US3180418A - Casing descaling method and apparatus - Google Patents

Description

April 27, 1965 N. A. MacLEoD CASING DESCALING METHOD AND APPARATUS 3 Sheets-Sheet l Filed Aug. 16, 1961 @alg April 27, 1965 N. A. MacLEQD 3,180,418

GASING DESCALING METHOD AND APPARATUS Filed Aug. 16, 1961 3 Sheets-Sheet 2 4 af andar/9k? www April 27,v 1965 N, A, MacLEOD 3,180,418

CASING DEscALING METHOD AND APPARATUS Filed Aug. 16. 1961 3 Sheets-Sheet 3 nited States Patent O 3,180,418 CASlNG DESCALDIG METHQD AND APPARATUS Norman A. lllaclleod, 1330 N. Fullerton Road, La Habra, Calif. Filed Aug. 16, 1961, Ser. No. ISLSIS i3 Claims. (Cl. 16o-43) The present invention is concerned generally with an improved method, system and apparatus for cleaning articles, or for removing scale, or similar foreign material, from the casing of a Water Well or oil Well, or from boiler tubes, tanks and the like.

The invention relates more particularly to an improved method, system and apparatus for performing the abovementioned cleaning and desea-ling functions by means of electrically produced shock Waves in a liquid.

A relatively small amount of energy is represented in' electrical spark discharges .under normal atmospheric conditions, such as those developed across the electrodes of an induction coil, or produced from a charged capacitor. This is because the resistance of the air in the path of the spark discharge drops to such a low value that the spark gap acts substantially as a short circuit.

The energy developed in any load, as is Well known, is expressed as the square of the current multiplied by the resistance of the load. Therefore, in order that a high energy spark may be developed, it is not enough for the activating potential to be high, but an appreciable resistance must .also be present in the discharge pat-h.

High energy spark discharges have been produced by immersing the electrical spark-producing equipment in Water. Then, an instant after the spark discharge is initiated, the path of the spark discharge is transformed into a volume of gas and .Water vapor expanding against the water. The inertia of the Water causes a build-up of the pressure which can be as high as 10,000 atmospheres. Y

VMost of the prior art underwater experiments have been made by discharging a capacitor into the electrical sparkproducing equipment, the capacitor having previously been charged to a potential level of the order of 2S kilovolts.I

Measurements in the prior art experiments show that the initial potential of the spark discharge absorbs power l of the order of 400 megawatts from the capacitor, and

that the current reaches a peak value of 85 kiloamps. The resulting shock wave propagated through the water is capable of exerting pressures up to 70 tons .per square inch.

The present invention provides a system and apparatus which is predicated upon the underwater spark discharge principles set vforth above, and which utilizes the tremendous shock Waves produced by electrical discharges under Water, or other iluid, for cleaning articles, descaling the casings of Wells, tanks or the like. The descaling operations particularly related to Wells have usually, heretofore, been carried out in the prior art by the use of explosives. The ultrasonic cleaning of articles in the prior art has usually been carried out by transducer-generated ultrasonic vibrations.

An important advantage of the present invention in its particular use in wells, therefore, is that, unlike many prior art systems, it does not require or use high explosives. The transportation and utilization of apparatus embodying the invention is not accompanied, therefore, by the usual hazards, regulations and inconveniences attendant to the use and transportation of high explosives to such wells.

Another important advantage of the present invention is that readily available electrical power sources can be used to produce the desired shock Waves in the liquid; and

ice

a convenient and flexible control is possible with respect to the duration, frequency and intensity of the shock Waves so that the desired degree of cleaning or descaling action can be obtained.

