There are several failure mechanisms that can be measured with Acquaint’s inline inspection technology. One of these mechanisms is corrosion. The best-known form is corrosion of iron, also known as rust. However, what other forms exist? And which forms are most commonly found in water pipelines? Identifying corrosion in pipelines is essential. Since corrosion poses serious risks to water pipeline integrity. Find out how Acquaint’s advanced technology can help detect corrosion in water and sewer pipes.
Corrosion is a natural process of deterioration that occurs when materials, usually metals, react with their environment. During this process, “non-natural” metals such as iron try to convert themselves into oxides or hydroxides, which are natural and stable compounds. The main process in corrosion is the conversion of iron to iron oxide. The corrosion process is affected by a variety of factors including, the type of metal, the environment, temperature, humidity and the presence of corrosive substances. Corrosion can weaken the structural integrity of the materials over time, leading to degradation and potential failure of the affected components. There are different types of corrosion, the type of corrosion most commonly found in water pipes is wet or also called electrochemical corrosion. Many of the corrosion types below are forms of electrochemical corrosion.
In electrochemical or wet corrosion, an electrochemical cell is formed. These cells consist of an anode, cathode and an electrolyte. In this cell, the anode is the sensitive material; the cathode is another conductive material. During a reaction between the anode and cathode, the cathode will absorb electrons and is protected from corrosion. The anode will give up these electrons. Electrons are metal ions that form the above-mentioned oxides and hydroxides, for example. (Arepa, 2020).
A form of corrosion is rust, which is caused by a reaction between oxygen and water or moisture. These combine to form an oxidation layer, which is better known as the brown layer that attacks the metal surface. An important characteristic of this layer is its open structure. This ensures that water and oxygen continue to use the surface easily, so that the iron will slowly but surely be affected (Doddema, 2021).
This form of corrosion refers to a corrosive attack that takes places evenly over the total stretch of an area. The material loses thickness over its entire surface (Potters, 2022).
When an acidic solution comes into contact with metal, which is situated below hydrogen in the periodic table, it causes corrosion in the form of hydrogen gas and metal salt. The degree of corrosion depends on the electrical voltage of the material. Each material has its own electrical voltage. If this voltage is lower than that of hydrogen, corrosion by acid can occur (Potters, 2022).
The above-mentioned electrical voltage that every material possesses also plays an important role when galvanic corrosion occurs. This form of corrosion can happen when two different metals are in close proximity to each other. Near contact between those metals, in combination with an electrolyte (water or a similar conductor), leads to corrosion due to a triggered reaction. The metal with the lower voltage will experience more corrosion than the metal with the higher voltage (Potters, 2022).
This type of corrosion occurs as a result of a very locally but deeply penetrating corrosion attack, which involves rapid reduction of the metal thickness. Pitting can be caused by irregularities in the metal surface, or by dissolved oxygen and chloride concentration in water. Compared to uniform corrosion, the decrease in metal thickness in pitting corrosion, albeit on small surface areas, can be 10 to a 100 times faster (Potters, 2022).
This occurs in cracks and crevices that are filled with fluid and where oxygen is scarcely available. As a result, the metal sheet becomes an anode at that location and crevice corrosion occurs (Potters, 2022).
Microbial corrosion is a corrosion process that involves microorganisms. It does not refer to a specific type of corrosion. Instead, it describes a microbe-driven process that accelerates the development of other forms of corrosion, such as pitting, crevice corrosion, uniform corrosion and so on (Potters, 2022).
Gray cast iron (GCI) is an alloy of iron, carbon and silicon. The condition of GCI pipes can deteriorate due to corrosion. In the process of corrosion, iron ions are dissolved in the presence of oxygen. As iron is withdrawn from the iron-carbon alloy, only carbon remains. This phenomenon is called graffitating or potting. Due to graffitating, the strength of GCI decreases. The reactions that the iron ions released during corrosion go through are very complex and only partially known. The corrosion products precipitate on the wall of the pipe, which may result in the formation of coatings on the wall in the course of the process. These coatings slow down the further corrosion process. (Beuken, van Eijk & Slaats, 2014).
Corrosion in drinking- and wastewater pipelines involves the gradual degrading of the material that makes up the pipe. This degradation occurs as a result of a reaction between the material that makes up the pipe and the environment of the pipe or the medium it transports. According to Hussein Fahr et al. (2023), the causes of corrosion in water pipelines can be divided into three main categories, namely environmental – , pipe-related – and operational factors. Within these three categories different factors play a role in the occurrence and propagation of corrosion within water pipelines.
Environmental factors are considered to be all factors that can affect corrosion from the outside of the pipeline. According to Hussein Fahr et al. (2023), the environmental factors can be divided into three different segments: soil factors, external factors and stray currents.
Soil factors include all the components that have to do with the soil in which the pipeline is located. This can for instance be the acidity, temperature or humidity of the soil. All these elements contribute to accelerating or sometimes slowing down corrosion.
Over time, changes may occur in the soil in which pipelines are located due to external factors. The changes in the soil composition can create favorable conditions for the occurrence of corrosion (Hussein Fahr et al, 2023).
Corrosion by stray currents is similar to galvanic corrosion. The difference with galvanic corrosion lies in the fact that it is not another metal where the voltage comes from. In this case the voltage is due to stray currents. Stray currents can be caused by a difference in de plus and minus of direct current (DC). This current finds its way back to the source through, for example, the ground. This form of corrosion is more common in pipelines that are close to railways and tramlines for example (Roeper, 2014).
