US1996747A - Method of preventing corrosion of metal walls of tanks - Google Patents

Description

April 9, 1935. B. BUTTERWORTH 1,995,747

METHOD OF PREVENTING CORROSION OF METAL WALLS OF TANKS Filed April 7, 1953 2 sheet s-she et '1 Q .WGATTORNEY.

April 9, 1935. I A. B. BUTTERWORTH METHOD OF PREVENTING CORROSION 0F METAL WALLS Of TANKS Filed April '7, 1933 2 Sheets-Sheet 2 #k ATTORNEN'. a

2 Patented Apr. 9, 1935 METHOD or PREVENTING coaaosron or METAL WALLS or TANKS Arthur B. Butterworth, Brooklyn, N. Y.

4 Application April 7, 1933, Serial No. 664,865

11 Claims.

This invention relates to the cheap and efficacious treatment of the exposed inner metal surfaces of tanks, more particularly the cargo tanks of vessels known as tankers, and has for 5 its particular objects the application tosuch surfaces of an adherent corrosion-inhibiting coating which E exceedingly cheap, is adapted to be sprayed on such surfaces,'is resistant to but inert toward and therefore without effect upon gasoline 19 or otherpetroleum distillates and petroleum oils ily ,and completely removed when it is desired to gas-free or clean such tank by a mere pressure jet cleaning operation, such for example as that described in my prior Patent No. 1,806,740.

It has long been recognized thatthe deterioration due to corrosion of tankers engaged in the transporting of gasoline and other oil distil- 20 lates is a vital problem insofar as the cost of upkeep of a fleet of such tankers is concerned, since the normal life of such tankers is shortened by many years as a result of such-corrosion. Many attempts have been made to protect the inner metal walls of the tanks of such vessels by applying thereto various coatings, either applied manually or by means of a gunsprayer manipulated by an operative stationed within the tank throughout the spraying operation. However, of necessity the choice of such coating compositions was greatly restricted because the gasoline acted as a solvent for the oil vehicles of any oil paints, thereby destroying the bond of such paint with the metal, besides becoming contaminated by such vehicle. Furthermore, the application of such paints whether applied by hand or by a hand gun necessitated the erection of temporary staging within such tank and required the presence of one or more operatives within the tank during the entire coating operation. Moreover,

and objectionably thick accretions thereof tend to .form in and on the channel irons and other braces for the walls of the tank and such coating does not lend itself to being readily removed from the walls of the tank by such tank cleaning operations as previously referred to; and, in the case of the latter type of coatings, the same are expensive so as to render the cost of coating a large tank almost prohibitive besides having other objectionable features. l My investigations have led to the discovery that the inner metal walls of such tanks can be satisfactorily coated with an adhesive, corrosion-inhibiting coating, inert to gasoline, water ballast and the. like, without necessitating the presence of an operative within such tank, through the employment of automatic coating apparatus of 5 the type described in my said prior Patent No. 1,806,740 or such as the type herein described and furthermore, that certain water paints and more particularly unslaked lime, preferably slaked in situ in the coating container, or even ordinary air slaked lime, are highly satisfactory for-this purpose.

In the accompanying drawings I have illustrated a form of automatic coating apparatus suitable for applying a corrosion-inhibiting coating to-the inner metal surfaces of tank walls and also have illustrated the manner in which my improved coating method is performed.

Referring to the drawings Figure l is a fragmentary elevation, partly diagrammatic, showing my improved apparatus in, position within the tank of an oil tanker;

Fig. 2 is a fragmentary detail elevation of the nozzle-driving mechanism; v

Fig. 3 is a vertical section, partly in elevation, of the spraying nozzles and certain associated 'parts of the apparatus; and

Fig. 4 is a fragmentary side elevation of the construction shown in Fig. 3.