Another advantage of the invention is that the danger of structural damage to a thin well casing can be reduced to a minimum by carefully controlling the size and frequency of the electrically produced shock wave.

yThe present invention is predicated 1on the abovedescribed principles which demonstrate that when an electric cable, constructed to provide a relatively small elec,- tric spark discharge area within a liquid, is immersed in the liquid, and if a high voltage is applied to the cable, the resulting spark discharge which is initiated in the spark area in the liquid will set up an extremely powerful shock .wave in the liquid. In the practice of the invention, these shock Waves are used for descaling the surface of the casing containing the uid, or for general cleaning purposes, as will Abe described. When the liquid is water, the shook is extremely intense because of the rapid vaporization of the water by the rapid yrelease of energy in the electric spark discharge. As noted above, the spark discharge can be initiated by discharging a highly charged capacitor into the cable or other conductive system.-

As also mentioned above, it has been found that the use of a capacitor of the order of 10 microfarads, charged to a level of 20 kilov-olts, and then discharged into the submerged electrical system, produces an extremely powerful shock Nvave in the liquid. A series of shock waves can be produced by using a plurality of similar capacitors, and sequentially charging and discharging the capacitors into the cable.' This control may be such that any desired frequency and intens-ity may be obtained, within limits dictated .by factors such as the impedance of the electrical system.-

It is, accordingly, an object of the invention to provide an improved method, system and apparatus for general cleaning purposes, or for descaling the casing of an oil well or water well, -or for general desca'ling purposes in conjunction with the casings of boiler tubes, tan-ks and the like; and which method, system and apparatus does not require high explosives and their concomitant hazards, not only in handling above ground but in causing structural damage underground when used for this purpose.

A further object of the invention is to provide such an improved method, system and apparatus which is relatively simple to construct, and Which'utilizes relatively inexpensive and readily available components.

Yet another object is to provide such an improved method, system and apparatus which is subject to convenient and iiexible control to be effective for general cleaning or descaling purposes in a Wide variety of applications and conditions.

The concepts of the present invention also have general utility in the cleaning of articles. When the method, apparatus and system is utilized for descaling the casings of Wells, and the like, electric cable of from to 10,000 feet is involved with attendant electrical impedance. With such an application, the usual high impedance of the cable precludes the rapidl successive discharges of high energy into the cable, with the attendant rapid series of electrical discharges at the spark gap area.

However, in its general application, the concepts of the invention can be applied, as will be described, to the cleaning of articles, and in this general application a large number of electrodes may be provided in a relatively shallow bath. These electrodes may be positioned peripherally, or otherwise arranged to have a minimum length of lead, with corresponding minimum impedance, and the electrodes may be tired in rapid sequence,

For example, ultrasonic vibrations may be derived by provide a spark discharge.

' sulated electric cable having an inner copper or alumi- Y num conductor, for example, is used.

In such embodiments, the lower end of the inner conductor is exposedto m A heavy iexible outer sheath may be provided on the lower ten feet of the cable, for example, to prevent kinking. This sheath may be cornposed, for example, of lead, or woven steel wire. The

electric cable is lowered into the well whose casing is to be'. `descaled, andit may be raised or lowered'at will during the treatment.

When a high voltage is vintroduced between the upperk f end of the inner conductor in the cable and ground, a

spark discharge is initiated at the *exposedV extremityv of the conductor at the lower end o f the cable down in the liquid in the well. This lspark discharge sets up the desired shock Vwaves in Vthe liquid for des'caling purposes; f

VTo facilitate the initiation and rapid dischargeof the spark into the liquid at the sparking area,'and in accordance with the teaching of the present invention, a suitable concentration of colloidal graphite,` line metal powder, electrolytic solution, gas, or other suitable Vsubstance may be dispersed into the liquid at the sparking area, as willbe described. n Y

The other more general embodiment of the invention, in'which the shock waves are initiated at high speed from a low impedance electrode system within the liquid for' cleaning purposes, may also make use of suitable Subtus and system of one embodiment of the invention being usedinr conjunction with the casing of a well and includving an electric Acablewhich'is lowered down into the well;

FIGURE .2 is an enlarged fragmentary view, partly in section, of a portion ofthe embodiment shown in FIGURE l;k .Y .Y a fragmentary sectional'view showingVV a modification of the lower extremity of the cable usedv in theapparatus of FIGURES 1 and 2; Y

FIGURE k2A is FIGURE 3 is a representationV of a further embodiment v temV of the invention/being used to impact wet concrete.

The representation of FIGURE 1 shows a sectional view of a well 10 which may, for example, be an oil well, a water well, etc. ln accordance with the invention, an

Y insulated electric cablerl'Z is lowered down into the well.

