It is well known that the major saving is great by using
available and economic practices to enhance corrosion prevention and control.
The designer should consider the initial material cost and also include
maintenance cost, service life, downtime cost and replacement cost. This type
of analysis helps better understand the cost-effectiveness of corrosion resistant
materials.
Studies have stated that the overall cost of corrosion is
surprising. The total cost of corrosion in U.S. is about $276 billion a year.
About 25 to 305 of cost of corrosion is preventable and can controlled by using
corrosion resistant materials and application of best anticorrosion technology
from the design through maintenance. As becoming commercially available material,
Nickel has become a crucial material in preventing corrosion. It is a major
element in the coating and claddings applied to steels, copper-nickel and
nickel-copper alloys as well as high performance nickel alloys. Nickel is not
just a corrosion resistant element, it also has high tolerance for alloying
that makes it possible to develop various high performance, special purpose
alloys.
Nickel-Chromium alloys can be considered as the base for
other alloys. Chromium offers resistance to oxidizing conditions and high
temperature strength. It helps alloys resist stress corrosion cracking and
corrosion in nitric acid, steam, and oxidizing gases. Alloys with high chromium
contnent resist melting sulphates and vandates found in the fuel ash.
Resistance to high temperature oxidation is also enhanced by alloying with aluminium
in conjunction with high chromium. Nickel is used as a corrosion resistant material
in food processing and in high temperature caustic and gaseous chlorine or
chloride conditions.
Alloys offering significant performance in aqueous reducing
acids, alloys for oxidizing chloride conditions and seawater- Inconel 625
and Hastelloy C276. Cobalt and other alloying element inclusions create
materials for use in jet engines that combine high temperature strength with
resistance to gaseous oxidation and sulfidation.
Other technologically important materials are high iron
alloys that are made to conserve nickel and are usually considered as moderate
in performance and cost between nickel alloys and stainless steels. Incoloy 800
is a general purpose alloy that has good high temperature strength and
resistance to seam and oxidizing or carburizing gases. Addition of molybdenum
and chromium similar to in Incoloy 825 and Hastelloy G enhances resistance to
reducing acids and localized corrosion in chlorides.
Other essential group of alloys is nickel-copper alloys.
Containing higher nickel, Monel alloys are the best for use in corrosive chemical
conditions such as with hydrofluoric acid and vigorous marine conditions.
Alloys with higher copper content such as copper-nickel alloys are commonly
used in marine conditions for providing high fouling resistance.
Nickel base alloys offer outstanding resistance to corrosion
in nitridingconditions and in chlorine or chloride gases. Corrosion in the
chloride conditions at the high temperatures speeds up with the formation and
volatization of chloride layers and high nickel alloys offer suitable
performance because nickel develops least volatile chlorides. On the other
hand, in sulfidiing conditions, high nickel alloys without chromium content can
be corroded due to the development of low melting temperature Ni-Ni3Si2
eutectic. Here Nickel-Chromium alloys
are fit to use.
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