS.

In your case making an open butt weld with SAW can be tricky with some type of backing.

Have you looked at a ceramic or fiberglass backing tape for the SAW?

Can you describe your joint?

 

[carbonear59]

it's 2 pieces of 7/16 plate butted together ,they are forming a wall in a 120 ft dia. tank. they both have the tiniest beveled edge on them ( bevelled @60* included angle making it a single Vee groove ). so it isnt an issue of needing a backing bar unclesyd, there is lots of meat there to ACT like a backing bar . my problem is trying to understand whether it's permissable by code to allow the welders to use the subarc portion of the procedure on one side to effectivly make a backing bar for welding from the other side . i realize that the first pass is eliminated during gouging/grinding from the back side . i am looking for someone to explain how this works from a code perspective .
thanks again folks

 

[unclesyd]

Like I stated this is done all the time using different processes. As you state your procedure calls for backing and I assume that there is nothing specific about the call out for the backing. I think the AI will go along with your procedure as stated as his only problem would be the first pass without the backing. He migh call for a quick radiographs to insure the weld integrity. Aside from the AI what does the tank fabricator say about this approach.

Right be before I left work there were 2 large SS,1/2" being fabricated with the exact same procedure you are looking at. The welding machine accomplished 90% of the welding from the outside and the weld was finished from the inside.

 

[JoeTank]

Here's a shorter answer. A weld that is back-gouged and welded is "welded with backing" per ASME IX. Backing does not imply backing bars only. Weld metal can be backing too. It's not an indictable offense. It's compliance with the code.

Joe Tank

 

[carbonear59]

thanks joe , it seems that i havent done a good job of explaining the crux of the problem (if there even is a problem !)i agree totally that weld material is useable as backing and (weld with backing) is what we do when we back gouge and weld from the BACKSIDE , no question on this at all . my question is on the front side weld . the very first bead we lay in this whole affair is with a SAW wire .
what i am trying to establish is the following ; is this first SAW bead which is completed without backing (even though the procedure calls for backing ) and is then gouged from the other side compliant with the weld procedure ?
If this whole approach is legitimate (and i believe it is ) can someone walk me thru some references i can use .
eg ; does the fact that we removed the unbacked SAW bead somehow 'make it all right ' to weld without backing ?
i hope i nailed the explaination this time , thanks folks

sf

 

[weldtek]

carbonear,
The SAW process requires backing. You may choose base metal, weld metal, ceramic or flux, but it has to have backing. The practice you describe is very common and is considered to be a weld made with backing. The backing being base metal.

 

[weldtek]

carbonear,
Going a little further. Look at QW 254, Welding Variables for SAW. Note that QW 402.4 applies as a non essential variable for the deletion of backing. Now turn to
QW 402.4 and note the second sentence.

 

[carbonear59]

thanks weldtek , my understanding of backing has always been that the backing has to be CONTIGUOUS . ( as in continous within the boundary ) , if this definition is applied , then 2 plates butted together cant qualify as backing for the SAW portion . what do you think ?

 

[weldtek]

Not to say backing can't be contiguous. For this question, I think you must consider the word 'backing' within the context & bounds of ASME Sec IX and I also think the second sentence of QW402.4, puts the question to rest.

' Double welded groove welds are considered welding with backing'

 

[carbonear59]

thanks weld tek , i think my question is more along the lines of doesnt the backing have to be contigous ? ie; does 2 pieces of plate butted together that you can see daylight thru qualify as backing underSection IX?

 

[chicopee]

I dont want to get involved in the arguments presented above, however it know that using weld material as a backing strip is a lot more expensive in terms of manpower, material and power supply than using a strip of steel as a backing ring.

 

[weldtek]

Carbonear,
Two plates butted together welded from both sides is considered a joint with backing. Of course, you have to have a process and parameters that allow you to deposit a weld properly. We sometimes 'seal' the joint by depositing a layer using the FCAW or SMAW process to support the following passes made by the SAW process. The joint is still considered one with backing. It would not be considered a joint with backing if you use a process to weld from one side only.

Chicopee,
I'm not sure what you're referring to when you say using weld material as a backing strip, but, in the real world of vessel manufacturing backing strips are a last resort. It's much more cost effective to butt two plates together with the appropriate bevels and land, weld one side and backgouge to sound metal, as opposed to welding from one side. For one thing, most customers and designers for that matter, don't want permanent backing strips, and if you have to remove the backing strip, you'd be way ahead to follow the process outlined above.

 

[chicopee]

weldtek, I accept your argument if you can not have a permanent backing strip.

 

[carbonear59]

weldtek i am glad you mentioned "We sometimes 'seal' the joint " that is the crux of this issue as far as i am concerned . the procedure we are using calls for a GMAW "
'seal' (can be done with or without backing -as usual ) , THEN followed by a SAW pass(es )because the SAW requires backing , the whole backgouging from the other side is a red hering in this discussion .
my issue since i started this thread has been that by not putting that 'seal 'between the plates before using the SAW process we are not following our procedure or Section IX .
further to that backgouging and welding from the other side doesnt somehow magically fix the issue of welding across an open seam with SAW wire .
what i am looking for is a code reference /interpretation that either agrees with /disputes what i am saying ;that is backing means solid pieces . no holes even if they are just small skinny ones !
let me know what you think

sf

 

[weldtek]

carbonear,
The only reason we seal the joint is to avoid burning through while welding with the sub arc. 'Small skinny' holes don't matter to us if the process is capable of welding over them without burning through. In some cases the sub arc can handle joints with small gaps if the land is sufficiently thick and other minor adjustments are made.
Instead of placing a 'seal' pass from the backside of the joint, what if you were to put your first pass in using a lower heat input process, like stick or fluxcore, would you consider that welding without backing just because you're weling over some small gaps? The answer is no. The weld would be made with backing because you're not trying to make a weld from one side.
Have you reviewed QW402.4?
The matter can be summed by asking, Am I making a full penetration weld from one side only, or am I going to back gouge and weld from two sides? If you're back gouging and back welding, you're making welds with backing.

 

[GenB]

The best defense is: the procedure has to indicate
Backing? which you say you already have, then you specify the backing material as metal or weld metal and as long as you use the same weldmetal(fillermetal)you are allowed w/o having a combination weld.

I guess you can have a WPS with weldmetal and get the bless from your AI. Be sure you do not get cought in a review...
withiout the proper docs.

I agree with JoeTank on this one.

 

[Bonswa]

Yes, JoeTank hit it on the head. Just like with doorsheets or shell inserts, the first side welded is CREATING the backing for the weld on the opposite side. The ONLY time that I have pushed for an actual backing bar was when the bevels were overdone and removed too much metal, creating too large of a void to get the weld metal to stick.

The only time that you can not get around using backing is when welding annular ring plates or doing butt-welded floor plates. With no access to the opposite side for back gouging, you MUST use a backing bar.