Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR CLEANING AND
SANITIZING THE INTERIOR OF PIPELINES
This invention pertains to a novel method for
treating the interior surfaces of pipelines uslng -
aqueous, cross-linked gelled pigs.
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Pipeline efficiency and volume of product
being conveyed through the pipeline can be lost by a
build-up of scale on the interior surface of the pipe.
~ Mechanical pigs and/or gelled chemical pigs have pre-
; viously been used to remove scale from the interior
; surface of a pipe. Mechanical piys are, normally solid
bullet-shaped devices which have wire brushes or abrasive
surfaces to physically abrade the scale adhered to the
interior surface of the pipe. Gelled chemical pigs, on
` the other hand, remove suxface deposits on the interior
surface of a pipe by dissolution and/or by picking up
loose debris as they pass through the pipeline.
In many instances, scale also contains bac~
teria which attack the product to be conv~yed by the
pipeline. ~For example, sulfate-reducing bacteria can
generate copiou~ quantities of gaseous hydrogen sulfide
from certain crude oils, which causes severe corrosion
of pipeline walls and also contaminate the product
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flowing in the line. Hydrogen sulfide is also a noxious,
toxic gas which makes it difficult and dangerous to
handle from a personnel standpoint and also from a pump-
ing standpoint. Gases in a liquid can cause pumps to
cavitate, lose prime, or to function less efficiently.
Bacteria are also known to consume h~drocarbons, result-
ing in a 105s of the product.
Because water is an undesirable foreign matter
in any oil or gas pipeline, the treatment of pipelines
with gelled pigs also includes their drying. One method
of drying a pipeline is described by G.D.H. Crawford,
Gas Journal, Volume 341, No. 5549, 282 (March 18, 1970).
In Crawford, the bulk of the water is removed from a
pipeline by a conventional mechanical pig and then swab-
bing the interior of the pipeline by passing a quantity
of methanol through the pipeline sandwiched between a
pair of pigs. Crawford found it necessary to use this
technique to remove residual water from pipelines carry-
ing natural gas having a high proportion of methane.
Residual water was said to form hydrates with the methane
mder certain conditions of temperature and pressure and
lead to serious transmission difficulties.
The invention resides in a method of cleaning
the interior of a pipeline comprising passing through said
pipeline an aqueous gelled pig containing an aqueous cross-
linked gelled galactomannan gum, or derivative thereof,
wherein said gum, or derivative thereof, is present in
said gelled pig in an amount of at least about 40 pounds
per 1000 gallons of water.
The invention further resides in a method of
sequentially passing through said pipeline (a) an aqueous
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crosslinked gelled pig containing an aqueous crosslinkea
gelled galactomannan gum, or derivative thereof, wherein
said gum, or derivative thereof, is present in said
gelled pig in an amount of at least about 40 pounds per
1000 gallons of water; (b) a fluid mobility buffer com-
prising a non-crosslinked gelled alkanol of from one to
three carbon atoms, and (c) a dessicating amount of a
liquid alkanol of from one to three carbon atoms. The
mobility buffer permits the user to derive the benefits
of both the gelled aqueous pigs and a liquid dessicat-
ing alkanol.
The aqueous gelled crosslinked pigs used in
this invention are superior to other pigs which utilize,
for example, polyacrylamides and the like for the gel
matrix. This superiority is shown in their shear sta-
bility, ease of hydration in water, and the convenience
with which the gelled pigs are broken when the job is
complete. This facilitates waste disposal and enhances
the commercial viability.
It has also been discovered that pipelines
can be cleaned and simultaneously sanitized by pas~ing
an aqueous gelled pig containing at leas-t one bacteri-
cide through the interior of a pipeline. By the term,
"sanitize" is meant that the bacteria level of the pipe-
line surface in contact with the aqueous gelled pig is
reduced. Normally, the bacteria level is reduced to
essentially zero or some other very low value~
The aqueous gelled pigs of the present inven-
tion are easily formulated, are easy to use, and elimi-
nate the need for completely filling a pipeline with an
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antibacterial solution and thus represent an advance-
ment in the art of pipeline cleaning.
The aqueous-based pig compositions comprise
water, a galactomannan gum or derivative thereof as a
thickening agent, and a crosslinker. The pig composi-
tions may optionally contain a bactericide as an addi-
tive.
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Other additives may include an abrasive in solid particu-
lat~ form (e.g. sand) to promote the cleaning ability
of the pig as it passes through the pipeline, or other
conventional additives which stabilize the piy.
