Note: Descriptions are shown in the official language in which they were submitted.
a~3
METFIOD OF REMOVING DEPOSITS FROM
TEE INSIDE WALIS OF A PIPELINB AND
APPLYING P~OTECTIVE COATINGS THhRETO
- This invention relates to the practice o~ operatin~
main and di~tribution networks o~ pressure and gravity-
flow steel pipelines. ~ore particularly, it concer~s a
method o~ protecting the inside surfaca of a pipeli~e ~rom
deposits and applying a protective coati~g thereto to ~ind
application in meliorative, industrial, utility and drink-
ing water suppi~ systems, as well as in ce~tral heating
pipelines and pips~ used for ~eeding water to gas and oil
~ella.
~ he proposed method ca~ be used both for repairing
pipelines already i~ operation a~d protecting ~rom corro-
sion pipslines under construction.
.
The prior axt know~ a range o~ methods ~or cleanin~
the inside o~ pipellnes or re~ovlnÆ deposit~ there~rom.
However, while solvi~g the problem of plpe cleaning,these
fail to provide reLiable protection o~ the pipeline inside
walls ~rom corro~ion along with cleaning.
~ or e~ampleS there is known a method of cleaning pipe-
line interior accompanied by protecting the inside walls
of the pipaline ~rom subsequent contamination in which a
protective layer i~ formed in the course o~ clca~ing by
removin~ excesslve deposits and co~pacting tho remaining
deposit layer with all th~ pipeline improvement operation~
executed mechanic~Lly (c~., USSR Inventor's Certi~lcate
,,
. :
.
~s~al~3
- 2 -
No. 1,018,729, rPC B 08 B 17J00, published 1982). ~owever,
this method fails to prevent pitting which affects the
pipeline sur~ace, because pit~ remain in the thus compact
ed layer.
Widely popular is a hydromechanical method of remov-
ing deposits ~rom -the interior of pipelines, which resides
in that a self-contained pipe-cleaning unit is moved along
the pipeline under a liquid overpressure, whereby part of
the liquid passed through this unit acts to entrain the
deposits scrubbed away Erom the pipeline walls ( cr ., USSR
Inventor's Certificate ~0.856,59g, IPG B 08 B ~J04; and
USSR Inventor~s Certificate No. 7169647, IPC B 08 B 9/04,
published 1976).
Although this method ensures inside pipe wall cleaning
; to the pipe metal, the extent to which pipe deposits are
removed i9 ~ot sufficient for applying a corrosion-resist-
ant coating, because pits and ~laws of t~e pipe inside
surface retain some corrosive deposits conductive to sub- ;
: sequent pitting. Also, another disadvantage of the method
includes the susceptibility of the freshly cleaned and un-
protected m~tal surface of the pipe to vigorous corrosion a
while pipe thickness reduces due to the loss of metal
Provision of a protective layor on the pipe surface
oleaned from deposits i5 possible in a number of ways.
There i5 known, ~or e~ample, a method o~ treating such
cleaned pipe surface ~or a period o~ si~c days by a ~olu~
: tion of corrc)sion inhibitor composed of a high co~centra--
/ (~t tion sodium polyphosphate(75 mg/l in terms of P205),after
- - -
~L5 sg~ 33
which the ~hus ~ormed coating is co~ti~uously reple~iahed
with a weaker solution o~ sodium polyphosphate (5 mg/l
P205) (cf., Klyachko V.A. and Apeltsin I.E. "Ochistka
prirodnykh vod" - Natural Water Purification, in Russian,
the t'Stroiizdatr' Publishers, 1971; pp~ 507 to 512).
However, such i~hibitor fails to protect drinking wat-
er pipelines from corrosion9 since the amount of sodium
polyphosphate continuously added to the ~low o~ liquid
carried by the pipeline e~ceeds that prescribed for drink-
ing water, Converselyq without continuously adding the
inhibitor the coating e~hibits signs o~ rapid wear. Other-
~ise stated, it is necessary that a definite ratio between
the contents o~ calcium and sodium polyphosphate be main-
tained throughout pipeline operatio~, or the sodium poly-
phosphates promote corrosion.
