Rust on the NPT threads... normal or not?

[k-daddy]

I relocated a temperature probe on my K-Rims system and had to disassemble several parts on my Spike BK & MT. I noticed what appeared to be rust/staining on the threads inside some of the NPT couplings. Unfortunately, I didn't capture a picture before putting everything back together. There was a post by someone on this site who mentioned "sugaring" but I'm not exactly sure what that means and if it's anything to be worried about. Should I be concerned?

 

[Bobby_M]

Surface iron at most. Mix up some hot water and citric acid and flood those areas for an hour. Use a ratio of 1 gram of acid per 100ml of water.

 

[k-daddy]

Thanks Bobby. Will that solve the issue from happening in the future or just clean up the areas temporarily?

 

[augiedoggy]

Are you using teflon tape on these threads? Im trying to picture bare exposed threads inside of couplings but they are supposed to have a couple layers of tightly wrapped teflon tape to prevent galling https://en.wikipedia.org/wiki/Galling (which could contribute to rusting coincidently)

 

[RPh_Guy]

Citric acid at 4% (4g per 100mL) at the right temperature for the right duration (60 minutes at 140°F or higher) will selectively remove iron from the surface, reducing the chance rust will form in the future. It's called passivation.

+1 for Teflon (PTFE) tape.

 

[k-daddy]

Are you using teflon tape on these threads? Im trying to picture bare exposed threads inside of couplings but they are supposed to have a couple layers of tightly wrapped teflon tape to prevent galling https://en.wikipedia.org/wiki/Galling (which could contribute to rusting coincidently)

Yes, 3-4 wraps or so on all threads, and while I gave them a good tightening, believe I stopped short from applying enough pressure to gall. When I removed the old teflon tape, everything underneath was shiny bright. I think the rust was on threads not mated to the fittings/valves due to the depth of the "full" 1/2" NPT Spike couplings, even when hardware is installed on both sides of the coupling. I think it is in that "gap" where the rusting has occurred. Never would have noticed had I not re-fitted my system.

 

[Bobby_M]

Machined and welded parts are just more susceptible to surface rusting without the passivation process being performed. It shouldn't rust again after the surface iron is removed.

 

[day_trippr]

Well...it'll clean up what was exposed with the original installation and then removal of the threaded fitting, but any tapered fitting is going to re-expose threading surface when reinstalled. It's the nature of the thread type (which was designed for iron pipe!) and while dope or tape will definitely reduce the affected area it's not going to totally stop it on the outer thread faces that are doing all the work.

In any case, it's not something I'd skip a nap over

Cheers!

 

[k-daddy]

Well...it'll clean up what was exposed with the original installation and then removal of the threaded fitting, but any tapered fitting is going to re-expose threading surface when reinstalled. It's the nature of the thread type (which was designed for iron pipe!) and while dope or tape will definitely reduce the affected area it's not going to totally stop it on the outer thread faces that are doing all the work.

In any case, it's not something I'd skip a nap over

Cheers!

So I won't be able to blame it for any future "drain pour" batch? Ha!