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Up Topic Welding Industry / Technical Discussions / Question for other fabricators regarding galv'd material
Poll Galvanized Material Poll
Send Galv'd material straight to job 3 14%
Bring back to shop for inspection 18 86%
- - By jwright650 (*****) Date 03-02-2011 17:42 Edited 03-08-2011 14:22
1) How many of you fabricators send your galvanized material directly to the job from the galvanizer?
2) How many of you fabricators bring your galvanized material back to the shop for inspection, straightening, etc?

reason for my questions:
My estimating department says they have spoken to other fabricators and claim that we are the only fabricator of structural steel in North America that brings their galvanized material back to the shop for inspection, straightening, etc.....so they do not understand why we spend the extra $'s shipping it back, man hours unloading, reloading, and all the inspection that I do to ensure that we have a quality product for the erector to hang in the air.
EDIT: Added poll so people can vote and not feel awkward about answering the question. Voters are anonymous.
Parent - - By jrw159 (*****) Date 03-02-2011 19:15
John,
  You guys are not the only ones. Every place that I have been that deals with galv brings it back for inspection. There are many reasons for this as I am sure you know. I have seen you mention how careless they can be about cutting vent holes that were missed (I have also seen this first hand and it can be quite ugly). Also, excessive buildup, poor finish, ect.

Even if there was a rush we would send an inspector to the galv shop to inspect before shipping direct to jobsite.

jrw159
Parent - By kkfabricator (**) Date 03-03-2011 00:56
I second that. Too many times we have had trouble with various parts of the process, and no matter how much it costs for the extra handling, it doesn't compare to the costs of having problems on the jobsite.
Chuck
Parent - By welderbrent (*****) Date 03-03-2011 18:09
The only legitimate exception in my mind would be with your own people receiving and erecting in the field so that any problems can be picked up and corrected by them without a problem from another sub, the General Contractor or Customer.

I don't do much galv work anymore, but we always inspected it before shipping.

Have a Great Day,  Brent
Parent - - By jwright650 (*****) Date 03-03-2011 19:05
Thanks for the replies guys,
After speaking with our estimating depart. we have decided to keep bringing it back to the shop for inspection but track the cost for awhile so they can create a line item/percentage to add in at bid time to cover the anticipated costs.

I MT'd over 200 pieces yesterday that returned from galvanizing and there were no cope cracks in any of the copes, but there were a few columns that needed straightening to get the sweep and camber out of them.

Two days ago, I MT'd about 35 pieces and 12 of those had cracks in the copes that had to be repaired and all of them had to be straightened. I'm expecting 3 more truck loads to come back in the next few days with hundreds of small galvanized beams on them. I'm tracking these repairs in an Excel spreadsheet that has a bar chart inserted to visually show the hours required for repair of galvanized material.

To me the liability of one beam failing is worth any trouble it causes me to inspect/repair this stuff....but I guess that is just the inspector coming out of me....plus, I don't like to climb high up on the steel structure to look at or inspect a piece with a crack in the cope....LOL(been there, done that, many years ago with a W24x104 roof beam)
Parent - - By 803056 (*****) Date 03-05-2011 14:23
Hello John;

I have a question with regards to the material being HDG. Are you HDG ASTM A36 or ASTM A992 beams? Are you experiencing more cracking in the A992 or the A36?

I suspect the problem will be more prevalent with the A992 since it is a higher strength material with less spread between the yield strength and the ultimate tensile strength when compared to A36.

In essence, in the area of the reentrant corner, you have two intersecting lines, each with a residual stress in tension on the order of magnitude equal to the yield strength of the base metal. The residual stresses can be added as vectors. When the RS is added, the resultant can be greater than the UTS of the base metal (much more so when working with high strength materials). This isn't the case with A36, a rather low strength base metal that has a wide spread between the YS and UTS. When the RS is added as vectors with A36, the resultant is lower than the UTS and no cracking will result. The same cannot be said with A992. When the RS is added as vectors, the resultant is greater than or on par with the UTS of the base metal and there is an increased probability of cracking.

When you introduce hydrogen rich environment, i.e., the acid pickle used before the dunk in the liquid HDG bath, you also have the potential for hydrogen induced cracking. The longer the material is held in the acid pickling bath, more diffusible hydrogen can diffuse into the hardened HAZ in the area of the reentrant corner. Fun stuff.

I suspect notches or a small radius in the area of the reentrant corner will accentuate the problem. Likewise, a hardened heat affected zone from the torch cut will accentuate the problem because the hardened HAZ will have a higher UTS and less spread between the YS and UTS of the HAZ. Once again the residual stress raises its ugly head.

