welding from one side 1

[HgTX]

Need to do some fracture-critical welding with access only from one side of the weld once both plates are in place. Tensile stress across the weld, so can't use stay-in-place steel backing (which would be welded to one side of the joint before the plate is put into place, if this weren't a tension connection).

Thought about ceramic backing (and qualification per AWS D1.5 section 5.7.7), but is there a version of ceramic backing that doesn't require access to both sides of the joint in place? The only stuff I've seen involves a strip of tape that runs across the ceramic and tapes to both sides.

If not, AWS D1.5 section 5.7.7 allows qualification of PJP as CJP even without any backing at all, I think. There's a bend test & macroetch to demonstrate adequate fusion & penetration at the root, but wouldn't melt-through still be a fatigue concern? (Or is the no-backing case blocked by other provisions of D1.5 such as 4.6.9 and 4.7.6?)

Hg



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[pipewelder1999]

Ceramic backing would allow you to "countour" the backside of the weld depending upon the shape of the backing itself.

A preplaced consumable insert would not lend itself to being easily welded in a plate tee joint configuration if the root side contour needed to be controlled and the re-entrant angle of the weld toes small .

You could contact someone at imperial or some other insert supplier to see if they have any ideas .

http://www.imperialweldring.com/

Gerald Austin
Iuka, Mississippi

http://www.weldinginspectionsvcs.com

 

[unclesyd]

Something else to cloud your mind.

Here is all types of ceramic backup tapes. The only problem is that I can't find a US distributor, only the Netherlands. You might Email, you have a good address, the company and see if they have a US distributor.
It looks like they have all angles covered under the three headings. Especially look at CBM 8601(4G).

http://www.dicera.com/eng/e_main.html

http://www.lascentrum.com/en/ceramic+backing+material/

 

[HgTX]

Ceramic backing was our initial thought for this situation--until I remembered (insert dope slap here) that one needs access to the back of the weld to put the backing on. The tape goes across the back onto both sides of the joint.

The good thing about fused steel backing is that it can be tacked to just one side before the joint is assembled and the connection is rigid enough that the other side doesn't have to be tacked.

Meanwhile, back on the ranch, the Fabrication Consultant Dude says that he doesn't think bridge applications have good enough fitup for a consumable insert to work.

Hg



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[unclesyd]

Toured 3 (2 small, 1 large) ship yards in quest of an answer to you problem. Most of the comments were in the “smart ass category, like don’t get yourself in this trap”. Also talked to QC person about heavy wall submersibles, essentially the same answer they never got into this situation.
The just of the discussions were the use of a inserts and backing plate of various sorts from a Z bar to flux coated Cu and Steel. Most used a backing bar with a groove and if possible purged the backside of the weld through the groove. I’m still try to get some information from another yard that works on good old big ones.


Here is an article from the UK concerning similar situations in respect to fatigue. Starting about page 60 there are some joint descriptions that might be of interest. .

http://www.hse.gov.uk/research/otopdf/2001/oto01083.pdf

 

[billMcL]

Just an FYI-
AWS D1.1 does not consider any weld joint, welded from one side with backing, that is not steel to be pre-qualified. welding with copper backing, ceramic backing, etc.will require procedure qualification.

 

[HgTX]

unclesyd--handy document, thanks!

billMcL--this is a D1.5 job, so nothing is prequalified. But this wouldn't even fall into the category of standard qualifiable joint, and I'm hesitant to let them qualify it as a nonstandard joint based on a single test plate that doesn't include any fatigue testing.

I'm a big fan of the "avoid the situation" technique myself. Now that the situation's here, I think what they're going to do is size everthing for some godawful fatigue category. Still waiting to hear about that...

Hg



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[unclesyd]

HgTX,
In addition to and on the lighter side.

Talked to my oldest (96 yrs old) source this morning and just for curiosity asked him about one side welding of thick materials, say 2.5".

