For nearly a century, beginning in the late 1800s, asbestos cement (AC) was used widely for pipe works. But the past few decades have seen a decline in the installation of new asbestos pipes thanks to the availability of better pipe materials such as high-density polyethylene (HDPE) and polyvinyl chloride (PVC) that are cheap, long-lasting and easy to maintain.
However; the main reason for the decline lies in the concern about the adverse effects of asbestos fibers in drinking water. The health effects of chronic inhalation of asbestos dust resulting in asbestosis and mesothelioma (cancer of the lung) are well established.
This fact, in turn, has led to concerns about effects on health by ingesting asbestos fibers through drinking water especially in cases of peritoneal mesothelioma. (Read Asbestos Cement Pipe: Why It's a Problem and How Trenchless Can Fix It.)
Miles and miles of AC pipelines are reaching the end of their serviceable life in North America and Canada. Over 560,000 miles of pipeline were used to install water and sewer pipelines in these countries between the 1940s and 1960s. (Read How a Sewer is Installed.)
AC pipes were considered very valuable in pipe manufacturing due to its low cost, long service life, and resistance to corrosion.
It was pressure from governmental agencies such as Environmental Protection Agency (EPA) and Occupational Safety and Health Administration (OSHA) that finally phased out asbestos from commercial, residential and industrial piping in the 1980s.
But replacing these pipelines will not be easy considering that many of these pipes may be very difficult to locate in the labyrinth of pipelines underneath. (Read The Complex World of Sewer Networks.)
The Necessity to Rehabilitate Asbestos Cement Pipes
Asbestos is a fibrous silicate material containing iron, magnesium, calcium or sodium. Contamination of water supply can occur naturally through the erosion of mineral deposits of serpentine or other asbestos-containing material in surface water systems, improper disposal of asbestos wastes, and/ or deterioration of AC pipes in water distribution systems.
Over time, AC pipes deteriorate either by internal leaching due to the flow of water or external leaching due to groundwater. This reduces the effective cross-section of the pipe resulting in the softening of pipe material and loss of mechanical strength.
Considering the age of our pipelines, AC pipe failure is inevitable but difficult to detect unless a comprehensive condition assessment of pipelines is undertaken. Replacing or rehabilitating AC pipelines should be done before catastrophic failure occurs.
Waiting too long can lead to an increased risk of contamination of potable water and increased cost of rehabilitation.
The Safe Drinking Water Act (SDWA) has limited asbestos fiber content in drinking water to 7 million fibers per liter (MFL). Consuming water with a higher content than that over an extended period of time can lead to the risk of developing benign intestinal polyps.
Carrying Out Proper Condition Assessment
As the age of the asbestos cement pipes increases so does the number of pipe failures, but there may still be pipes that are structurally sound and do not need replacement. Condition assessment of these pipelines is essential to understand the remaining useful life of the pipelines and to come up with a suitable plan for repair and rehabilitation. (Read Your Comprehensive Guide to Condition Assessment of Buried Pipelines.)
The planning process for the replacement of asbestos cement pipes can be undertaken by following some important steps.
The existing system has to be analyzed first for the identification of pipe failure mechanisms such as pressure bursting and joint failure. Factors that affect pipe failures such as age, size, manufacture and class, water composition and pressure, soil properties, overburden pressure, and climate also need to be considered.
Municipal records showing AC pipe leak record with respect to a geographical location is also useful for analysis.
Inspection, Sampling and Testing
Asset inspection gives the current status of an asset in terms of its structural stability, rate of deterioration, capacity, and need for repair or replacement. An asset management plan (AMP) should be put into place to outline assets that are to be inspected, how to inspect them and when to inspect them.
Inspecting an entire system is very expensive and hence prioritizing based on the purpose of condition assessment is essential. Sampling of pipes for condition assessment and laboratory testing should be taken system-wide. This will give a complete picture of the entire network and allow for a more comprehensive assessment.
Some of the tests that can be carried out are:
- Crushing strength, hydrostatic pressure and flexural strength test – ASTM C 500.
- Tensile strength test – ASTM C 496.
- Petrographic examination – ASTM C 856.
- Compression set test – ASTM D 395.
- Hardness test – ASTM D 1415.
- Fourier transform infrared spectroscopy (FTIR).
- Calcium leaching depth.
- X-ray spectroscopy.
After assets have been inventoried and inspected, the data obtained is organized and analyzed. Comparing previous data can also help determine if some areas show a trend towards a particular type of problem. Data management and analysis can be done using asset management and condition assessment software available in the market.
The software has the additional advantage of incorporating a Geographic Information System (GIS) mapping into the system that helps understand location such as proximity to schools, hospitals, railroads, etc., and thus understand the criticality factor of a utility better.
Structural defects and the level of service provided by a pipeline should be quantified, processed, evaluated and analyzed.
The final condition assessment will involve making calculated assessments about high risk and critical pipelines that need repair or replacement. Acting on the assessment before further deterioration or failure occurs is what condition assessment is all about. Action taken should begin with pipelines that are at the highest risk of failure and those that will have the greatest impact on the community or environment.
It should also include alternatives that can be used to prevent failure and also the cost associated with rehabilitation or replacement of the asset. Future intervention needed should also be outlined in order to manage the assets at the right time by conducting failure risk analysis and remaining life estimation.
Critical Pipeline Inspection Methods
Predicting the failure of AC pipes is not limited to internal checks using closed-circuit television inspections (CCTVI) as they only give details of internal pipe damage. (Read Using CCTV to Inspect Pipes.)
Since AC pipes can also be affected by corrosive groundwater damaging the pipe from outside, the Asbestos Cement Pipe Scanner (ACPS) is an effective tool to study the AC pipe inside and out.
It was first used for the condition assessment of the Harbourgreene line in Surrey, British Colombia.
ACPS is a remotely operated robot that uses pipe penetrating radar (PPR) technology for a complete assessment of non-ferrous pipes using high-frequency radar antennae.
Deployed inside the pipe, it can measure wall thickness, detect exposed reinforcement or cover to reinforcement, and measure the extent of voids that have formed in the soil outside the pipe.