Asbestos-cement (AC) pipe was used extensively in the mid-1900s in potable water distribution systems, particularly in the Western United States. The Chrisotile Institute estimates AC pipe lifespan at 70 years, but actual service life depends largely on pipe condition and working environment. Because thousands of miles of AC pipe installed in distribution systems in the U.S. is nearing the end of it's useful life, AC pipe condition assessment and strategic replacement planning will need to be done in the coming decade.
Over time, AC pipe undergoes gradual degradation in the form of corrosion (i.e., internal calcium leaching due to conveyed water and/or external leaching due to groundwater). Such leaching leads to reduction in effective cross-section, which results in pipe softening and loss of mechanical strength. Accordingly, as the water distribution system ages, the number of AC pipe failures increases with time. In light of these risks, an AC pipe condition assessment is essential to determine the remaining useful service life and develop a suitable, proactive replacement plan for the distribution system. Exponent engineers and scientists assist water agencies in development of strategic and cost-effective AC pipe replacement plans, customized to the individual challenges of the distribution system.
The condition assessment and proactive replacement planning process consist of the following steps:
1. Collection of System Data
Identification of prevalent AC pipe failure mechanisms (beam failure, bursting under pressure, joint failure, etc.)
- Analysis of historical AC pipe leak records with respect to geographic location in the distribution system, incorporating geographic information system (GIS)
- Identification of factors affecting AC pipe failure propensity, which may include:
- Pipe age
- Pipe diameter and pipe manufacturer
- Internal/external water chemistry
- Internal water pressure
- Soil physical and chemical properties
- Groundwater table elevation
- Overburden
- Climate
2. System-Wide Sampling and Condition Assessment
- Evaluation of in-situ AC pipe condition using a series of laboratory tests:
- Crushing test (ASTM C 500)
- Hydrostatic pressure (ASTM C 500)
- Flexural test (ASTM C 500)
- Petrographic examination
- Determination of calcium leaching depth
- Scanning electron microscopy and energy dispersive x-ray spectroscopy
- Assessment of O-ring condition using compression set test (ASTM D 395), hardness test (ASTM D 1415), and Fourier transform infrared spectroscopy (FTIR)
3. Modeling and Implementation
- Development of AC pipe failure prediction models
- Implementation of system-wide optimal pipe maintenance and replacement schedule
Additional Capabilities
In addition to the assessment of asbestos-cement pipe, Exponent has expertise in many areas that can benefit the operators of water districts:
- Geotechnical
- Embankment design and monitoring
- Seepage flow
- Slope stability and failure mechanisms
- Settlement
- Seismic safety and stability
- Earthwork and grading
- Foundations and retaining structures
- Water Resources
- Hydrology, hydraulics, and sediment transport
- Flood hazard risk analysis
- Watershed evaluation and analysis
- Water availability projections
- Reservoir and pipeline assessment
- Materials Science
- Concrete and cement-based infrastructure
- Polymer-based materials
- Corrosion assessment and control
- Risk Assessment
- System wide assessment of vulnerability to earthquakes or other disasters
- Environmental Sciences
- Water contaminant transport
- Water and wastewater treatment management and recycling
- Ecological and environmental risk assessment
- Environmental engineering and modeling