Inconel 718 has effective resistance to carbon dioxide,
hydrogen sulfide and acetic acid containing environments. Corrosion rates of
below 1 mil per year occurred to high temperatures. Only with acid, oxygen or
elemental sulfur corrodes Inconel 718. So, the pitting corrosion resistance is
counted as the most vigorous environment occurred in the industry. There are
several alloys considered to be corrosion resistant in the most production
conditions. Inconel 718 has pitting corrosion resistance similar to duplex
stainless steels. Alloys like SS 304 are slightly used due to their corrosion
resistance. Inconel 719 applications are usually not limited to corrosion
resistance.
The general corrosion resistance and pitting corrosionresistance of Inconel 718 are influenced by heat processing. The effect of
aging temperature on the pitting corrosion resistance in the yellow death
solution. Increase in pitting temperature shows enhanced corrosion resistance.
The reproducibility of this test is about 5 C. Heat treatments to 1350oF do not
create a detrimental effect on the pitting temperature in the yellow death
solution. Although, heat processing at 1450oF affects the pitting corrosion
resistance. The loss in pitting resistance can be added to the precipitation of
carbides and to segregation of alloying elements during precipitation hardening
treatments. It is found that higher annealing temperatures are detrimental to
pitting corrosion resistance of Inconel 718. Although, except in the extreme
cases, pitting corrosion resistance is not a limiting characteristic, although
in the 1450oF heat processing conditions evaluated. Both localized corrosion
and generalized corrosion resistance reduce with increase in temperature of
aging treatments.
Inconel 718 offers adequate resistance to corrosion in
acidizing conditions. Relative corrosion rates of alloys in 10% boiling
hydrochloric acid is evaluated. This acid is unpreventable and causes highest
corrosion rates anticipated for short-term exposures. Inconel 718 corrodes at 4
mils per day, in fact in the uninhibited acid. The corrosion resistance is
comparable to alloys 825 that are a likely combination with Inconel 718 in the
various severe completions. From a practical perspective, the corrosion
resistance in oil field acidizing environments is sufficient, particularly as
these conditions will comprise of corrosion preventors to further decrease the
corrosion rates. The influence of heat processing on corrosion resistance of
alloy 718 in hydrochloric acid is not evaluated. The effects of H2S on acidizing
have also not been tested.
Inconel 718 is sensitive to hydrogen embrittlement
particularly in the high strength heat processed conditions. Although various
studies of hydrogen embrittlement have been done with high strength materials.
So, the results from study with these high strength materials for the aerospace
industry may not be relevant in describing the chance of failure in oil field
applications. Although the effects of heat processing or other environmental
factors may be relevant to oil industry applications. The effect of heat
processing on the hydrogen embrittlement resistance in the high pressure
hydrogen at room temperature is evaluated. It is found that high temperature
aging processing about 1400oF enhance the resistance to hydrogen embrittlement
of Inconel 718.
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