Last time I came here with some market research questions and got some great responses. I'm back, but this time thinking about steel purlin usage for metal building (for roofs, primarily). I have been trying to work through how much of the market is preferring HDG over traditional galvanization processes. I had one guy in the west tell me that there split is 75% HDG, and said traditional galavanized purlins are non-existent. On the other hand, I had someone more east that said that maybe his region was about 25% share traditional galv usage, but didn't differentiate between HDG and traditional. What do you all make of this? How much of the market is truly galvanized, and how much of is HDG? I would love to hear any perspectives
When you say 'traditional' galvanization are you referring to electroplating?
If that is the case we tend to use HDG over electroplating for exterior use when the members aren't visible. Of course the HDG coating always gets damaged during assembly and needs to be patched.
Yeah, we pretty much only specify HDG for things that can be HDG... we have had some issues in recent times with specs showing HDG screws, when a lot of screws are not readily manufactured as HDG... funny stuff.
Doesn't the HDG coating thickness mess with the threading of smaller fasteners or nuts
? I'm guessing HDG is common with anchor bolts and the like but those fastener diameters tend to be very large.
When I practiced in Minnesota (eh) we HDG everything at least 6 mils. Structural engineers would take into account the thickness of the HDG coating when designing these connections and thread type.
Holes are usually "overtapped" (tapped slightly larger than normal) to accommodate the extra thickness of the galvanizing on the bolt's threads. I've also seen that you can wait to tap holes until after galvanizing and the zinc on the bolt will protect both the hole and the bolt. This saves you from having to chase threads with a tap after galvanizing. https://galvanizeit.org/design-and-fabrication/fabrication-considerations/fasteners-bolts-and-nails1/tapping-threads
"Doesn't the HDG coating thickness mess with the threading of smaller fasteners or nuts ?" Yes, that is where I have found issue with specs. I want to say I've had this issue with wood screws if I recall correctly a couple times where they just don't make them as HDG because of the impact of the galv on the threads. This is about the only case where we might use another kind of galv, otherwise anything else is HDG if galvanized.
Popularity of traditional galavanized vs HDG in industrial buildings
Hello all,
Last time I came here with some market research questions and got some great responses. I'm back, but this time thinking about steel purlin usage for metal building (for roofs, primarily). I have been trying to work through how much of the market is preferring HDG over traditional galvanization processes. I had one guy in the west tell me that there split is 75% HDG, and said traditional galavanized purlins are non-existent. On the other hand, I had someone more east that said that maybe his region was about 25% share traditional galv usage, but didn't differentiate between HDG and traditional. What do you all make of this? How much of the market is truly galvanized, and how much of is HDG? I would love to hear any perspectives
When you say 'traditional' galvanization are you referring to electroplating?
If that is the case we tend to use HDG over electroplating for exterior use when the members aren't visible. Of course the HDG coating always gets damaged during assembly and needs to be patched.
HDG or GTFO is the moto in my frozen and salty backyard.
Yeah, we pretty much only specify HDG for things that can be HDG... we have had some issues in recent times with specs showing HDG screws, when a lot of screws are not readily manufactured as HDG... funny stuff.
Doesn't the HDG coating thickness mess with the threading of smaller fasteners or nuts ? I'm guessing HDG is common with anchor bolts and the like but those fastener diameters tend to be very large.
When I practiced in Minnesota (eh) we HDG everything at least 6 mils. Structural engineers would take into account the thickness of the HDG coating when designing these connections and thread type.
Holes are usually "overtapped" (tapped slightly larger than normal) to accommodate the extra thickness of the galvanizing on the bolt's threads. I've also seen that you can wait to tap holes until after galvanizing and the zinc on the bolt will protect both the hole and the bolt. This saves you from having to chase threads with a tap after galvanizing. https://galvanizeit.org/design-and-fabrication/fabrication-considerations/fasteners-bolts-and-nails1/tapping-threads
We'd used the 'over-tapped' and 'after-tapped' methods. Each have their positives and negatives. We've typically use the 'over-tapped' method.
Thanks all, TIL!
Photo from EA's link is an overtapped hole with a coated thread.
P.S. my new fav Doc is Dr. Galv!
"Doesn't the HDG coating thickness mess with the threading of smaller fasteners or nuts ?" Yes, that is where I have found issue with specs. I want to say I've had this issue with wood screws if I recall correctly a couple times where they just don't make them as HDG because of the impact of the galv on the threads. This is about the only case where we might use another kind of galv, otherwise anything else is HDG if galvanized.
Thanks all! This has been very helpful!
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