CA1251003A - Method of removing deposits from the inside walls of a pipeline and applying protective coatings thereto - Google Patents

Abstract

METHOD OF REMOVING DEPOSITS FROM THE INSIDE WALLS
OF A PIPELINE AND APPLYING PROTECTIVE COATINGS THERETO

Abstract A method of removing deposits from the inside surface of a pipeline and applying a protective coating thereto includes cleaning the pipeline inside surface and treating this surface with a solution of corrosion inhibitor to form a coating on the pipeline inside surface followed by a subsequent treatment with a solution of corrosion inhi-bitor to maintain the strength of the coating thus applied.
According to the invention, the proposed method offers cle-aning the inside surface by jets of liquid which produce a pressure differential between the core of deposits and their surface to separate the deposits from the pipeline walls, while simultaneously impregnating the remaining layer of deposits with a solution of corrosion inhibitor carried by such liquid, or treating the layer with a cor-rosion-promoting agent and subsequently impregnating the layer with a solution of corrosion inhibitor to form a coat-ing.

Description

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 ,, . :

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~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-' ;

.

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 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 ~

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~

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 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 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 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 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 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.

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 i~ 0.8 MPa.
Te~t re~ults are repre~ented in Table 2 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.

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 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 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~

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.

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 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 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 ~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.

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Claims (12)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A method of removing deposits from the inside sur-face of a pipeline and applying a protective coating there-to residing in that the inside surface of the pipeline is cleaned by jets of liquid producing a pressure differential between the core of such deposits and their surface to se-parate most of the deposits from the inside surface, while simultaneously the remaining layer of deposits is impreg-nated with a solution of corrosion inhibitor carried by the liquid to form the costing, or the deposits are sub-jected to the action of a corrosion-promoting solution to be followed by impregnating the layer with a corrosion in-hibitor solution to form the coating, after which the thus formed coating is treated with a solution of corrosion in-hibitor capable of maintaining the properties of the coat-ing.

2. A method as defined in claim 1 in which a pressure differential within a range of from 0.2 to 1.25 MPa is produced.

3. A method as defined in claims 1 and 2, in which prior to cleaning the inside surface of the pipeline is treated with a composition capable of reducing the mecha-nical strength of the deposits, such as an aqueous solu-tion of chlorine of 5 mg/l concentration, or with an aqu-eous solution of aluminum sulphate of 20 mg/l concentra-tion.

4. A method as defined in claims 1 and 2, in which prior to cleaning the inside surface of the pipeline is treated with a rust-converting agent, such as a polyvinyl-acetate dispersion or a dispersion of methylvinylcerasin latex.

5. A method as defined in claims 1 and 2, wherein the corrosion inhibitor is an aqueous solution of sodium polyphosphate of 0.5 to 3.5 mg/l concentration in terms of P2O5, or an aqueous solution of aluminum alloy of the following composition, in wt. per cent- magnesium 0.1 to 1.0, gallium 0.1 to 3.5, aluminum - the balance, or an aqueous solution of sodium polyphosphate, sodium silicate and phosphoric acid in a ratio 2:1:1, respect-ively, or an aqueous solution of polyphosphate and sodium silicate in a ratio of 10:1, or an aqueous solution of cement.

6. A method as defined in claims 1 and 2, in which the corrosion-promoting solution is an aqueous solution of chlorine, phosphoric acid or aluminum sulphate.

7. A method as defined in claims 1 and 2, in which polyacrylamide in the amount of 2 to 100 mg/l is added to the liquid jets during cleaning the inside surface of the pipeline.

8. A method as defined in claims 1 and 2, in which cleaning of the inside surface of the pipeline and impregnation of the remaining layer of deposits with a solution of corrosion inhibitor to form a protective coating, or the treatment of the inside surface of the pipeline with a corrosion-promoting agent followed by a subsequent treatment of the remaining layer of deposits with a solution of corrosion inhibitor is carried out in an electric field induced at the surface of the pipeline and movable therealong in step with the pipeline portions which are being cleaned and impregnated.

9. A method as defined in claim 1 in which the solution of corrosion inhibitor maintaining the coating strength is an aqueous solution of sodium polyphosphate of not more than 3.5 mg/l concentration, the sodium polyphosphate being subjected to partial depolymerization accompanied by the formation of polycompounds having not more than 6 atoms of phosphorus.

10. A method as defined in claim 9, in which the solution of corrosion inhibitor maintaining the coating strength is a mixture of the aqueous solution of sodium polyphosphate with ammonia.

11. A method as defined in claim 9, in which the solution of corrosion inhibitor maintaining the strength of the protective coating is a mixture of the aqueous solution of sodium polyphosphate with carbon dioxide.

12. A method as defined in claims 1 and 2, in which the treatment with a solution of corrosion inhibitor proceeds until iron content in water at the outlet from the pipeline is between 0.1 and 0.15 mg/l.