US1758810A - Method of and in apparatus for treating the tubes of surface condensers and the like to prevent corrosive action - Google Patents

Description

May 13, 1930. J AUS-HN ET AL l b E m h F S RN- www ST FC h OAS SE EVB BI US TO .n E HO TC GT N5 WEZ TV9 AE1 Em R 6, T01 RT. O C FEB KD SI AE1 RHi MTF Pm AA N IS R Dm N N Aw F N OO DC O H T E M May 13, 1930..

J. AUSTIN ET AL METHOD OF AND 1N APPARATUS FOR TREATING THE TUBES 0F SURFACE CONDENSERS AND THE LIKE TO PREVENT CORROSIVE'ACTION 2 Sheets-Sheet 2 Filed Deo. 16, 1925 Patented May 1.3, 1930 .UNITED STATES PATENT OFFICE 'JOHN AUSTIN AND HARRY SMITH, OF LIVERPOOL, ENGLAND METHOD 0F ANDiIN ABIPABATUS FOR TREATIN G THE TUBES OF SURFACE CONDENSEBS i AND THE LIKE T0 IE'R-EVEITT CORROSIVE ACTION Application led December 16, 1925, Serial No.` 75,797; and in Great Britain, December 30, 1984.

This invention relates to improvements in the' method of, and in apparatus for treating the tubes of surface condensers and the like to prevent corrosive action;

Recent developments in steam engine andturbine design necessitating a comparatively high vacuum, and in condensers necessitating a comparatively high rate of flowI of condensing water to compensate for the reduction of area of the heat transferring surfaces, Anow adopted per unit vof power developed, have resulted in' a very marked increase in the corrosiveV action of the condensing water upon the inner surfaces of the condenser tubes, particularly kwhen the circulating water is, as in the case of marine engines, sea-- water; in recent years the difficulty has assumed very serious proportions, active corrosion takin@ place in newV condensers within twelve months of service, and in some cases necessitating entire re-tubing, at considerable expense, after a comparatively short period of service. The secondary results of leakage of sea-water to the steam flow, due to the corrosion, are also very serious in respect to the boiler and propellin machinery, especially when the latter is o' the turbine type; in the boiler, production of scale, priming and damage. to furnaces, and in the turbine plant, corrosion and incrustation.

Various attempts have been made to overcome these difliculties; l.various metals and alloys have been used for the condenser tubes; the kinteriors of the tubes have been coated with tin or the like non-corrosive metal; and counter-electrolytic methods have been employed to avoid electrolytic corrosion of the tubes; but we have found, as the result of a ,very wide experience, that by none of these known methods has a substantial improvement been effected. From a very careful examination of a large number of corroded tubes taken from the condensers of different types of ships we found that the corrosion was different in character from that which took place in the older types of condensers fitted to reciproca-ting engines working under a moderate vacuum, in which case the corrosion was in the nature of pitting or dezincification, whereas in the. more modern type of plant the condenser tubes were corroded or eroded from end to end.

stances are, of course, comparatively bad conductors of heat, and y'for this reason appeared at first to be objectionable and unsuitable.

When, however the inefficiency due to the leakage of salt-water into the boilers resulting in scaling and priming and leading to deterioration of turbine plant consequent upon the deposition of sediment, together with the heavy charges for consequent overhauls and renewals, wereconsidered, it was believed that the saving effected by the elimination of these losses would more than compensate for the decrease of efficiency, in respect to heat transfer, ofthe coated tubes.'

We found in carrying out our invention that they coating solution must be such as would withstand the action ofl salt-water driven through the tubes at a comparatively high velocity, and be such` as would provide from end to end of the interior.

-tube an insulating coating adequate to prevent corrosive, erosive or electrolytic action; that the solution must be such as could be applied, in the manner herein described to the interiors of tubes of say 5/8 inch bore and 10 feet long so as to provide an even` tenacious and protective coating of mini-r mum thickness consistent with continuity from end to end; and that for practical reasons the coating must be capable of being applied to tubes in situ in the condenser, and without having to disturb the fer-rules; we also found that to obtain successful results in the case of condensers which had been in service a preparatory treatment of the 'interiors of the tubes was necessary; that preferably more than one coating had to be applied with an intervening treatment of the lapplied coating; and that suitable drying applied by spraying the interiors of the tubes, from both ends, by means of an inserted nozzle of a spraying device, using compressed air to atomize the solution and applying it as a coating to the interiors of the tubes; and the object ot' our present invention is to provide a mode of, and apparatus for, carrying outl the coating of the interiors ot' the tubes of surface condensers and the like with a preservative solution in accordance 'with the above requirements.

