What Is an Iron Flange?

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  • Written By: Lori Kilchermann
  • Edited By: Lauren Fritsky
  • Last Modified Date: 02 December 2019
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An iron flange is a device used to connect valves, corners and other fixtures into a steel pipeline. Manufactured from black cast iron, an iron flange is a device cast onto the end of a piece of pipe or a pipeline fixture so that the pieces can be bolted together. The connections using the many iron flange joints are made leak-proof through the use of a thick copper or other type of gasket material being sandwiched between the two flanges. Strong bolts are then placed around the outer edge of the flange to form the final connection.

Similar to a steel flange, the iron flange is connected to the pipeline to form removable sections, switches and other connections. Unlike the steel flange that must be welded to the pipe, the cast iron flange is cast onto the ductile iron pipe section as it is manufactured, creating a corner, cross or similar section with a built-in connection device. This is required due to the inability to safely and reliably weld cast iron pieces together. The flanges allow the sections to be bolted together, resulting in a strong and leak-proof pipeline. Due, in part, to the very heavy weight and rigidity of the ductile iron components, the cast iron pipe is commonly not to be used in underground applications, such as large water and sewer lines.


The cast iron flange is not only found on the smaller sections of pipe and fittings, the flanges are also cast onto the ends of long, straight lengths of pipe. The sections must be bolted together once they are situated in a very level position. If there is a large variance in height from one length of cast pipe in relation to the other, the pipe could crack or break with the tightening of the flange bolts. This occurs as the flanges are attempting to be pulled into a straight line with each other as the flange bolts are tightened. This causes the pipes to attempt to bend into a straight line with each other, causing damage to one or both sides of the connection.

Most types of iron flange connections and pipeline are manufactured in either lined or unlined versions. Unlined pipe is just that, a raw iron pipe. The lined type of ductile pipe and flanged fittings are lined with a cement-mortar lining when used for the transportation of water. The fittings also include an asphalt coating on both the interior and exterior of the pipe and fittings.


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