VAPAR examines the data on its pipe assessment platform, which processes and organizes inspection recordings from inside sewer pipes.
background
Pipe inspections and condition assessments are an important part of the work of water utilities and city councils that manage sewer networks.
The collection and analysis of this information has traditionally been managed individually by each organization, making it difficult to gain general insights.
VAPAR has developed a pipe assessment platform that allows pipe plant owners and CCTV companies to process and organize video footage of the inside of sewer pipes, and to detect and classify defects in those pipes either manually or automatically.
The footage and information gathered from various places and organizations as part of this process has provided some interesting insights that are summarized in this article, with the full version available online.
Rainwater vs. sewer pipes
Diameter: In urban areas, plots of land need to be connected to sewers, and the pipes they are connected to usually start at 150mm in diameter – a relatively small diameter.
Conversely, rainwater pipes are laid where the overland runoff depths in curb profiles are insufficient.
Rainwater pipes have to carry a greater capacity from the upstream location, which usually starts at a diameter of 300mm.
Material: Due to the large number of sewer pipes to be laid and the mixture of gray, black and commercial waste, price and material accessibility play a major role, so that many more sewer pipes are made of PVC or stoneware than rainwater pipes.
Since rainwater pipes are typically larger in diameter (and therefore require larger reinforcement), more expensive materials such as concrete are more commonly used for installation.
Environmental factors: Sewer pipes generally contain less dirt (road litter, leaves, branches) than their rainwater counterparts.
However, since sewer pipes usually have a smaller diameter, are always flowing and have more lateral connection / connection points, there is a comparatively greater risk of clogging.
Sewer pipes are also more prone to pipe material degradation due to constant flows and chemical by-products of sewage, e.g. B. Hydrogen sulfide, which causes pipe corrosion.
The rainwater lengths are on average slightly longer than their counterparts in the sewer system, as they have fewer connection points and changes in direction and therefore fewer maintenance pits are required on average.
Data sets for analysis
The footage used for the analysis was uploaded to VAPAR’s cloud platform for automated analysis at the end of 2020 and was obtained from customers in Australia, New Zealand and the UK.
Structural defects in sewer pipes
Concrete: Surface damage is the most common structural defect found in concrete sewer pipes, typically caused by flow turbulence and the chemical composition of the sewage material.
Once concrete aggregate is exposed from initial surface damage, the rate of corrosion accelerates as the concrete cover decreases, steel rebars are exposed to air and moisture, causing them to corrode.
Small cracks were the second highest error rate found.
Because of the reinforcement, large cracks in the concrete are less common – when the cracks get large, they often turn into fractures.
Stoneware (VC): In contrast to concrete, stoneware pipes are not reinforced, so longitudinal, circumferential and multiple cracks are very common mistakes with this type of material.
This was the case for the analyzed data, with most of the cracks being characterized as longitudinal cracks. Almost 80 percent of the defects reported to VC were cracks.
The second most common mistake was breakage, likely due to cracks.
Flexible plastics: Due to the “flexible” nature of flexible plastics, it is not surprising that deformations of a small order of magnitude were the most common defect found in this type of material.
Different characterizations of crack formation were also observed.
Structural defects in rainwater pipes
Reinforced Concrete: A surprising amount of circumferential cracks, spalling, and minor infiltration can be introduced through lifting holes (also known as lifting eyes located in the pipe at 12 o’clock for ease of handling and installation).
Similar to concrete in sewers, concrete rainwater pipes are also at risk of cracking; Surface damage was less common, however, as rainwater is typically less gaseous and corrosive than wastewater.
PVC: Small, medium, and large deformation defects accounted for more than 80 percent of the defects found in rainwater PVC pipes.
Most PVC pipes deform during their lifetime. The degree of deformation and the length of time that deformation is observed are the important factors that plant owners need to understand when making maintenance decisions for these pipes.
Service shortages on sewer pipes
Displaced joints: Minor radial displacements were the most common type of defect and were 2.5 times more common than longitudinal displacements (also known as “open joints”).
The prevalence of dislocated connections within the pipe infrastructure is most common with clay pipes, especially older designs without rubber rings in the connections.
Roots: Roots were the second most frequently observed category. Roots often enter the pipes through joints, so it is interesting to note that misplaced joints are the most common type of defect and there can be several causes and effects.
A study conducted by the University of Melbourne1 outlined the most common factors that cause a higher frequency of root penetration, namely tree proximity, tree maturity, tree species, soil type and temperature / evaporation rates.
The study found that “blockages occurred most frequently when temperatures and evaporation were at their lowest, that is, from August to October”.
Service shortages on rainwater pipes
Debris: Small amounts of debris (up to 20 percent) in rainwater pipes were the most common defect found.
Aside from reducing the cross-sectional area, small amounts of debris and debris become a problem as the presence of that debris / debris increases the risk of additional debris accumulation over time.
An additional challenge is that debris builds up in the maintenance manholes and entry points of rainwater drains, making total clogging in these areas more likely.
Infiltration: Infiltration / infiltration in underground pipelines is another common observation in the rainwater CCTV sample dataset and, more generally, in rainwater CCTV inspection recordings.
Groundwater infiltration and other water source interactions with storm sewers are responsible for this deficiency.
Infiltration / infiltration is not as serious with rainwater pipes, although it should be taken into account during CCTV inspections as they can indicate poor joint sealing or other less visible defects.
Avoidance of Errors
Structural defects: Structural defects often result from initially minor defects that worsen over time.
It is important to be aware of the rate of deterioration in order to take the right remedial action at the right time to optimize spending.
In addition, there are a number of details that, when taken into account at the time of installation, can extend the structural life of a pipe.
Examples are the right bedding material and compaction, sufficient cover and suitable hydraulic grading of the pipe according to specification.
Operational defects: In the event of structural defects, correct assembly and the use of socket and socket connections (or similar)
Applying herbicidal foam to sewers is one of the leading solutions to reduce the regrowth of roots that enter sewer pipes.
This is more likely to result in better performance than root cutting because the roots get thicker and faster as you cut.
In rainwater, the debris is ideally collected in coarse dirt traps or waste traps at key points in the network and the pipes should be laid with a sufficient gradient so that the dirt can flow more smoothly through the network.
Summary
There are a variety of factors that contribute to the structural and operational deficiencies that affect sewer systems.
Understanding the trends in various materials can help make maintenance decisions to extend the life of a piping facility and optimize maintenance expenses.
Please visit the VAPAR website for more information.
This article was featured in the June 2021 issue of Trenchless Australasia. Click here to view the magazine on your PC, Mac, tablet or mobile device.
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