Page 36 - Gi flipbook - November 2018

IGEM NEWS | Young Persons Paper Competition 2018

SEVERE THIRD PARTY

DAMAGE TO A 30IN HIGH

PRESSURE PIPELINE

How changes in threats to pipeline integrity can

lead to an existing feature being viewed differently

By Chris Rodgerson, Integrity Engineer, Northern Gas Networks

he gas networks are
critical infrastructure, FIGURE 1: The Enterprise Products LLC pipeline rupture in the United States, which
providing the vast resulted in a fatality
majority of the energy
used in the United
T Kingdom. Northern Gas
Networks (NGN) offtake gas from the
national transmission system through
a high pressure pipeline network
before the gas is regulated to the
appropriate pressure for delivery to
customers in the North of England.
NGN’s promise to ensure the
continued safe operation of the high
pressure pipeline network is robust, as
demonstrated by its operating record.
The consequences of a rupture on a
high pressure pipeline can be
catastrophic – from an ignited release
of gas resulting in an explosion and its
immediate devastation, through to the
loss of supply which could impact restoring the pressure-containing Figure 3 shows the damage when
vulnerable customers and major capability of the pipeline. This is the compared with a 20 pence coin.
industry. An example of such a rupture most severe categorised feature found
can be found in the United States on a high pressure pipeline in NGN’s Note the following details:
where, in 2010, an Enterprise Products operating history. • There is no visible associated
LLC pipeline was struck by an auger I investigated the event including denting
1
truck resulting in the death of the why the feature classification was • The spalling is in a circular pattern
auger operator (see Figure 1). changed, when and how the feature • Material has been smeared around
The inspection report from the had been introduced, and what could with repetitive ‘chatter’ marks
scheduled 2015 in-line inspection (ILI) be learnt from this event which may • The damage has a distinct step, with
of an NGN pipeline with a maximum benefit the wider industry and reduce an outer ring and deeper inner circle
operating pressure of 38bar classified the probability of another occurrence. • The inner circle is relatively flat-
a single feature as ‘unknown’. This bottomed
feature was previously classified as an DAMAGE OBSERVATIONS • The spalling pattern around the
external manufacturing feature. With A desktop study and site visit showed main feature is similar to that of the
the change in classification and the no obvious cause of the ‘unknown’ secondary feature (see Figure 4)
feature being oriented at 12 o’clock feature, so to investigate further an A coring bit (to recover core
with a circular profile, NGN decided to excavation was planned in 2016 with samples) would generally give a
further investigate. Once excavated the appropriate precautions rugged, flattish profile to the bottom
and grit blasted, the remaining wall implemented to manage the risk to of a hole made in rock, very similar to
thickness was measured as 1.6mm personnel and the pipeline. Figure 2 the profile of the main feature. A
(from a nominal wall thickness of shows what was found upon mechanised drilling bit boring the
12.7mm). The P/11 defect assessment excavation – a four inch diameter hole pipeline would generate heat,
2
judged the feature as severe. It was penetrating a reinforced concrete slab resulting in work hardening of the
repaired using an epoxy sleeve, fully directly above the ‘unknown’ feature. low-carbon pipeline steel. This

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