Considerations for Wastewater Applications
In selecting a pipe material with special considerations of sewer pipe design, the design engineer must evaluate the pipe’s expected performance and consider the many factors affecting it. These factors include physical strength, available joints, ease of handling and installation, resistance to corrosion, life expectancy and system economics.
Most Ductile iron gravity sewer installations laid in accordance with good engineering practice should serve for a minimum of 50 years—with a goal of 100 years—without failure or infiltration/exfiltration in excess of 10 gallons per day per inch diameter per mile. Zero infiltration is achievable with Ductile iron pipe due to its pressure-tight joints. Realistic allowance, however, should be made for infiltration/inflow at manholes, service laterals, and roof/foundation drain connections, etc.
Ductile iron pipe is especially suited for pressure sewer applications because its standard pressure classes provide for high operating pressures with a minimum 100 psi surge allowance. Surges, or hydraulic transients, are a very serious problem for pressure sewers as pump stations are vulnerable to power outages and surge control devices for raw wastewater are not always dependable. The surge forces, which can rupture some piping materials, are caused by momentum in the liquid due to change in velocity.