Cadmium plating of A325 bolts 3

[enginerding]

We have been asked by a client to specify cadmium plated A325 bolts. I checked the ASTM Spec to see how to call that out, and it does not provide any information. I could not find any prohibition for cadmium plating of A325 bolts, but I also could not find anything that said it was permissible.

Can someone help with this matter?

 

[CoryPad]

You should make sure why cadmium is being requested. It is a restricted substance for many applications and is being replaced for fastener usage by many end users with many different coatings.

ASTM A 325 usually is specified plain or zinc coated (hot dipped galvanized, mechanical galvanized, inorganic Zn). You can learn more about specifying these types of fasteners here:

http://boltcouncil.org/files/2009RCSCSpecification.pdf

You may want to just create your own drawings and specifications for this application. You can use ASME standards for the fastener geometry, and one of multiple ASTM standards for the material (e.g. ASTM A 325, A 354, A 574, or ...), although you may want to identify specific paragraphs rather than the whole standard.

For the cadmium coating, you can specify ASTM B 766 Standard Specification for Electrodeposited Coatings of Cadmium. Due to the potential for hydrogen embrittlement, you should review and specify one or more of the ASTM standards:

ASTM B 849 Standard Specification for Pre-Treatments of Iron or Steel for Reducing Risk of Hydrogen Embrittlement

ASTM B 850 Standard Guide for Post-Coating Treatments of Steel for Reducing the Risk of Hydrogen Embrittlement

ASTM F 326 Standard Test Method for Electronic Measurement for Hydrogen Embrittlement From Cadmium-Electroplating Processes

ASTM F 519 Standard Test Method for Mechanical Hydrogen Embrittlement Evaluation of Plating/Coating Processes and Service Environments

ASTM F 1624 Standard Test Method for Measurement of Hydrogen Embrittlement Threshold in Steel by the Incremental Step Loading Technique

ASTM F 1940 Standard Test Method for Process Control Verification to Prevent Hydrogen Embrittlement in Plated or Coated Fasteners

ASTM F 1941 Standard Specification for Electrodeposited Coatings on Threaded Fasteners (Unified Inch Screw Threads (UN/UNR))

 

[connectegr]

Are you sure they want Cadmium? There have been many environmental issues raised with regard to the use of Cadmium. Is this an aluminum structure? Is the concern galvanic compatibility?

There may be other structural bolting options.

http://www.FerrellEngineering.com

 

[enginerding]

They specifically requested cadmium. I am trying to figure out why that is right now.

These are steel outdoor advertising structures. They are exposed to the weather for their entire lifetime.

 

[connectegr]

Is the structure painted or galvanized?

http://www.FerrellEngineering.com

 

[enginerding]

The structures are painted. Sometimes they will use an epoxy paint.

I did find out one of the reasons: typical galvanized bolts have been hard for their erectors to start by hand. The cadmium is easier for them to thread the nut.

 

[MintJulep]

That's a pretty weak reason to specify cadmium.

Cadmium plating is outright banned in Europe, and is getting more and more hard to find in the US (and correspondingly more expensive). The materials used in the plating process are all considered hazardous waste material, and (proper) disposal is not cheap.

Sounds like the erectors are complaining about hot-dipped galvanized, as those can tend to have drips hardened onto the threads.

I'd suggest an electro-deposited zinc, possibly with a supplemental chromate conversion treatment. (although the chromate is not particularly environmentally friendly either).

There are a bunch of new organic platings available too.

 

[TVP]

You should investigate a zinc flake coating with a lubricated topcoat, such as one of the products from Magni, Doerken, or Metal Coatings (Geomet). Just google one of the above together with bolt or fastener, or someone else will provide suitable links shortly.

 

[hokie66]

Cadmium plated fasteners are not much good for exposed conditions. The plating is very thin, and corrosion occurs quickly. Galvanized is the way to go. Galvanized bolts are the norm. Sometimes, you can't give a client what he wants.

 

[connectegr]

We typically used plain bolts and paint in the field for painted structures. And use galvanized bolts for galvanized structures. For aluminum or stainless structures, we use stainless bolts.

But if your client has a specific concern with the bolts, I would probably suggest galvanized bolts.

http://www.FerrellEngineering.com

 

[Duwe6]

Good A325 galv bolts will *all* start by hand. Buy something 1st-world like Lejeune of the folks that use a triangle for their symbol. Best nuts are the ones overcoated with the light blue teflon after galvanizing. I have never had a problem with 'real' A325 galvanized bolts, just the cheap stuff - Grade 2 & 5.