Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEM AND METHOD OF FIELD-MOULDING OF FOAM
INSULATION OF INSULATED PIPELINE FIELD JOINTS
This invention relates to an improved method of
field-joint insulating of pipelines.
It is recognized in the art of pipeline construction
that metallic pipe when placed in the ground is suhject to
external soil corrosion. This corrosion occurs in spite of
the application o protective coatings and cathodic
protection and is particularly aggravated at field-joint
intervals where successive lengths of pipe are field-welded.
In gas pipelines particularly, thermal insulation is
applied to the exterior of pipelines, in order to reduce heat
transfer from the gas being transported in the pipeline, to
`the adjacent soil. The use of foam materals for thermal
insulation purposes is well-known (see, for example, U.S.
Patents 3,722,225 and 3,380,258). Such thermal insulation
conventionally being a foamed pol~mer such as polyurethane or
polystryrene, is shop-applied before the pipeline lengths are
delivered to the ditch excavation, where they are welded
together to form a continuous pipeline.
In order to facilitate field-welding of the joints,
such shop-applied insulation is cut-back from the extremities
of the lengths of pipe. Once welded together, this joint
cut-back area must be coated using compatible coating with
the shop-applied coating. Following coating, it has been
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conventional to apply sleeves of rigid thermal insulating
material over the joint cut-back area, such sleeves
conventionally being pre-formed half-shells, of suitable
length, adapted ~o join together around the pipeline at the
joint to fit between the ends of the shop-applied insulation,
thereby to form a more or less continuous thermal insulation.
Heat-shrink backing is conventionally applied to the
half-sections in order to closely engage the short length of
insulation thus applied to the pipe, which is followed by
external wrapping applied over a suitable adhesive coating.
The problem to date resulting from the system thus
described has been the lac~ of bonding of the heat-shrunk
sleeves to the adjacent shop-applied thermal insulation and
the resulting lack of integrity of the insulation, which
permits water intrusion notwithstanding the e~ternal pipe
wrapping applied over the sleeves. Once the integrity of the
outer moisture barrier is lost, the space between the edges
of the pre-formed hal-shells and the shop-applied insulation
allows moisture ingress to the steel below, necessitating
entire pipeline segment replacements, extensive repair of
joint areas and advanced pipeline inspection programs. The
problem has had significant implication for pipeline
operators involved with insulated pipelines.
To address this problem, a novel joint coating
~5 insulation system has been developed whereby following
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application of the corrosion barrier coating, the insulation
is applied by injection moulding, using clam-shell type
moulds and portable insulation equipment.
The object of the present invention is to overcome
the above-identified problems by providing a unique system in
which a pipeline is protected from destructive corrosion by
encapsulating field-joints in foamed-in-place
thermally-insulating corrosion protecting materal bonded to
adjacent ends of shop-applied thermal insulation, thereb~ to
provide continuously competent corrosion protection.
It is another object of the present invention to
provide a s~stem and method whereby following field welding
of adjacent lengths of shop-insulated pipe, the exposed joint
thereby formed is thermally insulated and protected from
corrosion with an organic foam material, by injecting the
foam material into the annular space between the pipeline and
a clam-shell mould applied over the open joint.
A still further object of the invention is to
provide a system and method of insulating pipeline
~0 field-joints whereby the resulting insulation has uniform
dimensions with the shop-applied insulation.
These and other objects and features of ~the
invention will be more fully understood from the following
description and appended claims taken in conjunction with the
~5 accompanying drawings.
.
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Figure 1 is is a schernatic view of a section of a
pipeline, following the welding of the joint, depicting the
cut-back shop-applied thermal insulation and corrosion
protection in the area adjacent the welded joint.
Figure 2 depicts the clam-shell mould installed over
the open field-joint, with foam injection hose connected.
Figure 3 depicts the moulded foam following removal
of the clam-shell mould.
Figure 4 depicts the outer wrap system, applied over
the moulded foam thermal insulation.
Reference is now made to the drawings wherein like
parts are designated with like numerals throughout.
Conventionally, a pipeline is constructed alongside
a previously prepared trench, a method of pipeline
construction known in the area as "over-the-ditch", from
shop-prepared lengths of coated and thermally insulated
pipe. In order to permit field welding of the pipe lengths,
a short end-portion of the pipe is left unprepared and
accessible for welding, as depicted in Figure 1, in which a
section of pipeline generally designated 10, ground-supported
as at 11, has been weld-connected from two sections, 12, 12'
at weld 13, and is readied for insulating and wrapping in
accordance with the method of this invention.
In shop preparation, thermal insulation and coating
has been terminated a short distance from the end of the pipe
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in each section 12, 12', as depicted in Figure 1, in order to facilitate the welding
operation.
Following the inspection of the weld and coating of the bare steel,
the joint is ready for insulation. A two-part mould, generally designated 13,
Figure 2, is field portable and transported to the site. The mould 13 comprises
a pair of clam-shell halves 14, 14' longitudinally hinged at 15, having an
adjustabie I.D. equivalent to the O.D. of the wrapped, insulated pipe 16. A pairof adjustable clamps 17, 17', positioned at the ends of the mould 13, lock the
mould in position over the open weld area, as depicted in the drawings.
Foam insulation is delivered to the mould from an external source
(not shown). The foam may be of any suitable type, for example, a two-
component foam including isocyanate and polyol mixture used with a catalyst and
Freon ( a registered trade mark) gas, as supplied by BASF Canada Inc.,
Montreal, P.Q., Canada, under designation Polyurethane No. 1022 Seven Second
Polyurethane Foam. The foam is delivered under pressure from a two-
component self-cleaning nozzle to a suitable fitting 18 on the mould 13.
Venting means 19, formed in the rnould 13, permits the escape of
air displaced by the injected foam, thus permitting the foam to completely fill the
annular space between mould and pipe, and to come into bonding contact with
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the exposed ends of the shop-installed pipe insulation 20,
20', therPby to form a fluid-tight seal.
Since a fast-setting foam will normally be used,
following injection of foam the mould may be immediately
removed and ex~ernal wrapping 21 appliea over the
newly-formed insulation area as depicted in Figure 4. Such
pipe wrapping technology employing tape-application machines,
is well-known in the art to which this invention relates and
will ~e familiar to those skilled in such art.
By employing flexible metal in the construction of
the ~ould half-shells 14, 14', and clamps 17, 17' having
screw-adjustments, the clam-shell mould can be adapted to fit
a significant range of insulated pipeline outer diameters.
In order to prevent the injected foam from adhering
to the mould 13, a suitable non-stick coating is applied to
the interior surface of the mould, such as an oil, greasP or
a polymer such as supplied by Dupont ~ nc under the trademark
"` Teflon. It has been found that a c~nb~-wax in combination
with a petroleum base, as supplied by T.R. Industries Inc. of
Los Angeles, California, under designation TRllO Seal Wax,
aords a quick release of the mould when appIied with a
wiping cloth.
The foregoing system offers the following advantages:
(i) a field-applied insulation, bonded to the pipe
insulation, to form a corrosion-resistant, water-tight
section having the integrity of ad~acent insulated pipe;
(ii) resulting insulated joint is of uniform
dimension with the shop-applied insulation;
(iii) cost-effectiveness is achieved with
maintenance problems significantly reduced;
The invention may be embodied in other specific
forms without departing from its spirit or essential
characteristics. The described embodiment, while simple in
scope and operation, is to be considered only as illustrative
and not restrictive and the scope of the invention is,
therefore, indicated by the appended claims rather than by
the foregoing description.
