Note: Descriptions are shown in the official language in which they were submitted.
21579 16
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HETHOD OF CLEANING AND IrIAINTAINING POTABLE WATER
DIBTRIHUTION PIPE BYSTEMS
HACKGROOND OF T8E INVENTION
It is well known that hardness and suspended
solids in water sources vary widely in composition
depending on the source and will result in scale
deposition and sedimentation on surfaces wherever water
is used. Scale deposition and sedimentation is
particularly troublesome in water distribution pipe
systems which service the residential and commercial
customers of municipalities, private water companies
and the lils:e along with industrial process water
distribution pipe systems as found in the mining,
petroleum, agriculture and the like industries. In
these system:, the formation of scale and sediment can
WO 94/21865 PCT/US94/03065
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reduce the water flow through the pipe system which
will limit the capacity of the pipe to service the
requirements of the customers or to provide the _
required water necessary for an industrial process,
irrigation, etc. For instance, in municipal systems an
increase in the fire risk would be obvious if the fire
hydrant did not supply sufficient water to extinguish
the fire due to scale and sediment deposits in the feed
pipe 7:ine. At some point, the water distribution pipe
would have to be replaced due to these restrictions at
a high cost and with prolonged interruption of service.
Additionally, scale and sedimentation will
increase the possibility of corrosion in the water
distribution pipe along with promoting the growth of
organisms. The organisms also can be a health hazard,
promoting corrosion and biomass which binds scale and
sediment together and to the surfaces of the system.
Corrosion will eventually lead to the leakage of the
systeau and the necessity to replace the leaking
sectia~n.
Strong acids have been used to clean water
wells, however, submersible pumps are removed prior to
treatment to prevent corrosion by the acids employed.
Also, organic acids, mixtures of mineral acids and
organic acids or inhibited acid compositions have been
found to clean water wells without the necessity of
removing the pumps or other equipment. These methods
~1~ ~9~_~
-3-
for cleaning w<~ter wells have involved static and surging
treatment.
A proper cleaning and maintenance program for
water distribution systems will prevent decreased water
flow capacity, corrosion and the necessity to replace the
system or portions thereof. A simple and effective method
for cleaning and maintaining these systems is needed.
ES-A-533818 discloses a method for eliminating
lime incrust.ations from domestic water supply
installations which represents the prior art as referred
to in the preamble to Claim 1.
US-A-4025359 discloses an inhibited acid
composition fo:r cleaning water systems which has a reduced
tendency to attack galvanized pipe or steel pipe.
WO-A-92/20629 discloses soap compositions of
carboxylic acids and amines useful in removal and
prevention of scale containing calcium or magnesium
carbonate, oxide or hydroxide.
FR-A-2602571 discloses a method and apparatus for
cleaning a con~~uit of a potable water distribution network
in which pulsE~s of fluid under pressure, such as water,
are passed through the conduit.
In accordance with the present invention, a method
of cleaning a potable water distribution pipe system of
scale comprising providing a reservoir for containing an
aqueous cleaning solution for the removal of the scale,
sealing off a section of pipe in the system for
circulation of the cleaning solution therethrough,
circulating the cleaning solution from the reservoir
through the pipe section and returning the solution to the
reservoir for the removal of the scale, characterised in
that the aque~~us cleaning solution is adapted to remove
scale associated with sulfate-reducing and iron bacteria
consisting pr~_marily of iron oxide, biomass and sediment
from inside surfaces of the pipe section, in that the
section of pipe is an underground section of a
A(~E~:DE~ SHEET
X21 g 7 9 1 ~6
-3a-
distribution pipe system and in that the circulating
cleaning solution is monitored and the cleaning solution
circulated for a sufficient period of time until the scale
and sediment i.s observed to be dissolved, loosened and/or
suspended in t:he circulating cleaning solution.
This invention is directed to a method of cleaning
and maintaining water distribution systems. Water systems
having interior scale and sediment deposits are cleaned by
introducing and - circulating an effective amount of an
aqueous treatment solution for a sufficient period of time
which results in the solution, loosening and suspension of
the undesired scale and sediment. Thereafter, the spent
treating solution containing the dissolved or suspended
scale and sediment is flushed from the water distribution
system to pro~ride a clean system with improved water flow
and operation. Additionally, further flushing with high
pressure water will also remove additional scale that had
been loosened by the treating solution.
