Galling of SS hardware
Galling of SS hardware
(OP)
When specifying outdoor electrical equipment, we typically specify stainless steel hardware to prevent/reduce corrosion. I have had one manufacturer request the substitution of silicon bronze nuts to prevent galling. In this instance, the hardware is used on a component that might be removed in several years. Using dissimilar metals concerns me given that some stainless steels are seperated from silicon bronze on a galvanic table I have seen. Note: This hardware is not used to conduct current.
Is this an appropriate application of these two metals? What problems can occur as a result of their use?
Thanks
Is this an appropriate application of these two metals? What problems can occur as a result of their use?
Thanks





RE: Galling of SS hardware
RE: Galling of SS hardware
Thanks for your input.
RE: Galling of SS hardware
I am mostly experienced with the military and aerospace industry but done few projects for industrial and coammercial indusrtries.
As you pointed out "using dissimilar metals concerns me given that some stainless steels are seperated from silicon bronze on a galvanic table" (MIL-STD-889 titled dissimilar metals is the reference).
In the Aerospace industry the use of copper alloys is very restricted, just look in the MIL-HDBK-5 and see that almost the only copper alloy listed there is Copper Berylliun Alloy and they are usually plated against corrosion.
In the military they use more copper alloys such as aluminum bronze, phosphore bronze and naval brass but always they are protected with grease, for example in the cannons, fire arms etc.
If you can plate/coat the silicon bronze nuts with a coat such as Zinc etc. or keep them always coated with a grease then it may be OK. You should consult a corrosion specialist for the exact environment you have or follow the leads in MIL-STD-889.
There is one more option and it is to use anti gall alloys such as Nitronic 60 etc.
However the common practice in the industrial fittings bussiness to use stainless fittings with silver plated thread nuts. I am familiar with the products of the Ham-let compny who trys to compete with Swagelok and they use the silver coating to avoid galling. There web address is http://www.ham-let.com/ you may find more info there.
RE: Galling of SS hardware
More common is the use if SiBronze bolts and nuts on Electrical equipment. In our plant this was the standard in all substations, silver plated bus bars bolted with SiBronze fasteners.
RE: Galling of SS hardware
Some very interesting and helpful comments. To reiterate unclesyd "...that does not stay wet." Keep in mind that for the couple to conduct, there needs to be an electrolyte to complete the circuit. This could be moisture (not necessarily plain H2O)in the air.
Since this application is not "...used to conduct current." this means there is reduced chance for electrical pressure to drive the galvanic couple.
Given these two points, and unclesyss' comment "...It is not unusual..." and if it will always be used in a controlled environment, then it would appear to be a fair choice of materials. However, I would suggest that you supply a disclaimer(s) internally and for end users to dissuade misapplication.
I am not a corrosion expert just my 2 cents so maybe my suggestion is overcautious.
Jesus is THE life,
Leonard
RE: Galling of SS hardware
I agree with the previous comments regarding galvanic corrosion probably not being an issue in electrical connections.
RE: Galling of SS hardware
It is also very important to use a thread form that eliminates thread crest-to-root interference. This is accomplished by selecting a thread form with some truncation of the crest. If the crest is too high and "digs into" the root of the mating thread, you will have galling no matter what you put on the threads.
Carpenter Technology makes a stainless steel called "Gallthough" that is specifically developed to reduce galling. It is similar to Nitronic 60.
RE: Galling of SS hardware
At first glance, asking for stainless steel hardware to reduce rust on outdoor electrical equipment seemed to be an easy solution. So much for first glances.
These forums are a great place to benefit from the experience of others.
Thanks again.