Atmospheric Corrosion
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to permit martensite formation with rapid cooling. Other elements such as
nickel or molybdenum may be added for improved corrosion resistance.
The corrosion resistance of the martensitic stainless steels is inferior to
that of the austenitic steels. These alloys are usually used in mildly corrosive
applications such as atmospheric.
Alloy 17-7PH is a semi-austenitic stainless steel. In annealed condition, it is
austenitic but in the aged condition, it is martensitic.
In rural and mild industrial atmospheres, it has excellent resistance to general corrosion, being equivalent to type 304 stainless steel. In marine atmospheres, alloy 17-7PH will gradually develop a slight rusting and pitting in all
heat-treated conditions. It is almost equal to type 304 in these applications.
4.7.8.4 Duplex Grades
The duplex stainless steels are alloys whose microstructures are a mixture
of austenite and ferrite. Type 32550 and related alloys containing molybdenum have an atmospheric corrosion resistance superior to type 316 in highchloride environments. The duplex grade would be used when the greater
strength of these alloys is required for application in a marine atmosphere.
4.7.9 Nickel
Nickel outdoors becomes dull and acquires a thin adherent corrosion-resistant film that is usually a sulfate. The rate of corrosion is extremely slow;
however, the rate increases with an increase in the sulfur dioxide content of
the atmosphere. Nickel 200 has a very low corrosion rate in both rural and
marine atmospheres.
4.7.10 Monel alloy
Monel is a nickel alloy containing 30 to 33% copper. The corrosion of monel
is negligible in all types of atmospheres. When exposed to rain, a thin graygreen patina develops. In a sulfurous atmosphere, a smooth brown adherent
film forms. Because of its low corrosion rate and the pleasant patina that
forms, Monel 400 is used for architectural applications such as roofs, gutters,
and flashings.
4.7.11 inconel alloy 600
Inconel 600 is a nickel-chromium-iron alloy having approximately 16.0%
chromium and 7.0% iron. In rural atmospheres, the alloy remains bright for
many years. When exposed to an industrial atmosphere containing sulfur,
a slight tarnish may develop. It is preferable for Inconel 600 to be exposed to
the atmosphere rather than be sheltered. This will permit rain to wash the
surface, and the sun and wind to dry the surface.
125
to permit martensite formation with rapid cooling. Other elements such as
nickel or molybdenum may be added for improved corrosion resistance.
The corrosion resistance of the martensitic stainless steels is inferior to
that of the austenitic steels. These alloys are usually used in mildly corrosive
applications such as atmospheric.
Alloy 17-7PH is a semi-austenitic stainless steel. In annealed condition, it is
austenitic but in the aged condition, it is martensitic.
In rural and mild industrial atmospheres, it has excellent resistance to general corrosion, being equivalent to type 304 stainless steel. In marine atmospheres, alloy 17-7PH will gradually develop a slight rusting and pitting in all
heat-treated conditions. It is almost equal to type 304 in these applications.
4.7.8.4 Duplex Grades
The duplex stainless steels are alloys whose microstructures are a mixture
of austenite and ferrite. Type 32550 and related alloys containing molybdenum have an atmospheric corrosion resistance superior to type 316 in highchloride environments. The duplex grade would be used when the greater
strength of these alloys is required for application in a marine atmosphere.
4.7.9 Nickel
Nickel outdoors becomes dull and acquires a thin adherent corrosion-resistant film that is usually a sulfate. The rate of corrosion is extremely slow;
however, the rate increases with an increase in the sulfur dioxide content of
the atmosphere. Nickel 200 has a very low corrosion rate in both rural and
marine atmospheres.
4.7.10 Monel alloy
Monel is a nickel alloy containing 30 to 33% copper. The corrosion of monel
is negligible in all types of atmospheres. When exposed to rain, a thin graygreen patina develops. In a sulfurous atmosphere, a smooth brown adherent
film forms. Because of its low corrosion rate and the pleasant patina that
forms, Monel 400 is used for architectural applications such as roofs, gutters,
and flashings.
4.7.11 inconel alloy 600
Inconel 600 is a nickel-chromium-iron alloy having approximately 16.0%
chromium and 7.0% iron. In rural atmospheres, the alloy remains bright for
many years. When exposed to an industrial atmosphere containing sulfur,
a slight tarnish may develop. It is preferable for Inconel 600 to be exposed to
the atmosphere rather than be sheltered. This will permit rain to wash the
surface, and the sun and wind to dry the surface.