The Schankegraecht to Nospelt Mainline helps provide a critical supply of drinking water to 80 percent of the population in Luxembourg. The pipeline, installed in 1966, is non-redundant. Leaks and failures directly impact the ability of national drinking water supplier Syndicat des Eaux du Barrage d’Esch-sur-Sûre (SEBES) to provide reliable water service to its end users.
The mainline experienced leaks in 2015 and 2020. SEBES considered replacing the pipeline due to its leak history and age. The most recent leak in 2020 had a high leak rate of 1,600 cubic m (423,000 gallons) per hour, enough to satisfy the daily water demands of more than 250,000 households in Europe. Leaks on metallic pipelines can signal trouble, as these pipes often leak before they break. However, a leak does not indicate that an entire pipeline is in bad condition.
SEBES takes a proactive approach to repairing its pipelines within regular operations to ensure service uptime and reliability. Before embarking on an expensive and disruptive replacement project, they considered several options to understand the condition of the 900-mm (35-in.) pipeline.
In 2021, the utility decided to complete an inline assessment on 15.1 km (9.4 miles) of the ductile iron and steel mainline to understand its condition and determine if replacement was necessary.
Challenges with Metallic Pipeline Inspection
Even though utilities have been assessing pipeline condition for more than a decade, each poses a unique set of challenges. While the inspection of the Schankegraecht to Nospelt Mainline posed several typical challenges, it also featured challenges that conventional methods could not address.
First, water mains were not designed for inspection and many are non-redundant. For SEBES, shutting down the pipeline for a detailed inspection was not an option given its vital role in Luxembourg’s water supply. Additionally, water mains were built with features like valves and bends that make them difficult to inspect with inline tools. Many inspection technologies available today require shutdown, pipeline modifications, and disruptive civil work. While there are non-intrusive pipeline inspection options available, they do not offer the resolution SEBES required. Historically, identifying the condition of metallic pipelines at the pipe segment level has been difficult, even though metallic pipes are very common.
This mainline also posed a rarer challenge because it is comprised of multiple pipe materials. The desired inspection length included both ductile iron and steel sections.
Over time, corrosion is usually the biggest threat to steel and ductile iron water pipelines. Corrosion occurs when pipelines are exposed to stray electrical currents or corrosive substances in the soil or product flow. Any loss in wall thickness due to corrosion immediately affects the structural integrity of metallic pipelines. External loading and internal pressure can deform damaged pipe sections, leading to holes, cracks, and leaks.
Assessing Structural Integrity
To assess the structural integrity of the Schankegraecht to Nospelt Mainline, SEBES partnered with Xylem to use the PipeDiver Ultra platform. It operates while the pipeline remains in service and can navigate inline bends and valves. Using ultrasonic technology, the tool collects high-resolution wall thickness data on lined metallic water mains and assesses liner condition and out-of-roundness. The tool can also differentiate between internal and external pipeline defects.
While the PipeDiver platform has been used by water agencies for more than 10 years, SEBES was among the first in the world to use the tool with its new ultrasonic capabilities.
At the start of the inspection, the tool was inserted into an isolated and depressurized entry port. The pipeline was then repressurized, and the tool launched while the pipeline remained in operation.
During inspection, the tool travels with the flow of water in the pipeline, and it is tracked above-ground at regular intervals. Tracking the tool enables analysts to later correlate the inspection data with the individual pipe segments.
Traveling through the pipeline, the tool emits ultrasonic pulses that reflect off the pipe wall. The amount of time it takes these signals to return to the tool changes with variations in pipe wall thickness. The tool records the receiving time of the reflected signals. Using the recorded data, analysts calculate internal and external wall loss around the circumference of the pipe. The data is visualized as a heat map.
At the end of the Schankegraecht to Nospelt Mainline inspection, the tool was extracted at a 500-mm (20-in.) access point.
Majority of the Mainline in Good Condition
Data analysis confirmed the overall design safety of the pipeline, and more importantly, that the entire mainline did not need immediate replacement.
Of the 2,356 pipes inspected on the mainline, 341 ductile iron sections were identified with wall loss defects. Localized wall loss ranged from 17 to 77 percent over areas ranging from 9 to 6,200 sq cm (1.4 to 961 in2). On the steel section, the tool identified only one pipe section with a defect. The defect covered an area of 325 sq cm (50 in2) with a maximum wall loss of 16 percent. The tool also found 26 pipes were out-of-roundness.
SEBES chose to excavate and repair all pipes with more than 50 percent wall loss, as these posed the greatest risk to the pipeline’s integrity. Initial excavations for pipeline repairs confirmed that the largest defects were identified correctly through inline inspection. The utility is repairing these pipes with fiberglass wrap to renew their structural integrity.
SEBES now has restored confidence in the Schankegraecht to Nospelt Mainline after assessing the pipeline’s condition. Making targeted, proactive repairs on the highest-risk pipes enables SEBES to mitigate short-term failure risk and extend the pipeline’s useful life. Because the pipeline does not require immediate replacement, SEBES has more time to determine future management plans for the mainline.