The cleaning solution may be acidic, neutral or
basic. In th~~ most preferred form, in potable water pipe
systems, mineral acids or organic acids, and mixtures
thereof, are employed as acidic treatment solutions. The
acidic treatment solution may contain
.,..
-w WO 94/21865 ~ ~~ PCT/US94/03065
furthsar additives such as inhibitors, chelating agents,
penetrating and/or dispersing agents to assist in the
removed of scale and sediment and to minimize any
adver::e effects on the pipes, valves, or other system
surfaces due to the acids employed.
This invention provides a simple, low cost
and effective method of removing water scale and
sediment from water distribution systems in order to
maintain proper water flow, operation and to prevent
corrosion of the system which would require the high
cost a.nd inconvenience of replacement.
Other advantages and objectives of this
invention will be further understood with reference to
the following detailed description and drawings.
DETAILED DESCRIPTION OF THE INVENTION
Among the acidic treatment solutions found to
be useful in practicing the method of this invention
are aqueous solutions of mineral acids such as
hydrochloric, nitric, phosphoric, polyphosphoric,
hydrofluoric, boric, sulfuric, sulfurous, and the like.
Aqueous solutions of mono-, di- and polybasic organic
acids have also been found to be useful and include
formic, acetic, propionic, citric, glycolic, lactic,
tartaric, polyacrylic, succinic, p-toluenesulfonic, and
the like. The useful treatment solutions may also be
aqueous mixtures of the above mineral and organic
acids.
21579 1a
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Alkaline, acid, or neutral cleaning solutions
may also beg employed, as indicated above, depending
upon the t:~pe of scale that needs to be removed.
Sequestering or chelating agents such as ECTA
(ethylenediamine tetraacetic acid), NTA
(nitrilotria~cetic acid), and derivatives, i.e., basic
alkali saltsc, and the like have also been found to be
useful in th,e treatment solution in certain cases.
Th.e acidic treatment solution may also
contain acid inhibitors which substantially reduce the
acidic act~Lon on metal surfaces of the water
distribution system, particularly valves, fire
hydrants, etc., and these various inhibitors for acids
have been well documented in the patent art. Typical,
but not necessarily all inclusive, examples of acid
inhibitors a:re disclosed in the following U.S. Patents:
2,758,970; 2,807,585; 2,941,949; 3,077,454; 3,607,781;
3,668,137; 3,885,913; 4,089,795; 4,199,469; 4,310,435;
4,541,945; 4,554,090 4,587,030; 4,614,600; 4,637,899;
4,670,186; 4,780,150 and 4,851,149.
The treatment solution may also contain
dispersing, penetrating or emulsifying agents to assist
in the removal of the scale and sediment. These
surface active agents may be anionic, cationic,
nonionic or amphoteric as defined in the art.
Compounds such as alkyl ether sulfates, alkyl or aryl
sulfates, al.kanolamines, ethoxylated alkanolamides,
b ,
~, WO 94/21865 ~ ~. a~ PCT/LJS94/03065
-6-
amine oxides, ammonium and alkali soaps, betaines,
hydrot.ropes such as sodium aryl sulfonates; ethoxylated
and propoxylated fatty alcohols and sugars, ethoxylated
and poopoxylated alkylphenols, sulfonates, phosphate
esters, quarternaries, sulfosuccinates, and mixtures
thereof, have been found to be useful in admixture with
the acid treating solution.
DRAWINGS AND OPERATING ERAMPLES
Fig. 1 is a schematic of a laboratory test
system illustrating the method of this invention.
Fig. 2 is a diagram of a field system for
cleaning a potable water distribution system.
With reference to Fig. 1, a laboratory test
system is shown to evaluate the removal of scale and
sediment by acidic treating solutions from a test pipe
sample taken from a water distribution system. This
system includes a 15 gallon acidic treating solution
reservoir 5, submersible acidic treat;n~ ~~~"+;.",
circul~3tion pump 6 rated at 1200 gallons per hour, 1"
inlet transfer line 7, drain valve 8, heavy rubber
diaphragm seals 9 for the ends of the test pipe
specimen 10, 1" outlet transfer line 11 and the
treating solution 12. The test pipe specimen 10 is
mounted at about a 30 degree angle so that the test
solution will contact essentially the entire inner pipe
surface' to be treated.
