US2655218A - Equipment for treating wells - Google Patents

Description

Oct. 13, 1953 R. CRAIN 2,655,218

7 EQUIPMENT FOR TREATING WELLS Filed June 3, 1949 4 Sheets-Sheet l ATfoRuEYi Filed June 3, 1949 Oct. 13,1953 R. L. CRAIN 2,655,218 EQUIPMENT FOR TREATING WELLS '4 Sheets-Sheet 2 ATTOR N EY$ Filed June 5', 1949 Oct. 13, 1953 R. L. CRAIN 2,655,213

EQUIPMENT FOR TREATING WELLS 4 Sheets-Sheet 3 Ewe/2:5. 6M1,

ATTOR N EYJ Oct. 13, 1953 R. L. CRAlN EQUIPMENT F OR TREATING WELLS 4 Sheets-Sheet 4 Filed June 5, 1949 mmmw wvv'vvvvww vvvvwww l/Ill!ka fi522:. a!adv1//IIIIIIIIIIIIIQIII% a! 4 INVENTOR.

Z6 Z- 5742' BY @YM) Patented Oct. 13, 1953 EQUIPMENT FOR TREATING WELLS Robert L. Grain, Houston, Tex., assignor to Gray Tool Company, Houston, Tex., a corporation of Texas Application June 3, 1949, Serial No. 96,941

8 Claims.

The present invention relates to equipment for permitting the introduction of anti-corrosion inhibitors into the stream of oil being discharged from the well without interfering with, limiting, or complicating the operations normally performed on a well, and while providing for the essential control of the well by the use of the various temporary and permanent seals now used on the well during the performance of the various operations in drilling and completing the Well.

In the flowing of oil wells, it is well-known that deposits of paraflin and the like in the well tubing reduce the efiiciency of flow therefrom. Various method and apparatus for cleaning the well have been devised, and methods are known whereby solvents, acids and other chemicals are introduced into the well tubing to eliminate the undesirable deposits.

Up to the present time, the equipment employed for such practices has not been satisfactory because it has introduced complications in the structure, particularly at the well head, which complications have made difllcult the performance of the normal operations in drilling and completing the well. The equipment heretofore used has also introduced complications making it more diificult to provide that necessary mechanical control of the well which is essential to insure preservation of life and property.

Details of the objects and advantages of the invention referred to above, and the nature of other objects and advantages of the invention will be apparent as the specification progresses.

Figures 1 through 9 are side elevational views of the equipment at and adjacent the top of the well, partly in section, showing the various stages of the operations involved in introducing the equipment of the present invention into the well, for the purposes stated, while permitting the usual operations incident to the completion of the well and providing the mechanical control which is recognized as being necessary in present day practices.

Figure 10 is an enlarged sectional view of the equipment at the well head and adjacent thereto showing the arrangement of the parts when the equipment of the present invention has been installed, and with the well in condition for flowmg,

Figures 11 and 12 are detail views showing respectively the lower collector coupling of the invention and the stuffing box coupling for adjacent sections of the relatively small pipe used to deliver the treating fluid into the well,

Figure 13 is a horizontal sectional view through a special type of blow-out preventer which may be usefully employed in connection with the present invention.

It will be understood that while the equipment disclosed herein is employed for purposes of introducing an inhibitor fluid into the well, the equipment may be usefully employed for other purposes where the same double conduit arrangement may be utilized.

Referring to Figures 1 through 9, the well head equipment disclosed is of the general type described in considerable detail in the patent to Smith et al., No. 2,148,327 of February 21, 1939, comprising the casing l0, lower casing head l2, the hanger l4 for the inner casing l6, and the upper casing or tubing head [8.

The present invention is adapted to cooperate with this well-known equipment just referred to in such manner that flow tubing equipped with apparatus of the present invention may be introduced into the well, and suspended and locked in the tubing head l8, after which the control equipment used during the completion operationsmay be removed. The control equipment is shown as including a master drilling valve 20 of conventional type, a blow-out preventer 22 of conventional type and a blow-out preventer 24 of special construction, as hereinafter described.

It will also be understood that the practice of completing the well at the stage where the Christmas tree is landed on the tubing head is generally similar to that disclosed in the patent to Yancey No. 2,241,288 of May 6, 1941.

