Alternate to Cadmium Plating

Yes lllqiqi, Hydrogen Embrittlement is a problem, we had spring clips zinc plated and passivated and they had to be placed in an oven for 24 hours, I think around 100 - 150C, this solved the problem. The first ones snapped as we put them on.

I've also noticed Embrittlement on galvanised tie wire after moisture has been on it, the tie wire snaps off.

There is a process which peens on zinc powder mechanically and galvanising which is excellent corrosion protection but tend to fill up holes and grooves.

Tony

A quick google search

http://www.sae.org/technical/standards/AIR5919

Hot dip galvanising is a problem for quality 12.9 bolts and above but will not generally give rise to hydrogen embrittlement for 8.8 and 10.9.

Sheradising is another process as is hot zinc spattering.

Cold coated alu/zinc can also be an option.

Stainless steel.

Most economical is probably hot dip galvanising.

Don't forget electroless nickel plate.

How about blackodising or elctro galvanising?. Will it be o.k for your application?.

Suresh Sharma.

The obvious is missing: Hot dip galvanizing. The zinc is the same zinc that you electroplate with, but the coating thickness is typically thicker. Since there is no electrical current, that source of hydrogen embrittlement is eleminated

I apprecite your guys' comments. Will check each out for details.

Once again there are some ill-advised replies on here!

A lot depends on the part(s) being plated:-

Hot dip galvanising could cause thread galling on threaded items.

Electroplating will cause hydrogen embrittlement, particularly on spring/carbon steel parts, (but most platers will advise on how to combat this).

I very much doubt that electroless nickel plate or blackodising will give the corrosion resitance you require.

There are many grades of plating, depending upon the corrosion resistance required. Most likely you'll require an electroplated zinc finish, (but see above regarding hydrogen embrittlement), but other options are mechanical zinc plating, and several "dip and spin" processes which avoid the embrittlement issue.

Illqiqi, advise what your parts are made of, if they are threaded or not, what the salt spray rating required is and I'll do my best to point you in the right direction. If you cannot ascertain the salt spray rating I can probably hazard a guestimate from the current specification, i.e. what is the thickness of cadmium plating you are replacing and are there any other coatings(passivate, etc.) added?

The parts to be plated are fasteners like bolts, nuts, cap screws, etc, made in steels per ASTM A194, A193, F436, A320; SAE GR 2, 5, 8.8 or higher. Some are fully threaded, some are partially threaded, to 1-2.5" dia. I don't see they are fine threaded.

The applications are in oil & gas, HPI pumps, bolting the pump case covers, pipes. Temp in the field could go over 600 F and less than -20F, so that Cd and Zinc plating would find limitations from that.

Thank you for your help!

Given this information - and the environment that the parts are to encounter - I would certainly talk to a plater/finisher to obtain the optimum coating.

The Magni group have some info on replacing Cadmium at http://www.themagnigroup.com/images/PDFsheets/MagniCadAutoFinWeb.pdf

and most platers offering this range of finishes should also be able to advise on Delta finishes, see http://www.deltagbn.co.uk.

Other than these, mechanical zinc plating would avoid hydrogen embrittlement problems and, again, your plater should be able to advise a suitable passivate/top coat on the zinc to cope with the environment that your fasteners need to stand up to.

Let us all know the outcome of your research.

Dear all,

After extensive research, I narrowed mu scope on 2 types of plating that could replace Cd plating: Electroless Ni plating and Teflon based coating (like Xylan). Both of them could resist high temp up to 1000 F, good corossion resistance and low risk of Hydrogen embrittlement.

Xylan coating cost lot more than Ni plating. So I think elctroless Ni plating is preferred on my list. Please let me know you guys thoughts. Thanks!!