Galactomannan gums and derivatives thereof
are well known thickeners for water and water-based
fluids. Examples of ~uch gums include natural gums
(e.g. guar gum, locust bean gum, endosperm seed gums,
and the like) and derivatives thereof (e.g. hydroxy-
alkyl galactomannans, carboxyalkyl galactomannans,
hydroxyalkyl carboxyalkyl galactomannans, and the
like). These are known classes of compounds and
essentially any member can be used in the present
invention. The most common commerically employed
galactomannan gums are guar, hydroxypropyl guar,
hydroxyethyl guar, hydroxyethyl carboxymethyl guar, and
carboxymethyl guar gums. Because -the aforementioned
gums are readily commercially available, these gums are
preferred thickeners, and of these, guar gum and hydroxy-
propyl guar gum are the most preferred. It should be
; noted that;in some references the galactomannan gums
are referred to as polysaccharide and polysaccharide
derivatives. Any member of this known class of thickening
agents can be used in the invention. Such thickeners
are normally used in amounks of from 40 to 150 pounds
~ per 1000 gallons of water (i.e. from 0.5 to 1.8 percent
; by wt). They are preferably used in amounts of from 40
; to 80 pounds per 1000 gallons of water (i.e. from 0.5
to 1.0 percent by wt). The actual amount used, however,
can b~ adjusted to convenience by the practitioner.
~ queous compositions containing the abovethickeners are normally cross-lin~ed using a polyvalent
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metal ion. The cross-linker is normally added as a
soluble salt or as a soluble organometallic compound in
an amount sufficient to achieve the desired amount of
cross-linking. Borates, organotitanates, and organo-
zirconium salts are commonly used. The cross-linking
ability of such compounds is pH dependent in many
instances (e.g. the borate systems). This factor
presents a convenient mechanism for dealing with the
thickened fluids in a non-crosslinked form unkil the
properties of a cross-linked fluid are desired. In the
non-crosslinked state, the thickened aqueous fluids are
normally pumpable at conventional pressures. Sub-
stantially elevated pressures are required to pump the
fluids in the cross-linked state.
The galactomannan gums and cross-linkers are,
as noted, known classes of compounds and are disclosed
in U.S. Patent Nos. 3,058,909; 3,974,077; 3,818,991;
3,779,914 and 3,696,035. Reference is also made -to
the disclosure in the text by Davidson and Sittig,
"Water-soluble Resins" Second Edition (1968) and the
text by Smith and Montgomery, "The Chemistry of Plant
Gums and Mucilages", Biograph Series No. 141 (1959).
Normally, the pig is formulated outside of
the pipeline as a pumpable mass and the cross-linker or
cross-linker/activator is added to the pumpable mass as
it is being pumped into the pipeline. This "on-the-fly"
approach has several procedural adv~ntages, not the
least of which is ease of placement at con~enient low
pressures~. In this manner, the pig forms a cross-linked
gel network after it enters the pipeline and conforms
to the general shape and size of the pipeline. To
illustrate, an aqueous pig comprised of a borate cross-
linked polysaccharide (or polysaccharide derivative)
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gel is a preferred pig composition where the pig may be
subjected to considerable shear. Such pig formations
are conveniently prepared and used by first blending
boric acid (from 2 to 4 pounds) with an aqueous slurry
or solution of the polysaccharide or polysaccharide
derivativé ~from 60 to 80 pounds) to form a pumpable
homogeneous mass. Sufficient base (e.g. aqueous NaOH)
is then metered in to change the pH to a basic pH
(pH 8.5-10 normally) as the homogeneous aqueous mass
is being pumped into the pipeline. The desired quan-
tities of boric acid and polysaccharide or derivative
are present per 1000 gallons of water in each instance
in the pipeline. The gel-time of these borate-cross-
linked systems is easily adjusted by the quantity of base
added (cross-linking occurs faster at higher pE values).
After the gelled pig has been formed in the
pipeline, it is normally driven through the pipeline by
the driving force of a fluid under pressure. This
fluid may be a gas or a liquid and will vary depending
upon the needs of the user. For example, if the user
wishes to leave the pipeline in a dry, empty state, one
would normally use a dry inert gas such as, for example,
nitrogen, carbon dioxide, ethane, propane, or liquified
petroleum gas. If the user desires to refill the
pipeline with a liquid product such as, for example,
crude oil or gasoline the pig could be driven with the
liquid product, so long as the product does not adversely
affect the properties of the pig before its purpose was
complete or substantially complete in the pipeline.
