The longest pig run was performed along the Nord Stream pipeline between Germany and Russia last year. Elaine Maslin found out more.
At 1224km (759mi.) long, the Nord Stream’s twin offshore pipeline gas transportation sys- tem from Russia to Germany, through the Baltic Sea, offers its operator a number of challenges.
One of those is inspection. In 2013, for the first time since the pipelines became operational in November 2011, and October 2012, respectively, operating company Nord Stream AG carried out an internal inspection along the full length of the lines.
Image: Arrival of the inline inspection tool at Lubmin, Germany. Courtesy of ROSEN Inspection Technologies.
Pipeline-specific equipment had to be built for the inspection, which was recorded as the longest run performed by a pipeline integrity gauge (pig). The internal inspection set a world record, in terms of length and thickness of pipe walls (up to 41mm) to be analyzed.
The inspection means Nord Stream now has baseline data to confirm the quality of the Nord Stream pipeline building process, and provide a data set, against which all future inspection results can be compared.
Andrey Voronov, offshore manager operations, Nord Stream, said: “Never before has a pipeline with the similar dimension been “pigged:” two 1224km- long 48-in.-diameter pipelines with wall thicknesses up to 41mm and up to 110mm of concrete coating around it. Both the length and the thickness are unique and posed engineering challenges for which our inspection team and our partners at Rosen Group had to find solutions.”
Image: ROVs carry out external inspections of the pipeline.
Inspection, as part of integrity manage- ment measures for the system, was part of the pipelines’ design from the start, says Nord Stream.
Integrity management measures on Nord Stream cover its automation systems, landfall installations, and the 1224km offshore section of the twin-pipeline.
The offshore section runs from Vyborg, Russia, to Lubmin, Germany. Each pipe- line is made up of about 100,000 concrete segments, each around 12.2m-long, with a constant 1153mm inner diameter.
The pipes are made of 41mm-thick, high-tensile steel, with an internal anti- friction coating—a two-component epoxy resin, which increases flow capacity by reducing friction—and an external anti- corrosion coating.
Inspections
An external visual and instrumental inspection was carried out by remotely operated vehicles (ROVs) operated from support vessels.
For the internal inspection, three different tools were sent through the pipeline, propelled by the gas flow.
All three were designed and built by Germany’s ROSEN Group, specifically for Nord Stream. They are: a gauge tool, a cleaning tool, and an in-line inspection tool, which maps potential corrosion and metal loss, as well as the exact curvature of the lines via an inertial navigation system.
Before its use on Nord Stream, each tool underwent extensive testing, which included the inline inspection tool being tested on a similar, shorter, 48-in. pipe- line in Malaysia.
A pig run
The inspection process started on the first pipeline on July 1, 2013. The gauge pig, like all the other pigs, started its run at the Landfall Facilities Russia (LFFR), at Portovaya, by being inserted into the line via a pig launcher.
The gauge tool, at 2.2m-long and weighing 1.5-tonne, is used to detect substantial anomalies of the internal diameter along the pipeline, which may potentially obstruct the inline inspection tool during its run. The gauge tool’s aluminum plates are designed to detect any anomaly starting at 3% (35.5mm or 1.4-in.).
Any protrusion would chip away at the gauge plate, with the damage later analyzed to determine the extent of the potential obstruction.
Image: (Top) The gauge tool. (Bottom) The cleaning tool.
The gauge tool took five days to travel with the gas flow to Germany, where it was retrieved. The plates were found to be undamaged, which indicated that the pipeline had not experienced any mechanical impact since construction.
The cleaning tool
At 2.6m-long and weighing 1.8-tonne, the cleaning tool removes any dust or particles of coating material from the pipeline’s insides that may have accumulated or become loose.
It has brushes, to pick up dust particles. The dust is also pushed ahead in front of the tool by sealing discs sized larger than the pipeline’s interior diameter. “Differential pressure is used in order to guide an amount of natural gas through the cleaning tool body to the very front where nozzles create a flushing effect. This setup is comparable to a pres- sure washer on a dry basis,” says Nord Stream.