AWS D1.1-2010 has a clause requiring the reentrant corner to be ground in the area of reentrant angles when HDG is to be performed. Check out clause 5. 17.2. I suspect it is to remove much of the hard HAZ as well as possible notches that can be initiation points for cracks. 

Please provide us with some feedback on the type of base metal you are HDG. It might be interesting.

The photographs you provided a while back depicted cracks that would be exactly as I would expect if my hypothesis is correct. The cracks were essentially at a 45 degree angle to the intersect between the two torch cuts. The reentrant corners should not crack if you drill the reentrant corner and then torch cut the cope using the drilled hole as the point of intersection.

Best regards – Al
Parent - - By jwright650 (*****) Date 03-05-2011 19:41
Hi Al,
We have tried lots of the suggestions given to us over the years and it really doesn't seem to matter if the copes are drilled or burned and ground. The AISC had even asked us to try welding a bead around the cope on both sides of the web to see if that would make any difference. The copes would still produce a crack perpendicular to the radius in the cope. I doubt very seriously if you can even purchase an A36 WF structural shape any longer. Even if you do, the material certs are very close to 50ksi.

I appreciate your suggestions though, I would love to figure this out so we could put this 60 plus year old mystery to bed once and for all, and I'm sure the AISC would love to know too.
Parent - By welderbrent (*****) Date 03-08-2011 19:22
I think a lot of us would like to see this resolved John.

Most here have had these experiences at one time or another and I'm sure many will again.  And even if I don't, I like to know things like that.  Hopefully it will be good information to have in the future for someone. 

This is one of those issues that has wider application than what is immediately seen. 

I keep wondering about the change in temps being part of the problem as it gets dipped from ambient. 

Have a Great Day,  Brent
Parent - - By jwright650 (*****) Date 03-08-2011 13:55 Edited 03-08-2011 14:15
Al, I have a new one for you this morning. A36 Clip angles seal welded to a TS. On one of these the weld cracked along the toe(bottom picture) and I suppose it let the action begin, but the other is still completely sealed 360 degrees around and it still busted.
Parent - - By yojimbo (***) Date 03-08-2011 17:47
Mr Wright- Can I ask about the angle clips in your picture- how many sides of the angle were welded, it can't be seen from the photo.  I ask because that is a hideous lookng crack, I have never seen steel misbehave so badly from a HDG bath- I was told when I began in this trade a clip like that should only be welded on 3 sides to allow for thermal expansion- My galvanizer requires full seal welding on attachments of course to avoid trapping pickling acids, but I am wondering if the seal weldment is not the source of the problem in cracking.  I apologize if this rather obvious observation has already been made and refuted by more informed minds.  Very informative posting by Al indicates a much deeper understanding and analysis but could the obvious be getting overlooked?
Parent - By jwright650 (*****) Date 03-08-2011 20:44
Yes, the clip angle is seal welded 360 degrees around the perimeter of the angle. There are literally hundreds of these clips on this screenwall framing, only these two in the pictures acted this way.
Parent - - By Mikeqc1 (****) Date 03-07-2011 02:31
I did QC in a bridge bearing fab  shop and we would alway inspect the plates, ive see exessive mils, flaking corners , debonding, then i would take and record thickness readings to insure it was done to the contract and state codes, ive seen plates welded plates blow apart. So yes we bring em back. How else besides a road trip do you know things havebeen done right.
Parent - - By 803056 (*****) Date 03-08-2011 21:30
My understanding of HDG is that you should never use seal welds, but should always leave an opening that will permit hot gases to escape.

The Ideal Gas Law states that P1 x V1 / T1 = P2 X V2 / T2, where the values of P and T are in terms of absolute pressure and temperature. The pressure that develops as a result in the change in temperature is very large. Initially, V1 = V2 until the metal begins to yield under the influence of the high pressure. As the steels yields at high temperature (remember YS is reduced to about 50% at about 800 degrees F), a bulge develops to accommodate the high pressure.

It would not come as a complete surprise if the cracks were associated with liquid metal embrittlement. The liquid zinc, with some of the "tramp" elements that may be present, can wet the grain boundaries of the steel thereby weakening the grain boundaries. The grain boundaries are subjected to very high tensile stresses on the bulging surface of the steel angle. The wetted grain boundaries act as notched stress risers which are great initiation sites for cracks to develop.

The detail is not conducive to successful HDG because of the void between the tube and connection angle that provides not escape path for the hot gases. The detail should be changed to eliminate the void or by leaving a hole for the hot gases to escape.