According to the invention the method of protecting the surfaces of condenser tubes and the likeagainst the corrosve action of a circulating fluid consists in coating the said surfaces after they have been cleaned and dried, by spraying thereon by means of an air-jet a medium containing a protective suhstance Which when dried forms a tough adherent protective layer. on the said surfaces. l

The medium is preferably in the Jform of paint containing bitumen or the liketough, plastic adherent substance adapted to resist the said corrosive action,y mixed with a suitable drier'lquid,the coating so applied being dried by passing over it currents of air.

In carrying out the invention the method of cleanine the tubes and applying the coating is prelerably carried out in the manner and by means of apparatus as hereinafter described and claimed.

We have illustrated the apparatus em- -ployed in carrying out our invention to coat the interior of condenser tubes, in the accompanying drawings, in Whieh:-v

Fig. 1 is an elevation in longitudinal mcdial section showing improvements in spraying devices for coating the interior of tubes.

Fig. 2 shows the general arrangement ot the apparatus employed in combination with a spraying device.. I

Figs. 3 and 4 and 4A show the improved brush cleaning device.

Fig. 3 shows the device in situ in the tubes of a condenser. i

In Figs. ft and A which are views to a larger scale it has been necessary ier convenience of illustration to show the length from the end l to the point 2 in Fig. 4, and

the length from the point 2 to the end 3 iny Fig. 4A; the actual device when connectedA is, of cour =i-, in one length, the part 2 of Fig. 4 coineidnfg` with the part 2 of Fig. 4A.

Our invention as applied to the coating of condenser tubes is carried out as follows Preparation of the tubes ;-The interiors ot the tubes should be effectively dried; this may be accomplished by admitting steam to the condenser so as to dry the tubes by heat applied to the outsides.

This may be effected by allowing a slight leak of steam into the steam side of the tubes just before cleaning. Each tube is then preferably treated as follows If' the tubesl are Very dii-'ty or choked a scraperv is first, used; this is followed by thc application ofl a very severey steel Wire brush, with a strong thick core, the Wire: bristles being in the form of a slow spiral g preferably the brushes are screwed at the end to tit they end of a strong rod by means of which the brushes are pushed in from each end of'tube.. By means of this severe brush an attempt is made to open upany Weak places in a tube, thesloW spiral form being useful as a first cleaning brush, as the dirt does not clog this form of brush: as easily as is the case with a close Wire bristled brush. This operation lofsens the dirtlwhich still remains in the tu e.

To remove the dirt and clean the tubes the brushing device illustrated in F igs. 3, 4 and 4A is employed.

The device consists ot' a lclosely Woundspi ral spring or snake A, the ends of which arcl fitted With adapters a1 and a2', the adapters being connected b a flexible but non-extensible member a3. T e portion A for condenser tubes of the usual size Wouldl be about twelve feet long, and thespiral is closely Wound so that Whilst itcan `transmit a considerable pull without distortion, it is flexible enough to permittof its lbeing passed through two comparatively' adjacent tubes in the manner shown in Fig. 3.

To the adapter a1 on the leading end is fitted a slow-spiral, steel Wire brush B which is first pushed Ithrough the tube to be cleaned,

the connection between the brush and the adapter being. conveniently made by means of a s crewed'union. The adapter a2' at thetrailing end of the snake is tilted with a very tightly Wound, closely bristled, steel Wire brush'C, the adapter 01 of which screws into the adapter azfof the snake; attached to the brush C by a shackle '02 is a hair brush D adapted to be. a tight tit in the tulle,l which brush is fitted with an adapter` di to which further brushes may be attached if necessary. i

