METHOD OF REPAIRING CORROSION RESISTANT PASTE TYPE COATING OF OPERATING PIPELINE EXTERIOR SURFACE

METHODE DE REPARATION D'UN REVETEMENT PATEUX ANTICORROSION A LA SURFACE EXTERNE D'UN PIPELINE

English Abstract

Abstract of the Disclosure
A method of repairing a corrosion resistant
paste-type asphalt enamel coating of the exterior surface
of an operating pipeline includes the removal of the prior
paste coating parts having an inadequate adhesion to the
pipe, followed by the application of a primer of the
composition similar to that of the prior paste, which
results in a partial softening of the prior paste. A
new insulation coating is further applied with a layer
smoothing the exterior surface of the pipeline and filling
all the pits thereon by using for this purpose a heated
adhesive paste of the composition similar to those of the
prior paste and the primer with the result that a uniform
plastic coating consisting of the prior paste, the primer
and the new paste is provided. Thereafter, the pipe with
this coating applied is covered with a polymeric film.

Claims

The embodiments of the invention in which an exclusive
property of privilege is claimed are defined as follows:
1. A method of repairing a corrosion resistant paste-
type asphalt enamel coating of the exterior surface of an
operating pipeline, including the steps of first removing
portions of a prior paste coating featuring an inadequate
adhesion to said pipe, followed by the application of a
primer coating of the composition similar to that of said
prior paste, which results in a partial softening of said
prior paste, applying a new insulation coating with a layer
smoothing said pipeline exterior surface and filling all the
pits therein by using for this purpose a heated adhesive
paste of the composition similar to those of said prior
paste and said primer, which provides a uniform plastic
material of said prior paste, said primer and said new paste,
whereupon said pipe with said coating applied is covered with
a polymeric film, said adhesive paste when applied, being
heated to a temperature lower than the temperature of decom-
position of said polymeric film.
2. A method according to claim 1, wherein said prior
paste comprises bitumen and said primer comprises a mixture
of bitumen and petrol.
3. A method according to claim 2, wherein said
adhesive paste comprises a mixture of bitumen and solar oil.
4. A method according to claims 1, 2 or 3, wherein
said polymeric film is a polyvinylchloride film.

Description

The present invention relates to pipeline
transportation means and more particularly to methods
of repairing a corrosion resistant paste-type coating
of the exterior surface of an operating pipeline.
Known in the art is a method of repairing a
corrosion resistant coating of a pipeline exterior sur-
face including the steps of cleaning the pipe till it
glitters, priming it and coating with the main insulation
coating.
A disadvantage of the known method if applied
to an operating pipeline is that the process of removing
the prior insulation from the pipeline exterior surface
till it glitters is highly labour-consuming and is very
expensive in the field. In addition. with the known
method employed the quality of a corrosion resistant
coating is inadequate and its life-time is less than
the service-life of the pipeline metal.
An object of the present invention is to reduce
the cost of cleaning the exterior surface of the pipeline.
Another object of the present invention is to
improve the quality of a newly-applied corrosion resis-
tant coating.
One more object of the present invention is
to increase the life-time of a newly-applied corrosion
resistant coating.
In accordance with a broad aspect of the
invention, there is provided a method of repairing a
corrosion resistant paste-type asphalt enamel coating
of the exterior surface of an operating pipeline, which
includes the steps of first removing portions of a prior
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paste coating featuring an inadequate adhesion to the
pipe, followed by the application of a primer coating of
the composition similar to that of the prior paste, which
results in a partial softening of the prior paste. A new
insulation coating is further applied with a layer smoothing
the pipeline exterior surface and filling all the pits
therein by using for this purpose a heated adhesive paste
of the composition similar~to those of the prior paste
and the primer, which provides a uniform plastic material
of the prior paste, the primer and the new paste. Thereafter,
the pipe with this coating applied is covered with a poly-
meric film. The adhesive paste when applied is heated to a
temperature lower than the temperature of decomposition of
the polymeric film.
This method of repairing a corrosion resistant
paste-type coating of the exterior surface of an operating
pipeline provides a high quality corrosion resistant protec-
tion of the pipeline for the whole period of its service-life ;
without increasing the cost.
;

~$;~
The invention will now be described in yrea-ter
detail with reference to a preferred embodiment.
The section of an operating pipeline, which is to be
repaired, is raised by a pile-lifting means to -the height
sufficient Eor mounting and traversing of a cleaning, priming
and insulating machines thereon. The portions of a prior
paste coating having an inadequate adhesion to the pipe are
removed by a cleaning machine from the exterior surface of
the pipe, exposing thereby ~lefective areas of the pipe exte-
rior surface. The portions pitted with corrosion are repaired9if necessary. A primer coating is further applied, its com-
position being similar to that of the prior paste, thus
providing a high quality adhesion on the entire pipe surface
and the softening of the remaining prior paste. Thereafter,
an insulating machine applies a new insulation coating layer
of 3 mm to 6 mm smoothing the pipeline exterior surface and
filling all the pits therein by employing for this purpose
a heated adhesive paste of the composition similar to those
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o~ the prior paste and the primer, and providing therewith a
uniform coating, featuring an ade~uate adhesion to the pipe
surface and to the polymeric film~
For example, if the prior paste coating consists of bi
tumen, the primer composition is as follows: I part of bitu-
me~ and 3 parts of petrol, ~hile the adhesive paste composi-
tion is: bitumen, solar oil (2 - l~/o~ and, if necessary, fil~
lers up to 20% providing the xequired strength and temperatu-
re characteristics of -the coating depending on the maintenan-
ce conditions thereof, used as fillers may be debituminiza-
tion products, waste products of the pol~mer, rubber produc-
tion etc. The pipe with the coating applied is further cove-
red with a polymeric film b.y the same insulating machine,
uhereas the adhesive ~aste, when being applied, should be hea-
ted to a temperature low~ than the decomposition temperatu-
re of the pol~meric film.
~ or example~ if a polyvin~lchloride film is used the
adhesive paste is heated in the temperature range of 100
150 C. ~he lower limit is dependent on the maximum viseo-
si~y of the adhesive paste, which permits of applyi~g
thereof by a mechanical means; the upper limit is conditio- :
ned by the elimination of the polymeric ~ lm destruction.
~he proposed method makes it possible to use a pol~meric
film without a prior application Or an adhesive coat thereo~.
If it is necessary to reinforce the i~sulatio~, reinforcing
materials are applied over the coatingO
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