Best regards – Al
Parent - - By welderbrent (*****) Date 03-09-2011 00:20
So the angle could have a hole punched or drilled in it during it's prep stage on the surface that goes against the tube in order for the expanding gases to have an escape route..??  If I understood you right Al, that should greatly reduce the possibility of that crack occurring.  Sounds like a very cheap way to keep it from happening compared to the repairs involved even if only two out of all the parts John had resulted in the cracks shown.

The only other alternative would be as another poster suggested and only welding three sides to allow for the expanding gases. 

I'm wondering why there seems to be so many different opinions from those, the engineers and the galvanizers, who should have the technical information to tell the fabricators how it needs to be done.  Why were these parts called out for a seal weld all the way around.  Wasn't it known that this could cause a problem?

Have a Great Day,  Brent
Parent - - By yojimbo (***) Date 03-09-2011 01:40
One concern I am warned against by the galvanizer I use is trapping pickling acid.  Creates some nasty reaction if any acid is left trapped when it gets dipped in galv.  That is the reason I am given for compete seal welding or maintaining a minimum .035 gap between steel surfaces.  Drilling/punching a hole in the angle might not do the trick for draining the acid  if the angle was in close contact to the tube  residual amount of acid might remain.  A possible soluton might be to gap the angle clip away from the tube using some .035 wire when tacking, then weld just 3 sides to minimize restiction of thermal movements and maybe even adding the hole as an extra precaution and escape route for the acid.  If the 3 sided weldment didn't compromise structural integrity I might look into it and the hole might not represent a very large fabrication cost for the additonal insurance.  The fabrication would still have to be handled correctly by the galvanizer to take advantage of the additional drainage provided.  I work with ACE Galvanizing in Seattle, WA and they are very easy and helpful to work with, lots of access to their QC guy to plan these things out.  They have some diagrams on the wall for fabricators to keep these things in mind when planning a production run, I'll be sure to take another look next time I get through there.  Aso just occured to me, since the tube will naturall have to have drain holes in it, what about a drain hole under the clip itself?  Again structural integrity and cost would decide but might be a solution.
Parent - - By 803056 (*****) Date 03-09-2011 05:17 Edited 03-09-2011 05:29
I would be inclined to change the detail to eliminate the clip angle and use a detail that didn't create a large void that either traps hot gases if not properly vented or traps acid if a vent is provided. Perhaps an end plate detail would work. It is difficult to say what detail would work best since we don't know the configuration of the connection, the loads that need to be transferred, etc.

It is the detailer's responsibility to detail the connections that are conducive to HDG when such protective coatings are required. In situations that are not typically encountered, the detailer should work with the Engineer and the vendor providing HDG services to devise proper connection details that will function as intended and permit HDG without introducing other complications such as those John is experiencing. The vendor can provide useful information on the type of connection details that lends themselves to HDG and the Engineer can provide verification that the alternative joint detail will provide the structural integrity necessary to properly transfer the loads though the connection. 

I don't have the title at my finger tips, but there is a guide available that provides suggested connection details for applications that will be HDG.

Best regards - Al
Parent - - By eekpod (****) Date 03-09-2011 11:11
John,
Question, I know you have been dealing with this issue for quite awhile now so I'm sure those are real indications, but they look like they could be "magnetic writing" on the surface.  I assume you grind into them to confirm right?

Also, what's the fix for that? do you repair the clip angle? or do you replace it and re galv the entire part?

Chris
Parent - By jwright650 (*****) Date 03-09-2011 13:25
Chris, no magnetic writing...cracks. Yes, we gouge the clip off and replace it with a new one.

Seal welds are a necessity, if you do not seal it it WILL blow the clip off (almost every time) and acid will drip out from behind the clip and the customer will not be happy with all of that staining all over their steel.

["All edges on an overlapping surface should be seal by welding."] - quote straight out of the "The Design of Products to be Hot Dip Galvanized After Fabrication"...booklet published by the AGA.
Parent - - By jwright650 (*****) Date 03-09-2011 13:37
expanding gasses...

This doesn't explain the cracking on open ended square tubing,
...or cracking in the copes of beams,
...or cracking of angles.....let me refresh this with some pics.

We are starting to bounce all around with the guessing. I'm sure if the AISC and the AGA knew exactly what causes these problems they would spell it out precisely and have petitioned the code bodies to write some code prohibiting certain practices, but these situations seems to defy any of the reasoning. Perfectly drilled copes have cracked, and others that were burned with a torch and shaped so that they should have induced cracking survive the process just fine. This is precisely why we just cross our fingers and then just repair when it happens. Pointing fingers at the fabricator, or the galvanizer has not worked to solve these issues in the last 60 plus years.
Hang on for a minute and let me attach some pics to this post.
Parent - - By jwright650 (*****) Date 03-09-2011 13:55
more....
Parent - By jwright650 (*****) Date 03-09-2011 14:50
http://smg.photobucket.com/albums/v345/jwright650/galvanized/

A link to photobucket in case some can't view the pics. I resized them, but some are still very large and you have to scroll to see the area of concern....they were all sized to 800x600, so I don't know what's up with that.
Parent - - By 803056 (*****) Date 03-09-2011 15:15 Edited 03-09-2011 15:19
Those are some great photographs. Do you mind if I use a couple in my presentations?

