Separate Threading Dies for Different Materials?

[TwoBlocked]

Hey, I am trying to remember what I read once about using separate dies for different conduit materials like galvanized, stainless, and aluminum and why?

 

[infinity]

The NEC requires only one specific type of tapered die for field threading any type of RMC. 1 in 16 taper or 3/4" taper per foot.

 

[TwoBlocked]

Thanks, what I mean, is there a problem if the same die is used for, say, galvanized conduit and SS pipe? I thought I read something about that.

 

[Deltaforce]

Die longevity less ss case

 

[retirede]

Die longevity less ss case

Of course the die will wear faster on harder material. But his question is about the consequences of using the same die on different materials.

 

[Deltaforce]

Of course the die will wear faster on harder material. But his question is about the consequences of using the same die on different materials.

Same die on different materials, no issue for different materials thread quality
Rather same die cutting liquid on different materials, issue

 

[synchro]

I've seen recommendations for keeping separate dies -- even if they have the same part number --for ordinary steel and for stainless steel. That's to keep any ordinary steel particles from being imbeded in the stainless and leading to localized corrosion. I could see this maybe being an issue with, for example, process piping, but much less of an issue for electrical conduit.

 

[Joethemechanic]

I can see if you are doing production runs of threading, you might want to hone-in on your die selection. But for field work it's not going to make a difference

 

[Eddie702]

I know Ridgid makes "alloy" dies which AFAIK are usually furnished in the dies used for hand threading. They also make "HSS" dies high speed steel which are the ones used for power threading.

Of course, many hand dies are used with machines as well. I used to try to buy the HSS only as in most cases or use HSS for replacements. The only real difference is the HSS should last longer.

There may be a different cutting oil recommended for SS.

SS is a lot harder on the dies

 

[winnie]

I've seen recommendations for keeping separate dies -- even if they have the same part number --for ordinary steel and for stainless steel. That's to keep any ordinary steel particles from being imbeded in the stainless and leading to localized corrosion. I could see this maybe being an issue with, for example, process piping, but much less of an issue for electrical conduit.

My _guess_ is that properly (and completely) cleaning the die will prevent problems, but I don't know if this is true.

I recall reading that small iron particles can allow pits and cavities to form; the particles of ordinary steel can penetrate the 'passivation layer' in stainless steel and lead to localized corrosion, and then the cavity is oxygen deprived enough that you don't get a passivation layer and the corrosion increases. I don't fully know the details. Here is a quick reference that I found:

https://nickelinstitute.org/media/1678/fabricationandpost_fabricationcleanupofstainlesssteels_10004_.pdf

 

[Joethemechanic]

Stainless is funky to work with. The 400 series is harder than the 300 series. The 300 stuff is a lot more ductile. And the more alike your stainless alloys, the more it will gall and cold-weld which becomes a real PIA if you ever have to unthread a treaded connection. So if you can get away with using stainless and carbon steel together at a treaded coupling, the next guy will thank you.

One thing that sucks about working with SS is any kind of hot-work with stainless produces hexavalent chromium (Cr(VI)), a form of the metal chromium that is a toxic human carcinogen linked to respiratory, nasal, skin, and kidney damage, as well as cancer

That's the Hinkley California chemical that this chick made famous

 

[BarryO]

On a tapered thread I don't think it's very critical. It might be a different story on straight threads where you have to hit the specified dimensions.