We are building a costomer handrails made from flatbar. It requires all welds to be ground smooth and then hot dipped galvanized. When the handrails return from the galvanizer, the area that was welded can be clearly seen because it is now raised in that spot and looks as if it were never ground smooth. Any ideas on why this is happening and how to stop this from happening?
Hi Travis, I had the same problem a while back with splice welds in pipe columns. The welds were beautifully blended with a series of sanding discs so that the welds were not at all noticible. Hot dipping however, brought the welds right back out in the open. I never could figure out why, and the customer wound up rejecting the columns and requiring replacement. Sorry this info is of no use to you, but I sure would like to know the answer to your question as well.
Hi Tim Our customer has rejected a few of our handrails as well. We have made an attempt to use a buffing wheel on some weld and are waiting for them to return from the galvanizer to see if it makes any difference. After reading your post I have very little faith that the buffing will help. There has to be something at the origin of the weld that is attracting the galvanize. Maybe that area is now somewhat magnetized due to the welding process? That is just a guess, I dont know if the hot galvanize would even be affected by magnetism. Hope someone on here can give us an answer and a solution.
Hey Travis, we run into the same thing all the time....however have not had any rejections due to it. Most of the designers have seen this and realize it's gonna happen. My uneducated guess as to why this happens is the rate at which the cooling happens after being pulled from the dip....expansion and contraction, the weld material cools quicker than the material around it not letting it contract back down hence leaving a risen band. but then again, I'm just the janitor. I was thinking about this months ago and actually came to a logical reasoning (to me anyway) as to why it happens, but it has somewhat escaped me....friggin memory. different material components make for different expansion and contraction rates.
Hey JJ Well your guess as to what causes this definately sounds better than my guess. I wish the customer knew to expect the galvanize band but unfortunately they didnt and dont like it. I have no idea how to solve this problem or if there even is a solution to it. Not sure why they would even want to galvanize a handrail anyway, but they do so now its our problem. Thanks for your help.
T.C. Run into this problem on every Hot Dip Galv. job on railing. Alot of Architects/Engineers are coming to the realization HDG isn't an acceptable "Architectual Finish", only solution to your problem is to regrind/finish welds again and then spray w/ cold galv. touchup spray.( this spray is commonly used by galvinizers to touchup areas that didn't galv. right. IE. hook marks,rack areas, etc.) I feel your pain, have a 1000 ft. rail job now, thats installed and the inspecter is wanting to know why are there holes at every rail/midrail/post intersection????? Doesn't have a clue rail needs to be vented so air can escape and galv. will coat inside 100%, also safety because heated air will pressurize and explode causing alot of problems for the galv. labor. (Inspector wants holes "plug welded" closed which will burn off galv.?????) HDG coating has a 40 yr. "useful life", if it could be colorized somebody could become a millionare!!!!!! Pittsburgh home of" J. Harrison"/ Best linebacker in the game today playing for the "STEELERS"
Plugging vent holes.....found a solution that works well for us, check these people out. Aluminum tapered plugs, drill the vent holes before galv'ing and when it comes back from the galvanizer, drive these in with a hammer and finish them off with a sander/grinder.
Bruce Reichelt Enterprises 20160 SW Johnson Street Aloha, Oregon 97006
Weld metal often contains alloying elements that are different than the base metal. During hot dip galvanizing the alloyed metal sometimes attracts more zinc than the surrounding metal. .Even base metals that have different alloy composition often get thicker zinc deposition and end up with a different color and spangle. Thickness and heat absorption also can affect the appearance of the galvanized product.
Travis Collins Welding Electrode Selection When selecting a welding electrode, make sure that it provides a deposited weld composition as close as possible to the parent metal’s chemical composition. The composition compatibility will yield a more uniform zinc surface appearance. As with galvanizing high silicon steel, welding rods high in silicon may cause excessively thick and/or darkened galvanized coatings to form over the weld.
In regards to the handrail issue read this article. http://www.galvanizeit.org/images/uploads/drGalv/silicon_welding.pdf. (looks like you're going to have to cut and paste this URL). A while back I witnessed the same weld metal expansion but it was with Stainless Steel. A rack structure was welded up, all the welds were ground to a flush, #4 finish and sent out to have a electro/chemical polishing done to each one of them. When they returned all the welds had popped up. Consequently the customer wanted them fixed to what was spec'd. The chemical solution that the racks were dipped in was heated to about 400* Fahrenheit (if memory serves me right) and allowed to stay in the tank for a certain amount of time. I believe what happened is that the heated solution released the compressive state that the weld metal was in allowing to expand to a relaxed state.
Plugging vent holes.....found a solution that works well for us, check these people out. 
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