In Figure 1, tubing 30 is shown being lowered into the well through the control equipment. At this stage, all strings of casing will have been previously set, and the control equipment shown is that of size adapted for the tubing inserting and allied operations. If a non-retrievable packer is used, it will already have been set at this stage, and the bottom joint of the tubing 38 would be adapted to pass into the packer and open the back pressure valve'therein. As an alternative, an ordinary retrievable hook wall packer may be passed into the well on the bottom section of tubing 30, but these packer-devices and their operation form no part of the invention.

In the upper part of Figure 1, equipment of the present invention is shown ready tobe introduced into the control equipment during the first step of completion of the well, there being a lower collector coupling 32 connected'into the tubing between its bottom section 30 and its next adjacent section above numbered 34. The lower collector coupling provides for the introduction of the treating fluid into the lower end of the flow tubing, the treating fluid being supplied by a separate and smaller pipe line, the lower section of which is shown at 36.

It will be apparent from the preliminary description just made that the apparatus provides for introducing the treating fluid into the flow tubing adjacent the lower end of the latter so that the treating fluid passes upwardly with the flow of oil, acting all the while to prevent the accumulation of paraifin and the like in the flow tubing. Obviously, the introduction of the separate pipe section 36 into the well assembly raises complications which must be overcome by the equipment in order to permit the necessary well completion operations with control.

The lower collector coupling is shown in detail in Figure 11. It has upper and lower threaded sockets to rigidly connect with the ends of the tubing sections 30 and 34, and it has a fluid way therethrough comprising the vertical portion 40 and the lateral port 42, the latter, entering the interior of the coupling, thereby providing for the delivery of the treating fluid into the tubing adjacent the lower end thereof. The passages 48 and 42 are separated by a valve seat as shown, and this seat is normallyengaged by a ball valve member 44 which is arranged to be caused to engage its seat by pressure from the interior of the tubing, whereby this valve member normally prevents escape of oil from the well upwardly through the small pipe section 36 while permitting downward flow of fluid under pump pressure through the smaller pipe section 36 in order that the inhibitor chemical can be introduced into the flowing stream of oil passing upwardly through the tubing.

In Figure 2, the lower collector coupling 32 is shown as having arrived at a point below the upper end of the casing it, it being understood that alternate sections of the flow tubing and of the smaller treating pipe will be attached or coupled to one another in a conventional manner and lowered into the well. The smaller pipe for the inhibitor fluid is attached to the tubing at spaced points by suitable straps or brackets 48. During the making up of the tubing, as just referred to, and the insertion of same into the well, the blowout preventor 22 may be closed at any time around the larger tubing by simply lowering the tubing to an extent where the upper end of the last section of the smaller pipe attached would be below the shoes of the blow-out preventor 22, at which time the latter could be closed around the larger section of tubing.

As an alternative to the above, a special blowout preventor 24 may be used having shoes of special design, as shown in Figure 13. The opposite shoes of this blow-out preventor are shown at 49 and 50, and each shoe has a large opening 52 and a relatively smaller opening 54, whereby these shoes may grip around and seal against the exterior of the large tubing and the smaller pipe carried by the larger tubing, forming a seal as is well-known in connection with the construction and operation of such blow-out preventors.

The shoes of this blow-out preventor may be moved from and toward one another in any wellknown manner, either by fluid power or by mechanical power, as is well-known in the art, a conventional arrangement for the application of mechanical power being indicated in Figure 13.

In Figure 3, the apparatus is shown in tha condition wherein the lower end of the tubing has almost reached its final position adjacent the bottom of the well, and at this time, a special temporary hanger W of the wrap-around type may be applied to the large and small parallel pipes. This type of hanger is of a construction well-known in the art, comprising two half sections which are applied against one another around the pipe and lowered into the seat of the casing or tubing head Hi, this wrap-around hanger or blow-out preventor being of such size as to be capable of being lowered through the control equipment to the seat in the tubing head 18, where the hanger or preventor is locked in place by the conventional locking screws G0 as shown in Figure 4. The general arrangement of the half sections of this wrap-around device is illustrated in Figure 7. The two sections are provided with exterior packing iii to seal in the bowl of the tubing head and also with interior packing 62 to seal around the pipes on which the device is carried. The inner meeting faces of the two sections are provided with respective large and small aligned semi-cylindrical grooves 62, 63 which receive and seal around the large and small pipes respectively. The device has a circular groove 64 on its exterior wall as shown in Figure 3 to receive the inner ends of the locking screws 60 when the wrap-around device is landed in the bowl of the tubing head.