Referring to the construction of the apparatus illustrated in the drawings, the letter A designates a tanker having cargo tanks B, the latter having side walls I, bottom 2 and top 3, The top of each tank is provided with a man hole 4 adapted to be closed by a cover 5, the vertical flange of said man hole being apertured to receive a flexible air hose 6 and said cover being apertured to receive a cylindrical casing l which is tapped into the bottom'of agear box 8 wherein it is rigidly secured against rotary motion by set screws 9 or by a suitable spline. Said gear box comprises a two-piece casting, the lower half of which has an integral vertical flange on' which an air-motor C is mounted, the same serving to drive a gear ll through an intermediate worm l2 carried by the motor shaft. Journals I3, l3 areprovided in thetop and bottom of the gear box, the former journal serving to receive the hub M of said gear and the latter receiving an internal supply pipe l5 which is rigidly secured to said hub and held against by means of set screws H5, or being otherwise splined thereto. As shown, said gear I0 is alined between washers I! interposed between the resp'ective top and bottom faces of the gear and the adjacent journals of the gearbox.

Said internal pipe is threaded at its upper end into a flanged bushing 25 which is rotatably mounted within an ordinary stuffing box 26 that is closed at the top by a screw cap 21 and which 60 is laterally apertm'ed to receive a, pipe nipple 28 to which the main water conduit is connected. The top flange of said bushing normally rests on and is carried by the shoulder 30 in said stuffing box and a set screw 3| serves to limit the upward movement of the bushing 25.

A ring gear 35 is splined by a spline 36 on the lower end of the casing I. A T 31 is threaded on the lower end of the pipe IS, the same being provided with a removable keeper 38 which admits of the-insertion into said T of a hollow sleeve 39 that is provided with a series of apertures 40. Said sleeve is provided with peripheral guides or beads 4| and its respective ends are threaded to receive the opposing nozzles 42. A gear 43 having either one less or one more tooth than the ring gear 35 is keyed to the sleeve 39, being locked in position by a lock nut 44.

A portable stripping pump D, having a suction leg 50 that projects into close proximity to the low point of the tank and which is driven by a belt or chain 5| connected to an air motor F, serves to elevate the liquid coating composition that has previously been introduced into the tank, through the valve controlled return pipe 52 and delivers the same to the supply main 29.

The said air line 6 as shown, is connected to a T' 53 from which branches thereof lead to the respective air motors C and F respectively.

Inorder to coat a tank with a preservative coating in accordance with my invention, I preferably proceed as follows:-

The coating solution, which preferably comprises milk of lime is formed in situ in the tank by slaking lime with sea water in the proportion of about 1 "pounds of such quick lime to a gallon of water. The advantage of slaking lime in situ is the fact that the slaking reaction being highly exothermic generates sufficient heat to virtually raise the temperature of the liquid to the boiling point and this heated coating mixture is far more efiective for coating metal tank walls than a 'cold solution, as the hot coating, when applied. under pressure dries to a hard, dense, resistant layer which is substantially unaffected by th'e'swashing of gasoline cargoes or of salt watercargoes. Preferably, moreover, the water employed for the slaking should be salt water, as the coating prepared with saltwater also has a more effective bond with the metal of the tank walls and is more resistant to erosion by the swashing of gasoline or other distillates or salt water ballast than coatings prepared by slaking the lime with fresh water. Furthermore, salt water is always available. v