In view o~ the a~oredescribed, none o~ the ~nown me
thods o~ chemicall~ protecting a pipeline from corro~ion
pxovides reliable and long-lasting coatings.
It is therefore a principle object of the present
invention to provide a method ~or simultaneou~ly removing
deposits ~rom the inner surface of a pipeline and apply-
ing a protective coa-ting thereto which would ~eature high
stre~gth and long aervice li~e.
~ he objects a~d attending adva~tage~ o~ the invention
are attainecl by that i~ a method o~ removing deposit~ from
the inside ~ur~ace o~ a pipeline and appl~ing a protectiva
coating thereto in which thi~ sur~ace is cleaned from the
deposits and treated with a ~olution o~ corrosion i~hibit-
' ;
.
-- 4 --
or to form a coating thereon accomPanied by a subsequent
application o~ corrosion inhibitor to maintain the coating,
according to the invention, the inside sur~ace o~ the pipe-
line is cleaned by fluid aetc; producing a preqsure diffe-
rential between the core o~ the deposits and their sur~ace
to thereb~ remove most of the deposit layer, the remain-
ing layer of deposits being simultaneously impregnated
with a solution of corrosion inhibitor contained in the
cleaning fluid to form a coating, or with a corrosion-pro
moting solution followed by a sub~c~equent trea-tment of the
layer with a corrosion inhibitor to ~orm a protective coat-
ng .
Pre~erably, the pressure di~ferential ranges ~rom 0.2to 1.25 ~Pa.
The jets of liquid which produce the pressure diffe-
rential between the core of the deposi-ts and tneir surfaca
within a range oL from 0.2 to 1.25 ~Pa act to remove most
of the deposits leaving on the pipeline inside walls the
hardest and dif~icultly soluble corrosion products o~
high adhesive capacity (normally a layer of deposits 1 to
5 mm thick). Therewith~ by virtue of the pre~sure di~fe-
rential, slimy products of corrosion are evacuated ~rom
pits and pi~-holes o~ the deposit ~or these pit~ and piu-
holes to be immediately ~illed with the solu~ion o~ cor-
rosion inhibitor and ~orm a eafe protective la~er through
chemical reaction~ with the substances making up the de-
posits bridging the duposit pores.
The aforedescribed cleaning proceqs does not envisage
. -
.. ~ -
~-
3~25
-- 5 --
exposure o~ or dama~e to -the metal of the inside pipeline
surface, whereas the remaining deposits form on this sur-
face by means of the corrosion inhibitor a stro~g a~d dur-
able protective layer.
Prior to cleaning the i~ner surface of the pipeline
is advisably treated with an agent capable o~ reducing the
mechanical strength of the corro9ion products, such a~ a
water ~olution of chlorine of 5 mg/l concentration, or an
aqueous solu~ion of aluminum.. sulphate of 20 mg/l concent-
ration. This promotes corrosion processes which cause the
deposits to separate into layers and ~acilitate clea~ing.
In additio~, e~cessive amount o~ iron ions ~ormed in the
deposits enter into reactio~ ~ith the corrosion inhibitor
accompaniad b~ the formatio~ of hard-to-dissolve compounds.
Advisably, before cleaning the inner surface of the
pipeline is treated with a rust converting agent, such as
a polyvinyl acetate dispersio~ or a methylvinylcerasi~
late~ ~his is accompanied by improved adhesion of the de-
posits to the pipffline wall to form a lay~r having a mulki-
tude o~ pin-hole~ w~ich are therea~ter filled with vari-
ous inhibitors. Used as the corrosiou inhibitor solution
is preferably an aqueous solution o~ aluminum alloy of the
following composition, in wt. per ce~t: magnesium ~
~ loO~ gallium 0~ .5, aluminum - the balance3 or an
aqueous solution o~ 90dium polyphosphate, sodium silicate and
phosphoric acid taken in a ratio of 2:1:1, respectlvel~ or,
alternatively, an aqueous solution of sodium polyphosphato
and silicate in the ratio of 10:1, or an aqueous solution
~
- 6 -
of cement. These solutions o~ corrosion inhibitor te~d to
~orm with the elements present in the deposits and water
compounds capable o~ a sudden increase in the volume to
thereby fill the pores and pin~-holes of the remaining de-
posit and ensure the ~ormation of a protective layer o~
high densit~.
