Posted by Dr. R.D. Kane on July 02, 1996 at 22:26:11:
In Reply to: Corrosion inhibition performance: wet gas production tubing posted by Chris Craft on July 02, 1996 at 14:25:11:
I agree with your observations;
Sour systems generally have lower corrosion rates
than do CO2 system in many cases - at least at
temperatures <100 C. The sulfide films are more
protective than carbonate films. However, there
can be conditions where localized corrosion can
occur. These are generally related to underdeposit
corrosion (high chlorides), the influence of
velocity or impingement which removes protective
films or oxygen ingress. Unlike CO2 corrosion,
most of these relationships are highly qualitative
since much less fundemental work has been done
in sour systems.
My only other comment is that I see inhibition
more in a dynamic sense. There are forces of attraction
between the metal surface and the inhibitor molecules.
There are also shear forces on the surface by the flowing
medium which try to remove the molecules from the surface.
Therefore, any factors that increase this wall shear stress will
tend to accelerate the removal of the inhibitor film.
For example, shear forces increase with water
production since water droplets can be accelerated
to near the gas velocity. This causes droplet
impingement which is highly damaging for both
inhibitor and corrosion films.
One of the reasons why continuous inhibitor treatments
result in higher inhibitor performance is that the
inhibitor films are replenished.
Dr. R.D. Kane
P.S. You may be interested in the paper being submitted
by my colleague Mr. Srinivasan on modeling
CO2/H2S corrosion.