TECHNO
TECHNO
From late May to mid-July, a large-scale scraping
operation was conducted on a section of our
Transitgas pipeline in Switzerland. This operation
in a mountainous area required the use of an
ultrasound pig: a major technical challenge!
air pressure
adjustment
vent
ultrasound
pig
expanding
stoppers
Ruswil
high-pressure
pumps
Wallbach
THE RHINE
Ultrasound scraping
OGE ON THE MOVE
In order to ensure that the infrastructure is in
good condition and does not exhibit any
traces of wear or corrosion, Transitgas
decided to inspect the interior of the pipeline
this year over a distance of 70 kilometres
between Wallbach, at the Swiss/German
border, and the Ruswil compressor station.
This scraping was carried out using an
ultrasound pig propelled through the pipeline
by means of water pressure. This operation
is practically unheard of in Europe, which is
why Transitgas enlisted Open Grid Europe,
the operator of the German grid. Up until
now, only the OGE’s teams had any prior
experience with this technology, in a section
of the TENP pipeline in Germany. While the
inspected section of the TENP was longer,
the differences in altitude, for their part, were
less: Transitgas is nestled in a particularly
mountainous and difficult-to-access area of
Switzerland. The operation involved 10 OGE
collaborators in total as well as some forty
10
other persons from different contractor
companies.
PIG AND EXPANDING STOPPERS
In order for the ultrasound pig to properly
record all data to assess the condition of the
pipe, its travel speed must remain between
0.7 and 1.8 km/h. Further, in order to
compensate for the water pressure pushing
it along inside the pipeline, air was used to
exert a back pressure. This water pressure
and air back pressure were adjusted to keep
the speed within the proper range at all
times. Throughout the operation, the
ultrasound pig was preceded by three
expanding stoppers whose job was to block
free space to prevent any contact between
the air and water.
An additional challenge had to be
tackled: considerable differences in altitude,
at times as much as 500 metres. Therefore,
it was necessary to prevent the pig from
getting stuck underway at all costs. This is
the reason why a long preparation phase
was necessary before the operation: during
the preparations, the operation teams
analysed the whole route, down to the
smallest details, to determine the precise
water pressure and air back pressure that
needed to be applied at each point in the run
in order to keep the pig at the proper speed
at all times.
SUPPLY TO THE CUSTOMERS
Because the pipeline was going to be filled
with water for the scraping, it had to be taken
out of service for a period of 11 weeks.
Although the operation was planned for May
to July, a period when consumption is at its
lowest, a solution had to be found for the
customers receiving natural gas via this
pipeline. Fortunately, the Transitgas
infrastructure is made up of two parallel
pipelines at this location; customers were
temporarily connected to the twin pipe
throughout the operation.
THE OPERATION ITSELF
The gas present in the relevant section of
the pipeline was first evacuated through the
downstream network. Then a cleaning pig
was introduced into the pipe to eliminate any
impurities which might interfere with the
proper functioning of the ultrasound pig.
Once the cleaning was complete,
compressors installed in Wallbach injected
air into the pipe section at a pressure of 26
bar: this is the air used to counterbalance the
water pressure (see point 2). Finally, water
was drawn from the Rhine with a pumping
system and transported over a distance of
1.5 km to Wallbach to be injected into the
pipe and push the expanding stoppers and
ultrasound pig along. In total, 46,000 m3 of
water were needed to propel the three
stoppers and the pig another 70 km up to the
Ruswil compressor station. This operation
took almost 85 hours, i.e. 3 and a half days.
Once the scraping was complete, the
pipeline was cleared of its water: an
activated carbon filtration device had been
installed at Wallbach to purify the water
before dumping it into the Rhine. Then, the
entire section had to be dried using foam
pigs and hot air to prevent humidity inside
the pipeline which could lead to corrosion
problems.
DATA ANALYSIS AND
RESTORATION
As soon as the ultrasound pig had been
liberated from the pipeline at Ruswil, the
data recorded were scanned to make sure
the entire section had been properly
inspected and that no major anomalies were
detected. As this analysis did not indicate
anything abnormal, the operation team was
able to get down to remove the temporary
connections to the parallel pipeline and to
reconnect customers to the original pipeline.
Written in French by Fluxys and translated
into English and German by Transitgas; All
rights reserved.
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