Used as the solution which promotes corrosion is pre-
ferably a solution of chlorine, phosphorio acid or alumi-
num sulphate. Impregnation of the remaining layer o~ depo-
sits with the corrosion-promoting solution ~acilitates
evacuation o~ slimy products of corrosion ~rom pits a~d pin-
holes exposed during cleaning~
; During cleaning the in~er sur~ace of the pi~eline it
i9 advisable to introduce to the jets of cleaning liquid
polyacrylamide in the amount of 2 to 100 mgjl.
Addition o~ polyacrylamide to the jeta of cleaning li
quid enhances the hydrody~amic effect exerted thereby on
the deposits a~d ensures a lower pressure of water in the
pipeline being cleaned, which in tur~ makes it possible to
e~tend the le~gth o~ pipeline cleaned within one pass,as
~vell as to clean pipes of small dia~eter (to 100 mm) not
subject to cleaning b~ tha prior art techniques, since
such cleaning requires a pressure o~ liquid exaeeding the
strength o~ pipe materials.
Cleaning the intarior o~ the pipeline a~d impregnating
the remaining layer of the deposits by a corro~ion inhi-
bitor, or by an age~t promoting corrosion with subsequent
treatment o~ the remaining deposit with a corrosio~ in~
-- 7 --
hibitor to form a protective coatin~ are preferably carried
out in an electric ~ield induced at the sur~ace o~ the
pipeline and movable therealong in ~tep with the portions
of the pipeline being cleaned and impregnated.
~ he provision of the electric current at the surface
of the pipeline where it is being cleaned and impregnated
makes the process of protective coati~g formation more
vigorous on the one hand through electroactivation of wat-
er and increase in the conce~tration of the OH ions in
the thin layer o~ coating formation, and on the other
through facilitating t~e processes of electrophoretic
precipitation o~ calcium, magnesium, a~d alu~inum either
prese~t in the natural water or specifically added thereto
to form chemically stable hydrate bonds with iro~.
Advisably, used as the solutio~ of corrosion inhibitor
preservi~g the protective coating is a water solution of
sodium polyphosphate of not more tha~ ~ mg/l in concent-
ration, or a mi~ture thereo~ with ammonia or carbon dio~ide,
the sodium polyphosphate being preferably subjected to
partial depolymerizatlon resulting in the formation o~
polycompound~ with not more than 6 atoms of phosphorus,
the treatment with such a solution of corrosion inhibit~
or proceeding until the iron content in water at the out-
let`fro~ the pipeline amounts to between 0.1 and 0~5 mg/1.
~he treatment with the 901utio~ of corrosion inhibitor
promote~ the for~ation o~ hard-to-dissolve compounds ln
the protective coating. ~he mechanism of formation of the
above compoul~ds resides in that in the presence in water
.
: '
~ L215~3
-- 8 --
o~ small amounts of sodium polyphosphate the latter tends
-to undergo 4ydrolysis accompanied by the formation o~ or-
thophosphate-ions wAich ~orm di~ficultly ~oluble compounds
with the iron ions. Addition to the solution of ammonia
or carbon dio~ide, while promoting corrosion, increases
the amount o~ iron ions necessary ~or the coating forma-
tion. Partial depolymeriæation of sodium polyphosphate
provides su~ficiency o~ orthophosphate-ions ~or the re-
actions. In order to maintain (replenis~ the thus formed
protective layer on the pipeline, use is made of a sodium
polyphosphate solution o~ not over 3 mg/l in conce~tra-
tion, which is not in excess of the amount speci~ied for
drinki~g water, whereby its use for chemically protecting
drinking water pipelines become~ advantageous. The treat-
ment o~ the pipeline with low concentration inhibitors re-
sults in products of reaction o~ sodium polyphosphate with
iron rather than with calcium.
