Unexpected pipe material surprises inspection team
For the Township of Ocean Sewerage Authority, proper planning, quick thinking and late night tool modifications keep critical pipeline inspection on track and on schedule.
As every utility manager knows, a critical pipeline inspection can be temporarily derailed for unanticipated reasons. Especially when the assumed pipeline turns out to be composed of a completely different material, with a smaller than expected internal diameter, all of which could affect the condition assessment methods.
If you’re the manager under a time-critical deadline, you face pressure to resolve the issue and successfully move the inspection forward.
Fortunately, with proper planning, quick thinking and an experienced mobilization team in place, an unforeseen challenge like this can turn into an opportunity to gain a better understanding on the state of your linear assets.
In November 2016, Pure Technologies (Pure) was contracted by Hazen and Sawyer (Hazen), consultant to the Township of Ocean Sewerage Authority (TOSA) in Oakhurst, New Jersey, to conduct a non-destructive evaluation of TOSA’s 36-inch diameter Ocean Outfall Pipeline constructed between 1966 and 1968. The pipeline was (supposedly) a 1.1 mile steel pipe that carries treated effluent to diffuser piping located 40 feet beneath the Atlantic Ocean.
TOSA had sought Hazen’s assistance in exploring ways to help them better understand the wall loss condition of their outfall pipeline in order to evaluate the need for repairs and or reconstruction options using the inspection data.
Understanding the pipe material determines inspection methods
In addition, the line is broken up into 4,000 foot and 2,000 foot sections by a drop manhole. According to profile assumptions, the Ocean Outfall Pipeline was thought to be steel. Understanding the pipe material is an important step in the selection and justification of condition assessment methods.
Based on the assumed steel material, Pure recommended the free-swimming PipeDiver® tool to deliver electromagnetic technology for the inspection method. The PipeDiver tool is equipped with Pure’s proven electromagnetic technology, which can be used on metallic pipe materials such as steel and ductile iron to detect cylinder corrosion. Electromagnetic sensors also provide the location and an estimate of the area and depth affected.
“This assessment using the latest in-pipe inspection technology, provided TOSA significant value in cost savings and avoided unnecessary public disruption, all while providing a better understanding of their infrastructure for the long-term management of their ocean outfall. With this understanding comes peace of mind in knowing that the most economical and effective in-kind replacement will be implemented to ensure long-term reliability of this vital asset.” William S. Gettings, P.E., MBA, BCEE, Senior Associate and NJ Office Manager Hazen and Sawyer
As a precaution, two models of PipeDiver tool assembled
Different PipeDiver tools are used for assessment of different pipe material. The optimized 24-detector PipeDiver tool uses electromagnetic technology to locate and identify steel pipes that have indications of wall loss, while the 6-detector PipeDiver tool is designed to identify PCCP pipes that have indications of broken wire wraps, the leading indicator of problematic pipe.
While it was known that the 2,000-foot (Section A) was made of steel pipe, there was no definitive information on the 4,000-foot (Section B) of pipeline material. In response, two models of the PipeDiver tool (a 24-detector tool for steel and a six-detector tool for PCCP were brought on site, assembled and balanced).
The metallic PipeDiver was run through Section B, where data determined that the section was not steel pipe, but rather PCCP, with a small section of cast iron pipe.
That was good call.
Sections of pipeline 3 inches smaller than anticipated
During the planning stage, it was thought that the pipeline had a 36-inch internal diameter. However, it became apparent after seeing some highly anomalous data sets from the 24-detector PipeDiver tool that the internal diameter was at least 3 inches smaller, which was confirmed at both the inlet and outlet by direct measurement using onsite divers.
This necessitated some late night heroics from Pure’s analysis group, research and development and on-site staff to modify the neutrally buoyant tool to fit into the smaller pipeline.
From here, the inspections went off without a hitch.
In the end, multiple PipeDiver runs were performed over the five-day inspection. On Section A of the steel pipeline, three pipes displayed anomalies indicating wall loss from 30 percent to 50 percent. One pipe contained a single location of wall loss, while two pipes had multiple locations of wall loss.
Analysis of the PCCP data obtained during the inspection determined that one pipe section in Section B displayed an electromagnetic anomaly consistent with five broken wire wraps, and one anomalous signal shift that could be caused by an undocumented feature or a change in pipe property.
TOSA has a better understanding of their linear assets
Pure worked closely with Hazen and TNJ Marine, Inc. throughout the inspection. It was recommended that a portion of Section A undergo replacement due to pipe sections with anomalous electromagnetic signals, apparent pipe wall degradation and visible wall loss anomalies. In addition, where five wire breaks were found, it was recommended that a 16-foot length of 36-inch PCCP including plated access port within a sealed access manhole be replaced. Finally, it was recommended Section B undergo re-inspection within the next five years to monitor existing damage and re-evaluate the pipe section with anomalous signal.
All in all, a successful inspection despite the many challenges.