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Case Study

Tacoma, WA, USA

In early 2015, Pure Technologies (Pure) conducted a condition assessment of Pipeline No. 1 owned and operated by The City of Tacoma (Tacoma Water), as part of their proactive asset management program. Pipeline No. 1 is a critical link in Tacoma’s transmission system, conveying up to 72 MGD of potable water over a 26-mile stretch to the McMillin Reservoir. Tacoma Water provides water service to more than 300,000 residents throughout Pierce and King Counties in Washington.

While the critical pipeline has had previous condition assessment and repairs on targeted sections, the goal of the latest survey was to provide Tacoma Water with detailed assessment information to determine future repair, rehabilitation and re-inspection strategies.

Project Details

Services
PureEM™ manned electromagnetic inspection

Handheld ultrasonic thickness testing

Structural engineering analysis using 3-dimensional nonlinear finite element analysis (FEA)

Remaining useful life projections using Monte Carlo simulation

Timing
48 Hours
Pipe Material
Welded Steel
Inspection Length
917 feet (279 meters)
Diameter
48-52 inches
Transmission Type
Water

Project Highlights

Survey covered 917 feet and spanned 125 pipes

12 pipes identified with electromagnetic anomalies

Defects identified ranged from 15 to 35 percent wall loss

Inspection deployed 48-detector electromagnetic tool

Challenge

By the end of 2013, Tacoma had repaired approximately 15 leaks at 3 locations along the section of Pipeline No. 1 located near Boise Creek. In order to investigate this section of pipeline further, Tacoma decided to excavate the pipe in select locations to observe the condition of the pipeline.

Several areas with minor pitting were identified during the investigation. Due to the critical nature of this pipeline, Tacoma decided to take further action on the main and considered a replacement project.  However, before proceeding, Tacoma wanted to validate the need to replace this section of pipe.

As a result, a comprehensive condition assessment of the main was performed to confirm its condition before initiating an expensive and disruptive replacement project. Owing to the criticality of the line, Pure had only 48 hours to conduct the non-destructive condition assessment, using its proprietary electromagnetic technology (PureEM™) on just over 900 feet of pipe.

Solution

Assessing the condition of metallic pipelines is a challenging task best performed using a combination of assessment methodologies, engineering science and experiential judgment. Pure’s PureEM electromagnetic tool was used to evaluate the condition of the pipe wall and identify localized areas of wall loss. The significance of the results were evaluated through structural engineering, and long-term recommendations were made based on statistical modeling and remaining useful life projections.

As the pipeline could only be taken out of service for 48 hours, this required careful planning and extensive tool preparation. The PureEM tool was inserted through an existing manhole access and assembled in the pipe. During the inspection, technicians gathered electromagnetic data, numbered the pipe, and took detailed notes on the internal visual condition of the pipe. UT thickness measurements were also collected on the pipe in several areas.

A pre-inspection calibration of the PureEM tool allowed for more precise quantification of the defect identified through the EM inspection. This involved destructive testing on an above-ground 52-inch welded steel pipe of similar vintage to calibrate the EM signal changes for this particular type of pipe.

Following the inspections, Pure’s structural engineers used finite element modeling to evaluate the significance of the defect identified. Finally, a Monte-Carlo simulation was employed to estimate the pipe’s remaining useful life.

Results

Analysis of the electromagnetic data obtained during the inspection determined that of the 125 pipes surveyed, 12 pipes had electromagnetic anomalies consistent with wall loss ranging from 15 percent to 35 percent.

The results of the structural analysis indicate that the internal stresses in the subject pipeline are very low compared to the structural capacity of the pipe. None of the detected anomalies are at or near a point of concern, and the pipeline can be operated without immediate rehabilitation.

With the remaining useful life estimated at the pipeline operating without significant risk of structural failure in the next 30 to 50 years, Tacoma Water now has data-driven confidence in the short and long-term management of Pipeline No. 1.

As a result of Pure’s Assess and Address® approach, the City of Tacoma avoided near-term replacement of the main, which was estimated between US$2 to 3 million.

Quote

“With the remaining useful life estimated at the pipeline operating without significant risk of structural failure in the next 30 to 50 years, Tacoma Water now has data-driven confidence in the short and long-term management of Pipeline No. 1.  As a result of Pure’s Assess and Address® approach, the City of Tacoma avoided near-term replacement of the main, which was estimated between US$2 to 3 million.”