The cleaning tool run also took five days. The tool was then cleaned, with the material collected on the run analyzed. Results from the tool confirmed the pipeline was clean. The amount of the material collected during the internal inspection program was small, as expected, and a second run was not required.
The inline inspection tool
The pipeline was then prepared for the 7.3-tonne, 6.3m-long inline inspection tool to be sent through.
The inline inspection tool is also called an intelligent combo tool, because it combines arrays of sensors to perform different integrity inspection tasks. First, the tool constantly measures distance travelled via wheels rolling along the inner pipe walls. This helps map measurements along the length of thepipeline. The tool works best at a speed of 1.5m/sec. A speed control valve is mounted to the front of the tool. It allows the regulation to a preset tool velocity in order to optimize measurement conditions independent from the gas flow. A high- density memory device is used to record during the inspection, for later analysis.
Image: The inline inspection tooling, weighing 7.3-tonne
An internal diameter (ID) mapping caliper detects and characterizes any deviations from the original pipe shape, some even smaller than 1mm. Internal diameter changes, ovalities and dents, will be detected, localized and identified. The tool is also able to detect and map any misaligned welding joints.
The sensors function by measuring incremental changes in how far any of the spring-loaded caliper arms that guide the sensors along the pipe wall are bent when the sensors run through even very small dents or ovalities.
The inline inspection tool is able to detect variations in the pipeline manu- facturing process to a sub-millimeter level (below 0.04-in.) and provides a very accurate baseline for future inspections.
At the end of July, the inline inspection tool was received at the German Landfall Facilities, after a run time of 10 days.
Image: The inline inspection tool arrives at Lubmin, Germany.
The recorded data on the tool was retrieved and sent to post processing and a three-stage analysis. The inline inspection tool was then completely refurbished by Rosen and taken by land back to the Russian Landfall Facilities to start its run down the second pipeline. Inspecting the second Nord Stream pipeline with the three tools started mid- August, and was finished at the end of September.
Nord Stream believes the data from the inspection tool is the longest data set from an inline inspection ever recorded. With more than 2000 measure- ment channels and one sample recorded every 2.5mm over the pipeline length of 1224km, each tool arrived in Germany with more than 1,000,000,000,000 (1012), or more than one trillion, data samples.
Data sets recorded in both lines are being evaluated. Preliminary results have shown the pipelines are free of any corro- sion spots or deformation.
Corrosion was not expected during the operation of the pipelines. Gas going through them is constantly measured at the inlet, to exclude contamination from water. The internal flow coating seals the steel from potential corrosive influences.
The inline inspection tool also has a shallow internal corrosion sensor, con- sisting of a proximity sensor attached to the caliper arm, which can map surface metal loss defects. Small defects on the surface of the inner pipe wall change the sensor’s proximity to the pipe wall, which the sensor is measuring.
A magnetic flux leakage sensor detects any material loss or corrosion in the steel, or between the steel and the outside concrete coating. A strong magnetic field magnetizes the pipe wall and an electro- magnetic sensor records any changes in magnetic feedback from the pipe steel through its entire 41mm thickness.
Nord Stream believes this is the stron- gest magnetic field ever developed for an inline inspection tool: even inside a 41mm pipeline joint, it creates a magnetic field leaking out to 6m (approx. 20ft.) distance.
An inertial navigation system, or XYZ- unit, on the inspection tool, maps the pipeline’s geometry, to detect any incre- mental movement in the pipeline that could result in bending strains. The tool measures the strain placed on the inertial gyroscope sensor when it traverses a curve in the pipeline.
It was used together with informa- tion from the external inspection, and confirmed that the twin pipelines shifted only marginally after operating under pressure.
An inline inspection is now scheduled to take place every few years on the Nord Stream pipelines, to confirm the absence of corrosion or mechanical defects, with reference to the extensive baseline data now gathered, including its geographical coordinates. OE
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