The aforesaid coating solution having been prepared within the tank, and the above described apparatus having been installed within the tank as illustrated, the two air motors are caused'to operate by compressedair supplied through the respective branches of the hose 6. The lower motor F thereupon causes the pump D, which as stated is so positioned that the suction leg thereof projects into proximity to the bottom of the tank at the low point thereof, to elevate the coating solution through the pipe 52 to the delivery main 29 from whence it passes into the internal supply pipe l5, thence through the T 31 into the sleeve 39 through the apertures 40 and out through the jet nozzles 42. The worm and the gear interconnecting the shaft and air motor and the supply pipe l5 serve as a reduction gear which results in the slow revolution of the pipe l5 and the worm gear 34 carried thereby and the T 31 mounted on the lower BDdthGIEOf. Such revolution of the ring gear l4,-which meshes with the perpendicular gear 43, the latter preferably having one more tooth than the gear 34', together with the simultaneous rotating of the T 31 with such ring gear 34, results in the nozzles constantly changing their path during the rotation thereof and sweeping in a curvilinear and constantly changing path until the jets projecting from such nozzles have impinged against all portions of the inner surface of such tanks within which such T carrying thev nozzles is substantially centrally mounted, all in the mannerdescribed with reference to the jet spraying apparatus disclosed in my prior Patent No. 1,806,740. As a consequence, the coating solution is delivered under pressure against all the surfaces of the tank. Preferably, I employ a nozzle pressure of less than 75 lbs. rather than in excess of 7 5 lbs. when applying the coating solution to the tank walls, since the walls to which the coating is applied have been previously cleaned and scaled either by manual methods or by the method described in my said prior patent and if excessive pressure is employed which is more than suiiicient to cause the projection of the jets from the nozzles to the surfaces to be coated, there will be not only unnecessary spattering of the said paint coating from such surfaces, but there will be a tendency for the coating to not adhere as efiectively to the surfaces as if just sufficient pressure is employed to impart to the jets suficient force to cause the same to reach every portion of the tank within which the machine is mounted. As stated, the surplus liquid which drains from the walls will collect at the low point of the tank and be recirculated by the pump D through the spraying nozzles and consequently it is only necessary to insure that suiiicient coating solution is supplied to the leg 50 to continuously maintain a liquid seal'between .the bottom of said, leg and the tank bottom throughout the coating operation and thereby such coating is accomplished continuously without any halts or shutdowns being required to blow out the accumulated masses of solid material or residues from the paint solution. Furthermore, the presence of an operative in the tank is not required at any time throughout the entire coating operation.

At the end of the operation, any residual coating solution in the tank can be removed by means of the pump or in any other desired manner.

In lieu of a special portable pump, a suction leg connected to the ship's pump may be employed and such suction leg is then connected by a pipe, such as 52, with the supply main 28.

My improved coating can be readily removed by means of hot salt water applied under high pressure in the form of jets in the manner described in my aforesaid Patent No. 1,806,740 and consequently with each cleaning operation it is possible to obtain a smooth scaled surfa'ce which is ideally adapted to receive a smooth and even coating applied in the manner herein described.

If desired, a pump, such as the ships stripping pump, or even the cargo pumps, located in a compartment outside of the tank to be cleaned may be employed, and in such event, the suction side of such pump will be connected either with the container for. the coating solution, or with the body of coating solution. in the tank and the discharge of such pump will deliver into the main 29. In those cases where a number of tanks are to be coated, then the necessary piping, as here- I tanks, for example, the pump in the fire line can.

be employed merely by suitably connecting the same so as to supply the coating solution to the nozzles.

Preferably the coating liquid is propelled against the surface in the form of solid jets or streams as distinguished from an atomized spray, since thereby there is practically no tendency for the [nozzles to become clogged with solid material carried in suspension by the coating solution.

The application of a preservative coating in the manner herein described to the metal walls of tank, particularly of tankers, is particularly suitable, not only for tankers carrying cargoes of gasoline, but also for tankers carrying crude oil on one trip and which are intended to carry color specification gasoline or petroleum oils on the other trip, as after the tanks have been cleaned, this buffer coating would constitute'an ideal coating for the tank adapted to receive the aforesaid color specification oils.- Furthermore, where, as is frequently the case, tankers are required to lay idle for long periods, the pre-coating of the walls of the tanks in the manner herein described, tends to reduce corrosion of such tanks, during such periods of idleness, to a minimum.

One of the especial advantages of quick lime is that it is strongly alkaline in reaction and thereby tends to neutralize any acid or acid-reacting compounds in or on the walls of the tanks so treated, besides serving to ideally prevent corrosion, due to the fact that corrosion of the metal walls of such tanks does not occur, or is materially inhibited, where the metal surfaces are maintained wholly neutral or slightly alkaline in reaction.

Among the additional advantages, in addition to those heretofore noted that are secured through the employment of salt water as the vehicle of the coating, is the fact that it is universally available for marine vessels and furthermore, that being of a considerably greater density than fresh water, dueto the salt content thereof, the calcium hydrate (Cami-Dz) resulting from the slaking of the quick lime (CaO) or other insoluble compounds employed is more uniformly held in a state of suspension in such vehicle.

