Summary for citric acid hydrogen embrittlement Discussion
Citric acid solution and hydrogen embrittlement are the main concern in this thread: Michael Formberg asked whether a 2% citric acid solution at pH 6 could embrittle high-strength steel springs (Rockwell C 40) if used for polishing. Geoff Smith answered that, based on his earlier discussions, unrelieved hydrogen embrittlement requires hydrogen to be sealed into the steel, which he said would not happen in this case. He added that citric acid is a very weak acid, so the amount of hydrogen generated would be very small and would self-relieve rather than remain trapped. His practical conclusion was reassuring: the proposed polishing use should not be a hydrogen embrittlement concern, and he closed with a lighthearted “Don’t Worry, Be Happy.”
Q. For high strength steel springs (Rockwell C of 40) would a 2% solution of citric acid
⇦ on
or
Amazon [affil link] measuring a pH of 6 cause hydrogen embrittlement? The intention is to use this solution for polishing.
Michael Formberg
– Chardon, Ohio USA
courtesy of Wikipedia
A. Please take a look at the discussions on Letter 1216 et seq. and particularly my response of 11/26/13. For there to be unrelieved hydrogen embrittlement, there needs to be some sealing of the hydrogen into the steel. Since there is not in your case, any hydrogen will self-relieve. Besides, citric acid is a very weak acid and the amount of hydrogen will be very small. As Bobby McFerrin said (from Meher Baba) “Don’t Worry, Be Happy.”
Tom Rochester
CTO – Jackson, Michigan, USA
Plating Systems & Technologies, Inc.
September 22, 2014
A. I have no specific information on hydrogen embrittlement with citric acid but I am inclined to go with Tom.
But I do have an observation on pH. I am a little surprised to find 2% citric acid giving a pH of 6. I have seen DI water near that. From a quick back of envelope/guess, I would expect to find a pH in the range of about 2 – 3.
How do you measure pH?
Geoff Smith
Hampshire, England
September 24, 2014
October 20, 2014
Q. Thank you Tom! That discussion is very interesting and seems to pertain to my situation. Appreciate the feedback.
Geoff – To check the pH I used test strips from Hydrion. The citric acid had a pH of 3-4 before diluting with water. Once diluted with water to a 2% solution it had a pH of 6.
Michael Formberg
– Chardon, Ohio USA