In addition to the previously mentioned external influences, corrosion can also be affected by factors directly related to the pipeline itself.
Operational factors refer to the conditions inside the pipeline. Factors like, the medium the pipeline transports, the water pressure and the water quality.
According to H.M Hussein Fahr et al (2023) the two most important reasons for corrosion in a water pipeline are the water quality and the water type the pipe transports. Based on research these factors contribute most to corrosion in water pipelines. In addition, electrical infrastructure, soil quality and external pressure are also important causes of corrosion. Electrical infrastructure refers to trams, train tracks of high-voltage pylons, which can cause stray currents that can cause corrosion.
As beforementioned, corrosion causes the deterioration of the pipeline material. This poses several dangers. The deterioration corrosion causes can lead to structural damage and the weakening of the pipeline. Eventually, this could result in leaks, ruptures or even the collapse of a pipeline. This can result in, among other things, an interruption in the water supply or drainage, but this also involves safety risks. For example, the release of water in undesirable locations can cause erosion of the soil the in which the pipeline is located. This can lead to different kinds of dangers like sink holes. The leakage of sewer water can lead to severe environmental damage and subsequent fines. Unplanned interruptions to the water supply of sewage disposal can lead to addition costs for repairs and possible damage claims. In addition to these risks it is also possible that, if the corrosion is inside a drinking water pipeline, the quality of the drinking water deteriorates. If corrosion particles leak into the water it can cause color, odor and taste changes.
To prevent the above risks, it is important to have a good understanding of the condition of a pipeline. Acquaint’s technology has been developed specifically for this purpose. Their tools are equipped with ultrasonic sensors. These sensors operate by emitting pulses of high-frequency sound waves to the wall of the pipeline. As these waves travel through the material of the pipe wall, they reflect back to the sensor at the front and the back of the pipe wall. The duration taken for the sound waves to complete this round trip and the amplitude of the returning waves offer valuable insights into the material’s characteristics. This includes details about thickness, density, and the identification of potential anomalies within the pipeline. Such an ultrasonic measurement can then be represented in a so-called A-scan (Amplitude scan). This scan displays the amplitude, indicating how much energy of the ultrasonic signal has returned to the sensor. Additionally, it shows how much time it took to travel through the beginning and end of the pipe wall and return to the sensor.
Just like any measuring instrument, ultrasonics also has its limitations. Micro-cracks or very small starting corrosion cannot be distinguished by ultrasonic sensors from the healthy surrounding material. The measurement accuracy and the probability of detecting a defect depends on various contextual factors, as well as the configuration of the ultrasonic sensors. In a conversation, Acquaint’s advisors and engineers can explore what accuracy can be achieved under any conditions.
An example of a smart tool from Acquaint, that is very suitable for measuring corrosion in pipelines is the Acquarius. The Acquarius is a PIG (Pipeline Inspection Gauge) that, thanks to its ultrasonic sensors, can perform a complete condition measurement of a pipeline in one run. In addition to corrosion, the Acquarius also measures other failure mechanisms, namely: Leaching in AC, H2S deterioration, condition of a joint (Angular displacement and joint width), ovality, axial deformation, leaks and the precise location of the pipeline (XYZ-mapping). This intelligent tool can be used in any pressurized drinking water or wastewater pipeline with a diameter of DN200 or more of any material. The Acquarius can handle diameter reductions of up to 30% and it can pass bends of up to 90%. The pipeline does have to be freely accessible and the Acquarius is not able to pass butterfly valves.
As described above, corrosion is a natural process of gradual deterioration and oxidation of metals by chemical reactions, often caused by moisture, oxygen and other environmental factors. The main factors contributing to corrosion in a pipeline are: water quality and the type of water the pipeline transports, electrical infrastructure that runs above the pipeline, the quality of the soil the pipeline lies in and excessive external pressure from above the pipeline. Corrosion poses risks, for example: leaks,ruptures or failure of a pipeline, with all the consequences this entails. It is therefore important that a water pipe can be inspected for corrosion. Acquaint’s technology offers the perfect solution for this. With ultrasonic technology for example, a complete condition measurement of a pipe can be done in one inspection run with the Acquarius tool, including the degree of corrosion in a pipe.
Arepa. (n.d.). Soorten corrosie; dit zijn de verschillen én effecten op metaal. Retrieved from Arepa: https://www.arepa.nl/kenniscentrum/blog/soorten-corrosie-dit-zijn-de-verschillen-en-effecten-op-metaal/
Beuken, R., van Eijk, R., & Slaats, N. (2014). De waarde van exitbeoordelingen op AC en GGIJ leidingdelen. Nieuwegijn: KWR.
Doddema, F. (2021, september 29). Alles over de verschillende soorten corrosie in pijpleidingen. Retrieved from Montipower: https://montipower.com/nl/pijpleiding-corrosie/
Hassan m. Hussein Farh, M. E. (2023, september 15). Analysis and ranking of corrosion causes for water pipelines: a critical review. Retrieved from NPJ clean water: https://www.nature.com/articles/s41545-023-00275-5#Sec28
Potters, D. G. (2022). Staal en corrosie. Retrieved from Corrosielabs: https://corrosielabs.com/sites/default/files/2023-10/Corrosie%20en%20staal%20AMA%20cursus.pdf
Roeper, T. (2014). From AC to DC.
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