Page 37 - Gi flipbook - November 2018

increase in hardness would cause
blunting of the bit, slowing and FIGURE 2: The damage after exposure. A circular hole approximately four inches in
eventually halting further penetration. diameter had penetrated the full thickness of the slab directly above the pipeline damage.
The hole through the concrete slab,
the characteristics of the main and
secondary features indicate the damage
was by mechanised drilling; the main
feature caused by the drill penetrating
the concrete slab (and contacting the
top of the pipeline), the secondary
feature caused by the drill bit glancing
off the edge of the pipeline.
INSPECTION
This pipeline has been inspected four
times with magnetic flux leakage
(MFL) technology. The main feature at
12 o’clock was detected and reported
as a manufacturing feature in the 1994
and 2000 ILI reports and as an
‘unknown’ feature in 2015. MFL is a
measurement of the magnetic field
induced in the pipeline, recorded by
the inspection tool sensors. The data FIGURE 3: Close-up of main feature with a 20 pence coin for perspective
analysis uses automatic and manual
processes to sentence features.

Reasons for changing the feature
classification include:
• The ILI in 1985 was during the early
development of pipeline inspection
and involved reviewing a printed
copy of the data. What was reported
was at the discretion of the analyst.
• In 1994, the analyst classified it as a
manufacturing feature based on their
experience at the time. The feature
did not display the characteristics
associated with corrosion.
• Due to its classification in 1994, and
the fact it had not changed between
inspections, the feature was
categorised as a manufacturing
feature in 2000.
• In 2015, the analyst made the
conservative decision to classify the
feature as ‘unknown’. This was due
to a slight indication on a single
calliper arm which was not
representative of a dent, integrating Pylon owner land. The council does have a
30 years of experience inspecting The pylon within 10 metres (see database of boreholes, but no
pipelines and data analysis. Figure 5) of the pipeline damage was records of bore-holing activities on
• The change in threats to pipeline constructed after the pipeline. The the land of interest. There is regular
integrity, especially the prevalence pylon owner specified that no bore engagement with the council to
of illegal taps in liquid pipelines. holes were carried out in close ensure that the location of all high
• The analyst’s own experience proximity to the pipeline damage and pressure gas pipelines is current.
supported by the wider data that bore holes are not performed
analysis team. for every pylon construction. They Marker posts
The inspection vendor was present on also do not necessarily hold records There was one aerial marker post
site when the features were exposed. for failed bore holes. in the area of the damage, located
This gave them the opportunity to in the trees before the pipeline
further their knowledge and feed the Landowner bears north-west (see Figure 5).
data into their models. The inspection The local council owns the land There were no other marker posts
vendor had not seen a feature like this where the damage was located but a in the field where the pipeline
3
on any other NGN pipeline. wildlife charity currently uses the damage was found.

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