Precast concrete cylinder pipe (PCCP) has been widely used successfully for both water transmission and wastewater force mains for many decades. In the case of water conveyance, the majority of failures occur due to soil side deterioration. This includes chloride intrusion and low pH soils and ground water promoting corrosion of the prestressed wires. High sulfate bearing ground waters can also cause expansive degradation of the cement mortar coating exposing the prestressed wires to corrosive conditions. Internal corrosion rarely results in PCCP failure in potable water conveyance.
In force mains, the same soil side damage mechanisms experienced by water transmission pipelines are commonplace. But, force mains also fail due to internal biogenic sulfide corrosion where air pockets are present.
Under both external and internal corrosion scenarios, PCCP manufactured with Class IV (and to a lesser extent with Class III) prestressed wire can be susceptible to rupture associated with hydrogen embrittlement and dynamic strain aging or DSA. Understanding the background design data on the pipe can highlight the likelihood of this propensity.
Diagnostic technologies for acoustically identifying wire breaks and electromagnetic tools for locating wire breaks are available and useful, but very expensive and intrusive to operations. These indirect assessment tools are often not necessary.
Experience has shown that direct assessment of soil corrosivity and pipe integrity based on known damage mechanisms provides sufficient data to determine pipeline conditions and ascertain likelihood of failure.
This paper presents a protocol for direct pipeline condition assessment that establishes prioritized risk and rehabilitation or replacement needs for PCCP pipelines. Case histories describing this condition assessment approach are included.
The major damage mechanisms for Precast Concrete Cylinder Pipe (PCCP) are well-known for both water transmission mains and wastewater force mains.
Soil side corrosion is the most prevalent cause of PCCP failures. This is caused by chloride intrusion through the cement mortar coating to the prestressed wires. Soil side corrosion can be the result of exposure to acidic groundwater and soils. In these cases, the cement mortar coating is broken down by acidic attack and the wires are subjected to the corrosive electrolyte. High sulfides bearing ground waters can also promote cement mortar coating degradation. Sulfate reactions cause expansive deterioration of the cement mortar exposing the prestressed wires to corrosive soil conditions.1
