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Fundamentals of Corrosion
4.7.12 inconel alloy 625, incoloy alloy 800, incoloy alloy 825
Inconel alloy 625 is a nickel-chromium-molybdenum-columbium alloy,
Incoloy 800 is a chromium-nickel-iron alloy, and Incoloy 825 is a chromiumnickel-iron alloy similar to alloy 800 but having a higher nickel content.
These alloys remain bright and tarnish-free in rural and industrial atmospheres. Alloy 800 develops a very thin oxide film after prolonged exposure
in marine atmospheres, whereas alloys 625 and 825 remain bright.
4.8 Atmospheric Corrosion of Nonmetals
Atmospheric corrosion has been defined as an electrochemical reaction
requiring the presence of an electrolyte. This is true of a metallic material.
However, there are other materials of construction that do not corrode by
electrochemical mechanisms. Among these are such materials as plastics,
elastomers, masonry materials, ceramics, and wood.
4.8.1 Plastics
Plastics are, in reality, polymers. The term “plastics” is defined in the dictionary as “capable of being easily molded,” such as putty or clay. The term “plastics” was originally adopted to describe early polymeric materials because
they could be easily molded. Unfortunately, many of today’s polymers are
quite brittle and once formed cannot be molded.
There are two distinct groups of plastics: the thermoplasts and the thermosets. The thermoplasts can be melted, cooled, and remelted without destroying the physical or mechanical properties of the polymer. The thermosets
begin as a powder or liquid that is reacted with a second material, or which
through catalyzed polymerization results in a new product that has properties differing from those of either starting material.
Polymeric materials in outdoor applications are exposed to weather
extremes that can be deleterious to the material. The most harmful weather
component, exposure to UV radiation, can cause embrittlement, fading, surface cracking, and chalking. Most plastics, after being exposed to direct sunlight for a period of years, exhibit reduced impact resistance, lower overall
mechanical performance, and a change in appearance.
The electromagnetic energy from sunlight is normally divided into ultraviolet (UV) light, visible (VIS) light, and infrared (IR) energy. IR energy consists of wavelengths longer than the VIS red wavelengths and starts above
760 nm. VIS light is defined as radiation between 400 and 760 nm. UV light
consists of radiation below 400 nm. The UV portion of the spectrum is further
Fundamentals of Corrosion
4.7.12 inconel alloy 625, incoloy alloy 800, incoloy alloy 825
Inconel alloy 625 is a nickel-chromium-molybdenum-columbium alloy,
Incoloy 800 is a chromium-nickel-iron alloy, and Incoloy 825 is a chromiumnickel-iron alloy similar to alloy 800 but having a higher nickel content.
These alloys remain bright and tarnish-free in rural and industrial atmospheres. Alloy 800 develops a very thin oxide film after prolonged exposure
in marine atmospheres, whereas alloys 625 and 825 remain bright.
4.8 Atmospheric Corrosion of Nonmetals
Atmospheric corrosion has been defined as an electrochemical reaction
requiring the presence of an electrolyte. This is true of a metallic material.
However, there are other materials of construction that do not corrode by
electrochemical mechanisms. Among these are such materials as plastics,
elastomers, masonry materials, ceramics, and wood.
4.8.1 Plastics
Plastics are, in reality, polymers. The term “plastics” is defined in the dictionary as “capable of being easily molded,” such as putty or clay. The term “plastics” was originally adopted to describe early polymeric materials because
they could be easily molded. Unfortunately, many of today’s polymers are
quite brittle and once formed cannot be molded.
There are two distinct groups of plastics: the thermoplasts and the thermosets. The thermoplasts can be melted, cooled, and remelted without destroying the physical or mechanical properties of the polymer. The thermosets
begin as a powder or liquid that is reacted with a second material, or which
through catalyzed polymerization results in a new product that has properties differing from those of either starting material.
Polymeric materials in outdoor applications are exposed to weather
extremes that can be deleterious to the material. The most harmful weather
component, exposure to UV radiation, can cause embrittlement, fading, surface cracking, and chalking. Most plastics, after being exposed to direct sunlight for a period of years, exhibit reduced impact resistance, lower overall
mechanical performance, and a change in appearance.
The electromagnetic energy from sunlight is normally divided into ultraviolet (UV) light, visible (VIS) light, and infrared (IR) energy. IR energy consists of wavelengths longer than the VIS red wavelengths and starts above
760 nm. VIS light is defined as radiation between 400 and 760 nm. UV light
consists of radiation below 400 nm. The UV portion of the spectrum is further