JPE - Sept09 - cover2-4.pmd - Pipes & Pipelines International ...

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calibrated by means of the finite-element results. Additional
work is currently being performed to develop equations to
estimate s ref /s M1 . The outcome of these activities, in terms
of equations that can be used to predict M J and/or s ref /s M1
in routine assessments, will be published in 2010.
Plastic strain in ligament
In order to enable an assessment of strains in the ligament
adjacent to embedded flaws, data on strain concentrations
in the smaller of the two ligaments (below and above the
flaw) were obtained for all cases. Figure 12 shows typical
contour plots for the equivalent plastic strain in the ligaments
adjacent to an embedded flaw. The example shown illustrates
contour plots in model E1BH6L50L3M0, which indicate
that strain concentration occurs in two plastic zones
issue
The Journal of Pipeline Engineering
Fig.12. Contour plots for the equivalent plastic strain in the ligaments adjacent to an embedded flaw (model
E1BH6L50L3M0). Sample
extending from the flaw tip towards the surface at 45 o with
respect to the plane of the flaw.
The plastic strain at the surface on either side of the flaw
corresponding to a remote axial strain on the pipe OD of
1% is given in Table 3. It can be seen that such strains,
which increase as the flaw height or length increase or the
ligament decreases, can be as high as 11.5% (model
E1BH9L50L3). It should be noted that these strains were
obtained in models which were perfectly aligned. Had axial
misalignment been included, the strains in the ligament
would have been even higher.
Further research is required to produce guidance on strain
concentrations in the ligament in the presence of axial
misalignment and strength mismatch. Such guidance can