Referring again to Figure 3, the upper end of the tubing is provided with a collar 66 and a short nipple Bil to which is attached a back pressure valve assembly Til, the latter being in turn connected with a conventional landing joint of tubing 12. The back pressure valve assembly lii is only generally indicated, but it will be understood that this assembly is a special collar in the tubin with interior threads to removably receive a back pressure valve arrangement as shown in Figure 5 of the said Smith Patent No. 2,148,327. In that patent, a special collar is shown at 62 connecting the tubing and the hanger 74, and it will be understood that in the present invention, the as sembly Ill constitutes such a special collar threaded interiorly to connect with the landing joint 12 and the short nipple 6B, and is further provided with interior threads to remcvably carry the back pressure valve in the manner shown in Figure 5 of the said Smith et al. patent.

At this point, the string of pipe 36 may be reduced in diameter, for instance, from one inch size to one-half inch size by means of a special steel bushing which adapts the smaller section 36 to the larger section of this pipe.

When the wrap-around device and the back pressure valve are lowered through the control equipment and landed, as shown in Figure 4, the lift nipple i2 is removed, and the well being sealed both in and around the tubing, the control equipment may then be removed leaving the well in condition illustrated in the lower part of Figure 5, the locking screws 68 in the head 18 serving to hold the wrap-around device in its seat, the upper end of said device being engaged by the tubing collar 66 whereby the tubing is properly suspended and sealed in the head i8.

A special well head or Christmas tree assembly indicated generally by the letter C in Figure 5 is then made up as a unit and connected to the upper end of a short sub of pipe 82 which may, for example, be approximately six feet in length. In a manner to be hereinafter described, and upon removal of the wrap-around device W. this assembly 0 is lowered into and onto the well head equipment in a manner generally similar to the procedure described in the said Yancey Patent 2,241,288 in order to complete the well with all of the advantages described in said patent, but the assembly is of modified and improved construction as illustrated in Figure 10, in order to provide for the particular practices of the invention.

The assembly is best illustrated in Figure 10 which shows the condition of the equipment after completion of the well.

An upper collector coupling is shown at 84, same being connected into the tubing at the upper end of the sub 82. The coupling 84 has a somewhat restricted bore 86' threaded at its upper end as at 88 to receive the short interior tubing section 90, and it is threaded at its lower end as at 92 to receive the threaded upper end of the tubing section 82. The coupling is chambered above its restriction as at 94, and this enlarged portion is interiorly threaded to connect with the relatively large outer section of tubing 85 which constitutes a slick joint capable of adjustment through the permanent tubing hanger in a manner hereinafter described. The coupling 84 has a vertical fluid way Iflil therethrough in order to establish communication for the inhibitor fluid on the inside of the slick joint 96 to the small pipe 36'.

The upper end of the slick joint passes through the stufling box of the permanent hanger S, which is of construction the same as described in the said Yancey patent with respect to the hanger S of that patent, i. e., a stuffing box hanger adapted to be mounted on tubing and landed through control equipment into the tubing head, but permitting adjustment of the tubing therethrough to permit operations in the well as described in said Yancey patent. The upper end of the slick joint 96 is threaded as at I82 into the lower end of a flanged well head fitting I84 provided with a suitable inlet I86 and valve I28 for controlling the inlet of the inhibitor fluid. The fitting I04 is further provided with a stuffing box I89 to receive the upper end of the inner joint of tubing 98, and there is a flanged adaptor IIEl mounted above the fitting I94 on which the valve I I2 of the Christmas tree is carried, said valve corresponding with Christmas tree valve 64 of Figure 5 of the said Yancey Patent 2,241,288.

With the construction as shown in Figure and with the equipment landed and secured in the manner hereinafter described, it will be understood that the inhibitor liquid or chemical may be introduced into the well through the valve I08 and downwardly through the hollow space H4 in the fitting I04, thence downwardly through the space between the inside of the slick joint 96 and the outside of the tubing section 92, through the passage I GO in the upper collector coupling 84 and thence downwardly through the smaller pipe sections 36' and 36 for the treating fluid, the treating fluid discharging inwardly into the lower end of the tubing 34 via the passages 40 and 42 in the lower collector coupling; as shown in Figure 11. With this construction, the reagent being used to prevent accumulation of paraflin and the like in the tubing will join with the upward flow of oil through the tubing and will be carried upwardly by the natural flow of oil from the well.

