14.1 Pipe Materials & Pipe Selection

Materials in the California Ground

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How Pipe Is Specified

Ductile Iron: Pressure Class and Thickness Class

Modern DIP is ordered by pressure class (PC 150, 200, 250, 300, 350) - the rated working pressure in psi - which replaced the older thickness class (Class 50 through 56) for most sizes. Standard laying length is 18 or 20 feet. Interior is cement-mortar lined per AWWA C104 in nearly all potable applications.

PVC: Dimension Ratio

$\text{DR} = \frac{\text{Outside Diameter}}{\text{Wall Thickness}}$

A lower DR means a thicker wall and a higher pressure rating. AWWA C900 pipe is commonly specified as:

[!TIP] The relationship is counterintuitive the first time and is a reliable exam item: higher DR = thinner wall = lower pressure rating. DR 14 is stronger than DR 25.

HDPE: Dimension Ratio and Material Designation

HDPE is specified by DR and by cell classification (commonly PE4710). Because HDPE is joined by butt fusion, a properly fused line has no bell-and-spigot joints at all, which eliminates the leak path that dominates other materials and makes HDPE the material of choice for trenchless installation (horizontal directional drilling, pipe bursting, slip lining) and for seismic applications, since a fused line can deform substantially without separating.

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The California Minimum

22 CCR 64573: newly installed water mains in a community water system shall have a nominal diameter of at least four inches.

That is the state floor. In practice:

• Local fire codes typically require 6 or 8 inches on any main serving a hydrant, because a 4-inch main cannot deliver meaningful fire flow.
• 6-inch minimum is the common utility standard for looped residential mains; 8-inch for anything with hydrants; 12-inch for arterials.
• A 4-inch main is generally acceptable only for a short residential run with no hydrant, in a fully looped system.

Undersized mains are a permanent hydraulic penalty: head loss varies with diameter to roughly the 4.87 power, so upsizing from 6 to 8 inches cuts head loss at the same flow by about 75 percent.

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Legacy Material Handling

Asbestos Cement

AC pipe is safe in the ground and safe carrying water. The hazard is airborne fiber when the pipe is cut, ground, or broken dry. California requires:

• Work practices that keep the material wet - wet cutting with a snap cutter or a wet saw, never a dry abrasive wheel
• Trained workers, appropriate respiratory protection, and disposable coveralls
• Compliance with Cal/OSHA asbestos standards and the applicable air district rules; large jobs may require notification
• Proper disposal of cut sections and debris as regulated waste

An operator who breaks an AC main during an emergency repair must recognize the material and switch to the correct work practice - AC pipe cannot be treated like PVC just because it is white and brittle.

Unlined Cast Iron

The dominant legacy problem: tuberculation builds a rough, thick internal deposit that destroys the C-factor, harbors biofilm, releases red water when velocity changes, and exerts chlorine demand. Options are cleaning and lining (mechanical cleaning followed by cement-mortar or spray-applied polymer lining) or replacement, decided by break history, remaining wall thickness, and disruption cost.

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Selection Factors

A real pipe specification weighs:

1. Internal pressure - working pressure plus surge allowance plus test pressure
2. External load - depth of cover, traffic loading, trench width and bedding
3. Soil corrosivity - the AWWA C105 ten-point evaluation; a score of 10 or higher requires protection for ductile iron
4. Water chemistry - aggressive water attacks unlined iron and cement mortar
5. Seismic exposure - fault crossings, liquefaction zones, and lateral spread favor restrained joints, HDPE, or earthquake-resistant ductile iron joints
6. Installation method - open cut versus trenchless
7. Tapping and repair - how the crew will connect services and make repairs
8. Contaminated soil - hydrocarbon-contaminated ground can permeate PVC and polyethylene, so barrier pipe or ductile iron is specified
9. NSF/ANSI/CAN 61 certification for every material in contact with potable water
10. Life-cycle cost, not first cost

[!IMPORTANT] Permeation is the selection factor operators most often forget. Where a main will cross a former fuel station, a solvent plume, or an area with known hydrocarbon contamination, thermoplastic pipe and elastomeric gaskets can allow organic compounds to migrate through the pipe wall into the water. The specification response is ductile iron with a suitable gasket, or barrier pipe, plus documentation of the contaminated area on the map so future work knows.