As noted above, the ycable l2 includes an inner conductor V13 which may be composed, for example, of aluminum or copper.

The inner conductor 13 is surroundedV by an insulating sheath 15. However, the lower extremity 14 of the inner conductor is exposed, as best shown in FlGURE 2.

f The lower end` of the cable 12 may be enclosed by a sheath composed of lead, or wire mesh, for example, to prevent kinking as mentioned above. As shown in FIGURE 1, Ythe lower end of theA cable l2 has a helical A configuration, and Vit is composedof a viiexible-material.-V

This conliguration of ther lower end of the cable assures' propinquity to-one side of the casing of the lower extremity' of the cable. Then, the'cable may be rotated as it is lifted or lowered in the well to assure that adequate descaling shock wavesV will reach all portions of the casing.

VThe-well 10 includes V.atubular metal casing 16 which, in accordance' with usuat practice, is. perforated to permit the water, oil or other'liquid'to seep into the well. As is well known, afterl prolonged periods of time, scale and similar foreign material formon the inner'surface of the casing 16. It is the purpose and-intention of the present invention in one of its aspectsto provide an improvedl system and apparatus forV removing such scale and foreign material from the inner surface of the metal casing.

A control and energizing unitl l Vis coupled to the upper end of the cable l2. The cable is fedY out from the unit v l and down into'the well. When a descaling operation of the invention, and is a fragmentaryV sectional view of a portion of apparatus incorporating the further embodiment; 1. -Y i FIGURE fl is a fragmentary sectional View of yet another embodiment of theinvention; v

yFIGURE 5 is a fragmentary sectional view of a still further embodiment of the invention;

FIGURE 6 is a schematic block diagram of a suitable energizing system foi-'the cable used ,in the Vabove-mentioned embodiments ofthe invention;

' FIGURE 7 is a side sectional viewof a further embndii ment of the invention, in which the conceptsV cr ftheinfver1 tion are used'for general cleaning purposes; n,

FIGURES is a bottom view of the embodiment of FIG- URE 7;

FIGURE` is aschematic representation Yof an electrical. system suitable foruse in conjunctionwith the embodi-V ments of FIGURES 7 and 8;,and` FIGUREv 10 is a schematicrepresentation of thefnsys- Vis to be carried out, the unit l applies ahigh voltage between the upper end of the conductor 114 and ground.-

The unit l may be a portable unit and it may include,v for example, Ygenerators andV power packs supportedon a truck, or on any other appropriate vehicle. TheV unit l may also include a bank of capacitors which can be charged successively from the power pack and discharged Y into the cable T12.

it is preferable that highvoltages be used, since the use .of high voltages results in low line losses and permits a 'sr'nall rdiameter cable to be used.

The introduction of such a high voltage between the A Oxygen whichrecombine and condense, theresults of thisl actionbeing the generation of aY hard, single shock wave in Vthe liquid. This shock wave impinges on the inner sur# faces of the casing 16 for descaling purposes.

The discharge rate is limited bythe line impedance,- as-mentioned above. The de signmay beV such VthatV successiye discharges maybe made to occur at the lower eX- trernity 14 of the conductor i3, so that the desired descaling action can be continuously carried out as the cable is'lifted or lowered 'in the well, andas the cable is rotated so' as to bring the lower extremity la of'the'inner con. Vductor 13 adjacent diiferent portions ofthe inner surfaceA of the-casing 10V, Y

AThe resulting mechanical shocksxcan range, for example, up to 10,000 joules forwater wells, .and fnom 10,000 to 50,000 joules foroil wells. At,10,000 volts, and using Va 10 mie'rofarad .capaci-tor, 500 joules'can be produced.