The apparatus would be employed to clean the tubes of a con-denser as follows :,-Assuming E and E2 to be the inboardand outboard tube plates of the condenser, ot' which three tubes e only are shown, an operato-r would be located at each end of the condenser, the brush B would then be inserted in, say, ,the tube el by the operator in front ot' the tube plate E, and would be pushed through thisI tube in the direction of the arrow 4, emerging from the end E2 ot' the tube before the brush V enters the end' FX; the operator at the end FP Would then reverse the brush B and push it through the tube e? in the direction ot the arrow 5. aud by exerting a'pull ou the snake A. would -then pull the brushes C aud D through the tube e1 in the direction indicated, simultaneously feeding the brush B through the-tube e2; when the brush B emerges from the end :be "left behind, each :tube is bloivn through with. air'at 4 5 lbs. pressureby'means of a jpipe leadn from .the .air compressor, tobe describe and afquick opening air cock tapered to 'fit lin the end .of .the tubes lThe spraying plant-employed is shown in 'the general arrangement. Figf2, Vand comprises;-A suitably driven portableair-compressor F, `preferably air-cooled with automatic suction release f1; asuitable size for two .sprayin'gdevices is one 'providing from 7 to 12 cubic feet -atfrom 300 to 500 revolutions, respectively, per minute, ata pressure at 40 to 45 pounds 'per square inch. An air reservoir Gr fitted With gauge 'g1 and safety valveg2 to wliichthecompressor delivers the compressed air :through l.the vpipe f2. An air purifier H fitted with any suitable filtering arrangeinenusay a Wire mesh and cloth bag filtering medium (not shownlto which air- .is deliveredby the pipe g3 controlled by the cock g4. A solution container K fitted with .a quick :action coverlockingdevice c1 and an pipe h1 has a connection h2 to the upper part ofthe container 'through areducing valve 7c3, by which the pressure on lthe-surface of the solutionis regulated to that necessary, (about 5 to 8 lbs. per square inch), to .deliver the solution to thefspraying device. Anda spraying device, which `is a modification of 4the spraying device employedwith compressed air'to apply paint in the-usual manner.

The air compressor F may conveniently be driven by an independent'electric motor, or off la Workshop line-shaft, and theconnecting vpipe to the air reservoir is preferably a fiexible metallic pipe of suitable length, so as to enable it quickly to be fitted up in `various ships. The air .purifier I-Iis set up as nearly as possi-ble to the condenser the tubes of which are to be coated, and is connected to the .air reservoirand to the solution containerbv means of rubber air piping in suitable-lengths'vvith union couplings. The air and solution pipesP-and Q from the regulating cocks p1 and 71 of the solution-container to the spraying device R are kept as short.

as possible so las .not to have anymore pipe than is neces-sary in the way of the men en- `gaged in spraying.

According tothe vinvention the actual nozzle from which lthe sprayed coating solution is discharged is at theendl of a tubular extension S ofthe sprayer partR containing the automatic control valve; the part R is. inthe usual manner common to sprayers of this type, connected by air and solution connections p2 and g2 tothe hand-,piece R2 pro'- vided with the usual hand'operated trigger r1 by which the air supply to R" is controlled.

'r2 is a needle-valve controllin'g'the How of the coating solution from thefinlet g2 through the seating r3; the needle-valve is normally closed by a spring r4, andis openedlin opposition to this spring by a piston r5when an' is admitted through the connection 712, by

the operation of a trigger r1 (Fig. 2) ,the air passing through ports r6 tothe interior of the cylinder T7; T12 is an adjustable nutby which the extent of opening of the needle valve is adjusted. The arrangement in these respects is substantially that employedin apparatus of this type, except that We pre -r to use a solid piston fitted with metallic rings r? in,- stead of the cup leather type, and that an additional gland r is fitted to prevent. the

flow of the coating solution into the air chamber; We also make the air supply ports r1 and the release ports fr larger than is usual for apparatus of this type so as respectively to prevent adrop of pressure in the extension S, and to ensure rapid action of the control piston.

The extension S consists of inner and outer vtubes s1 and s2 of length somewhat greater vthan half the length of the longest tubes to be coated.