I can see your concern; each situation appears to be unique in some aspect. However several appear to have some common features.

Many of the photographs depict cracks in the reentrant corners of copes. The copes with the cracks in the reentrant corners could be due to hardening in the HAZ if the cuts are made using a thermal cutting process. My question would be whether or not the HAZ was completely removed by grinding before HDG? You can check the mill test reports to determine the carbon equivalency to see if they are more susceptible to hardening and subsequent hydrogen assisted cracking. I don't have the experience you do with this situation, but I would suggest attempting to determine if the A992 currently used is more susceptible to the cracking problem than the A36 used in years past. As I noted previously, the residual stresses that develop from the two intersecting thermal cuts can exceed the tensile strength of the high strength steels. The characters of the cracks depicted by the photographs are exactly what I would expect if they were the result of residual stresses. The crack would be transverse to the residual stresses, or in this case, at an angle of approximately 45 degrees to the axis of the residual stresses.

The HSS could have been hardened in the area of the corner bends by cold working when the tubes were formed. The strain hardened regions are susceptible to hydrogen induced cracking from the acid bath or liquid metal embrittlement when submerged in the HDG.

It would be a good project for a graduate student's thesis.

Best regards - Al
Parent - - By jwright650 (*****) Date 03-09-2011 16:06
I appreciate your diagram Al, that helps see the vectors. Yes, please use the pics....hopefully someone will figure this out eventually if we keep after it. Like I've said earlier, the finger pointing of the past is not working to solve this. I would love to blame the galvanizer, since it appears to happen while the steel is in their tank, but I realize there are lots of variables and we can't seem to get them all to line up for a good evaluation.

For those who say that they have never had a single cope crack, just haven't inspected enough of the galvanized material to know for sure.
I'm willing to bet that for those who send their material to the field without inspecting have material currently in the air with cracks present, just waiting.

What scares me to death is that many of these cracks are not always visible to the naked eye, and need MT to see them. The cracks generally have zinc inside them and completely cover the crack so the naked eye sees a nice uniform surface. This tells me that it is happeneing while in the bath.
Parent - - By 803056 (*****) Date 03-09-2011 16:16
Hello John;

I deleted the sketch. It wasn't the right one. I deleted the original file and attempted to insert the corrected sketch, but each time I attempt to upload the new file it appears as the original. The original file was deleted, but still the new file will not upload. Go figure!

Good luck with finding a solution.

Too bad you didn't have several drops of A36 and several or A992 to compare the number of cracks each produces when prepared in like manners.

The correct sketch is attached to this post.

Best regards - Al
Parent - - By eekpod (****) Date 03-10-2011 12:24
John,

Do you always use the same galvanizer when this happens?
We have two different companies that we bounce back and forth, I'm curious if it only happens at this one.
Parent - - By jwright650 (*****) Date 03-10-2011 12:48
Well Chris...in my neck of the woods there were two different plants years ago, but now both locations are owned by one and the same....so does that really count as two different plants or not? LOL

I used to be pretty quick to announce that I didn't think that this happened at one plant and always happened at the other(<--my apology to that galvanizer who I gave such a fit to for a number of years)...but in the galvanizer's defense, I'm not sure that I had done enough testing of galvanized material back then (10 or more years ago) to say that I was sure it only happened through one vendor and not the other. The cracking after galv'ing was new to me back then and I had only spoken to a few people who were aware of that fact that it can happen, at that time.

What I do know at this point is...I am positive that cracking happens from time to time and that bringing it back to my shop is a must for me to be sure that a piece doesn't make it in the air without some magic MT dust being applied for some peace of mind. Hopefully I can convince our estimating dept of this reality and get them on board with me.

Now, the warping and plugging of vent holes is different matter all together, but is also a reason to bring our material back to the shop, rather than trying to deal with all of that in the field.

I'm not dissing anyone who has the confidence to send their material straight to the job, I'm just saying that isn't my preference based on my testing experience of our material.
Parent - By welderbrent (*****) Date 03-10-2011 14:47
This topic sounds to me like it would make a good paper for some of the people doing investigative research for their degree.  Then maybe we could get some money, time, and definitive results as they have with other issues through the years.

Have a Great Day,  Brent
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