~ hank~ to -the formatio~ o~ dif~icultly soluble com-
pounds in the course of replenishing the protective coating,
the latter progres~ively grows in strength, and subsequ~
ent to terminating the replenishing operation ~viz., at
iron conte~t in the water o~ 0.1 to 0.15 mg~l~ it becomes
strong enQugh to last up to 2 years of continuous service
or even longer.
~ he proposed method is carried out in the ~ollowing
manner.
A pipe cleaning unit is installed in the interior of
the pipeline for simultaneously cleaning the inner sur-
~2~ 3
g _
face of the pipe and forming a protective coating thereon.
The inner surface o:~ the pipeline is cleaned by jetsof liquid producing a pressure dif~erential between the
core of deposit~ ~ormed on the pipe and the sur~aGe of
such deposits, this pressure difrerential preferably rang~
ing between 0.2 and 1.25 MPa. Thanks to the pressure dif-
ferential, the deposits are partially ~eparated from the
surface being cleaned to leave on the walls a layer o~
3ubstantially solid deposits. Slimy products of corro-
sion are then evacuated ~rom pores and pin-holes o~ the
remaining deposits. Simultaneously~ these pores and pin-
holes are occupied b~ corrosion inhibitor carried by the
liquid jets for the inhibitor to enter into reaction with
the deposition products and reagen-ts present in water and
form dif~icultly soluble compounds which reliably bridge
the pore~ and pin-holes thus proYiding a corrosion-resist-
ant coatingL Prior to cleaning the intarior o~ the pipe-
line and forming the protective coating~ t~e inside pipe
walla can be treated with a chemical composition capable
of reducing the mechanical strength of deposits and their
capacity to adhere to the walls of the pipeli~e~
Pre~erably~ used as such a composition is an aquaous
solution of chlorine of 5 mgJl conce~tration, or a~ aqu-
eous solution of aluminum sulphate of 20 mgJl concentra-
tion. The thus reduced mechanical strength o~ tha depos~ts
produces a less damaging e~ect on the pipe m~tal struc-
ture to reqult in an increa~ed corrosion resistance. To
ansure that the protective coatings lsst longer, prior to
,
~L25~ 3
-- 10 --
cleaning and forming the coatings the inside surface of
the pipeline is treated with a rust converting agerlt, such
as a polyvinyl acetate dispersion, or a dispersion o~ ~e-
thylvinylcerasin late~.
Such a procedure improve~ adhesion o~ the deposits to
the walls o~ the pipeline to ~orm a layer of deposits with
a multitude o~ pits and pin-holes therea~ter occupied by
corrosion inhibi~ors.
Advisably, usea as the corro~ion in~ibitors are: an
aqueous solution o~ aluminum alloy of the ~ollowing com-
position, in wt. per cent - magnesium 0.1 to 1,0, gallium
0.1 to 3.5, aluminum - the balance; or a~ aqueous solution
o~ sodium polyphosphate, sodium silicate and ~hosphoric
acid taken in a ratio o~ 2:1:1, respectively; or an aqu-
eous solu~ion o~ sodium polyphosphate and silicate in the
ratio o~ 10:1; or a~ aqueous solution o~ cement.
To facilitate the evacuation o~ slimy products of cor
rosion from the pits and pi~-holes exposed after clean-
ing, it is advisable that prior to impreg~ating the re-
maining deposit layer by inhibitors this layer should be
treated with a corrosion-promoting agent~ such as a~
aqueous solution o~ chlorine, phosphoric acid or alumi-
num sulpha-te.
Desirably, in order to enhanca the hydrodynamic e~-
~ect o~ the jets o~ clea~ing liquid on the deposits ac-
cumulated on the pipeline sur~ace, polyacrilamide in the
amount o~ 2 to 100 mg/1 is added to the liquid jets,where-
b~ it becomes possible to reduce the pressure of water
;
~Z~ 3
-- 11 --
in the pipeline.
