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Stainless steel fastener galling


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This is a warning for the unaware about an issue that is peculiar to the use of stainless steel fasteners called galling.  Stainless steel fasteners often are used to replace cad plated or un-plated steel fasteners to get around rust.  I had 2 issues with galling while restoring my 1931 Buick coupe.  The first was pretty harmless because it was during bench build of running boards and access to the failed fasteners was easy, therefore it wasn't much trouble to replace the failed fasteners, just annoying because that was my first experience and I didn't understand the failure was in fact thread galling.  The second time I ran into this wasn't so funny.  This time I was trying to remove antique rear bumper trim caps, stamped sheet metal affairs with hidden brackets with square holes in them that attached carriage bolts to the back of the decorative trim pieces.  I had spent hours with a die grinder and other tools cutting old spot welds off the back of these parts to replace rusted out original fasteners.  I made new brackets, populated them with stainless carriage bolts and had the local metal shop spot weld the brackets on.   The nuts, which were also stainless were seized on the carriage bolts when I tried to remove the trial fit parts to send them to the chrome plater.  Before I knew what was happening the carriage bolts turned in the square holes of the attaching brackets destroying the brackets AND the nuts would not come off the carriage bolts.  I wound up taking the entire quarter bumper off the right side of the car to get access to the nuts and carriage bolts and had to saw thru the bolts an nuts to get the trim part off the bumper.   Then I had to grind off the spot welds on the square hole brackets, then fabricate new square hole brackets which eventually will have new stainless carriage bolts installed and I will have to have the new brackets spot welded in place.  

 

The fasteners came from Bolt Depot, a supplier I have bought thousands of dollars worth of fasteners from.  I sent an e-mail to customer service explaining my predicament and they identified the problem as galling which is friction welding of two stainless fasteners, the nut and bolt.  I also have stainless bolt installations in threaded mild steel of cast iron locations on the car and there is no problem there because the metals are dissimilar.  Stainless steel generates an oxide coating that prevents rust and prevents metal to metal contact of the soft stainless alloy.  Under light fastener loads you need nothing special to successfully safely install stainless fasteners.   As tightening torque increases you have to use an anti-seize grease to prevent galling.  The link below is to a page on the Bolt Depot website I never knew about until my encounter with customer service.  They were very apologetic and are replacing the fasteners.   Below that are some pictures of my particular horror story. 

 

https://www.boltdepot.com/fastener-information/Materials-and-Grades/Thread-galling.aspx

 

Cheers

Dave

 

This picture shows the back of the bumper trim caps.  You can see I fabricated 3 new

steel square hole brackets and was able to salvage the 4th that hold the carriage

bolts to the back of the trim caps for a hidden fastener mounting arrangement.

Rr bmpr cap 010.jpg

 

This is the right cap installation on the bumper brackets.  The stainless carriage bolts pass thru the chrome bumper

bars, then to an attaching bumper support bar bracket and apparently the tightening torque was too much for

the stainless nuts and carriage bolts on this side of the car, they were hopelessly seized when I tried to remove

the nuts.  The left side came apart without issue. 

Rr bmpr cap 017.jpg

 

The result was I had to remove the entire right side bumper and saw thru the end of

the carriage bolts and split the nuts with a die grinder and cutoff wheel to separate

the parts.  Once the square holes failed in the attaching brackets on the back of the

trim the bolt and nut just spun together. 

Rr bmpr cap 020.jpg

Edited by Str8-8-Dave
correct spelling (see edit history)
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That sucks, and I know exactly what you mean. We assume that stainless is a problem-solver in terms of corrosion and future disassembly, but it's actually quite soft as Dave describes. I used to use only stainless fasteners on a lot of my assembly, but I've gone back to cad plated steel bolts, grade 5 or grade 8, depending on the application (stainless fasteners aren't even a grade 5). Stainless is probably overkill given how our collector cars are used, stored, and treated. They're never going to see the kind of harsh environment that caused the original fasteners to rust so modern cad plated bolts should last pretty much forever. 

 

You could also head this off by using stainless bolts with cad plated nuts--the dissimilar materials won't have this issue, although the softer stainless can still make problems if you really torque it. In places where the fasteners are invisible, I use cad plated steel bolts and stainless nylock nuts so I don't have to over-torque them and they stay put.

