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Up Topic American Welding Society Services / Technical Standards & Publications / seal weld?
- - By supermoto (***) Date 05-04-2010 19:42
When we have gavlanize pieces a lot of our drawings have details/notes stating "seal weld all contact points".  My question is if this is just a weld that is sealing off a contact point from hot dip gavanize, than is it considered a structural weld and do we have to follow any code?  If not considered a structural weld than how about sealing them with a nice flat downhill weld?
Parent - - By jwright650 (*****) Date 05-04-2010 19:52
It is a weld that primarily seals the joints so that the cleaning/pickling solutions and whatnot can't get in or behind and blow the plates and stuff off when they are dipped in the 850°F plus molten zinc. Steam is very powerful and that is another reason for the weep holes in pipes and tubes that get hotdipped. Be sure, for the safety of the galvanizers workers, to properly vent any tubing before shipping to the galvanizer.
Parent - - By supermoto (***) Date 05-04-2010 19:58
I understand the use for this but my question is do we need to follow normal D1.1 procedures for this type of weld?  Especially considering that it isn't structural.

It is like saying we have material that is less than 1/8in thick, so we don't have to follow D1.1 code and we could possibly weld it with GMAW-S.
Parent - - By jwright650 (*****) Date 05-04-2010 20:07
Its a grey area that really doesn't get talked much about...

I think it is Ok to run smaller stringers than the min size per D1.1 to seal these joints as long as the structural welds are in place.

Does this fall under D1.3 by chance(you mentioned "not structural, less than 1/8"), since it is not covered by the scope of D1.1...See D1.1, clause 1.2.
Parent - By supermoto (***) Date 05-04-2010 20:34
No it doesn't fall under D1.3 but I used that as another example about th 1/8in not being considered structural steel. 

There are a lot of grey areas in D1.1 but I guess that is why this forum is such a great tool!
Parent - - By HgTX (***) Date 05-04-2010 20:37
Use caution:
http://www.jflf.org/pdfs/papers/design_file6.pdf

The seal weld doesn't "know" it's not supposed to be structural, and if load goes through it, it can crack.

Hg
Parent - - By jwright650 (*****) Date 05-04-2010 20:44
Hg,
Good article, thanks for sharing.
Parent - By 803056 (*****) Date 05-04-2010 21:18
The minimum weld sizes listed in D1.1 for fillet welds and PJP groove welds are based on the base metal thickness to prevent cracking, not due to strength requirements.

The minimum size weld in many cases is a single pass weld. It is sized to ensure sufficient heat input is used to prevent hardening and to reduce the susceptibility to hydrogen-induced cracks. 

Parts immersed in the pickling acid prior to being dipped in the galvanizing tank are prone to hydrogen cracking because of the [H] rich environment of the acid. [H] can diffuse in to the welded component if it is held in the acid for a sufficient amount of time.

My advice is to adhere to the minimum weld sizes listed in D1.1.

That brings to mind a problem mentioned by John regarding the cracks in the area of the web that had been torch cut. I have to ask the question, "Are the cracks found more often in the A992 steels than the A36?"

I suspect the answer is yes, more cracks are observed in the higher strength A992 steels. A992 is more richly alloyed than A36 making it more susceptible to hardening from the oxy-fuel cutting process than the A36 steel. Once immersed in the [H] rich pickling solution, hydrogen can diffuse into the torch cut surfaces and crack under the influence of the residual stresses that  resulted from the torch cut. Just a thought.

Best regards - Al
Parent - - By supermoto (***) Date 05-04-2010 21:18
Yes very good article, I guess it will be a job specific issue.
Parent - - By swnorris (****) Date 05-05-2010 22:40
Guys,

I don't mean to change the subject, but I have an issue where 26 pcs. of 1/4" thick A36 plates approx. 4' x 10' were dipped per A123.  The zinc coating is peeling off in sheets that look like tin foil.  The chemical composition on the mill cert for the plate is within ASTM tolerances.  The galvanizer came to the plant to see the plates and couldn't explain the cause.  He asked us to send the plates back to them.  They stripped the coating and went through the process again.  They called, said they were ok and ready for pick up.  When we got them back, we scratched the surface with a knife blade and the same thing happened again.  Have any of you ever experienced this or heard of it happening? This is a first for me.  The galvanizer then said that the plate may have contained just enough aluminum to rise to the surface of the plate at the mill, preventing the galvanizing from bonding to the plate. I did notice a very small amount of Al indicated on the MTR.
Parent - - By ssbn727 (*****) Date 05-05-2010 23:20
I read something that suggested also to having too much trace amounts of Al as a cause for certain issues involving galvanizing somewhere... If you give me some time (like a day), I'll search for the articles/papers regarding similar issues which you're experiencing and see what I can come up with okay??? Besides it'll keep me sort of busy as opposed to staring at the ceiling like I have for the past few days - CAPECHE???

Respectfully,
Henry
Parent - By eekpod (****) Date 05-06-2010 20:20
are they abrasive blasting them or are they dipping them in acid to etch them for preperation before the hot dipped galv?
Chris
Parent - - By jwright650 (*****) Date 05-06-2010 11:04
Sorry Scott, I have not seen that issue before either......let us know what you discover is the cause.
Parent - By swnorris (****) Date 05-07-2010 16:53
Acid bath.
Parent - - By CHGuilford (****) Date 05-12-2010 16:31
I'm curious - did the zinc completely disbond from the steel? Or did a layer peel off but there was still zinc on the surface? 

Basically, you should have 3.3 mils average for that steel thickness.

These days you will see a higher level of Aluminum on the CMTR's - the mills use that as a deoxidizer to "kill" the steel.  Silicon is used as well.  And a lot of steel is now made to comply with A36 and A572-50 specs.

I'm not sure what effect aluminum has on the galvanizing but I do know that higher silicon levels will cause a thicker zinc layer that appears dull gray and almost porous.  That is usually just a cosmetic problem, but it can promote cracking in some cases.
Parent - - By swnorris (****) Date 05-13-2010 17:15
Chet,

The galvanized coating disbonded completely off both sides of the plates.  Peeled off and reminded us of Reynolds Wrap.  The chemical requirements on the MTR were within A36 range and the over/under limits were within A6.  The MTR indicated Al, and I was told that Al. can rise to the top of the plate, causing the galvanized coating to fail.  When we checked the bottom side, the coating peeled off it as well.  So much for the theory of the Al. rising to the top.
Parent - - By aevald (*****) Date 05-14-2010 04:38
Hello Scott, your AL rising theory might still be a part of this as the "rising" statement could possibly be describing "leaching from the material" meaning on all exposed surfaces? Best regards, Allan
Parent - By CHGuilford (****) Date 05-17-2010 16:16
I thought that too about the aluminum - strange things can happen at galvanizing temperatures.

But that's a little disturbing about the Reynold's Wrap effect.  It sounds like the plate is not actually A36, or something is very wrong in the zinc bath.  If other materials hot-dip galvanized OK in the same kettle, then I would double check the CMTR and the actual material identity.
Parent - By Mikeqc1 (****) Date 05-06-2010 00:30
ive seen plates blow apart b4 not good! like small bombs in the solution.
Up Topic American Welding Society Services / Technical Standards & Publications / seal weld?

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