Duplex Threaded Components
Duplex Threaded Components
(OP)
Hi,
I was wondering if someone could advise. Basically I have two super duplex (UNS S32760) components that are required to be threaded together with a M40x1.5 thread, torqued to 750Nm. Hence I was wondering how susceptible the threads will be to galling issues, as there seems to be little or no information available. Is duplex as prone to galling as the austenitic grades of stainless? Due to he application I could not use a different mating material of different hardness to reduce the galling effect as generally recommended.
Any advice on this would be greatly appreciated. Thanks in advance.
I was wondering if someone could advise. Basically I have two super duplex (UNS S32760) components that are required to be threaded together with a M40x1.5 thread, torqued to 750Nm. Hence I was wondering how susceptible the threads will be to galling issues, as there seems to be little or no information available. Is duplex as prone to galling as the austenitic grades of stainless? Due to he application I could not use a different mating material of different hardness to reduce the galling effect as generally recommended.
Any advice on this would be greatly appreciated. Thanks in advance.





RE: Duplex Threaded Components
RE: Duplex Threaded Components
RE: Duplex Threaded Components
RE: Duplex Threaded Components
RE: Duplex Threaded Components
Here's a reference for 2205 duplex:
http://www.specialtysteelsupply.com/brochure/nitro...
RE: Duplex Threaded Components
http://namis.alionscience.com/conf/tscc/search/pdf...
Just as I suspected, low galling threshold for 2507 in the dry and salt-water sprayed condition, but surprisingly better when submerged in salt water for 90 days prior to testing. Maybe has to do with a change in surface roughness or passive layer strengthening after submersion? Regardless, surface treatments (nitriding, carburizing, TiN, etc.) and lubrication (PTFE impregnated coatings, MoS2 coatings) will help, as well as keeping the surface roughness between 10-70 microinches.
RE: Duplex Threaded Components
RE: Duplex Threaded Components
Even if nitriding, it would be a good idea to use a PTFE/MoS2-impregnated coating as well.
RE: Duplex Threaded Components
I just got done with one of those failure analysis.
You really need to try to roll the male thread. It will be smoother and harder, both will help you greatly.
Why such a high torque?
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Plymouth Tube
RE: Duplex Threaded Components
If the purpose is solely joining, and the joint does not require a break out capability, is galling an issue anyway?
Steve Jones
Materials & Corrosion Engineer
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.
RE: Duplex Threaded Components
RE: Duplex Threaded Components
RE: Duplex Threaded Components
1. Use forming tap instead of turning, etc. I would investigate Cut and Form taps from Emuge:
http://www.emuge.com/technical/pdf/Threading/zp100...
Using a forming tap in super duplex to create 100% of the thread form is not optimal (high forces, low tool life, etc.), which is why Cut and Form may be a good option. Emuge has a standard 5-flute forming tap called Robust 2X-VA that is available in M38x1.5 and M40x2, so you might be able to get a custom M40x1.5 tap made.
2. Use thread milling instead of turning, etc. Thread milling produces far better surface quality, especially in difficult to machine materials like SDSS. Emuge has a number of options in this category as well, maybe their GIGANT-IC product. It will be custom, so you would need to contact them for application assistance:
http://www.emuge.com/technical/pdf/2013-EMUGE-LEAD...