What is a CCTV Drain Survey?
Recent infrastructure studies underline the general deterioration of sewer systems and the risk to public health, the environment and increasing costs (ASCE, 2009). Since the origin of sewer systems in the 19th century, sewers have been installed in different
periods using available standards and technologies. Sewer assets have a limited service life and it is crucial to assess their condition throughout their life cycles to avoid potential catastrophic failure and expensive emergency rehabilitation due to their deterioration
(Hao et al., 2011).
This report first presents the wide panel of inspection technologies available to obtain information about sewer defects and conditions. Visual inspection (e.g. Closed-circuit television CCTV Drain Survey equipment, zoom cameras) appears to be the industry standard for sewer inspection. It provides visual data (images and/or videos) of the internal surface of the pipe. Defects are usually coded manually by the inspection technician according to standard coding methods.
In Europe, the current codification system is the normative EN 13508-2 for visual inspection (EN 13508-2, 2011) used by the CEN-Members (European Committee for Standardisation). In addition, physical techniques are available that can give further
information and details about pipe defects.
These techniques do not replace the CCTV drain survey inspection but can give deeper insights into the type and severity of defects. Sonar and Lasers enable you to analyze pipe geometry and can identify defects such as deflections, cracks, sediments or corrosion. Ultrasonic testing and magnetic flux leakage (MFL) are applied directly to the pipe wall. They enable you to measure wall thickness and detect pipe
defects such as corrosion, deflections and cracks. Ground Penetrating Radar (GPR) and Infrared Thermography are used from above ground and are useful to locate pipes and identify bedding conditions, voids and leaks. Finally, network-wide inspection technologies like smoke testing or Distributed Temperature Sensing (DTS) can locate cross-connections and/or sewer infiltration. The purpose, inspection procedure and limitations of these methodologies are briefly presented.
In a second stage, this report presents the available classification methodologies developed to interpret automatically visual CCTV inspection reports and evaluate sewer conditions. These methodologies enable to transfer of the extensive amount of visual inspection data from CCTV drain survey inspection into a more easily manageable number, useful to support asset management practices. Most approaches have a similar goal: they aim to rank rehabilitation priorities and support municipalities in the definition of rehabilitation
programs. They do not pretend to replace the knowledge and analysis skills of a local expert but can help him or her to identify rehabilitation priorities.
All methodologies provide an overall condition score for each sewer segment or sub-scores for different requirements (e.g. structural and operational conditions) or dysfunctions. From the review of available methodologies, two main approaches can be distinguished: priority-based and substance-based methodologies. For priority-based methodologies, the calculation of sewer condition grades is based on the most severe defects, the density of defects and/or the length of the defect.
Condition grades express the priority of rehabilitation, i.e. the emergency of action regarding the probability of failure or collapse. For substance-based methodologies, the final score is calculated based on the length of sewer that will be affected by rehabilitation actions. Substance based methodologies do not aim to assess the condition of sewers but rather to rank sewer pipes considering the amount and type of rehabilitation needs: replacement, renovation and repair.
Each methodology aggregates and combines sewer defects in a very different way making very hazardous the benchmarking of final scores from different methods. Therefore, municipalities using different evaluation systems are not able to benchmark the condition of their networks. Finally, the accuracy of the classification results remains a key issue, crucial for the further use of inspection data to support asset management strategies.
Asset management is an increasing concern for wastewater utilities and municipalities. According to a need survey conducted by EPA (2008), the total funding needed for replacement, rehabilitation and expansion of existing collection systems for a 20 year period in the USA is 82.7 billion dollars, i.e. 28% of the total need of public agencies for wastewater treatment and collection. According to a French ministerial survey (OIEau, 2003), the total need in France for sewer rehabilitation is about 7 billion euros. Average yearly investments in the wastewater system in France are about 1.7 billion euros (including capital costs for replacement, rehabilitation or expansion of existing collection systems). In Germany, a national study estimates that about 17% of the sewers have severe defects and should be immediately or in short term rehabilitated (Berger and Falk, 2009).
In the last 30 years, most municipalities have invested in sewer system expansion and treatment plant upgrades but a relatively small
amount has been allocated to the improvement of sewer system conditions. Part of the funds needed to upgrade the condition of sewer systems will be generated through increases in municipal taxes and user fees (Allouche et al., 2002). Other efforts will focus on the reduction of overall costs through the definition of cost-effective rehabilitation plans and the optimization of inspection and maintenance programs.
In this context, the condition assessment of sewers aims to evaluate the current condition of assets and support the prioritization of maintenance and rehabilitation activities. The assessment of sewer condition is crucial in implementing a successful asset management program since the cost of sewer failure may have significant economic impacts on the municipality or utility (Rahman and Vanier, 2004).
Most condition assessment methodologies aim to provide an overall grade to each inspected sewer, which represents the current condition of the asset. Input data to these classification methods are sewer defects recorded during CCTV inspections and coded according to standard coding systems. For that purpose, mobile and rotatable cameras are inserted into the sewer system to record pictures or movies from the inner side of sewer pipes. Damages, defects and other abnormalities are documented and additionally described using standard defect codes.
Besides CCTV drain survey inspection, a number of additional inspection technologies are available. They can be used complementary to CCTV to gain more precise information about sewer defects or to identify defects hardly visible using inspection cameras such as
deteriorated bedding conditions.
Read more here: https://publications.kompetenz-wasser.de/pdf/Kley-2013-662.pdf
We have been doing CCTV Drain Surveys in Derby, Nottingham, Stoke and Sheffield for many years. Please contact us for more information.