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igem news – yppc

Finite element analysis FIGURE 3 FIVE SITE EXCAVATION - FOUR SPOOLS CONFIRMED TO HAVE SCC
Two pieces of the jigsaw (ILI and in-
field investigation) had determined
that SCC was located on four of five
spools, with a likely cause being the
introduction of deformations into the
pipeline during construction.
The third and final part of the jigsaw
relates to operating stress. In order to FIGURE 4 FEA DEFORMATION PLOTS SHOWING THE DIFFERENCE BETWEEN COLD FIELD BENDED SPOOLS AND SPOOL 2,
investigate the potential connection WHICH WAS NOT SUBJECTED TO COLD FIELD BENDING
between the cold field bending process
and SCC, finite element analysis (FEA)
was used to investigate deformation
(and stress) across all five spools.
The FEA software plotted
deformations reported by the geometry
inspection tool. These plots found
that the four spools that had SCC
(Figure 3) were associated with fully
circumferential bands of deformation
(bulging and ID reduction). These
circumferential bands were
introduced by the cold field bending
process as the pipeline was bent to
accommodate the curvature of the
hill. The SCC indications were also
found to be located at the boundary
between bulging and ID reduction
– further evidence that SCC was
associated with the circumferential
bands of deformation.
Spool 2, not subjected to cold field A potential corrosive environment Is there a lesson for the UK gas industry?
bending and not displaying SCC, had formed during construction as the To our knowledge, stress corrosion
a noticeably different pattern on the cold field bending process damaged cracking (SCC) has never been found
FEA plots. The lack of circumferential the asphalt enamel coating. in the UK gas network. Is this because
deformations in Spool 2 meant Susceptible material; although operators are not actively looking to
that localised stress had not been the steel was high grade (X65) and identify SCC?
introduced into this spool, which relatively young (< 25 years) all steel It is always safer to consider the
mitigated against the occurrence of has the potential to be susceptible to potential for SCC before you know you
SCC. Figure 4 shows the difference in SCC. have SCC. Susceptibility studies are
FEA deformation plots between the I participated in the discovery of a sensible place to start. Does your
four spools with SCC (example at top of a new method of investigating SCC; pipeline carry any of the hallmarks
Figure 4) and Spool 2 which had no SCC internal geometry data held the key to that SCC-susceptible pipelines are
(bottom of Figure 4). understanding this client’s SCC. The expected to have?
project has shown that SCC is not ‘one The UK gas transmission network is
Lessons learned? size fits all’, SCC can occur on a broad an ageing asset and parts of it are over
Stress corrosion cracking (SCC) was range of pipelines worldwide, a pipeline 50 years old. In addition, some of the
occurring on a pipeline which did not may not seem susceptible at first, but network pipelines operate at stress levels
tick all the standard SCC susceptibility hidden factors, such as localised stress in excess of 60 per cent SMYS. The UK
boxes. The pipeline was relatively concentrations due to construction gas network has the conditions that
young (<25 years), of high grade (X65) practices, may cause SCC to occur. could support the occurrence of SCC. In
and operated at relatively low hoop It is best practice to anticipate an SCC addition, SCC has recently been identified
stress (<60 per cent SMYS). However, problem before it becomes difficult to in Western Europe, in a particular region
the pipeline had an asphalt coating, manage and if SCC is found, to use all that had no previous history of SCC.
which is susceptible to disbondment, the data available to better understand Our experience would suggest that
leading to possible external corrosion. the issue, i.e., in-line inspection data, there is no good reason why the UK
An EMAT inspection found a significant in-field verification data and detailed should remain immune to external
number indications of SCC throughout analysis (in this case, FEA). SCC. The industry should take steps
the pipeline. In summary, this simplified process to understand this potential threat to
I attended an excavation site for an can be undertaken: its pipeline assets to ensure the future
in-field verification of SCC, which at Consider the threat of SCC integrity of its pipeline assets.
this location can be attributed to: Evaluate the threat
Increased localised stress If found, understand the threat Watch Andrew deliver his winning
concentrations introduced by a Quantify the threat presentation at this year’s YPPC Final.
cold field bending process during Only then can SCC be managed Register for IGEM webinars at www.
construction. effectively. gotostage.com/channel/igemyppc2019

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