Corrosion of Cast Iron Pipe
Cast iron has been the most popular piping material all across the world for drain pipes as well as water distribution.
It is due to the fact that gray iron can be transformed into a pipe at a very cheap rate.
It has wonderful strength properties.
Unique corrosion resistant features make cast iron soil pipe suitable for plumbing applications.
Cast iron contains graphite.
It has an insoluble graphite layer of corrosion products.
This material is very dense.
It usually has a considerable strength and form a blockade against corrosion.
Due to the absence of free graphite in steel, the corrosion products have almost little or adherence.
It deteriorates as they are formed.
Therefore, it presents fresh surfaces for extra corrosion.
In various researches on cast iron pipe, it has been found that the graphite corrosion products have bore pressures of hundreds of pounds per square inch despite corrosion percolating the pipe wall.
Most of the soils throughout the world are non-corrosive to cast iron.
More than 329 gas and water utilities in America have distribution mains along with a service record of above 100 years made of this material.
Nine have mains more than 150 years old.
Over ninety-five percent of all cast iron pipes that have ever been installed in underground service in the United States and Canada are still in use.
The constant corrosion of metals underground is usually an electrochemical phenomenon of two primary forms: electrolytic and galvanic.
Galvanic corrosion is absolutely self-generating.
It takes place on the surface of a metal which is exposed to an electrolyte like moist, salt-laden soil.
The process is same as that which takes place in a dry cell battery.
Discrimination in electrical potential between the surfaces of the metal (pipe) with such soil may take place for a wide array of reasons, which includes the joining of various metals.
The probable differences also may take place owing to the characteristics of the soil which is in contact with the pipe surface.
Any one or more combination of these reasons may lead to a very minimal amount of electricity to flow between the pipes through the soil.
Where this electricity gets discharged into the soil from a particular area, metal is removed from the surface of the pipe and hereby corrosion takes place.
Over ninety-five per cent of the soils in Canada are non corrosive towards cast iron.
Some are: natural soils which have concentrations of decomposing organic matter such as peat bogs and swamp, salt and alkalis.
Corrosive soils which are man-made result from various mine discharges and other industrial waste products and these are transformed into landfills.
The National Bureau of Standards and the Pipe Research Association (presently called Ductile Iron Pipe Research Association, DIPRA) has examined underground corrosion of cast iron pipes for several years.
Internal corrosion of cast iron pipe mainly takes place due to strong acidic material.
If aggressive reagents containing 4.
3 pH or less are kept in touch with cast iron pipe for a without diluting for a prolonged time, the pH will rise above 4.
3.
If the run of piping in which the acid waste is released has enough upstream flow of non-acidic waste product, the rinsing movement is found to increase the pH of the combined waste so much so that it will not corrode cast iron.
Nevertheless, by averting reduced pH discharges completely, one can remove or control internal corrosion problems to a considerable extent, giving a hassle-free service in the years to come.
It is due to the fact that gray iron can be transformed into a pipe at a very cheap rate.
It has wonderful strength properties.
Unique corrosion resistant features make cast iron soil pipe suitable for plumbing applications.
Cast iron contains graphite.
It has an insoluble graphite layer of corrosion products.
This material is very dense.
It usually has a considerable strength and form a blockade against corrosion.
Due to the absence of free graphite in steel, the corrosion products have almost little or adherence.
It deteriorates as they are formed.
Therefore, it presents fresh surfaces for extra corrosion.
In various researches on cast iron pipe, it has been found that the graphite corrosion products have bore pressures of hundreds of pounds per square inch despite corrosion percolating the pipe wall.
Most of the soils throughout the world are non-corrosive to cast iron.
More than 329 gas and water utilities in America have distribution mains along with a service record of above 100 years made of this material.
Nine have mains more than 150 years old.
Over ninety-five percent of all cast iron pipes that have ever been installed in underground service in the United States and Canada are still in use.
The constant corrosion of metals underground is usually an electrochemical phenomenon of two primary forms: electrolytic and galvanic.
Galvanic corrosion is absolutely self-generating.
It takes place on the surface of a metal which is exposed to an electrolyte like moist, salt-laden soil.
The process is same as that which takes place in a dry cell battery.
Discrimination in electrical potential between the surfaces of the metal (pipe) with such soil may take place for a wide array of reasons, which includes the joining of various metals.
The probable differences also may take place owing to the characteristics of the soil which is in contact with the pipe surface.
Any one or more combination of these reasons may lead to a very minimal amount of electricity to flow between the pipes through the soil.
Where this electricity gets discharged into the soil from a particular area, metal is removed from the surface of the pipe and hereby corrosion takes place.
Over ninety-five per cent of the soils in Canada are non corrosive towards cast iron.
Some are: natural soils which have concentrations of decomposing organic matter such as peat bogs and swamp, salt and alkalis.
Corrosive soils which are man-made result from various mine discharges and other industrial waste products and these are transformed into landfills.
The National Bureau of Standards and the Pipe Research Association (presently called Ductile Iron Pipe Research Association, DIPRA) has examined underground corrosion of cast iron pipes for several years.
Internal corrosion of cast iron pipe mainly takes place due to strong acidic material.
If aggressive reagents containing 4.
3 pH or less are kept in touch with cast iron pipe for a without diluting for a prolonged time, the pH will rise above 4.
3.
If the run of piping in which the acid waste is released has enough upstream flow of non-acidic waste product, the rinsing movement is found to increase the pH of the combined waste so much so that it will not corrode cast iron.
Nevertheless, by averting reduced pH discharges completely, one can remove or control internal corrosion problems to a considerable extent, giving a hassle-free service in the years to come.
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