While quick lime, because of its many advantages, is preferably employed,I may also employ other water paints having an alkaline reaction or capable of neutralizing any acid ingredients contacting with the metal surfaces, even though the same'are less desirable, such other water paint comprising, for example, a mixture of sodium silicate (water glass) with whiting (natural calcium carbonate). If the proportion of whiting to sodium silicate be reduced to say one pound of whiting to the gallon of sodium silicate, the mixture sets too quickly to be satisfactorily sprayed. However, in those cases where a coating that is especially resistant to erosion by the swashing of salt water ballast is desired, the surfaces of the tanks after being coated with quick lime can be given a coat of sodium silicate whereby an insoluble coating of calcium silicate will be formed in situ on such metal surfaces, which coating. also possesses corrosion-inhibiting properties to a high degree, besides being as stated extremely resistant to the erosive action of ballast water.

While it isfar more satisfactory that the coating solution be projected upon the surface in the form of solid impact pressure jets, the coating may be atomized with air prior to its introduction into the supply pipe l and thence discharged through the nozzles 42 against the tank surfaces while thelatter are rotating in the man ner here- 1 in described. 5

In order that no objectionableclogging of the nozzles by the compounds suspended therein will occur and furthermore, in order that the momentum of the jets shall be sufficient to project the coating upon all surfaces of .a tank even as large as 30' square by 30' high, the nozzle apertures may desirably be of about A," in diameter and a nozzle pressure of fifty pounds per square inch may be employed. One advantage of a the delivery of solid impact jet of the coating solution upon the surfaces to be coated as distinguished from a mere atomized spray, such as obtainable by the employment of a gun sprayer, is the fact that the resultant c orrosion inhibiting coating produced on the metal surfaces when dry is very dense and has a much stronger bond, therefor, with the metal surfaces than otherwise would be the case, with the consequence that the coating is much more resistant to erosion by the swashing of saltwater ballast than would otherwise be the case.

As is apparent from the foregoing description of my improved method, it is feasible to project hot milk of lime, which is extremely corrosive to the human skin and hair, against the interior walls of tanks and to effectively coat the same without necessitating the presence of an operative within the tank, since the path of projection of the streams from the nozzles is mechanically changed by precise, predetermined increments of change. As a consequence, it is possible to preserve tankers and storage tanks against corrosion by a remarkably cheap and effective procedure and which protection, because of the high I in set forth may be made without departing from the spirit of my invention as embraced within the scope of the appended claims.

Having thus described my invention, what, I claim and desire to obtain by United States Let ters Patent is:

1. The method of preserving from corrosion the interior surfaces of metal tanks adapted to contain petroleum oils or distillates, which comprises applying to such surfaces a uniform corrosioninhibiting coating, which is substantially inert to petroleum oils or distillateg, by delivering to such surfaces, from a main body of a water suspension, which is substantially free from any organic binding agent, and whose solid content consists principally of a material selected from the group consisting of hydrates andcarbonates of alkaline earth metals, impact jets of such solution and while repeatedly effecting a uniform and predetermined change in direction of the impact paths of such jets upon such surfaces and con-' stantly removing from the tank bottom the surplus solution which drains off of the other surfaces of such tank and returning the same to the main body of coating solution for reuse in such.

coating operation.

2. The methdd of preserving from corrosion" the interior surfaces of metal tanks for the StO1'-,

- ing agent, and whose solid content consists principally of one or more members of a group consisting of the hydratesand carbonates of alkaline form change of direction of the paths of impact of such jets alongsuch surfaces and without substantially changing the zone of delivery of such jets into said tank.

3. The method of preserving the interior metal walls of tanks for the storing or transporting of petroleum oils or distillates against corrosion, which comprises causing milk of lime to impinge in the form of pressure impact jets against the surfaces of such walls, while effecting a predetermined and uniform change of direction of the paths of impact of such jets along such surfaces without substantially changing the'zone of delivery of such jets into said tank.

