Ductile Iron Pipe


Ductile Iron Pipe (DIP) evolved from it's forefather, Gray Cast Iron Pipe (CIP). CIP was reportedly first used in 1555 in Germany. King Louis XIV used it in France in 1664 when he installed a 15 mile run of CI to supply water to town fountains. That pipe was in service for more than 330 years.

The United States first used CIP in 1817 when Philidelphia utilized it in the installation of a new water system.

According to the Ductile Iron Pipe Research Association (DIPRA), today there are more than 600 utilities that have had CIP mains in service for more than 100 years. There are also at least 21 utilities with CIP mains in service for more than 150 years.

Ductile Iron Pipe (DIP) emerged on the scene in 1953. DIP is superior to CIP because of an improved manufacturing process. Magnesium is introduced in the smelting process and this changes the form of the graphite particles in the iron. The result is a pipe that is lighter, stronger, more corrosion resistant and more machinable than CIP. These qualities, thus, make it more cost effective than CIP, too.

Ductile Iron Pipe Sizes

DIP ranges in size from 3" to 64" and in pressure classes from 150 psi to 350 psi, although custom sizes and pressure ratings can be obtained.

Because of the strength of the ductile iron, it is possible to manufacture the pipe with a relatively thin wall thickness. For example, 8" class 350 (350 psi) DIP has a wall thickness of only 0.25". For comparison, 8" DIPS (Ductile Iron Pipe Size) DR 7 HDPE has a wall thickness of 1.232" and a resulting pressure rating of only 265 psi. Both of the pipes in our example have the same outside diameter, so you can see that DIP achieves a much higher pressure rating with a much thinner wall and, thus, a larger inside diameter. This increases the flow capacity and, at times, enables engineers to design smaller DIP pipes to achieve flow requirements.

Pipe charts are to be added to this site soon, so please check back often....

Corrosion Issues

Because DIP is an iron product, it can have the same corrosion problems prone to all iron products, especially when installed in corrosive environments.

DIP is commonly coated in the inside with a cement-mortar lining. This lining enables it to handle the rigors of transporting potable water, sea water, non-septic gravity sewers, sewer forcemains and reclaimed water.

DIP is also available with various epoxy liners. This is commonly used for septic sewer and other caustic environments.

An exterior polyethylene encasement is another popular coating for DIP. This is simply a polyethylene "bag" that is slipped over the pipe as it is installed. The bag is cut longer than the pipe joint and is overlapped onto the next pipe to be sure that no bare pipe is exposed. Whether needed or not, most municipalities now require the installation of a polyethylene liner when new DIP is installed. This is simply because it is a very inexpensive layer of protection, usually costing not more than $0.50 / LF for pipe up to 12".

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