Metal treatment – Process of modifying or maintaining internal physical... – Carburizing or nitriding using externally supplied carbon or...
Reexamination Certificate
2001-02-02
2002-11-19
King, Roy (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Carburizing or nitriding using externally supplied carbon or...
C148S217000
Reexamination Certificate
active
06482272
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for reducing and/or preventing nitridation and/or carburization of metal surfaces in contact with a fluid including nitrogen-containing compounds capable of nitriding the metal surfaces and/or carbon-containing compounds capable of carburizing the metal surfaces, where the method includes adding a preventative composition to the fluid and to surfaces so treated.
More particularly, the present invention relates to a method for reducing and/or preventing nitridation and/or carburization of metal surfaces in contact with a fluid including nitrogen-containing compounds capable of nitriding the metal surfaces and/or carbon-containing compounds capable of carburizing the metal surfaces, where the method includes adding a preventative composition including sulfur and phosphorus to the fluid and to surfaces so treated.
2. Description of the Related Art
It is known that ammonia in contact with a metal surface at an elevated temperature decomposes on the metal surface releasing atomic nitrogen. Atomic nitrogen, in turn, defuses into the metal, forming nitrides. This process, know as nitridation, drastically increase the hardness of the metal, and decreases its ductility, thus causing degradation of the metal's resistance to stresses and fatigue. In power systems utilizing a water-ammonia mixture at temperatures below about 800° F., nitridation does not occur because water acts as a temporary poison deactivating the catalytic properties of the metal. At higher temperatures, water loses the ability to deactivate the catalytic properties of the metal, and nitridation progresses. Moreover, the nitridation process increases rapidly with increasing temperature after the water loses the ability to deactivate the nitridation process.
Conventional ways to prevent nitridation using protective coatings are inapplicable in this case, because during the operation of power plants, equipment, especially vapor turbines are subjected to erosion of their surfaces by solid particles. Therefore, any coating would be removed after a relatively short time.
Similarly, in carbon-containing atmospheres at elevated temperatures, carburization of metal surface can occur. Carburization of metal surface also causes considerable difficulties because the introduction of carbon atoms into the metal lattice changes is properties increasing fatigue problems and other undesirable problems.
In both cases, nitridation and/or carburization, corrosion can occur only as a result of the decomposition of compounds containing nitrogen or carbon which are thought to be caused by the catalytic action of metal in contact with the compounds. Thus, it would represent a significant advancement in the art to have a method that prevents nitridation or carburization of metal surfaces in contact with atmosphere or fluids that cause nitridation or carburization of the metal surface.
SUMMARY OF THE INVENTION
The present invention provides a method of preventing nitridation and/or carburization of a metal surface in contact with fluids including a nitrogen-containing compound capable of nitriding the surface and/or carbon-containing compound capable of carburizing the surface. The method includes adding a composition to the fluid on a discrete or continuous basis in an amount sufficient to reduce or prevent nitridation and/or carburization of the metal surface. The composition comprises a compound or mixture of compounds having a higher affinity for the metal surface than the nitrogen-containing compound or carbon-containing compound. Preferably, the composition includes at least a sulfur-containing compound having the ability to deactivate or poison the catalytic sites on the metal surface that are thought to be responsible for nitridation and/or carburization, and particularly, a sulfur-containing compound and a phosphorus-containing compound.
The present invention provides a method of preventing nitridation and/or carburization of metal surfaces in contact with a fluid including a nitrogen-containing compound capable of nitriding a metal surface and/or a carbon-containing compound capable of carburizing the surface, where the method comprises adding, on a discrete or continuous basis, a composition including a sulfur-containing compound to the fluid in an amount sufficient to reduce or prevent nitridation and/or carburization of the metal surface.
The present invention provides a method of preventing nitridation and/or carburization of metal surfaces in contact with a fluid including a nitrogen-containing compound capable of nitriding a metal surface and/or a carbon-containing compound capable of carburizing the surface, where the method comprises adding, on a discrete or continuous basis, a composition including a sulfur-containing compound and a phosphorus-containing compound to the fluid in an amount sufficient to reduce or prevent nitridation and/or carburization of the metal surface.
The present invention provides a method of preventing nitridation of metal surfaces in contact with a fluid including a nitrogen-containing compound capable of nitriding a metal surface, where the method comprises adding, on a discrete or continuous basis, a composition including a sulfur-containing compound to the fluid in an amount sufficient to reduce or prevent nitridation of the metal surface.
The present invention provides a method of preventing nitridation of metal surfaces in contact with a fluid including a nitrogen-containing compound capable of nitriding a metal surface, where the method comprises adding, on a discrete or continuous basis, a composition including a sulfur-containing compound and a phosphorus-containing compound to the fluid in an amount sufficient to reduce or prevent nitridation of the metal surface.
The present invention provides a method of preventing carburization of metal surfaces in contact with a fluid including a carbon-containing compound capable of carburizing the surface, where the method comprises adding, on a discrete or continuous basis, a composition including a sulfur-containing compound to the fluid in an amount sufficient to reduce or prevent carburization of the metal surface.
The present invention provides a method of preventing carburization of metal surfaces in contact with a fluid including a carbon-containing compound capable of carburizing the surface, where the method comprises adding, on a discrete or continuous basis, a composition including a sulfur-containing compound and a phosphorus-containing compound to the fluid in an amount sufficient to reduce or prevent carburization of the metal surface.
The present invention also provides an apparatus for introducing a nitridation and/or carburization preventative composition into processing equipment in contact with a fluid including a nitrogen-containing compound capable of nitriding a metal surface and/or a carbon-containing compound capable of carburizing a metal surface in an amount sufficient to reduce or prevent nitridation and/or carburization of metal or metal surfaces of the equipment. The apparatus generally includes a reservoir of the composition and an injector system in fluid communication with the reservoir and the equipment for metering into the fluid a sufficient amount of the composition to prevent nitridation and/or carburization of the metal or metal surfaces.
The present invention also provides a metal surface treated with a nitridation and/or carburization preventative composition of the present invention.
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King Roy
Strozier Robert W.
Wilkins, III Harry D.
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