4. The method of preserving from corrosion, the interior surfaces of metal tanks for storing or transporting petroleum oils or distillates, which comprises directing against such surfaces pressure impact jets of a coating mixture comprising a water suspension, which is substantially free from any organic binding agent, and whose solid contents consist principally of one or more members of a group consisting of the hydrates and carbonates of the alkaline earth metals, which compound is substantially inert towards petroleum oils and distillates, while effecting, without manual manipulation from within the tank, a predetermined and uniform change of direction of the paths of impact of such jets upon such surfaces without substantially changing the zone of delivery of such jets into said tank or requiring the presence of an operative therein.

5. The method of preserving the interior metal surfaces of tanks for storing or transporting petroleum oils or distillates, which comprises delivering against such surface impact jets of a coating mixture comprising a water suspension, which is substantially free from any organic binding agent, and whose solid content consists essentially'of milk of lime and while simultaneously removing the used solution at a rate to maintain the bottom surface of such tank substantially bare of solution and in a condition to be coated by the same operation and during such coating operation effecting the repeated uniform change of direction of delivery of such jets so as to cause the same to successively impinge against different areas of such surfaces and to ultimately impinge against every portion thereof.

6. The method of preserving from corrosion,

the interior surfaces of metal tanks for storing or transporting petroleum oils or distillates, which comprises directing against such surfaces pressure impact jets of a coating mixture containing at least 10% of dissolved and suspended solids whichconsist principally of one or more members of a group consisting of the hydrates and carbonates of alkaline earth metals, which compound is substantially inert towards petroleum oils and distillates, while effecting, without manual manipulation from within the tank, a predetermined and uniform change of direction or the paths of'impact of such jets upon such surfaces without substantially changing the zone of delivery of such jets into said tank.

'7. The method of preserving the interior metal walls of tanks for the storing or transporting of petroleum oils or 'distillates against corrosion, which comprises causing milk of lime to impinge in the form of pressure impact jets against the surfaces of such walls, and then coating such surface with a coating consisting essentially of sodium silicate in solution, whereby through interaction of the two coatings so applied, a dense, hard gasoline and water resistant coating is produced on such surfaces.

8. The method of preserving against corrosion the interior metalwalls of tanks, which comprises causing the projection against the walls of said tank from moving nozzles disposed within such a tank of a mixture comprising a water suspension, which is substantially free from any organic binding agent, and whose solid content consists essentially of one or more members selected from the group consisting of hydrates and carbonates of alkaline earth metals, while mechanically changing the path of projection of the streams delivered by said nozzles by predetermined increments.

9. The method of preserving from corrosion the interior surfaces of metal tanks adapted to contain petroleum oils or distillates, which comprises applying to such surfaces a uniform corrosioninhibiting coating, which is substantially inert to petroleum oils or distillates, by delivering to such surfaces from a main body of salt water, containing a material selected from the group consisting of hydrates and carbonates of alkaline earth metals in suspension therein, impact jets of such solution and while repeatedly effecting a uniform and predetermined change in direction of the impact paths of such jets upon such surfaces and constantly removing from the tank bottom the surplus solution which drains off of the other surfaces of such tank and returning the same to the main body of coating solution for reuse in such coating operation.

10. The method of preserving from corrosion the interior surfaces of metal tanks adapted to contain petroleum oils or distillates, which comprises applying to such surfaces a uniform corrosion-inhibiting coating, which is substantially inert to petroleum oils or distillates, by delivering to such surfaces from a main body of salt water, containing calcium hydrate in suspension therein, impact jets of such solution and while repeatedly effecting a uniform and predetermined change in direction of the impact paths of such jets upon such surfaces and constantly removing from the tank bottom the surplus solution which drains off of the other surfaces of such tank and returning the same to the main body of coating solutionfor reuse in such coating operation.

11. The method of preserving the interior metal walls of tanks for the storing or transporting of petroleum oils or distillates against corrosion, which comprises causing a solution containing in suspension therein a material selected from the group of hydrates and carbonates of alkaline earth metals to impinge in the form of pressure impact jets against the surfaces of such walls, and then coating such surface with a coating consisting essentially of sodium silicate in solution, whereby through interaction of the two coatings so applied, a dense, hard gasoline and water resistant coating is produced on such surfaces.-

B. BUTIERWORTH.

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