For a long time corrosion resistant
materials like Inconel 625 and Hastelloy C276 have offered wide corrosion
resistance for equipments in chemical, power production, pollution control,
marine and various applications. The reason of the development of chemical
products and enhanced processes is the new challenges that have encouraged the
development of Hastelloy C-2000 and Inconel alloys that are widely being used
to prevent corrosion and safeguard product purity in conditions beyond the
capability of stainless steels or other materials. These alloys offer several
benefits including increased life cycle cost performance, better reliability,
lower maintenance and reduced downtime costs.
Presence of nickel, chromium, molybdenum
and other elements is essential for various applications where severe corrosion
resistance is needed. Chromium prevents corrosion in oxidizing media while
molybdenum enhances resistance to reducing media. Presence of chromium and
molybdenum maintains the stable austenitic single-phase structure. It is
essential in receiving suitable corrosion resistance in an alloy capable of
being economically made and produced.
Hastelloy C276, Hastelloy C22, Inconel 625
and Hastelloy C2000 are evaluated for corrosion resistance and how their
performance varies with changing acid temperature, concentration and mixture.
It is seen that alloy Hastelloy C22 wire and Hastelloy C276 offer great
flexibility and versatility in preventing corrosion in a great range of
environments.
Localized Corrosion Resistance
Localized corrosion attack is one of the
commonly occurring failure mechanisms of stainless steels and high
Nickel-Chromium-Molybdenum alloys. This kind of localized corrosion attack is
normally less predictable as compare to general corrosion and more limiting to
a materials performance. Pitting Resistance Equivalent Number can be calculated
by using chemical composition to estimate relative pitting resistance of alloys.
Hastelloy C22, Hastelloy C2000 are completely resistant to pitting and crevice
corrosion up to the temperatures of 85oC.
Seawater
Corrosion rates for
Nickel-Chromium-Molybdenum alloys in marine conditions are very nominal in
flowing and stagnant media. High nickel alloys are extremely resistant to
stress corrosion cracking in water based chlorides that may otherwise affect
the lower alloyed stainless steel 300 series. Nickel based alloys with a PREN
number more than 40 are highly resistant to crevice corrosion in marine water.
Although in tight crevice conditions for example in seawater cooled plate heat
exchangers that have multitudes of tight crevices, high alloyed materials for
example Hastelloy C22 and Hastelloy C276 are needed. Inconel 625 and Hastelloy
C276 have offered significant performance in seawater service.
Inconel 625 with a PREN above 40 is
commonly used as wrought and weldmetal in preventing seawater corrosion. This
material is widely used as a weld overlay on carbon steel components as an
affordable way of enhancing performance in corrosive conditions. Although high
alloyed weldmetal with larger PREN values find uses in severe seawater service
conditions.
High temperature seawater
Crevice corrosion tests are conducted in
high temperature natural seawater at 60oC for 60 days in stagnant conditions.
The test medium was chlorinated with 1-2ppm free chlorine to simulate service
conditions usually used in offshore oil and gas industry seawater service.
Hastelloy C276 and Hastelloy C22 were found to be fully corrosion resistant in
these conditions.
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