~ or improvin~ the quality of the protective coating
a~d extending its service life 1.5 to 2 times, it is re-
commended that the inhibitor be introduced to the pits and
pin-holes of the deposits by way of an electric ~ield in
which ions and molecules o~ the irlhibitor are activated
to ~orm compounds mainly with iron ion~, whereby t~e amo-
unt of the inhibi-tor to be consumed i5 reduced, since the
ions o~ the inhibitor penetrate more vigorously into the
pits and pores of the deposits. Therewith, orthophosphate
compounds with iron ions are ~ormed without the ~ormation
o~ intermediate compound~. In order to ~rovide a more re-
liable protective coati~g and make the pipeline more re-
sistant to corro~ion, be~ore introduci~gr sodium polyphos-
phate to the pipeline the latter should be preferably sub-
jected to partial depolymerization accompanied by the ~or-
mation o~ polycompounds with not more tha~ 6 atom~ oX phos-
pho~us.
Subsequent to cleaning o~ the pipeline and applying
a protective coating thereto, or during the regular opera-
tion o~ the pipeli~e in response to an i~crease in the amo-
unt of iron contained in th~ watar being pumped through
the pipeline to over 0.2 mg~l7 the protective coating
must be treated with an inhibitor, desirably an aqueous 90-
lutio~ o~ sodium polyphosphate o~ not more than 3 mg/l
concentration, or a ~i~ture thereo~ with ammonia, carbo~
dioxide, or sodium silicate~ such a treatment proceedlng
until iron content in the water at the outlet from the pipe-
;
;:
,
12 ~æs~0~3line is brought dow~ to between 0.1 and 0.15 mg/l.
~ he proposed method enables to simultaneously clean
corroded pipelines and apply a protective coating to the
inside surface thereo~ which could be strong enough to last
~or at Least 3 to 5 years. ~o restore the properties of
the protective coa-ting, only negligeable amount of inhibit-
or is re~uired, particularly 4 to 6 times less than ~or
the prior art methods.
The invention will be more full~ understood with re-
ference to various examples of the proposed method that
follow.
EXAM~ 1
; A drinking water pipeline o~ 500 mm in diameter used
for 10 years is cleaned by removing deposits. The inside
walls of the pipeline exhibit a continuou~ layer of depo-
sits 20 to 35 mm in thickness. Iron content at the pipe-
line outlet is 180 mg~l.
A cleaning u~it is mounted into the pipeline through
a special chamber, wherea~ter an aqueou~ solùtion of cor-
rosion inhibitor, viz., sodium polyphosphate having a con-
centration of 50 mg/l in terms of P205, is pumped into
the pipeline interior to remove the deposits and form a
protectivo coating through impregnating the layer of de-
posits remaining after cleaning.
Secured at the top part of the pipeline in a space
formed betw~en the pipe wall and the layer of deposits de-
veloped t~lereon at intervals of each 1 km of the pipeline
length are piezoelectric elements to monitor pressure in
~ 03
- 13 -
the deposits.
Subsequent to cleaning a pipeline len~th o~ 25 km the
delivery o~ the inhibitor is terminated and ohl~ water i~
pumped to the pipeline. By monitoring the pressure o~
the aqueous solution of inhibitor or water in the interior
o~ the pipeline downstream o~ the cleaning unit, the pres-
sure in the deposits and thereabove is varied withi~ a range
o~ from 0.2 to 1025 MPa (for comparison, a pressure range
of 0.1 to 1.3 MPa was tried) The pressure in the deposits
and thereabove is varied by subjecting the ~eposits to the
action o~ liquid jets escaping from the cleaning unit.
After the cleaning unit reaches the receiving chamber,
it is recoverea ~rom the pipeline a~d pre~sure i~ ~tered
at the piezoelectric elements. The pipeline i~ then cured
for 6 hours with the remaini~g i~hibitor, aiter ~hich it
is flushed to a conoe~tration of ~odium polyphosphate 3.5
mg/l i~ term~ of P~0
~ ater contai~ing 1 mg/l o~ sodium polyphosphate i~
conve~ed along the pipellne to the consumer.
Daily measurements of the amou~t of iron dissolved
in the water are taken at the pipeline terminal.
A~ter lc5 years of the pipeline operation the content
of dissolved iron in the water amounts to 1.1 - 0.15 mg/l~
The additio~ of inhibitor to the pipeline is stopped.