~0 Normally the pigs are formulated and used at
ambient temperatures or below and are pumped through
the pipelines at pressures sufficient to move the pig
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at a reasonable rate. Temperatures are therefore
normally below about 140F. Pressures are normally
below about 2000 psig. The predominant number of
pipelines will normally be cleaned at pressures less
than 500 psig. ~inear flow rates of up to about 5
feet/second are normally satisfactory, from a commercial
cleaning standpoint. Rates of from 0.75 to 1.25 ft/sec.
are preferred.
The size and shape of the pipeline is basic-
ally irrelevant because the gelled pigs are able to bepumped through the pipe over long distances and their
shapes will adjust to fit the size of the pipeline
during use. This makes the gelled pig extremely effec-
tive because stalactites and stalagmites in the pipeline
do not cause its destruction by ripping and tearing it
apart as they do solid mechanical pigs.
The aqueous gelled pigs can be used alone or
as an element of a pig train in the pipeline cleaning
process. In the latter instance, the aqueous gelled
pig is preceded and/or followed by other chemical pig
segments or mechanical pigs. Such chemical pig segments
could be of the same or diferent compositions. For
example, the pig train could be formed having an aqueous
gelled pig according to the instant invention as the
leading segment to remove loose scale and other deris
from the pipe followed by a bactericide-containing
gelled pig for sanitizing the pipe. Accordingly, this
combination would be very effective in cleaning as well
as sanitizing pipelines. Segments of the pig train
could likewise include fluids (liquids or gases) or
non-crosslinked gels containing various additives such
as corrosion inhibitors, and the like.
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After the aqueous cross-linked gelled pig has
passed through the pipeline, it can be recovered and
disposed of as such or "breakers" can be added to the
pipeline causing the cross-linked gelled pig to break-up
and lose its structure and viscosity. As noted above,
this is a very desirable property because it facilitates
; waste disposal. Additionally, in many instances the
aqueous gelled pig is of essentially inconsequential
volume xelative to the volume of the "product" following
it and therefore does not adversely affect the material
which follows. For example, a few hundred gallons of a
pig used according to the instant invention and dis-
charged into the hold of a ship transporting crude oil
would not adversely affect the properties of the thou-
sands of gallons of crude oil also present in thetanker.
Bactericides which are compatible with water-
based formulations are likewise a known class of compounds.
Typically such compounds are aldehydes, organic ~uaternary
ammonium compounds or water-soluble salts of halogenated
~particularly chlorinated) phenols. Examples of such
bactericides include formaldehyde, gluteraldehyde,
dodecyl trlmethyl ammonium chloride, and octadecyl tris
(2-hydroxyethyl) ammonium chloride. Bactericides that
are effective against sulfate-reducing bacteria are
particularly useful in the instant invention because of
the serious problems such bacteria can create, particu-
larly in oil pipelines. If the particular thickener
used is subject to bacterial attack, it may be desirable
to also include a bactericide as a preservative for the
formulated pig.
The fluid mobility buffer of the invention
used for drying the interior surface of a pipe comprises
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a non-crosslinked gelled alkanol of from one to three
carbon atoms. Preferred alkanols are methanol, ekhanol,
and isopropanol. Mixtures of alkanol can be used, if
desired. The thickening agent for such alkanols can be
5 galactomannan gums or derivatives thereof but are
preferably hydroxy (lower alkyl) celluloses and are
more preferably hydroxethyl or hydroxypropyl cellulose.
Such thickeners may be included in the alkanol in
substantially any concentration that has the effect of
10 gelling the alkanol and thereby lowering its volatility
and enabling the gelled material to be pumped as a
viscous slug through the pipeline. Concentrations of
from 50 to 20Q pounds of thickener per thousand
gallons of alkanol are normally used in making the
15 buffer. Sodium hydroxide or other strong base can also
be added to the buffer as a viscosity enhancer.
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The buffer of the present invention separates
the aqueous gelled pig from the liquid alkanol and
prevents interfacial mixing of these two components
20 which would destroy or substantially reduce the effec~
t tiveness of each. The gelled alkanol does not appear
to cause degradation of the gelled aqueous pig, such as
by dehydration, even though the gelled alkanol has the
capacity to take up substantial quantities of water as
25 it passes through the pipeline.
The dessicant used for drying the interior
surface of a pipe comprises a liquid alkanol of from
one to three carbon atoms. Preferred alkanols are
methanol, ethanol and ispropanol. The alkanol(s) is
30 used in an amount sufficient to dry the pipeline to
the desired degree of dryness, i.e. a dessicating
amount.
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It is preferred that the alkanol dessicant
and the buffer be the same, but they may be different
at the convenience of the user. For example, one would
ordinarily prefer to follow gelled methanol with liquid
methanol, but it would likewise be satisfactory to
follow gelled methanol with ethanol or isopropanol.
