Page 89 - Pipeline Pigging Technology

Pipeline Pigging Technology

pressures. To handle entrained hydrocarbon gases in well fluids on a more
routine operational basis, different flexible pipe designs utilize alternative
methods:

Methods for handling diffused gases:

a) especially-thin portions of external polymer sheaths can be incorpo-
rated in the structure [Makino etal. ,1988] so that as interstitial pressures in the
armour layer rises, the thin portions periodically rupture, thus reducing
internal area pressure;

b) interstitial spaces are connected so as to lead accumulated gases along
the pipe axis and then through "bursting discs" located at the pipe ends, so
that gases are continually released;

c) special polymers layer(s) are used in a bonded structure which will swell
when exposed to gas and saturate without permanently deforming. These
layers allow expanding gases to outwardly diffuse through the more perme-
able outer cover layers;

d) a non-permeable, gas-tight pipe is made using a continuous, corrugated
inner steel tube as the main fluid conduit. The advantages of using this non-
permeable structure are that (a) under normal operations, gas migration into
the polymers is prevented; and (b) even if the lines should leak, pressure will
be contained by the normal reinforcement layers; and (c) the liner's shape
itseli has sufficient residual strength to resist explosive decompression
effects.

COMPOSITE CONSTRUCTION AND COMPLEX
BEHAVIOUR

Flexible pipe construction, whether of the bonded or non-bonded type, is
made from a composite of layered or even sandwiched materials. Materials of
Kevlar or Aramid reinforced elastomer fabrics, for example, are used to
prevent elastomer extrusion during the application of cross-windings (bonded
pipes). Similar sandwiched layers are used to increase strength or burst
pressure capacities, particularly for pipes subjected to dynamic bending. As
another example, ceramic-impregnated elastomers are applied to the pipe

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