Samples o~ the pipeline wall are cut at points where
the piezoelectric elements are securedO
Non-working sur~aces o~ the sample~ are coatad with a
protective mastic. The ~amples are placed in a test stand
' . .
, ~ .
~ 3
- 14 -
wherethrou~h drinking water is conveyed at a speed of
5 m/s. The rate of steel corrosion in mm per year is de-
termined according to kinetic curves, whereas the rate of'
iron ions trans~er to the wat;er is determined by pipeline
surface coloration.
~est results are represented i~ Table 1.
~ABL~ 1
Pressure diffe- Rate of Service Visual ~eature~
rential in depo- sample life of o~ the surface
lylngan~COrrosi_ theicoat- bein~ protected
a protect1ve coat-n~ d t
ing, in MPa mm~yr ay~
O.I 0.5 24 ~he surface has a
porous layer o~
deposits 8 to 10 mm
thick
0.2 002 I80 The surface has a
dense layer o~ de-
posits~light brown
in color t 3 to 5 mm
thick
o.3 - 1.250.15-0.05 250 The surface has a
layer of deposits
~80 dark brown in color
1.3 0-3 ~ ~he ~urface has a
film o~ dark color.
Deposits are complete-
ly removed Yrom the
: inner wall of the
pipeline even from
the pores and pits
of the-metal sur~ace
'
~25~003
-- 15 _
EXAMP~E 2
A pipeline is cleaned and protected .~rom corrosion
in a manner substantially similar to o~e described in
E~ample 1.
~; Prior to starti~g the cleaning unit water containing
chlorine in t~e amount of 5 mg/l is pumped through the
pipeline~
All stages o~ cleaning and coating application are
carried out at an optimum pressure di~rerential o~ 008
~a in the deposits and thereabove.
Samples are tested as described in Example 1.
Resul-ts of tests are represented in Table 2.
TABIE 2
Example No Rate o~ corro- Life of the protective
sion of the coating, days
samples, in mm/yr
2 0.~9 ~00
3 0.08 65~
4 0.06 720
, .
EXAMPL~ 3
A pipeline is clea~ed~ coatedt and samples are sub-
jected to corrosion tests substantiall~ as described i~
~xample 1.
~, Prior to cleaning the pipeline is treated wi-th aQ~
aqueous solution of aluminum sulphate in the amount 20~g~1
in terms of AI ~+t,
Pressure di~erential i~ the deposits and thereaboYe
..,
' .
,
.~ , . . .
~L~5~ 3
16
i~ 0.8 MPa.
Te~t re~ults are repre~ented in Table 2
EXAMPIE 4
A pipeline i9 cleaned, coated, and ~ample~ are sub-
jected to corro3ion te~ts sub~tantially as described in
Example 1.
Prior to cleaning the pipeline is treated with an
aqueou~ ~olution o~ polyvinylacetate disper~ion 50 m~/l
in concentration.
Pressure dif~erential in the depo~its and thereabove
i~ 0.8 ~Pa.
Test result~ are repre~ented in Table 2.
EXAMPIE 5
A pipeline is cleaned, a protective coating i~ ap-
plied, and ~amples are tested ~ub~tantially a~ de~cribed
in ~xample 1.
Used a~ the inhibitor forming the eoating i~ an aqu-
eou~ ~olution of aluminum alloy of the ~ollowing compo~
tion, in wt. per eent:
: magnesiu~ 005
~ lliu~ - 3.0
aluminu~ - the ~alanGe.
Aluminu~ content in the solution i~ 40 mg~ t~r~
o~ AI~. Pre~ure di~Yer~nti~1 lo 0.8 ~Pa~
Resu~t~ oi ~a~ple te~t~ ar~ repre~ented in Table 3.
l~MPIæ ~ '
A pipeline i8 ¢le~ned9 ~ protectiva coatin~ i~ ap- :
plied, and ~ample~ ~r~ te~ted as d-~cribed in Exa~ple 1.
~ .
.
. .
: ~ .
. .
: L~2S~3
- 17 -
U~ed a~ the inhibitor ~orming the coating ia an aqu-
eous aolution of ~odium polyphosphate, sodium silioate and
phosphoric acid taken in a ratio of 2:1:1, re~pectively.
