profiling sonar: inspecting in-service, submerged pipes
Over 70% of the world is covered with water. What percentage of the pipe infrastructure is underwater?
The answer is: it varies widely. Flow levels in pipes can fluctuate depending on the time of day, weather events,
and numerous other factors. This is particularly true with larger diameter pipes, where it is common to have a
percentage of the pipe always underwater. Conventional CCTV works above the flow, but what can you use to inspect
below the flow? Use SONAR. Read on to find out how it works and what information it can provide.
Sonar, the acronym for SOund Navigation And Ranging (SONAR), is a measurement technique that determines the
location of a surface by measuring the time required for an emitted sound wave to be reflected by the surface
and return to the sonar unit. (You could say, we "ping" the surface.) In our industry, sonar is useful as a pipe
inspection tool that produces quantitative pipe condition data within charged pipes without requiring expensive
bypass pumping.
Pipe condition assessments are usually performed with a specific kind of sonar, called a profiling sonar.
Profiling sonar employs a single rotating transducer mechanism that is mounted to a pipe crawler or floating platform.
As the platform moves through the pipe, measurements from the rotating transducer produce a cross-sectional image
of the pipe. The image is referenced to the payout location of the inspection platform. These cross-sectional images
capture the condition of the pipe, including areas of interest on the walls, crown, and invert. Quantitative assessment
of pipe condition can be performed in pipes of all shapes and sizes by comparing cross-sectional profiling sonar images
to the as-built shape of the pipe, using software analysis tools. Sonar can also be used in conjunction with CCTV and
laser inspections. Used in this combination, it can provide a comprehensive pipe condition assessment that documents
pipe condition above and below the flow line.
Data obtained from profiling sonar inspections provides quantitative answers to several critical pipe condition
questions. For example, profilng sonar can be used to:
- Estimate the total volume and distribution of sediment and debris that is contained with a pipe
- Measure pipe ovality at regular intervals
- Provide the current storage capacity of a pipe
- Identify and localize major structure damage, e.g. collapse, blockages, etc.
Answering these questions can eliminate the guesswork and uncertainty in many operations and maintenance activities.
For example, pre-cleaning sediment quantification done with sonar eliminates uncertainties in the proposal and the bid.
Without that information, your cleaning costs will be higher. Post-cleaning sediment quantification can be used to verify
performed work and estimate material removed during cleaning operations. A periodic program of profiling sonar inspections
can identify pipe ovality, corrosion, and crown collapse. This will enable you to prioritize maintenance activities before
pipe failure occurs.
Profiling sonar is a flexible, capable, and quantitative pipe inspection technology that should be in every pipe inspector's
toolkit. For many large pipe systems, where it is prohibitively expensive to bypass, sonar is the only viable inspection means.
Profiling sonar utility in pipes also extends beyond profiling applications. Future newsletters will explore the three-dimensional
modeling capabilities or arrayed sonar and underwater video capabilities of imaging sonar.
