Dumb welding question

[dstig1]

I haven't had the need to do this yet, but I see mention of a backing strip for some welds. I get the general point in that it helps stop
blow out and holds everything together a bit better for a cleaner full penetration weld, but one thing is missing from every description I have seen of backing strips: What happens with it when you are done?

Do you grind off the backing strip tack welds and it falls off? Or do you have to beat it off? Do you leave it there? Use it to stir paint? ????

Everyone seems to assume that what happens next is obvious.... I guess they are not frequently used, and I also kind of guess it is left there, but Enquiring Minds Want To Know!

 

[Transit]

Have you tried googling, welding backing strip. NO. There are tons of pages to read with much more than you want to know.

 

[dstig1]

I read many pages in various sites on backing strips (forums, Miller, Lincoln, etc), but never seen this point addressed. I have never googled "welding backing strips" directly.

 

[Transit]

These are from every fifth line from the first page.

Fundamentals of Professional Welding

CR4 - Thread: About Backing Strips

Katbak Ceramic Weld Backing on Gullco International, Inc.

Fiback? Fiberglass Weld Backing Tape, by Aquasol Corporation

 

[gauthier]

Thats the thing with a backing piece of steel isn't it? Its welded to the back of weld when you get done,,you don't use them in places where they need to come off,[generally speaking],you use a full pen weld[welded from one side only],or you grind the back side a little to get to solid metal than weld the back side,and if you need back flush,you grind it flush,if your stick welding you use a rod that you can put a root in,[6010 not a 7018],and you got to know how to prepare joint[bevel it,put land or not,etc]

If you got room to put a backing strip on back[unless its pipe or square tubing of somekind where you can't],you got room to grind and weld back.

 

[sjames]

as a hobbiest its pretty doubtfull you will ever need to use a backing strip. If i needed a perfect backside on my weld I would backgouge it, thats faster than washing off a backing strip. I do use runoff tabs fairly often though.

 

[dstig1]

I said I hadn't done a Google search, not that I couldn't But thanks for the links. Sounds like the answer is "it depends". I was just curious..

Okey dokey...

 

[lostcause]

as has been said in a couple other posts, the backing bar is used to facilitate a complete penetration weld where the root pass would be awkward or impossible to be done with other processes (electrode types). as was also noted, it is often just as practical to backgouge with a carbon rod and then weld the backside as opposed to using a backing bar - when conditions allow. here's a couple of examples when i have found backing bars to be often used and occasionally removed:

when welding on a building construction jobsite it is often common to prepare all pieces so that as much as possible can be welded flat as opposed to out of position. rather than have to weld overhead, you can prepare a connection with a gap, tackweld a backing bar underneath, and fill the void from above. generally speaking, the backing bars can be left in place because the steel is hidden behind the finished wall or ceiling.

there are times when a piece of steel is intended to be exposed to view, and in those cases the backing bars may require removal. this is accomplished by gouging them off and then replacing the damage by welding. many may wonder why you go to the extra trouble instead of just using a process that would not require the backing bar? well, the biggest reason i know of is that building construction doesn't have tight enough tolerances to guarantee that the joint to be welded is fit up well enough to do so. 20-30 foot (and larger) pieces of steel, weighing tons each are not as precise as you might like them to be. using a backing bar allows for a lesser tolerance requirement. this is not intended to make it sound like sloppy work - it's just what is needed to allow everything to work together.

 

[gauthier]

They have different kinds of backing material other than steel you can use,ceramic is one,used in ship yards alot[or was],it don't bond to the weld metal.

But except in places like was said by lostcause,or sometimes in pipe[ain't seen it used in pipe lately either],you don't use backing strap[ring],,fillits of course don't need one,most piping calls for full pen welds made from one side,,[even if its big enough to go inside to back weld it],,

There are a few good uses for a metal backing but not many compared to full pen on one side or back gougeing and back welding.

Many times on welder qual tests,you might use plate coupons with a backing strap,they generally are x-rayed so they don't have to be removed,course welder who passes such test,will not be certified for open root weld on job,but would be for fillits.

 

[Shield Arc]

Backing plates make life easier on the welder, but not really needed.
Here are some pictures of the inside of a pipe welded from the outside with 7018.