Concentration of ~odium polyphosphate in the water
~olution i 30 mg/l in terms of P205.
Pressure differential in the deposits is 0.8 ~Pa.
Results of sample te~ts are repre~ented in Table 3.
E~A~PIE 7
A pipeline i9 cleaned, a protective coating i3 appli-
ed and samples are teated for corrosion aa described in
Example 1.
; Used aq the inhibitor forming the protective coating
; i~ an aqueo~ ~olution of ~odium polyphosphate and sodium
: silicate in a ratio 10:1.
Concentration of sodium polyphosphate in the soluti.on
i3 25 mg~l in terms o~ P205.
A pres~ure di~ferential of 0~8 MPa i~ produced in
the deposit 9
Test results of ~amples are repre~ented in Table 3.
~ E~AMPIE 8
; A pipeline is cleaned, a protective coating i8 ap-
; plied, and ~amples are teated a~ de~cribed in E~ample 1.
Used as the inhibitor ~orming the coating i~ a ~olu~
tion of Por-tland cement of 30 g/l in concentration.
` A pres~ure differential of 0.8 MPa i~ produced in
the depo~it fl .
Re~ultfl of ~a~ple tests are represented in Table 3
.
., :.. -.. : .. . .
' ~ '` ' .,
~` ~
~L;i25~H031
- 18 -
TABIE 3
Example ~o. Rate of corro- Life o~ the prot0ctive
sion formation coating, day~
in ~.mple~"mm/~r
. - -- . ~
.5 850
6 0.05 790
7 0.07 75
8 0.08 910
E~A~IPIE 9
A pipeline i~ cleaned, a protective coating is appli-
ed, and aample~ are tested a~ de~cribed in Example l.
Prior to the in~tallation o~ the cleaning device, a
similar device is firRt placed in the pipeline, and the
pipeline interior between the device~ i~ filled with a
corrosion promoter, such a~ an aqueou~ ~olution of chlo~
rine 7 mg/l in concentration.
15 km of pipeline length i8 occupied by this sQlu-
tion.
A pre~ure di~ferential of 0.8 MPa i~ produced in the
deposit~.
Re~ult~ of ~ample tests are represented in ~able 4.
EXAMPIE lO
A pipèline i~ oleaned, a protective ~oating i9 appli-
ed, and ssmple~ are tested a~ de~cribed in Example l.
Additionally, prior to mountine the cleani~g device
in the pipeline a second such devi~e i~ placed in the
~s~o~
-- 19 --
pipeline, and the space between the devices i~ filled with
a corrosion promoter, ~uch as an aqueou~ ~olution of alu-
minum sulphate of 25 mg~l concentration in terms of AI~ ~.
20 km of pipeline length i8 ;~illed with thi~ ~olution.
A pressure differential of 008 MPa i~ produced in
the depo~it~.
Test result ~re represented in Table 4.
E~AMPLE 11
A pipeline is cleaned, a proteotive coating is appli-
ed, and ~amples are tested as de~cribed in Example 1.
A second cleaning device is introduced to the pipe-
line and the interior between the two cleaning devices i~
filled with a corrosion promoter, such a~ an aqueous 90-
lution of phosphoric acid 15 mg/l concentration in term~
of phosphorus content.
10 km of the pipeline le~gth i~ occupied by thi~ ~o
lution.
A pressure differential-o~ 0.8 ~Pa i~ produced in the
depo~its.
Result~ of sample tests are repre~ented in Table 4.
TABIE 4
Rate o~ corro- Li~e o~ the protec-
E~ample No. ~ion *ormatlcn tive coating~ day~
in ~a~pl~ 8, ~m~yr
'~
9 0.07 820
0.07 890
11 0.06 g40
,
S~ 3
-- 20 _
A pipeline is cleaned, a protective costing is applied,
and sample~ ~re tested as described in E~ampla 1.
A pre~sure di~ferential o~ 0.8 MPa is developed in the
depo~its.
In contrast to the preceding example~, sub~equent to
the cleaning and coatîng operation~ am~oni~ in the amount
of 0~3 mg~l is added to water conveyed along the pipeline
during its regular operation.
