Neutrons detect clogs non-destructively through the metal walls of pipelines
From:
Technical University of Munich (TUM)
January 21, 2022 -- Industry and private
consumers alike depend on oil and gas pipelines that stretch thousands of
kilometers underwater. It is not uncommon for these pipelines to become clogged
with deposits. Until now, there have been few means of identifying the
formation of plugs in-situ and non-destructively. Measurements at the Research
Neutron Source Heinz Maier-Leibnitz (FRM II) at the Technical University of
Munich (TUM) now show that neutrons may provide the solution of choice.
Oil and gas pipelines are the arteries
of our energy supply. As with the Nord Stream pipelines, they transport the
sources of energy over long distances underwater to storage and production
facilities on land.
But it's not just supply bottlenecks, as
we have them now, that can lead to shortages. Under certain conditions, the
mixture in the pipelines -- which typically comprises gas, oil, and water --
can become very viscous and even form solid phases.
Especially inconvenient for operators
are solid hydrates that form from gas and water, for example when the mixture
cools down to the low temperatures of the seabed during longer pipeline
shutdowns.
Previous approaches do not work underwater
For a clog to be remediated in-situ, the
affected section of the pipeline must first be found. Localizing clogs from the
outside is challenging, since they can form anywhere along the length of the
pipeline.
To date, thermal imaging cameras and gamma
rays are used to detect the clogs. However, neither of these methods works
underwater. Ultrasound, on the other hand, has no problem penetrating water,
but the hydrate blocks can only be detected at close range from outside the
pipeline wall.
This constraint poses practical
difficulties because underwater pipelines are laid at depths of up to 2000
meters and are often naturally covered by seabed materials like sand or silt.
Another technical challenge associated with acoustic methods arises from the lack
of a clear difference between the acoustic impedances of the hydrate phase and
other phases of the crude oil mixture, which makes discrimination difficult.
Neutrons -- the perfect probe
TechnipFMC, a company with around 20,000
employees worldwide that specializes in subsea pipelines, was "Looking for
a more efficient method to find the plugs in a non-contact, non-destructive and
reliable way despite thick walls," says Dr. Xavier Sebastian, a project
manager at the company.
As suggested by Dr. Sophie Bouat, CEO of
Science-S.A.V.E.D. (Scientific Analysis Vitalises Enterprise Development),
"Neutrons are the perfect probe for the task at hand." She
established the contact to the scientists at the Heinz Maier-Leibnitz Zentrum
in Garching near Munich.
"Using prompt gamma neutron
activation analysis, light atoms and hydrogen in particular can be detected
very precisely," she continues. Since the hydrogen content of hydrates and
normal oil or gas is considerably different, it should be possible to detect
blockages by measuring the hydrogen concentration.
Feasibility study at FRM II
Dr. Ralph Gilles industry coordinator at
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 PGAA (Prompt Gamma Activation
Analysis) instrument, which utilizes cold neutrons from FRM II, the researchers
established that this approach can be used to differentiate between oil and gas
and the 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
underwater.
A small neutron source detects plugs
The results clearly demonstrate that
neutrons are ideally suited for this application. Moreover, "Our
experiments have shown that we can even distinguish an incipient blockage from
a fully developed one," says Dr. Ralph Gilles. "That's very
beneficial, because then one can even preventatively heat a pipe segment to
melt the blockage before it fully develops."
In practice, a mobile detector with a
small neutron source will move back and forth along the pipeline to look for
plugs. "We are very pleased that, with the help of the measurements at the
research neutron source, we have now found an efficient method that makes it
much easier to detect these plugs in the future," says Dr. Xavier
Sebastian.
Besides scientists of the Technical
University of Munich, researchers of Forschungszentrum Jülich and RWTH Aachen
University contributed to the analysis. The contact to the company TechnipFMC
was mediated through the company Science-S.A.V.E.D. (Scientific Analysis
Vitalises Enterprise Development). Access for beam time was paid by TechnipFMC.
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