Cadmium plating hi tensile studs 1

[Gazevs]

Hello everybody.

I wish to use cadmium plated hi tensile bolts and studs in a sub sea pipeline flange. I have previously used teflon coated but must have an alternative. Is hydrogen embrittlement an issue for Hi tensile cadmium coated fittings when used sub sea (55m) and cathodic protection applied?

Thanks

 

[TVP]

If the cadmium is deposited by an electroplating process, then yes, hydrogen embrittlement becomes a concern. The conventional practice is to perform a baking operation after plating but before chromating to relieve the fasteners from hydrogen embrittlement. SAE-USCAR 5 Avoidance of Hydrogen Embrittlement of Steel has the following requirements:

320 HV < core hardness < 380 HV: bake minimum of 4 hours at 200 +/- 5 C within one hour plating and before chromate treatment.

350 HV < surface hardness < 400 HV: same as above.

core hardness > 380 HV or surface hardness > 400 HV: bake minimum of 8 hours at 200 +/- 5 C within one hour of plating and before chromate treatment.

Since you did not list a fastener standard, I do not know what &quot;hi tensile&quot; means regarding the proper embrittlement relief. If the steel has been tempered at a temperature less than 200 C in order to attain the necessary mechanical properties, then the fasteners should be baked for a minimum of 8 hours at 115 +/- 5 C.

I would not recommend using cadmium plated bolts manufactured from medium carbon alloy steel for this type of application, especially if they are not produced to a proper fastener standard (ASTM, ISO, etc.). Nickel alloy or multiphase alloys (nickel-cobalt-chromium-molybdenum) perform much better in this type of environment, and with a suitable combination of cold working and heat treatment, can attain the necessary mechanical properties. I recommend you read the following article on multiphase fastener alloys from SPS:

http://www.spstech.com/aero/news/090602.html

They also have an excellent booklet on these alloys called Superalloys Developed by SPS Technologies for Aerospace Fasteners which you can obtain by clicking on the following link:

http://www.spstech.com/aero/prod_lit/index.html

 

[TVP]

I just came across a technical article from Avesta Polarit discussing fasteners for seawater applications:

http://www.avestapolarit.com/upload/documents/technical/acom/acom93_1.pdf

 

[BarryMartin]

Cadmium can be plated without hydrogen embrittlement. This is done for aircraft industry.

For info. contact Ron Saleker of Sifco Selective Plating 216-524-0099.

 

[CoryPad]

BarryMartin,

Zinc can too - the process is mechanical plating, rather than electroplating. If a member searched this website, and others, they would learn about cadmium vapor deposition, etc. There are numerous coatings, processes, vendors, info sources...

 

[CoryPad]

I mean cadmium _vacuum_ deposition in my previous message.

 

[BarryMartin]

I think I missed the question. Concern is whther the cadmium plating protects the high tensile substrate from hydrogen embrittlement when it is subsequently part of a cathodically protected subsea pipeline.

I would have concern about high strength materials in these applications, if you cannot find a way to prevent current from being applied after instalation. You might consider a way to cover the fasteners, to minimize any current reaching the fastener.