Results of s~mple tests are repre~e~ted in Table 5.
EX~IPIE 13
A pipeline i8 cleaned9 coated, and ~amples are te~ted
as described in Example 1.
A pressure differential o~ 0.8 MPa i~ produced i~
the deposits.
By contrast, during treat~e~t of the pxotective coating
in the cour~e of pipeline operatlon with an aqueous solu-
tion of ~odium polypho~phate, carbon dio~ide in the amount
o~ 3 mg/l i8 added thereto~
- Re~ults o~ sRmple teste are repre~ented in Table 5.
EXA~PIE 14
A pipeline i~ cleaned, coated, and ~ample~ ar~ teeted
for corro~ion as de3cribed in Ega~ple 1.
Thi~ modified ~orm of the propoaed method differ~ ~ro~
the preceding o~e~ in that ~od~u~ polypho~phate used a8
the oorro~io~ inhibitor producin~ the coati~ ub~ted
~o partial depolymeriæa~io:D aoco~panied by ~hs formatio~
of poly~ompounds ha~ing ~ot more than 6 ato~ of phoaphoru~.
~æs~003
- 21 -
For this purpose, the aqueou~ 801ution of ~odium polyphos-
phate i~ pa~ed through a condenser the oa~ing of whiGh
i~ subjeeted to electriG current~ of alternati~g polarity.
R~sult~ of ~am~le test~ are repre~ented i~ T~ble 5.
E~ PIE 15
A pipeline i8 cleaned9 coated9 and ~a~ples are te~ted
for ~orro~io~ a~ desorlbed in Exa~ple l.
A pre~ure di~ferentia~ o~ 0.8 MPa i~ produoed in the
deposit~.
By ~ontr~t, ~ub~equent to cleanlng ~nd applyin~ a
prote~ti~e coating, the coatin~ i3 traated ~ith an aqueous
~olution of ~odium polypho~phate u~til iron content in wat-
er be~omes le~s than 0.15 mg/l.
Thereafter, the treatment with sodium polyphosphate
i~ terml~ated.
Re~ulte of ~ample te~t~ are repre~ented in Table 5.
~ABIE 5
Rate of corro-h~fe o~~the prote~-
Exa~ple No. ~ion for~atio~ti~e ~oating, d~y~
in sa~pleo7 in
m~/yr
12 0.05 980
13 0.04 10~0
14 0.05 1200
0.04 1550
..
-
~2~ 3
22
EXAD~PIE 1 6
A pipeline iE3 cleaned~ coated and sampleEl are tested
for corrosion as described in B~ample 1.
~ he differenGe from the previously de~cribed modi~ica-
tion~3 of the proposed method re~ide~ in that polyacrylamide
o~ 50 mg/l in concentration is added to the aqueous solu-
tion of corrosion inhibitor pumped to the interior o~ the
pipeline downs3tream of the cllsa~ing device.
A pressure differential of 0.8 MP~ i~ produced in the
depoE3it 8 .
~ he introduction of polyacrylamide is advantageous be~
cause it allow~ a 40 % decrease in the pre~3sure of liquid
after the cleaning device.
For producing a pressure differential o~ 0.8 ~Pa, a
pres~ure on the order of 1.4 ~Pa must be de~eloped in the
pipeline interior after the pipe cleaning device. Addition
of polyacr~lamide makes it possible to bring this pre~sure
down to 0.94 MPa.
EXA~PIE 17
A pipeline is cleaned, a proteotive coating i~ appli-
ed, and sampleE3 are tested for corrosion a~3 described in
E~ample 1~ -
In contrast to the previously de~cribed, an electricfield of 10 mA/dm2 current den~3ity i3 induced at the wall
o~ the pipeline.
A prec3sure differential o~ 0.8 MPa i~ maintained in
the depo Bi ts.
~ he spE~lication of an electric field makes it pO8-
:~L2~ 3
-- 23 --
~ible to reduce the amount of corrosion inhibitor by 40 %,whereas the rate of corrosion formation in the ~ample~ i~
0.04 m~/yr, and the life of the protective coating extends
to 1850 days.
.
. ~ ~ ",