 

I also use a little dab of anti-seize or blue Lok-Tite goes on every single bolt I install, regardless of location, material, or application. It's cheap insurance.

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Thanks Str8-8-Dave for posting this PSA.

 

NEVER EVER EVER use a stainless bolt with a stainless nut unless you are forced, and then use plenty of anti seize. It won't rust, but what happens is worse than rust. At least with rust you would have some chance of getting things apart with penetrating oil.

 

I have seen stainless gall on assembly and seize before the bolt was even tight. Cutting was needed to get things back apart.

 

Stainless bolt? Use a steel or a brass nut. Stainless nut? Use a steel or brass bolt.

 

Someone will always point out in threads like this that if the alloy of the nut and the alloy of the bolt are correctly selected, stainless on stainless can be OK. That may be true, but does not help if you are buying generic stainless hardware online or at the hardware store.

 

 

Edited by Bloo (see edit history)
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Molybdenum disulfide grease is frequently used as an anti-seize lubricant for stainless steel to prevent galling.  Molykote is one brand, there are many others.  In some applications in the past, I've used silver-plated nuts to avoid the problem - silver is soft and slippery.  As a young engineer, I designed some parts for the focusing mechanism on a small telescope using aluminum parts with fine threads.  I think we got the 3-inch diameter mount through about five turns before it locked up solid.  I was soon instructed about the beauties of brass.

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  I’m perplexed by this conversation. For over 20 years I owned and operated a fleet of tank trailers that exclusively hauled and/or sprayed magnesium chloride year around. Retired now.

  We did all the plumbing and fabrication in house on these trailers, mostly 4” schedule 40 aluminum piping, flange connections and valves. Well over a hundred SS fasteners per trailer.   We bought SS bolts, nuts, and washers by the case (1/4” thru 7/8”) and used them exclusively. Also, bought anti seize by the case. Anti seize mainly to separate SS from aluminum.

   I can’t recall one galling of a SS fastener on these trailers. There was constant maintenance, changing valves, piping, parts, and ect.  air guns and air ratchets were always used where they could be used. 

   Pondering.

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At work, which is a plumbing company, if anyone is using stainless to stainless connections, is to use the Nicole antiseeze. Stainless to brass or steel doesn’t require to. To aluminum does need it to prevent corrosion. I always put antiseeze on the rims and lug nuts of all my vehicles so when I have to remove the tire to do maintenance they will come off. I’ve seen people use sledge hammers to get rims off because they have corroborated in place. 

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45 minutes ago, Mike "Hubbie" Stearns said:

I always put antiseeze on the rims and lug nuts of all my vehicles so when I have to remove the tire to do maintenance they will come off

 

And on the boss that centers alloy wheels on the rotor...............Bob

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The last company I worked for had this issue in production because we needed locknuts due to vibration in use. Tried a lot of different things and the final solution was to use brass nyloc nuts on all stainless screws. In the end it was less expensive than moly or any other wax style anti galling coating because of the labor of painting the threads. I still have some of that wax in my garage which is great for driving wood screws in.

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Chloride stress corrosion in stainless fasteners is another consideration for those who live and/or store their cars near salt water environments (not that anybody would want to do this).  I worked for a large manufacturer of industrial pumps & valves made in a variety of materials from cast iron-zirconium.  Although we made various stainless alloy valves, we never used stainless fasteners for stainless valves to be used in chloride environments like chlorine plants or sites near salt water.  Over time, chloride stress cracking eventually causes fastener failures that can result in fasteners becoming  projectiles!

 

 What is stress-corrosion cracking and why does it occur? | Fastener Engineering

 

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Different grades/specs of nut and bolt help reduce galling. On the industrial-chemical plant piping systems I worked on always specified different grades from a reputable manufactures. In recent years we tested materials and would not accept materials from some countries. (never trust the vendor paper work).

The "SS" n&b's bought from a hardware shop are likley to be "no grade" / "rubbish SS with a bit Cr".

 

In my mechanical engineering career may have purchased items from Mark Shaw's employer or equal.  Exotic engineering materials in aggressive environment/fluids were just an ordinary part of the projects.

Edited by 1939_Buick (see edit history)
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