"His comment was get you some good pattern pine 2x4's as backup along with a large torch and asbestos shirt, sleeves and balaclava.

The pine 2x4's were very dry long leaf yellow or white pine.
The torch he was speaking of is a twin carbon arc running about 400 to 500 amps at 60-90 volts using a 1/4" bare rod. He said hook two “pigs” togather with the voltage set at max.”

He also said that he didn't envy you your job based on some of the fit-ups he had seen on some local construction. He also told me to tell you to practice "CMA".

 

[HgTX]

Yeah...

I'd have a lot more whining to do, just for whining's sake, except that this is a public forum. CMA.

It'll all work out in the end. 10 years from now everyone will be happy.

Hg

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[unclesyd]

HgTX,
Could you possibly post the material specs on your job?

 

[HgTX]

Material specs? You mean the steel? ASTM A 709 Gr. 50.

One of the several reasons tubular members aren't in D1.5 yet is exactly this issue of one-sided welding. (Not that I have HSS in this project but it's a similar issue.)

And yet there are fancy signature spans out there with tubular members, like those French bridges with the corrugated webs coming down to a single tubular member in place of the bottom flange, or that AISC poster child with the big red freestanding tubular arches (some of you probably know what I'm talking about).

Oh, here it is:

http://www.aisc.org/ContentManagement/ContentDisplay.cfm?ContentID=567

Damen Ave. Bridge, Chicago

The article doesn't say how they spliced it, but the arch is probably in compression anyway.

Hg

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[unclesyd]

A cheap one.
Tubular Structures

https://ssl.lincolnelectric.com/lincoln/spmount/item.asp?prodnum=TS

An expensive one. Look at part nine. It would be nice to take a peek. There should have been another conference since this one.
This book is on Google Books.

https://ecommerce.tandf.co.uk/catal...e=TF&RedirectPage=PerformSearch.asp&curpage=1

Pickuped on these books while looking for another book.

I still have several queries out on you problems.

 

[unclesyd]

Found these references by chasing authors on some papers I had referenced previously.

http://www.isope.org/publications/proceedings/ISOPE/ISOPEVol_IV_1996.htm

http://www.ooae.org/omaedatabase/omae00dbmat.htm

If you have access to Metadex It would be a good place to start looking for a presentation if not available from the presenting organization.

http://www.csa.com/factsheets/metadex-set-c.php

Take care as you will see in both organizations the word arctic is quite prominent. It was common knowledge when I started work that if you didn’t solve the problem they would send you to Alaska. Just be careful or you might end up working on Senator Steven’s big bridge to nowhere.

 

[HgTX]

There's now a related thread in the AWS Eng-Tips forum, thread178-154004. Check it out. Slightly different questions from mine.

For my project, they decided to go with access holes for some of the welds, and redesignating others as non-tension welds (or low enough tension that bad fatigue category was okay, or something).

Hg



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[unclesyd]

I thought the author of that thread was a nom de plume for HgTX.
I guess it doesn't pay for me to think. That thread had me worried, how can you put rat holes at critical joint.

PS
I haven’t heard from my big city buddy about what he has ran into with fabrication problems similar to yours. I think he has been involved with some lift failures.

 

[HgTX]

We do rat holes at critical joints all the time; it's just a matter of sizing & finishing them properly. That thread addresses holes big enough to get welder body parts through, not just rats.

Hg

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[unclesyd]

Has your quandary been resolved yet?

I have just been appraised of a very similar situation where some components were welded out of sequence and have possibly created a very expensive problem.

 

[HgTX]

The whole project got delayed. How many of those details will survive into the next version, who knows. But the last version I saw handled the problems with a combination of fabrication sequence, access holes, and just going ahead and leaving backing in place, declaring the stress to be low enough at that location to support a Category E detail. (I don't mind if the designer violates D1.5 as long as they fully acknowledge that's what they're doing.)

Hg

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[unclesyd]

Thanks, I think your approach is the way to go. Just document the numbers, get the proper signatures, and start welding.