Likewise, `when .the l0 Vrnicrofarad capacitor Vis' usedy '1,000 volts produces 75 joulesg 20,000jvolts` Yproduces 2,000 joules; and 50,000 lvolts produces,12,5001joules. lf a20 microfaradcapacitor isy used, V50,000 volts Vwill produce 25,000 joules; 10,000 joules. l

n For many Vapplications electricallyconductive ground cable 20 to be `suspended vand 100,000 volts willproduce 'n it is`-desirable for a ,ilex-ilnle,r

snsofiis from the lower end of the cable 12. The ground cable may be so suspended by a plurality of bulged flexible spring spacers 22. These spring spacers serve to hold the upper end of the ground cable Ztl in spaced relationship from the lower exposed extremity 14 of the conductor i3. The spring spacers 22 also serve to engage the adjacent surface of the casing i6 to prevent direct contact between the lower exposed extremity .le of the conductor 13 and the casing,

With the illustrated arrangement of FIGURES l and 2, a reproduceable, highly localized spark discharge may be produced in the gap between the lower exposed extremity 14 of the conductor 13 and the upper end of the ground cable 2Q.

Graphite, or other electrically conductive particles may be dispersed in the spark area, as will be described, to facilitate the initiation of the spark discharge in the gap, and to modify its characteristics. The use of the ground cable 2l) provides a xed ground distance for the gap, and enables the discharge characteristics of the system to be conveniently controlled.

The ground cable 2d can be formed to have its lower end denne a helical spiral starting, for example, about l2 inches below the top of the cable. The cable can be made resilient, and the diameter of the resulting helix can be normally slightly greater than the diameter of the casing. This contiguration of the ground cable will assure that it makes a good connection with the casing 16. This is most desirable in oil wells, for example, Where grounding conditions are not as satisfactory as in water wells.

When graphite particles are used for the above-described purpose, it should be noted that such particles have a negative coeilicient of electrical conductivity. That is, as is well known, the resistivity of graphite decreases with temperature rise. This provides a rapid unloading of energy by providing an optimum path between electrodes formed bythe shortest, most conductive, chain of particles between the electrodes.

When colloidal or tine metal powders are used for the above purposes, such particles will atect the discharge conditions by providing a chain of particles which form the shortest path of least resistance. As pointed out above, electrolytes or gases, or any combination of the above-mentioned substances, can be used for this purpose.

The fragmentary diagram of FIGURE 2 shows on an enlarged scale, the details of the various components of the system of FIGURE 1 adjacent the spark area. As clearly shown in FIGURE 2, the spacer springs 22 support the ground cable in a spaced relationship with the lower extremity of the conductor 14 to provide the desired spark gap. As noted above, the assembly can be designed and constructed so that a desired distance exists between the lower extremity of the conductor 14 and the upper end of the ground cable 20 to provide a spark gap of desired characteristics.

If so desired, the lower end of the insulating sheath of the cable 12 may be formed, in the manner shown in FIGURE 2A, to have an inverted cup-shaped conguration surrounding the lower extremity 14 of the conductor 13. This cup-shape of the insulating sheath provides a gas pocket around the spark gap to facilitate the initiation of the spark discharge.

As shown in FIGURE 3, the lower protruding extremity 14 of the inner conductor 13 of the cable 12 may be threaded to receive a metallic connector 30, and a graphite electrode 32 may be threaded into the lower end of the connector 3B. Likewise, the upper end of the exible ground cable 29 may be equipped with a metallic connector 34, and a second graphite electrode 36 may be threaded into the connector 34. The graphite electrodes 32 and 36 are supported in spaced relationship, as shown in FIGURE 3, and the resulting current ilow through the inner conductor I3 results in a spark discharge between the graphite electrodes. This creates a dispersion of graphite particles in the iluid in the vicinity of the spark gap which facilitates the initiation of successive electric spark discharges through the liquid.

In the embodiment of FIGURE 4, the flexible, electrically conductive ground cable has a chamber formed in its upper end, and this chamber communicates with the spark gap area through a passageway 42. A exible plastic container, or other appropriate container, filled with graphite particles in suspension in oil or Aquadag, for example, is positioned in the chamber 40. Then, the shock waves from each successive electric spark discharge across the spark gap, cause the container 40 to become compressed. This forces the container to dischargeV an amount of graphite particles into the liquid in the vicinity of the spark gap to facilitate the ipitiation of successive electric spark discharges. `As mentioned above, other appropriate metal particles in liquid suspension, or an electrolyte solution, may be used for this purpose.