A laboratory test, for example, was run on a
four foot section of 6" diameter pipe which had been
WO 94/21865 ~ PCT/US94/03065
removed from a potable water distribution system that
had been used for over 40 years. The scale on the
inside: of the pipe consisted of nodules of up to 1 to
1 i inc:hes in height covering 100% of the inside pipe
surface which had substantially reduced the opening
inside the pipe for water to flow. Analysis of the
scale indicated it consisted of primarily iron with
some calcium, magnesium and manganese in the form
oxides, hydroxides and carbonates along with fine
mineral acid insoluble solids and some "biomass". This
is typical scale associated with sulfate-reducing and
iron bacteria along with the associated corrosion.
About 10 gallons of a 12.5% aqueous inhibited
hydroc:hloric/glycolic acid solution containing a
penetrating agent was placed in the reservoir 5 and
circulated through the test pipe 10 for a period of 24
hours. After 2 hours of circulation, particles of the
scale were breaking loose and could be heard in the
outlet transfer line 11 and observed entering the
reservoir 5. The color of the treating solution also
became increasingly darker with circulation time.
After 24 hours the circulation was stopped and the
system was drained of the treating solution. The
diaphragms 9 were removed and the inside of the test
pipe was observed to be about 80% cleaned of scale and
sediment solids.
On treating the test pipe with a second
identical treating solution for a period of 21.5 hours,
WO 94/Z1865 ~ '~ ~ ~, PCT/US94/03065
_g_
about 80% of the interior surface of the test pipe was
obser~;red to still be covered over with a scale and/or
sediment that was a soft and paste-like semi-solid
which contained some grit and could be easily removed
with a probe. The remaining scale nodules had been
substantially reduced in size since the end of the
first treatment. It was concluded that the second
treatiaent would probably not be necessary if a high
pressure water flush was employed to remove the
insoluble soft sediment which had coated the remaining
scale nodules after the first treatment.
With reference to Fig. 2, a field equipment
and system diagram is shown which may be employed in
the cleaning of a potable water pipe distribution
system. Two 500 gallon treating solution reservoir
tanks 20 and 21 along with a 100 gallon per minute
circulation pump 22 and sight glass 23 are mounted on
a flat: bed truck (not shown) . In this example, a 2~
inlet pipe 24 is secured to a 650 foot section of 6"
water distribution pipe 25 after the main shut off
valve 26. The fire hydrant 27 and fire hose 28 were
employed for the acidic treating solution return to
tanks 20 and 21.
The section of pipe 25 to be treated was
isolated by closing off the two water main shut-off
valves 26 and 29 along with all service line valves,
typically 30 and 31. With valves 32 and 33 closed,
1000 gallons of acidic treating solution was prepared
WO 94/21865 ~ ~ PCT/US94/03065
_g-
in tanks 20 and 21. With the coupling 34 open, the
treating solution w:a allowed to enter the system by
opening valves 33 and 35 and turning on the circulation
pump 22. The pH of the water- coming from the open
coupling was then monitored until a decrease was noted
which indicated the acid treating solution had
displaced the water in the section to be treated. The
circulation pump 22 was turned off and the coupling 34
connecaed. Valves 36 and 37 were then closed and valve
l0 32 opened for circulation. The circulation pump 22 was
then started again for the treatment period. Valve 37
was c:Losed to allow for scale solids to accumulate in
tank :?0 while the treating solution could overflow at
38 to tank 21 which reduces the chances of plugging
during treatment.
The treating solution was then circulated in
the system of Fig. 2 for a period of 5 hours.
Observation of the treating solution through the sight
glass 23 showed an increasingly darker discoloration
with time. At the end of the treatment period, the
circulation pump 22 was turned off, and valves 33 and
35 were closed. The main shut-off valve 26 was slowly
opened and fresh water allowed to enter the system
until the treating solution was displaced as noted when
the tanks 20 and 21 were full. Valve 32 was then
closed. The fire hose 28 was then disconnected from
the fire hydrant 27 and the main shut-off valve 26
opened full to allow high pressure flushing of the
WO 94/21865 PCTIUS94I03(~~
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treated water main 25. As the flush water emerged from
the fire hydrant 27 it was dark in color with
cons~iderahle scale and sediment solids. Flushing
continued until the flush water was clean of solids for
a period of time prior to putting the treated section
of the water distribution system back into service.
