Ductile Pipe Layout Measurements

Layout Recommendations

• The Ductile Iron Pipe Research Association recommends laying pipes 3 to 12 inches wide atop loose backfill on the bottom of a flat trench. Laying the pipe on the trench bottom with a light backfill halfway up the pipe is ordinarily acceptable for 14-inch or larger pipes. For extra stability, lay heavier pipes on 4 inches of loose soil with a light backfill to the top of the pipe, or embed them at one-eighth of their diameter in gravel, sand or crushed stone and add compacted backfill to the top. Embed the heaviest pipes up to one-half of their diameter in gravel, sand or crushed stone and add compacted backfill to the top. Leave at least 4 inches of compacted material under the heaviest pipes.

Pipe Size

• Ductile iron pipe is made in sizes ranging from 3 inches to 64 inches in diameter in 18-foot or 20-foot lengths. The typically marketed diameters are 3, 4, 6, 8, 10, 12, 14, 16, 18, 20, 24 and 30 inches. Pipe sizes are designed to accommodate water pressures of 150 to 350 pounds per square inch.

Ductile Qualities

• Ductile iron has a yield strength of 42,000 pounds per square inch, a tensile strength of 60,000 pounds per ounce and an elongation of 10 percent. Yield strength is the amount of pressure that causes a material to change shape. Tensile strength is the amount of pressure that makes it break. Elongation is how far it stretches before it reaches its tensile limit. Deflection — the angle to which you may bend ductile iron pipe when you lay it — is limited to 3 percent of the outside diameter of the pipe. This is one-half of the deflection that might damage the cement-mortar lining on the interior.

Flow Capacity

• Ductile iron pipes have a flow coefficient of 140. Flow efficient expresses the capacity of pipe in gallons per minute of water with a temperature of 60 degrees Fahrenheit and a pressure drop of 1 pound per square inch. A flow efficient of 140 means the water flows easily through ductile iron pipe using less power to pump fluids.