In the embodiment of FIGURE 5, a tube 50 extends down the side of the insulating sheath 15 of the cable 12 from the upper surface, and the lower end of the tube 5t) extends into the upper end of the ground cable 20, as shown. A passageway 52 is formed in the ground cable, and the passageway extends up through the upper end of the ground cable. Under the control of apparatus at the surface, a measured amount of graphite, or other metallic particles, or other substances, can be sent down through the tube 5t) from a pressurized source 54 to be dispersed through the passageway 52 into the area of the spark discharge. These particles, as in the previous embodiments, facilitate the initiation of each of the spark discharges at the spark discharge area.

As mentioned above, the high voltage can be applied to the upper end of the cable 12 by charging a capacitor to a high voltage, and then by discharging the capacitor down into the cable. This charging and discharging of capacitors is, per se, known to the art. As also suggested, a plurality of capacitors can be used, so that a first bank may be discharging into the cable, while a second bank is being charged.

Suitable apparatus for applying the high voltage to the cable 12 is shown in schematic block form in FIG- URE 6. The apparatus of FIGURE 6 includes, for example, a direct current generator 6i) which produces a charging current for a capacitor 62. This direct current generator may, for example, include a transformer for stepping the normal volt A.C. voltage up to 25,006 volts A.C. and it may also include a suitable full-Wave rectilier for converting the alternating current voltage into the desired direct current charging voltage. Vacuum tube rectiers designed for high voltage applications are available, and may be used. For example, a diode manufactured by the Radio Corporation of America and designated 5 825 has an inverse peak Voltage xrating `of 60,000 volts, and is well suited for the present purposes.

A switching system A is controlled to connect the direct current generator di) to the capacitor assembly 62 to enable the capacitor assembly to be charged to the desired high potential level. Then, a switching system B introduces the high potential charge from the capacitor assembly between the upper end of the inner conductor 13 of the cable 12 and ground. As indicated by the dotted lines, the switching systems A and E are interlocked, so that when the switching system A connects the direct current generator 64) to the capacitor assembly- 62, the switching system B is open. Likewise, when the switching system B connects the capacitor assembly 62 to the cable 12, the switching system A is open.

As mentioned above, the concepts of the present invention can also be used in conjunction, for example, with a relatively shallow bath for creating ultrasonic vibrations in a liquid contained in the bath for cleaning articles immersed in the liquid. The resulting system is advantageous over the usual prior art ultrasonic systems using magnetostrictive or piezoelectric transducers, in that there is no energy bottleneck in the spark discharge type of ultrasonic vibration system, as there often is in the prior art systems.

A typical bath is shown, for example, in FIGURE 7. The illustrated bath is formed of a cylindrical-shaped metallic container u which has a closed bottom and an open top. The container 109 is grounded, so as to provide a return for the spark discharges initiated in the Water, 'or other liquid, contained in the container. In accordance with the invention, a plurality'of ground elect'rodes 102 are formed in the inner surface ofthe wall of the container 100. The electrodes Nimay extend, for example, directly around the periphery ofthe container.

As illustrated, the electrodes 102` are inclined from the inner surface of the container Wall. For example, the electrodes 102 can number 32 for an appropriate'practical embodiment. l I

Extending through the bottom 164 oi' the container 16% are a plurality of insulated cables 166. The insulated cables 106 extend through the bottom in insulated relationship therewith, and veach has an inner conductor 16S.

The inner end of each of the inner conductors 1i8`is ex-V posed, and is spaced from a similar conductor of respective'ones of the ground Velectrodes 102.

VThe inner conductors 10S of the cables 1% may be yconnected to an appropriate energizing source, and relatively 'short leads may be used so that cable impedance is reduced to a minimum. This permits the rapid energizing ofV the cables in succession to set up the desired Y.

l Vultrasonic vibrations in the liquid in the container 16.v

These vibrations may then serve to clean any article placed in the liquid Vin the container. Because ofV the muchY higher individual energy capability from each capacitor discharge, this-embodiment of the invention can also work eifectively in the sonic frequency range.

