LEACHING IN ASBESTOS-CEMENT PIPELINES 

AC Pipelines: composition, properties, and usage

In the Netherlands, from the 1950s until the 1990s, many asbestos-cement pipelines (also known as AC pipelines) were installed by the drinking water sector and from the 1970s also by the wastewater sector. As the name suggests, these pipes consist of about 80 % cement and 20% asbestos (Stowa, 2023). It is estimated that about 25% of the water pipes in the Netherlands are asbestos-cement pipes (van Laarhoven, 2021), also worldwide a large part of the water pipes is made out of this material. Asbestos-cement pipes were used so frequently because of the material’s quality, strength and long lifespan. Under the right conditions, a protective layer forms in asbestos-cement pipes because calcium carbonate (lime) precipitates in the pipe, creating a protective layer on the inside the pipe (Zavašnik, 2021). However, this protective layer is not permanent. In conditions where the water quality changes or the pH level drops, this protective layer and the one underneath it can be affected. Thus, AC pipes, which were installed in the Netherlands between the 1950s and 1990s, are now between 75 and 35 years old. Despite the strong quality and long lifespan of the pipes, over time they can be affected by leaching. Leaching is the process in which calcium dissolves from the cement of the pipes. As calcium dissolves, the structural strength of the pipe deteriorates, and failure is imminent.

Leaching in an asbestos cement pipe: What is it and how does it occur?    

One of the prime components of cement is calcium. When leaching occurs in asbestos-cement pipes, the calcium from the cement dissolves in the water. This results in degradation of the material, deteriorating the integrity of the pipe. The material of the pipe remains, but its composition changes, reducing its density and weakening the material. Leaching often occurs in localized areas rather than uniformly across the entire pipe. 

This degradation manifests as a “Swiss cheese” effect along the pipe’s surface (Stowa, 2023). Leaching can occur both on the outside of the pipe and on the inside of the pipe. There are a number of factors that play a role in leaching namely,  

• The age of a pipeline is an important factor in the degree of leaching. The extent of leaching is similar across pipes in their early years, but over time, certain pipes become more susceptible to leaching. 

• In pipelines located in aggressive soils, soils with low PH and/or low lime content, are more likely to experience external leaching. This is because calcium dissolves in acid. Because lime neutralizes acid, lime-poor soils often go hand in hand with acidic soils. In practice, this involves peat soils and lime-poor sand and clay soils, specifically cat clay, which is very lime-poor and has a low pH.   

• In pipelines located in lime-rich soil, leaching on the outside is not to be expected.    

• For drinking water pipes, the saturation index (SI) of the drinking water plays an important role. The SI is a measure of the dissolution and precipitation of calcium carbonate. The SI value in drinking water must exceed 0.2 to prevent leaching.   

• The inside diameter of a pipe also plays a role. According to research, there is a clear upward trend where an increase in the degree of leaching is accompanied by an increase in pipe diameter.   

•  According to BTO research (2019), the degree of internal leaching in drinking water pipes is greater than external leaching. This is an indication that for such pipes, the effect of water quality is greater than the effect of the soil in which the pipes are located. According to Stowa (2023), this often seems to be the other way around for wastewater pipelines, with the exception of local H2S impairments. 

Risks: How Does Leaching Affect Water Pipes? 

With leaching, the healthy wall thickness of the pipe decreases, or the composition of the material may change, reducing the density of the pipe. This, of course, poses risks. As the pipe wall becomes less strong, there is a greater chance of leaks and pipe ruptures. The result is, among other things, an interruption in the water supply or discharge, but there are also safety risks involved here. For example, the release of water in undesirable locations can cause erosion, which in turn poses risks. Also, sewage leakage can lead to uncontrolled environmental damage. In addition, unplanned interruptions to water supply or sewage disposal can lead to additional costs for repairs and potential claims for damages.   

How does Acquaint measure leaching in AC pipes?  