It is normally convenient to follow the
liquid dessicant with a mechanical swab or with a
crosslinked hydrocarbon gel, such as the gelled hydro-
carbon pig described in U.S. Patent No. 4,003,393 or anungelled hydrocarbon pig described in U.S. Patent No.
4,152,289, but the use of an inert gas is also operable.
The aqueous cross-linked gelled pig; the
buffer, and the dessicant are normally driven through
the pipeline by the driving force of a fluid under
pressure such as hereinbefore described. If the user
desires to refill the pipeline with a liquid product,
the "pig train" could be driven with the product so
long as thexe was a satisfactoxy interface between the
product and the alkanol such that the product did not
adversely afect the dessicatiny ability of the alkanol
before the job was complete or substantially complete
in the pipeline.
The following examples will further illustrate
25 the invention. ~-
Example l
A 40 mile pipeline was cleaned by passing
through it sequentially (a) 2000 gallons of a borate
cross-linked aqueous gelled pig (pH 8.5-lO) having lO0
pounds of hydroxypropyl guar per 2000 gallons water,
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(b) 1000 gallons fresh water, (c) 16,000 gallons of 15
percent hydrochloric acid, (d) 8000 gallons of a com-
mercial passivator and neutralizer, and (e) several
polyurethane pigs for gas migration control. This train
was driven through the pipeline with fresh water pumped
at 90 gallons per minute. Samples of the pig were taken
as it passed through the pipeline. Data obtained from
such samples showed that the gelled aqueous pig retained
its integrity throughout the 40 mile journey. An
excellent cleaning job resulted from this treatment.
In Example 1 the pig train was driven through
` the pipeline at a rate of approximately 1 foot per
second. This is a very satisfactory rate from a com-
merical standpoint, but rates up to about 5 feet per
second have been used with success. The higher linear
velocity trains normally require somewhat longer pigs
or pig segments to achieve the same degree bf cleaning
(thought to be primarily a function of contact time)
and to minimize -the tendency of pig segments to mix if
turbulent flow is encountered.
Example 2
The effectiveness of a bactericide~gelled pig
was e~aluated by passing ten gallons of an aqueous
gelled pig containing 250 ppm of a commercial quaternary
ammonium bactercide (Dowell M 76) through a 65 foot
test loop of one inch steel and a section of one inch
polyvinyl chloride pipeline contaminated with river
water laden with bacteria. The gelled pig was~driven
through the pipeline with fresh water at approximately
six inches~per second. The gel discharged from the
pipeline and the pipeline was flushed with approximately
40 gallons of resh water. Samples were taken from the
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river water, from the gelled pig, and from the flush
water. Culture tests revealed an extremely high level
of bacteria of greater than one million bacteria/cubic
centimeter in the river water; no bacteria were detected
in the gelled pig, and less than 10 bacteria per cubic
centimeter were detected in the flush water. The
gelled pig was prepared by blending 60 pounds of hydroxy-
propyl guar and 3 pounds of boric acid and 250 ppm of
the bactericide per thousand gallon~ of water and
adjusting the pH of the solution to a pH of from 9-10
with agueous sodium hydroxide. The system cross-linked
as the ph became basic.
Example 3
Approximately 60 feet of a l-inch steel pipeline,
containing 25 feet of clear polyvinyl chloride sections
was filled with water, evacuated with compressed air,
and then dried by passing through it the following pig
train:
(l) A crosslinked gelled water pig was added
first. It was prepared by mixing 12 gallons
water, 354 grams of hydroxypropyl-guar, 16.5 g.
boric acid and 350 milliliters of a 5 percent
solution of sodium hydroxide in water. The sodium
hydroxide was added on-the-fly as the pig was
being pumped into the line. The pig crosslinked
; quickly (2-5 seconds) after entering the line to a
firm gel.
(2) A gelled methanol pig - prepared by
blending 3.5 gal. methanol, l91 g. of hydroxypropyl
cellulose (average molecular weight of approximately
l million) and 24 g. solid ~odium hydroxide - was
then charged.
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(3) Methanol - 15 gal.
The pig train was then driven through the
line at 1-2 feet per second with compressed nitrogen
(approximately 231 standard cubic feet used~.
Visual inspection of the line prior to drying
showed the walls wet with water and small puddles in
low points of the line. After drying with the pig
train, the surface walls had a dew po.int of -19F as
measured by the Bureau of Mines Dew Point Tester
~manufactured by Chandler Engineering Company~.
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