Referring now to Figure 5, and with the assembly C made up and suspended from the Kelly joint K as shown, back pressure valve I0 may be tested to determine if the tubing has accumu-- lated pressure from the bottom of the well. it has, the sub 82 is connected into the upper end of the back pressure valve 10, and the pumps are operated and mud is circulated until such time as the pressure within the tubing is safely balanced. The short section of pipe 83 and the back pressure valve assembly III may then be removed, and the assembly C lowered to connect the pipe section 82 into the collar 66, as shown in Figure 6, and the parts are then made up permanently with the lower end of the passage I60 in the upper collector coupling 84 (Figure 10) positioned in alignment with the treating pipe section 36, a coupling II6 being used in the small pipe sections 35' to finally make up that smaller pipe and permit its connection into the lower end of the passage I88 in the lower collector coupling 84. Suitable clamps H8 are utilizedto secure the smaller pipe sections 38 onto that portion of the flow tubing designated as 82. Clamps II8 are placed above and below the coupling I I6 to prevent the smaller string of pipe from parting under pressure.

After determining by test that there is no dangerous pressure within the casing I6, the locking screws 60 in the tubing head may be retracted and the wrap-around blow-out preventor W may then be removed, as shown in Figure '7, and thereafter the entire assembly is lowered into the well, as illustrated in Figure 8. During this lowering operation, the upper collector coupling passes into the well, and the stufling box hanger S is landed and locked in the tubing head I 8, and the tubing may be adjusted through this hanger in the manner described in the said Yancey Patent 2,241,288 in connection with any washing operations, while permitting the lower flanged end of the fitting I 04 to ultimately rest on and be bolted to the upper flange of the tubing head I8 as shown in Figure 9. Thereafter, the Kelly joint may be removed from above the Christmas tree master manifold control valve I I2, and any desired control valves or fittings forming a further part of the Christmas tree may then be connected above the said valve I I2 as shown in Figure 9 where an arrangement of valves and choke manifolds is shown.

The details of the stuffing box coupling H6 are shown in Figure 12, comprising an enlarged tubular member I20 connected by a collar to the lower section of pipe and being adapted to slidably receive the lower end of the upper section of :pipe therein with a suitable stuifing box ar-" rangement being provided at the upper end of the member I20 including packing which may be tightened by adjustment of the threaded cap I22 carried on the upper end of the member I28.

It will be understood that when the equipment is in the condition shown in Figure 8, with the hanger S seated and locked in the tubing head I8, and with the master manifold control valve I I2 and the Kelly K connected as shown, any washing and packer setting operations may be carried out, and the tubing strings may be raised, lowered or rotated, as desired.

With the above construction, it will be understood that the well may be completedin the general manner described in the said Smith Patent 2,148,327 and the said Yancey Patent 2,241,288, with the special equipment described and particularly illustrated in Figure 10 installed during the normal completion operations and with the well under control as described, the various necessary steps in completing the well as described in the saidpatents being capable of being performed even though this special equipment as described is introduced. With the well completed, the inhibitor chemical may be introduced downwardly through the smaller pipe sections 36 and 35', this chemical entering the tubing through the lower collector coupling and passing upwardly through the tubing with the normal flow of oil to accomplish the purposes for which the special equipment is intended. It will further be apparent that the completed well is in such condition that the control equipment may again be re-installed, after completion, to accomplish any of the operations subsequent to completion as are referred to in the said patents.

It will be understood that certain of the equipment only generally disclosed herein is now wellknown in the art. For instance, the casing hanger l4 illustrated in Figure 10 is generally of the type disclosed in the patent to Roye, 2,207,469, July 9, 1940, in that it is a double tapered hanger provided with slip suspension means, it also being generally indicated that this hanger may be provided with interior packing to seal around the casing. Oi course, various types of casing hangers might be employed in the well head wherein the practices of this invention are carried out.

While the fittings mounted on the well head such as 104 are of special design, it will be obvious that they may be considered as special parts of the Christmas tree in that they are assembled with the Christmas tree manifold valve HZ as shown in Figure 5 and thereafter ultimately landed on the casing or tubing head i 5 after the control equipment is removed.

It will be apparent that the circulating system for the treating fluid comprises an upper conduit portion constituted by the space between the outer wall of the tubing 90 and the inner wall of the larger tubing 96 (Figure and a lower portion constituted by the relatively small pipes 35 and 36' carried in parallel relationship along the length of the tubing proper.