To prevent the above risks, it is important to have good insight into the current condition of pipelines. Acquaint’s inline inspection tools make this possible in a non-destructive way. Acquaint’s tools are equipped with ultrasonic sensors. These sensors emit pulses of sound waves of a high frequency. This frequency is so high that it is imperceptible to human hearing. The sound waves travel from the tool first to the inner wall of the pipe. Some of the waves reflect from the wall back to the sensors, and some of the waves travel further through the pipe wall toward the outer wall of the pipe. Once the sound waves have arrived at the outer wall of the pipe, another echo is created. Some of the waves reflect back to the sensor, and some travel beyond the pipe wall. Such an ultrasonic measurement can then be displayed in a so-called A-scan (Amplitude scan). This scan shows the amplitude, which indicates how much energy of the ultrasonic signal has returned to the sensor. In addition, it shows how much time it took to travel through the beginning and end of the pipe wall and return to the sensor. This data can be used to measure whether and where leaching is occurring in a pipe and how much healthy wall thickness remains. An example of a tool from Acquaint that is well suited for measuring leaching in water pipelines is the Acquarius. The Acquarius is a PIG (Pipeline Inspection Gauge) that, thanks in part to its ultrasonic sensors, can do a complete condition measurement of a pipeline in one run.  In addition to leaching, the Acquarius measures other failure mechanisms namely: corrosion of metal pipelines, H2S degradation in cement-bound sewage pipelines, angular displacement and joint width of couplings, ovality, axial deformation, leaks and location of the pipeline (XYZ mapping). This intelligent tool is applicable in any pressurized drinking or wastewater pipeline with a diameter from DN200 of any material. The Acquarius can handle diameter reductions of up to 30% and it can pass bends of up to 90°. However, the pipe must be freely accessible, so butterfly valves cannot be passed.   

About Acquaint

About 25% of water pipes in the Netherlands are asbestos-cement pipes, and a large number of these pipes have reached the theoretical end-of-life. A property of asbestos-cement is that leaching can occur in the pipes over the years. Leaching is a process where calcium dissolves from the pipe material where the structural integrity of the pipe deteriorates. The weakening of the pipe presents various risks such as leaks or even bursting of the water pipe. To reduce these risks, it is important to have a good understanding of the condition of the water pipes. A very convenient way to keep a good grip on this is with Acquaint’s non-destructive in-line inspection tools. These tools are equipped with ultrasonic sensors that are very suitable for detecting leaching. An example of such a tool is the Acquarius, which can provide a complete condition measurement of a pipe in just one run.   

Bibliography 

J. Zavašnik, A. Š. (2022, Augustus 24). Degradation of asbestos – Reinforced water supply cement pipes after a long-term operation. Opgehaald van ScienceDirect: https://www.sciencedirect.com/science/article/pii/S0045653521024498  

K. van Laarhoven, J. v. (2021, april 2021). CT Scans of Asbestos Cement Pipes as a Reference for. Opgehaald van Acquaint.eu: https://www.acquaint.eu/nl/wp-content/uploads/2023/12/CT_Scans_of_Asbestos_Cement_Pipes_as_a_Reference_f.pdf  

KWR. (2020, mei 10). De invloed van waterkwaliteit op uitloging van cementhoudende leidingen. Opgehaald van KWR water: https://www.kwrwater.nl/projecten/de-invloed-van-waterkwaliteit-op-uitloging-van-cementhoudende-leidingen/  

N. Slaats, G. M. (sd). Leidingnetbeheer verbindt drink- en afvalwatersector. Opgehaald van Wageningen University & Research: https://edepot.wur.nl/339616  

N. Slaats, M. M. (2015 , januari 9). Conditionering van drinkwater: de aanbevelingen voor optimale samenstelling in 2014. Opgehaald van h2o Waternetwerk: https://www.h2owaternetwerk.nl/vakartikelen/conditionering-van-drinkwater-de-aanbevelingen-voor-optimale-samenstelling-in-2014  

Stowa. (2023). Degradatie van asbestcementen afvalwaterpersleidingen. Bennekom: Drukkerij Modern.