How to detect broken wires, cylinder corrosion and loss of pre-load in PCCP pipes
What Causes Concrete Pressure Pipe Failures?
Widely used across the world, Pre-Stressed Concrete Cylinder Pipes (PCCP) are commonly used for water and wastewater mains due to their strength and serviceability. Constructed with a thin steel cylinder that is cement mortar lined and coated, the pipe's burst-resistance comes from high-tensile-strength wires that are wrapped either on the cylinder directly ("Lined Cylinder Pipe") or within the outer cement coating ("Embedded Cylinder type"). PCCP pipes offer a wide variety of benefits, including resistance to physical damage, efficient installation, corrosion resistance and more. Despite their durable nature, however, PCCP pipelines require monitoring and inspection to keep on top of the issues that can occur over time. Read on to learn about the factors that can lead to PCCP failures, as well as how to conduct efficient inspection below.
Causes of damage to PCCP pipes
There are multiple factors that contribute to the degradation and failure of PCCP pipes. While many people attribute the majority of PCCP failures to broken pre-stress wires, it is usually a combination of degradation mechanisms that contribute to the failure process. Factors can typically be segmented into three different categories:
Soils that have turned highly corrosive due to chlorides, sulfides, sulfates and other chemicals in combination with high or variable water tables can degrade pipes, as can the cracking and de-lamination of mortar coating.
Stray electrical currents from nearby utilities (other pipelines, railway lines, electric wires etc.) can induce corrosion in the wires and cylinder. Usually this damage mechanism is localized to the area of the stray currents.
Pre-stress wires fail due to corrosion and/or hydrogen embrittlement. PICA is able to detect both types of wire failure and is working on a technique to determine if the wire breaks have resulted in a reduction of pre-load on the cylinder. It is important to know the difference because some wire breaks due to embrittlement can possibly be ignored if the cylinder pre-load is not affected.
Pipes constructed with poor wire or concrete quality may have low density and thickness, leaving wires and cylinders more vulnerable. Other construction issues include undetected coating damage, fabrication and construction damage, poor welding jobs, inadequate joint restraint, and more.
Ageing takes its toll on any line, especially as pipes are exposed to pressure surges and ground movement. Frost heave and the wet/dry cycle of clay soils can move the pipes around under the surface, even pulling pipe joints apart where settlement is severe or the pipe slowly moves down a side-hill. Hydrogen sulfide gas concentrations in wastewater pipes can slowly attack the concrete and the cylinder, eventually eating through to the pre-stress wires..
Prevent To Protect
Due to the larger size of most PCCP lines, the cost of a sudden failure can be catastrophic. Leaks and breaks can be extremely expensive to clean up and difficult to fix. Prevention through regular inspection is one of the best ways to avoid such issues, giving you the chance to catch minor problems before they have the chance to do major damage.
PICA Makes Inspection A Breeze
PICA Corp understands the inherent risks associated with PCCP Pipe failures and is proud to be a leading supplier of inspection services for customers worldwide. Our advanced selection of inspection technology, including our EMIT and RAFT tools provide reliable, high-resolution data that you can count on, catching signs of corrosion and cracking early on. PICA’s reputation for excellence has made us the valued partner of multiple counties, cities, and industry leaders throughout North America. Learn more about our CCP and PCCP condition assessments by contacting us now.