The energizing system forV the conductors 1% of the cables 1436 would include, for example, a capacitor for each Vof the cables. In the suggested arrangement of 32 electrodes, it would be possible to tire the electrodes successively atene-.tenth second intervals. This could be carried out by firing lthe electrodes in a staggered sequence to prevent adjacent after-effect interference. Forv example, the electrodes 1, 6, 1.1, 16, 21, 26, 31; Ii, 9, 1li, 19, 24, V29; 2, 7, 12, 17, 22, 27, 32; and so on couldbe sequentially fired. j..

f It is of course obvious that in thesequence ofiiring,

the number of electrodes in each successive tiringl must Y not be a factor of the totalnuniber Vof electrodes used. For instance, in using 32 electrodes, every 3rd, 5th, 7th, 11th, 13th, 17th,'l9th, 23rd, 29th, ctc., could be used,

It is evident thatV by increasing the number of electrodes and the rate ofL firing it would be possible to produce alfrequency in the ultrasonic range.

As noted above, an advantage of would setup interference of fthe shockwave so as to f produce a very intense and complicated vibrational pattern in theVV article being cleaned. v VA typical switching and energizing system forthe apparatuswof .FIGURES 7 and 8 is shown in FIGURES.

kThe switching Yand energizing system of FIGURE 9 may include adirect current generator 11i). This generator, as-was the `case with the generator d@ of FlGURE 6, Vmay include asuitable transformer and high voltage rectiier.A The resulting direct current voltagefrom the generator n Y the system of FIG-V URES 7 and 8 is'that there is no need for energy limitpulled.

1,10 is, applied to a commutator switching system 11?. l

which'is drivenV by an appropriate drive motor 114i. The commutator switching system A112 serves to connect the high voltage from the generator 11@ successively to `dif-.`

ferent ones of abank 116 of, capacitors.' The operation of the Vcommutating system 112 causes Vthe capacitorsin the bank 116 to be successively chargedv toa desired high.

voltage in each of asuccession of. recurrent cycles.`

tors of the bank 11d in aV phase displaced relationshipl from the commutating system 112. The commutating system 11S has a first arm 115A to contact the capacitors in bank 116, and also has a second Varm 118B which successively and cyclically Vengages a plurality of contacts in a bank 122. These latter contacts are connected to different ones of the inner conductors 16S of the cables of FIGURES ,A7 and 8.V Thus, the charge from each of the capacitors is delivered `tothe proper inner conductors w8. .Y

The comrnutating system 118 causes the charged capacitors-of the bank 116 to be successivelydischar'ged into selectedA ones of thercables Ido in a plurality of successivek cycles.- The connections from the conductors 108' of the cables 10o may be made ina predetermined pattern to the terminals of the bank'122, so that the above described sequence `of tiring may beV realized.

The improved system and apparatus of theinvention can further be used also, for example, for compacting gravelaround the casing of an oil or water well; and it can also be used, for example, to remove mill scale in metal rollingV mills. In general, the system and apparatus of the invention nds utility in applications where ultrasonic vibrationsare used for cleaning or descaling purposes. Y

A furtherapplication of the'system and apparatus of the invention, as shown in FIGURE 10, is in compacting wet concrete. In this latter application the apparatus can be removed from the concrete beforeV the concrete has completely hardened, or left abandoned in the concrete.

` In this application, for example, av series of discharge lines upl through the mass of concrete 156. These rods are at electrical ground potential. The cable 12 is clamped to vone of these rods Vby means of a clamp 154. Y The clamp provides a fixed spark dischargegap between the exposed end 14 of theV central conductor and theV adjacent grounded VreinforcingV 1 rod 152.

The resulting spark discharge between the end 14 and i the adjacent rod.152 in the'concreteY Vsets up the desired internal shock waves,l as described7 which perform Vthe impacting function. If the cable i2 is to be removed from the concrete, the clamp r154iV may be constructed to be capable.' of

The invention provides, therefore, an improved Vmeth-` od, system 4aind apparatus for Vdescaling casings .and for general cleaning purposes. As described` above, the apparatus serves to set up shock' Waves in a contained liquid, and these shock Waves `may be used to descale the Walls vof the. container, 'or for cleaning Varticles placed in the container. l Y.

