Clare Snyder writes:

On Tue, 08 Sep 2020 09:45:21 +0100, Richard Smith
wrote:

Saw this post and thought - why not ask the experienced pragmatic
folk?

Sadly these calipers emerged from an overnight dunking with the spring
broken. It looks like it's probably been cracked for some time.

...
spring steel does not respond well to acid derusting.

Working with weldable structural steels, I was once totally
disbelieving of how susceptible bolts and some hardened steels are to
hydrogen and the effect of acid pickling.

Millions of times more susceptible...

How many of you have been involved in sorting out delayed
cold-cracking breaking of bolts and studs?

Rich

I decided to clean up a couple mildly rusted bicycle chains with a
"rust remover" Put the chain on the bike, jumped on and promptly
snapped the chain. Repeated 3 times untill all 3 chains were broken,
then went and bought a new chain. About 6 years ago - still on that
chain.

Interesting.
When doing research on hydrogen in welds / steels, it was absolutely
not possible to get any hydrogen into structural steels by immersing
them in acid. Made a drilled "bobbin" for extra surface area and less
thickness from surface, visisble hydrogen evolution reaction at the
surface - but in a "Leco" analyser (thanks Esab) - no measurable
hydrogen.
One of reasons I needed to be corrected that highly hardenable steels
- notably for bolts and high-strength tie-bar "studs" - can be very
susceptible.
Regards,