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

186
Y
Rupture
U
circumferential direction is referred to as p y and the value
of p y for this pipe material was found to be 38.4MPa
(5560psi).
First, the axial load test was undertaken on each specimen.
The purpose was to simulate the initiation and growth of
wrinkle for two scenarios: (i) assuming the first possibility
that the wrinkle in the field linepipe may have formed and
grew when the linepipe was in operation and then; (ii)
assuming the other possibility, that is, the wrinkle may have
initiated and grew when the linepipe was in shutdown
condition. Accordingly, the internal pressure for Specimen
1 was 0.25p y during the axial load test when the wrinkle
formed and grew and no internal pressure was applied
during the axial load test for Specimen 2 (Table 1).
C
Rupture
Sample issue
Specimen 2 Specimen 1 Field Specimen
E
The Journal of Pipeline Engineering
Fig.3. Load-deformation behaviour.
Fig.4. Final deformed shape of
specimens.
The load-deformation behaviours of both specimens are
shown in Fig.3. The axial compression load was applied
with small incremental loads at an eccentricity of 20mm to
apply a moment along with the axial compression load on
the specimens. As the axial load was increasing, the pipe
specimens yielded (point Y in Fig.3) and then the axial load
reached the maximum load carrying capacity of the pipe, as
shown by point U in Fig.3. At this point, a wrinkle initiated
at about the mid-height of the specimens. Application of
axial load was then controlled by the displacement rather
than the load. With the application of furt her axial
deformation, the load-carrying capacity decreased as the
wrinkle began to grow and became more asymmetric. The
wrinkle at point C in Fig.3, closed from inside pipe wall and
as a result, the load carrying capacity started to increase, as