Ask the Expert Question-and-Answer Archive
(Hard Chrome Plating)

by Randy Taylor, Advanced Tooling Corporation
November, 2007

Ultrasonic Inspection

Q1. I came across your website during an Internet search, and was hoping you may be able to give me some quick thoughts on a chrome plating issue we have.

We plate industrial hard chrome on screw pump bores (6"), approximately .010" thick, and have been doing this for over 30 years.  For some reason a new customer of ours is insisting on the follow requirement:

"Ultrasonic inspect the finished chromed bores to ensure there is complete fusion to prevent hydrogen permeation."

We've never seen this requirement, nor understand how UT will even ensure this, nor what criteria to use.  Any comments would greatly be appreciated.

A1. Ultrasonic inspect refers to a process of using sound waves to detect faults. If the intent is to detect poor adhesion or a poor bond of the chromium to base metal, it is entirely possible a test can be developed if there is none already.

You'll need to investigate the level of testing to be performed and the test criteria you will be required to meet and then determine the cost to purchase equipment and train personal.    

I don't have a good answer for you regarding the last part of the sentence, "... to prevent hydrogen permeation through the chrome plated bore"?

That seems contrary to the conventional wisdom of embrittlement relief baking after plating which sole intent is to drive hydrogen absorbed during the plating, out of the base material through microcracks in the chromium coating and elsewhere.

Q2. It's your second paragraph that is the issue at the moment.  Our customer has requested (demanded) a UT test, but neither they nor us have any experience doing this.  Therefore there's no acceptance criteria to use. I was hoping you had something.

I believe the hydrogen embrittlement is just someone throwing out a key term and linking it to UT to force us to do this test.  Based upon some discussions I've had with some vendors, this is not an issue of Rc 22 maximum hardness carbon steel (WCB)...do you agree?

Thanks again !

A2. Most definitely I agree. Scientific data and most OEM specifications say steels RC 33 (327 Vickers 136° 10kg, 334 Knoop 500g, 311 Brinell 10mm ball 3000kg, 149,000 psi) and below, are not susceptible to hydrogen embrittlement and don’t require bake after plating.

Best of luck!  

RT