The apparatus and system of theinventionV is advantageous in that no highV explosives are required, and in that'the required shock waves are electrically produced in a simple, Vstraightforward and easily controlled manner.

While particular embodiments of the invention have been shown and. described, modifications may be made,

Vand it is intended inthe claimsto cover all such modiiications as fall withinthescope ofthe invention.

What Vis claimed isz. l. 'Ihernethod of descaling acasing containing a liquid including? introducing anelectricpally conductive cable into `the liquid Vin the vicinity Aof the casing, and applying anV electric potential to the Vcable to producean electric sparkdischar'ge in thevicinity loi the casing and thereby set up'descaling shock'waves-in the liquid.VV

being torn apart when the cable is.

2. The method of descaling a casing containing a liquid including: introducing down into the liquid in the vicinity of the casing an electrical conductor having an insulating sheath with the lower extremity of said conductor pro truding through the sheath, and applying an electric potential to the conductor to produce an electric spark discharge at the lower extremity thereof in the vicinity of said casing, and thereby setting up descaling shock waves in said liquid.

3. The method of descaling a casing containing a liquid including: introducing an electrically conductive cable into the liquid in the vicinity of the casing, applying an electric potential to the cable to produce a localized electric spark discharge in the liquid in the vicinity of the casing and thereby set up descaling shock waves in the liquid, and introducing electrically conductive particles into the liquid in the area of the spark discharge to facilitate the initiation of the spark discharge.

4. Apparatus for descaling a casing containing a liquid including: an electrically conductive cable adapted to extend down into the liquid in the vicinity of the casing, said cable having an insulating sheath and having an inner electrical conductor with the lower extremity thereof protruding through the lower end of said sheath, means for applying a potential to said inner conductor to produce an electric spark discharge at the lower extremity thereof in the vicinity of the casing and thereby set up descaling shock waves in the liquid and which includes means for introducing electrically conductive particles into the liquid in the vicinity of the electric spark discharge to facilitate the initiation of the spark discharge.

5. Apparatus for descaling a casing containing a liquid including: an electrically conductive cable adapted to extend down into the liquid in the vicinity of the casing, said cable having an insulating sheath and having an inner electrical conductor with the lower extremity thereof protruding through the lower end of said sheath, an electrically conductive flexible ground cable adapted to be positioned in said liquid, bulged resilient spacing members secured to said iirst-named cable and to said ground cable for holding the lower end or said first-named cable and the upper end of said ground cable in spaced relationship and to prevent direct contact between the exposed lower extremity of said inner conductor and said casing, and means for applying a potential to said inner conductor to produce an electrical spark discharge between the exposed lower extremity of said inner conductor and the upper end of said ground cable in the vicinity of said casing and thereby set up descaling shock waves in the liquid.

6. The combination deined in claim and in which said ground cable includes a chamber therein and a passageway extending from the chamber to the upper end of said ground cable, and exible container means for supporting conductive particles in said chamber to be discharged through the passageway into the area between the exposed lower extremity of said inner conductor and the upper end of said ground cable so as to facilitate the initiation of the electrical spark discharge.

7. The combination dened in claim 5 and which includes tubular means extending down into the liquid and terminating at the area between the exposed lower extremity of said inner conductor and the upper end of said ground cable to introduce electrically conductive particles into said area so as to facilitate the initiation of the spark discharge.

8. The method of setting up vibrations in a casing containing a liquid including: introducing an electrically conductive cable having electrode means associated therewith down into the liquid, and applying an electric potential to the cable to produce an electric spark discharge at said electrode means in the liquid, and thereby set up shock waves in the liquid to be transmitted to the casing.

9. The method of setting up vibrations in a casing containing a liquid including: introducing down into the liquid an electric conductor having an insulating sheath with Cil dll

the lower extremity of said conductor protruding through said sheath, and applying an electric potential to the conductor to produce an electric spark discharge at the lower extremity thereof, and thereby set up shock waves in the liquid to be transmitted to the casing.

