Neutrons detect clogs non-destructively through metal pipeline walls
Industry and private consumers depend on oil and gas pipelines that stretch thousands of miles under water. It is not uncommon for these pipelines to become clogged with deposits. Until now, there have been few ways to identify plug formation in situ and non-destructively. Measurements at the Heinz Maier-Leibnitz Research Neutron Source (FRM II) at the Technical University of Munich (TUM) now show that neutrons may be the solution of choice.
Oil and gas pipelines are the arteries of our energy supply. Like Nord Stream gas pipelines, they transport energy sources long distances underwater to onshore storage and production facilities.
But it’s not just supply bottlenecks, like we currently have, that can lead to shortages. Under certain conditions, the mixture in pipelines – which typically includes gas, oil and water – can become very viscous and even form solid phases.
Solid hydrates that form from gas and water are particularly troublesome to operators, for example as the mixture cools to low seafloor temperatures during longer pipeline outages.
Previous approaches do not work underwater
In order for a clog to be repaired in place, the affected section of the pipeline must first be found. Locating clogs from the outside is difficult, as they can form anywhere along the length of the pipeline.
To date, thermal cameras and gamma rays are used to detect clogs. However, none of these methods work underwater. Ultrasound, on the other hand, has no problem penetrating water, but hydrate blocks can only be detected at close range from outside the pipeline wall.
This constraint poses practical difficulties because subsea pipes are laid at depths of up to 2000 meters and are often naturally covered with seabed materials such as sand or silt. Another technical challenge associated with acoustic methods arises from the lack of a clear difference between the acoustic impedances of the hydrated phase and other phases of the crude oil mixture, which makes discrimination difficult.
Neutrons — the perfect probe
TechnipFMC, a company of about 20,000 employees worldwide specializing in subsea pipelines, “was looking for a more efficient method to find clogs in a non-contact, non-destructive and reliable way despite thick walls”, explains Dr Xavier Sebastian, project manager in the company.
As Dr. Sophie Bouat, CEO of Science-SAVED (Scientific Analysis Vitalises Enterprise Development) has suggested, “neutrons are the perfect probe for the task at hand.” She established contact with scientists at the Heinz Maier-Leibnitz Zentrum in Garching near Munich.
“Using gamma-neutron fast activation analysis, light atoms and hydrogen in particular can be detected very precisely,” she continues. Since the hydrogen content of hydrates and oil or normal gas is significantly different, it should be possible to detect blockages by measuring the hydrogen concentration.
Feasibility study at FRM II
Dr. Ralph Gilles, industrial coordinator of the Research Neutron Source FRM II, carried out a feasibility study on this topic together with other colleagues from the Technical University of Munich and the Forschungszentrum Jülich. Using the Prompt Gamma Activation Analysis (PGAA) instrument, which uses cold neutrons from FRM II, the researchers established that this approach can be used to differentiate between oil and gas and blockage.
At the NECTAR radiography and tomography facility and the FaNGAS (fast neutron-induced gamma-ray spectroscopy) instrument, they used fast neutrons from FRM II to show that a sufficiently large number of neutrons penetrate the metal walls of the pipelines to facilitate the respective measurement, and that the measurement also works well under water.
A small neutron source detects plugs
The results clearly demonstrate that neutrons are perfectly suited for this application. Moreover, “Our experiments have shown that we can even distinguish an incipient blockage from a fully developed blockage”, explains Dr. Ralph Gilles. “It’s very advantageous, because you can even preemptively heat a segment of pipe to melt the blockage before it fully develops.”
In practice, a mobile detector equipped with a small source of neutrons will go back and forth along the pipe in search of blockages. “We are very pleased that with the help of research neutron source measurements, we have found an efficient method that greatly facilitates the detection of such plugs in the future,” says Dr. Xavier Sebastian.
In addition to scientists from the Technical University of Munich, researchers from the Forschungszentrum Jülich and the RWTH University of Aachen contributed to the analysis. Contact with TechnipFMC was made through Science-SAVED (Scientific Analysis Vitalises Enterprise Development). Access for beam time was paid for by TechnipFMC.