The flow rate through the fire hydrant 27
prior to treatment had been determined by a Pitot Gauge
to be 588 gallons per minute. After treatment, the
flow rate was determined to be 790 gallons per minute.
This was an increase of 34.5%.
Also, improved mechanical operations of the
hydrants and valves of the system were achieved. The
flow of cleaning solution may also be reversed in the
system to further improve cleaning efficiency. The
above cleaning solutions met the requirements of the
National Sanitation Foundation (NSF International, Ann
Arbo~~, Michigan), Standard 60 for potable water
dist~_-ibution systems.
Other examples of cleaning solutions may be
employed as follows:
PrebJ~end Ingredients % by wt
31% Flydrochloric acid in water 87.14 +/- 2%
70% G:lycolic acid in water 5.27 +/- 0.3%
40% fiodium xylene sulfonate in water 2.06 +/- 0.2%
Triet:hanolamine and diethanolamine 2.96 +/- 0.2%
mi~,aure (85%/15%)
Water 2.57 +/- 0.2%
In a preferred form of the invention, the
above: preblended cleaning solution is used in an amount
of ax~out 12.5% by weight with water in the field for
WO 94/21865 ~ PCT/US94/03065
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cleansing an underground potable water distribution pipe
system. However, more generally, the solution may be
emplo!,red in amounts of from about 5 to about 50% by
weighi: with water in the field, depending upon such
variables as the amount of scale, pipe volume to be
cleanE:d, circulation time and other factors. The
amounia of anhydrous chemicals in a broader range of
ingredients are about 1% to 27% HC1, 0.1% to 4%
glycol_ic acid, 0.04% to 1% sodium xylene sulfonate and
a b o a t 0 . 1 % t o 2 . 5 % o f t h a
triethanolamine/diethanolomine mixture (hereinafter
referred to as "TEA").
It should be understood that the above
chemical ingredients may be blended in the field for
cleaning the underground potable pipes, for example,
hydrochloric acid may be added to a concentrate of the
glycolic acid, sodium xylene sulfonate and TEA. In the
potable water distribution systems, an underground
section of the pipe to be cleaned is sealed off from
the rest of the system. As illustrated above in Fig.
2, the cleaning solution is then introduced from a tank
into the pipe section and, if water is in that section
of pine, it is removed upon the introduction of the
cleaning solution. After the cleaning solution has
been introduced into the pipe section, circulation of
the cleaning solution through the underground pipe is
initiated for a sufficient period of time for
21578 15
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solubilization, loosening and/or suspension of the scale and
sediments.
In thE~ above preblends, a soap having a 1:1
stoichiometri<: equivalent of the acid (HC1 and glycolic
acid) and TEA base is formed with an excess of the acid.
This composition has been found to work effectively in the
field for the: removal of scale associated with sulfate-
reducing and iron bacteria consisting primarily of iron
oxide, biomas:~ and sediment. These 1:1 soaps have also been
described in co-pending Canadian Application Serial No.
2,103,141. These soaps may be more generally categorized
as soaps of mineral and/or organic acids and a base such as
an amine and ammonia. Further examples of these soaps
include 1:1 soaps of TEA and glycolic acid (also known as
hydroxyacetic acid); TEA and acetic acid; TEA and citric
acid; TEA and benzoic acid; hydrochloric acid and ammonia;
sulfuric acid and ammonia; nitric acid and ammonia; TEA and
hydrochloric acid; TEA and sulfuric acid; TEA and nitric
acid; ammonia and glycolic acid; ammonia and benzoic acid;
and ammonia a.nd p-toluenesulfonic acid. Accordingly, it
will be understood that other cleaning solutions of the
acidic type employing 1:1 soaps may be employed to
effectively solubilize, loosen and/or suspend the scale and
21.~'~~~~
-13-
sediment from the potable pipe in accordance with the
principles of this invention.
In view of the above detailed description, other
method variations to clean domestic and industrial water
distribution systems, like houses, hotels, plants,
offices, etc., will be apparent to a person of ordinary
skill in the ~:rt. The method is especially advantageous
in cleaning underground potable water distribution systems
having scale associated with sulfate-reducing and iron
bacteria consisting primarily of iron oxide, biomass and
sediment.