The inner end of the tube s1 is Connected by the union s3 to the block in which the seating r3. of the needle-valve is formed, so that when the latter is opened the coating solution passes to the interior of the tube s1. The inner end of the tube s2 `is connected by the union s* to the block r9 in which are formed the supply ports r1" through which air supplied to p2 passes to the annular space be` tween tubes S1 and 82.v The outer end of the tube s1 is connected by a union S5 to the inner part s of a spraying nozzle, the outer portion s? of which is attached to the end of the tube s2, the coating solution being delivered to the bore of the inner nozzle, and the air to the annular space 88. y

` The air pressure on the surface of the solution in the container K is usually sufficient to wholly or partially overcome the hydrostatic head between the jet and the solution container: the aspirating action of the air, delivered from the annular space between the tubes s1 and s2 into the annulus .e8 around the jet, inducing the necessary velocity of fiow of solution and atomizing it and spraying it in a fine spray in such manner as to deposit a uniform coating on the interior of the condenser tube as the extension S is gradually inserted into and Withdrawn from the condenser tube as shown in Fig. 2f

19 are supporting sleeves and maintain the inner and outer tubes s1 and $2 in proper relative position, the peripheries of the sleeves being grooved 'to form airways.

The regulating nut rw is adjusted to obtain the required spraying effect, this adjustment is best affected by trial, by spraying on a sheet of tin or the like, the marking on the tin by the spray affording, after little experience, a reliable guide as to the suitability of the spray.

Assuming that the condenser tubes have been tested and defective tubes removed, and that the tubes to be coated have been dried and cleaned as described, the coating by spraying is carried out as follows First coating, brushing and drying Each tube is sprayed for half its length from opposite ends of the gradual insertion axially into and the gradual withdrawal from each condenser tube of the extension S, the ferrules and portion of the tube plates in the vicinity of the tube being treated being adequately coated by the spraying effect asfthe jet is inserted and withdrawn.

It is advisable to divide the condenser into sections so that the men at opposite ends of the condenser are some distance laterally from each other and therefore are not spraying into the same set of tubes; as these sections -or portions are coatedv (half way along the tube only) the inboard and outboard men change positions and thereby the other half of the tubes in two sections are coated. `The spraying of other sections is then dealt with in a similar manner, and any pooling or flooding in the tubes of first section is dealt with by applying the spiral hair `brush referred to under cleaning. As soon as the first coat is completed fans are fitted at one end of the condenser to cause a circulation of air throu h the tubes. It is essential that the fans e started as soon as possible so as to speed up the drying ready for the second coat.

Second coating, brushing and drying;-

This is carried out as described in reference to the first coat, the fans require to be started as soon as possible so as to keep the air circulating through the tubes until the doors are put on the condenser. It is advisable to arrange the work so as to stop spraying 48 hours before boxing up the condenser, the longer time allowed for drying and hardening the solution the better.

The air solution passages being small and the coating solution tends to dry very quickly in the spraying device when the spraying is stopped; for this reason it has been found beneficial to keep the device in action continuously when once spraying has commenced. If for any reason spraying has to be stopped it is essential before doing-so to blow back through the spraying device into the solution container. To do this the cover of the container must be loosened to allow the air to escape, then, by placing a finger over the nozzle of the spraying device and pulling the trigger, the air is blown back through the solution passages in the spraying device, and through the tube to the container. If it be necessary to stop spraying for any length of time it is essential to disconnect the tube from the container and place the end in a suitable receptacle containing petrol, by pressing the uted except on the bottom where there is some'- v times a slight tendency fora small poolto form.

The operation of withdrawing and replacing the sprayer, as stated, also causes all vthe ferrules and tube plates to be coated with the i solution.

-If'the cast iron water ends and doors are also coated a condenser entirely protected from corrosion is obtained.

The invention may be applied to-tubes other than condenser tubes, and to new tubes, provided the surfaces of the latter rendered suficiently rough to take and retain the coating.

The mode of operation and the construction of the apparatus described. may be varigdd los rosive action, characterized as follows,- l

cleaning the tubes in situ in the condenser by abrasive action; then blowing through the tubes jets of compressed air to remove the dust and dirt detached by the abrasive action; then applying in the form of a spray a first coating of paint containing bitumen or the like tough plastic adhering substance mixed with a suitable drier liquid; then rendering the first coating even, and dealing with the pools of paint which may be formed, by

rushing; then drying the first coating by circulating air through the tubes; then applying a second coating of the paint; then rendering the surface of the second coating 'even

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