While metallic rising mains have been historically difficult to manage, a risk-based approach increases confidence in the condition of the pipeline.
Nothing grabs headline news like the failure of a rising main, which can be extremely damaging to the environment and harmful to a utility’s reputation.
Historically, wastewater rising mains have been difficult to manage, especially those made with ferrous materials, where the failure method is slow when compared to concrete pressure pipe. As well, sewer rising mains have special operational challenges that don’t apply to gravity sewer mains as they typically cannot be taken out of service for inspection, and due to the presence of solids in the fluid, rising mains represent a far more abrasive environment than potable systems such that assessment methods for water mains may not be applicable.
Gas pockets are of significant concern in rising mains.
The primary failure mechanism of ferrous rising mains is due to internal corrosion. Gas pockets are of significant concern in rising mains, as concentrations of hydrogen sulfide gas within wastewater can be subsequently converted to sulfuric acid by bacteria in the slime layer on the pipe wall. This may cause corrosion and eventual breakdown of the pipe’s wall.
Therefore, a first step in assessing rising main condition should be the identification of gas pocket locations within the pipeline.
Pure Technologies has performed an analysis of rising mains inspected using acoustic based technologies in order to better characterize the frequency and location of gas pockets. Based on the analysis, it was found that 72% of gas pockets were not at known high points or air release valves, therefore, the most precise way to identify gas pockets within a rising main is through the implementation of inline acoustic inspection technologies.
The collection of gas pocket locations alone will not indicate the condition of the pipeline, but instead identifies locations where an increase in corrosion potential is observed. To ascertain the true condition of a pressure pipe, higher resolution electromagnetic technologies are required. These technologies measure pipe wall thickness in ferrous materials and broken wire or bar wraps in concrete pressure pipe.
Once the condition data is collected, advanced analytics can be applied to estimate the pipeline’s remaining useful life.
“Previous analyses involved straight-line assumptions – comparing the pipe wall thickness at installation against what it is today. However this doesn’t give an accurate picture of how pipes degrade…by using statistical modeling we can develop a more predictable degradation rate based off of over 14,000 miles of inspection data Pure has collected over the past 30+ years.”Jennifer Steffens, Market Sector Leader, Water and Wastewater, Pure Technologies
Desktop studies are not always reliable.
While often the first thought is to replace the aging wastewater assets based on factors such as age and failure history, this option makes neither logical nor financial sense. With so many miles of buried pipelines and such limited capital budgets, utilities don’t have hundreds of millions to spend on replacing pipelines which still have remaining useful life.
At Pure Technologies, we believe there is a better way. A more feasible approach to ensuring the safe operation of rising mains is to undertake a risk-based approach to manage their operation. A risk-based approach will provide decision intelligence on which assets require rehabilitation or replacement to extend their useful life. Or which assets can be left alone.
Our approach is to help utilities evaluate the current state of their buried infrastructure and provide them with high confidence condition and operating data. We then couple this with our years of extensive experience and project history (more than 12,000 kilometers of pressure pipe assessment) to provide utilities with actionable information, which allows them to make informed decisions as to the management of these critical assets.
Value of a risk-based approach to manage rising mains.
Utilities that embrace a risk-based approach to manage their rising main inventory have found that on average they can safely manage their rising mains for roughly 5 to 15 percent of the replacement cost. This pragmatic approach focuses on providing real condition data through assessment, which can be used to selectively renew isolated areas of damaged pipe in lieu of capital replacement.
Four steps to a risk-based approach.
At Pure, we recommend a risk-based approach to manage wastewater rising mains by focusing on four main areas:
- Preliminary Risk Analysis
- Internal Corrosion Potential Surveys using Inline Acoustics
- Pipe Wall Assessment using Advanced Technologies
- Condition Data Analysis and Advanced Risk Assessment
Preliminary analysis includes collecting the right data to develop a prioritized plan for assessment, including the selection of appropriate technologies. To help make preliminary decisions, Pure collects all available information to understand the history of the pipeline and the likely failure modes. The data analysis will provide an understanding of the construction and context of the pipeline. Data of interest typically includes pipe characteristics, installation factors, environmental and performance-related data, operational data, and failure data.
Internal corrosion potential survey.
An internal corrosion potential survey uses inline tools to locate gas pockets that can increase the potential for corrosion and eventual breakdown of the pipe wall. Pure Technologies typically deploys its acoustic-based SmartBall® leak and gas detection tool, as well as its tethered Sahara® leak and gas pocket detection platform to locate gas pockets in pressurized lines of all materials.
Pipe wall assessment.
While the presence of gas pockets may indicate areas of potential concern, it will not give a quantifiable answer as to the structural life of the pipe.
Pipe wall assessment is completed using a variety of technology solutions to identify defects and deterioration of the pipe wall in a variety of pipe materials. For pipe wall assessment of metallic rising mains, common internal electromagnetic technologies include the PipeWalker® and PureRobotics® platforms, as well as the free-swimming 24-detector PipeDiver® assessment tool, developed to identify electromagnetic anomalies indicating pipe wall loss.
Condition assessment analysis.
Condition data analysis and risk assessment evaluates how to safely renew or extend the life of rising mains. The risk evaluation considers not only the probability of failure (condition) of the rising main based on inspection data, but also the consequence of failure in order to make sound engineering decisions.
Understanding the risk of the pipeline is an important step in selecting and justifying the appropriate condition assessment methods. As the risk of the asset increases, the value of using high-resolution comprehensive assessment techniques increases. Higher resolution data results in more confident decision making, and would justify and prioritize the application of assessment techniques.
Diagnostic analytics helps utilities move risk assessment forward.
In the past, inspections were done, the data analysed, and the results passed on to the utility. Pure Technologies now offers a more holistic program of diagnostic analytics. This includes analysis of what caused the corrosion problem within the pipe wall, what the impact the corrosion has on the life of the pipeline, and a prescriptive analysis of how it needs to be repaired or rehabilitated.
The next step gathering momentum? Predictive analysis to elongate service life.