[SEL] electrolysis

Orrin Iseminger oiseming at moscow.com
Fri May 19 17:16:38 PDT 2006


-----Original Message-----
From: sel-bounces at lists.stationary-engine.com
[mailto:sel-bounces at lists.stationary-engine.com] On Behalf Of Peter Scales
Sent: Friday, May 19, 2006 12:32 PM
To: 'The SEL email discussion list'
Subject: RE: [SEL] electrolysis

I'd have to say that in my experience, there isn't a great deal of chance of
hydrogen embrittlement at room temperatures.  As far as my understanding
goes, hydrogen embrittlement is caused by the presence of dissolved atomic
hydrogen in solid iron, and the solubility of atomic hydrogen in solid iron
below about 200 degrees Centigrade is virtually negligible.  The gas
produced during electrolysis is molecular hydrogen (H2) and as such has
effectively zero solubility in steel at room temperature.  The thinner the
section, the less the effect of hydrogen on it, as the time taken for
hydrogen to diffuse out of the section falls with the reduction in
thickness.

I worked in welding inspection for fifteen years, until 1989, and unless
there has been a great new body of experience since then, the rule of thumb
was to post-heat thick sections (> 1" or 25mm) (or at least to control
cooling) for 24 hours per inch of thickness at 200 Centigrade, to allow time
for any entrained hydrogen to diffuse out of the material.  Under an inch of
thickness, there usually wasn't much done other than to throw a blanket over
the weld, maybe.

If you have a critical component, such as a gun barrel or high pressure
vessel or receiver, then maybe there is a need to pay more attention to
this, but in my opinion, for thin low-stress items, at low temperature,
there isn't a great deal of cause for concern.

Regards

     Pete
-- 
Peter Scales  

~~~~~~~~~~~~~

Whenever a topic comes up, I don't care how it is resolved, as long as it
doesn't lead someone down the wrong path.  I don't want to sound
argumentive, but please allow me to point out the following link:

http://en.wikipedia.org/wiki/Hydrogen_embrittlement

It says, "The corrosion mechanism begins with hydrogen atoms diffusing
through the metal as an interstitial. Hydrogen embrittlement is a room
temperature phenomenon where hydrogen present inside the material makes it
brittle. High-strength steels, aluminium, and titanium alloys are most
susceptible.  

"Hydrogen embrittlement can happen during various manufacturing operations
or operational use, anywhere where the material comes in contact with atomic
or molecular hydrogen. Processes which can lead to this include cathodic
protection, phosphating, pickling, and electroplating. A special case is arc
welding, in which the hydrogen is released from moisture in the coating of
the welding electrodes; to minimize this, special low-hydrogen electrodes
are used for welding high-strength steels. Other mechanisms of introduction
of hydrogen into metal are galvanic corrosion, chemical reactions of metal
with acids, or with other chemicals (notably hydrogen sulfide in sulphide
stress cracking, or SCC, a process of importance for the oil and gas
industries)."

I know nothing about hydrogen embrittlement, except what I read on the
Internet.

Best regards, 

Orrin

Orrin Iseminger
Colton, Washington, USA
http://users.moscow.com/oiseming/lc_ant_p/index.htm
So many projects.  So little time.   







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