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How To Tell Ductile Pipe From Cast Iron Pipe

Mar. 08, 2021
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How To Tell Ductile Pipe From Cast Iron Pipe

Ductile iron pipes are lighter, stronger and more durable than cast iron. The difference between cast iron and ductile iron is the form of graphite. In nodular cast iron, the form of graphite is spherical; in cast iron, it is flake. The nodular graphite found in ductile iron is achieved by adding an inoculant (usually magnesium) to the molten iron during the manufacturing process. Ductile iron can be checked for its exact composition with a spectrograph in a laboratory environment, or identified by a tensile test.

Step 1

Check the pipeline. See how weathered it is. The ductile pipe was first invented in the 1950s. It was first commercially sold in the 1960s, and most installations were completed in the 1970s or later. If the pipe is older than that, then it is cast iron. Cast iron pipes appeared much longer than ductile pipes, and eventually ductile pipes replaced cast iron pipes. Cast iron pipes are similar in structure to ductile pipes and have been actively used in North America for at least 150 years. Another indicator to measure whether a section of pipe has ductility or castability is its smoothness. Cast iron is generally smoother than ductile iron. Most malleable products have a distinct "pointed" pattern, as if someone had hit it with a hammer.

Step 2

Look for the markings on the surface of the bell flange. Most ductile pipes have the letters "DI" or "ductility" cast directly on the surface of the bell flange. The cast iron pipe does not have these marks.

Step 3

Look for the mark on the outside of the pipe. Cast iron pipes and ductile pipes must be sprayed with one or more grade marks in the factory during production. The classification number of cast iron is 20. The number of malleability classes has been revised several times. When ductile pipes were first introduced, their classification was marked between "2" and "6". Later, around the 1970s, thickness classes were opened. The markings on the ductile pipes produced at that time ranged from "50" to "56". Later, in the 1990s, people began to mark the pipes to show how many pounds of pressure they can withstand per square inch. Most ductile iron pipes can withstand pressures from 150 psi to 350 psi, depending on the thickness of the pipe.

Step 4

Use a spectrograph to check the exact composition or use a tensile test for laboratory identification. The ultimate strength of cast iron is 20000 psi. The ultimate tensile strength of ductile iron is above 60,000 psi, and the yield strength is 42,000 psi. During the test, the ductile iron will elongate about 10% before breaking. This test result sequence is usually written as 60-42-10.

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