10. Apparatus for removing material from the surface of an article, which surface is in contact with a liquid, including: an electrically conductive element adapted to extend into the liquid and having a lirst electrode formed at the extremity thereof; electrically conductive means adapted to be positioned in the liquid for forming a sec ond electrode in spaced relationship with said irst elec trode so as to deiine a spark gap therebetween; means for introducing electrically conductive particles in the liquid in the area of the spark gap to facilitate the initiation of the spark discharge between said rst and second electrodes; and means for applying a potential across said lirst and second electrodes to produce an electrical spark discharge between said electrodes within said liquid to set up shock waves in the liquid for removing material from the surface of the article.

11. The method of removing material from the surface of an article, which surface is in contact with a liquid, which includes:

setting up a spark discharge in the liquid to produce shock waves therein for removing the material from the surface of the article, including the step ot introducing electrically conductive particles into the liquid in the area of the spark discharge to facilitate the initiation of the spark discharge.

12. The method of removing material from the surface of an article, which surface is in contact with a liquid, which includes:

setting up a spark discharge in the liquid to produce shock waves therein for removing the material from the surface of the article, including the step of introducing graphite particles into the liquid in the area of the spark discharge to facilitate the initiation of the spark discharge.

13. Apparatus for removing material from the surface of an article including:

a container adapted to hold a liquid into which the article may be immersed, a plurality of electrically conductive elements extending into the container, each having a first electrode formed at the extremity thereof, means forming a plurality of second electrodes within the container, one for each irst electrode in spaced relationship with said tirst electrode to form a spark gap therebetween, energizing means for applying a potential to said electrically conductive element to produce an electric spark discharge between said first and second electrodes to set up shock waves in the liquid for removing material from the surface of the article; and

means for controlling the energizing means to recurrently apply the potential across said pairs of electrodes in a sequential manner to produce a recurrent series of spark discharges between said pairs of electrodes so as to set up shock waves in the liquid `for removing material from the surface of the article.

References Cited by the Examiner UNITED STATES PATENTS 976,778 ll/l() Brown 313-232 XR 1,457,479 6/23 Wolcott 166-60 X 2,437,456 3/48 Bodine 166-43 2,559,227 7/51 Rieber 313-232 X 2,702,260 2/55 Massa 134-1 2,887,604 5/59 Bodine 313-232 2,946,217 7/60 Fruengel 313-232 X BENJAMIN HERSH, Primary Examiner.

CHARLES E. OCONNELL, CHARLES A. WILL MUTH, Examiners.

Claims (2)

1. THE METHOD OF DESCALING A CASING CONTAINING A LIQUID INCLUDING: INTRODUCING AN ELECTRICALLY CONDUCTIVE CABLE INTO THE LIQUID IN THE VICINITY OF THE CASING, AND APPLYING AN ELECTRIC POTENTIAL TO THE CABLE TO PRODUCE AN ELECTRIC SPARK DISCHARGE IN THE VICINITY OF THE CASING AND THEREBY SET UP DESCALING SHOCK WAVES IN THE LIQUID.

4. APPARATUS FOR DESCALING A CASING CONTAINING A LIQUID INCLUDING: AN ELECTRICALLY CONDUCTIVE CABLE ADAPTED TO EXTEND DOWN INTO THE LIQUID IN THE VICINITY OF THE CASING, SAID CABLE HAVING AN INSULATING SHEATH AND HAVING AN INLET ELECTRICAL CONDUCTOR WITH THE LOWER EXTREMITY THEREOF PROTRUDING THROUGH THE LOWER END OF SAID SHEATH, MEANS FOR APPLYING A POTENTIAL TO SAID INNER CONDUCTOR TO PRODUCE AN ELECTRIC SPARK DISCHARGE AT THE LOWER EXTREMITY THEREOF IN THE VICINITY OF THE CASING AND THEREBY SET UP DESCALING SHOCK WAVES IN THE LIQUID AND WHICH INCLUDES MEANS FOR INTRODUCING ELECTRICALLY CONDUCTIVE PARTICLES INTO THE LIQUID IN THE VICINITY OF THE ELECTRIC SPARK DISCHARGE TO FACILITATE THE INITIATION OF THE SPARK DISHARGE.

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