Page 93 - Pipeline Pigging Technology

Pipeline Pigging Technology

defects which can lead to a leakage including:
holes through the pipe structure;
excessive gas diffusion;
separation^) between pipe body and body/end fitting,
defects which cause a change in pipe cross-section including:
ovalization of the structure;
collapse of the inner carcass or liner;
erosion or build-up of deposits;
creep of the inner carcass or radial reinforcement.

FORMULATING AN INSPECTION PROGRAMME

In order to establish a reliable and cost-effective inspection programme,
pipeline operators should not only review relevant codes of practice, com-
pany and statutory requirements, but should also work with pipe manufactur-
ers to formulate specific inspection requirements. Such a programme has
been proposed and is now directed by SINTEF of Norway. A programme
would need as input criteria much of the information obtained by the
individual manufacturers [Neffgen,Subtech,1989].
In addition, for such a programme to be established, it is necessary to
Qamieson,1986]:
establish a methodology for inspection while prioritizing inspection
points;
develop a means to classify defects and interpret retrieved inspection
data;
ensure a ready access will be available to relevant areas to be inspected;
develop and have available suitable inspection tools which can distin-
guish signals received from flexible pipe's different layers.

Due to the layering effect in composite structures, this latter requirement
may be more difficult to achieve than for steel pipe inspection. For one point
when using ultrasound to examine pipe integrity, it should be remembered
that composite materials exhibit anisotropic behaviour. Rose [ASNT, 1984], in
the inspection of epoxies, has found that discriminating between pipe layers
is as difficult as discriminating between structurally-sound and -unsound
materials. Special considerations must therefore be paid to the fact that wave
velocities change through individual layers and the reflected signals tend to
be very noisy due to ply and material response echoes.

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