The terminology used in the specification is for the purpose of description and not limitation, the scope of the invention being defined by the claims.

I claim:

1. Oil well apparatus of the character described for use in an oil well having a casing and oil well flow tubing therein, comprising: an upper coupling in the casing having a first fluid way therethrough communicating with the upper end of the flow tubing and also having a second separate fluid way therethrough non-communicating with the flow tubing, a pipe section smaller than the flow tubing and having means for attachment to said coupling for communication with said second separate fluid way to convey treating fluid therefrom to the bottom of the flow tubing, well head equipment comprising a fitting having an outlet for discharging oil from the flow tubing and an inlet for receiving the treating fluid, and a pair of tubes arranged one within the other and connected between said coupling and said fitting, providing conduits separate from one another, one of said conduits extending between said inlet and said second separate fluid way and the other of said conduits extending between said outlet and the first fluid way communicating with the flow tubing.

2-. Oil wall apparatus of the character described for use in an oil well having a casing and oil well flow tubing therein, comprising; a casing head, a hanger seat in said head, an

upper coupling having a first fluid way there--- through communicating with the upper end of the flow tubing and also having a second separate fluid way therethrough non-communicating with the flow tubing, a pipe smaller than the flow tubing connected to said coupling and communicating with said second separate fluid way therein to circulate treating fluid in the well, a pair of tubes arranged one within the other and connected to said coupling to extend upwardly therefrom providing an inner conduit leading from the interior of the flow tubing and an outer conduit between said tubes communicating with said second separate fluid way, a hanger mounted on the exterior of the said outer tube and adapted to he landed in said seat to seal oiT the upper end of the well casing, and a Christmas tree mounted on said casing head comprising a fitting having separate means to seal off around the upper ends of said tubes, said fitting having an inlet communicating with said outer conduit and an outlet communicating with said inner conduit.

3. Oil well apparatus of the character described ior use in an oil well havin a casing, a casing head, and oil well flow tubing therein, comprising; a Christmas tree having a hollow fitting for mounting on the casing head and provided with an inlet to and an outlet from its hollow interior, a pair of tubes arranged one within the other providing an inner conduit within said inner tube and an outer conduit between said tubes, said fitting having means to seal off around the upper ends of said tubes and to secure the same in dependent relationship therefrom with said inlet communicating with said outer conduit and said outlet communicating with said inner conduit, and a coupling carried at the lower ends of said tubes and adapted to be secured to the upper end of the flow tubing, said coupling having a first fluid way therethrough communicating said inner conduit with the flow tubing and a second fluid way therethrough non-communicating with said flow tubing, a pipe section smaller than the well tubing tachment of control valves and the like to said side and top openings, a pair of tubes arranged one within the other providing an inner conduit and an outer conduit between said tubes, said fitting having means adjacent its bottom opening to seal off with the upper end of said outer tube to establish communication for flow of fluid between said outer conduit and said side opening, said inner tube extending upwardly through the interior of said fitting and having means to seal ofi its upper end in said top opening to establish separate communication for flow of fluid from said inner conduit through said top opening, and a coupling carried at the lower ends of said tubes and adapted to be connected to the upper end of the flow tubing, said coupling having a first fluid way therein communicating said inner conduit with the well tubing and a second fluid way therein, and a pipe section connected to said coupling in dependent relationship therefrom and in communication with said outer conduit through said second fluid way for circulation of treating fluid through the well.

5. Oil well apparatus for circulating a treating fluid in a well having a well head, a casing, and oil well flow tubing therein, comprising; a separate conduit to circulate the treating fluid into the flow tubing in said well through the lower end thereof, a lower portion of said conduit formed of sections of pipe smaller than the flow tubing with means to connect these sections to one another and to the outside of the flow tubing extending in parallel relationship therewith, and an upper portion of said conduit formed of a tubing larger than the flow tubing which is adapted to be positioned in surrounding relationship with respect to the upper end of the flow tubing, a hollow coupling adapted to be connected in the flow tubing and having a second separate fluid way extending therethrough in non-communication with said flow tubing, said coupling having means for attachment thereto of the uppermost of said smaller pipe sections and the lower end of said larger tube and both being in communication with each other through said second fluid way, and a Christmas tree on the well head having separate flow openings therein, means on said Christmas tree to seal off between the upper ends of said flow tubing and said larger tube and the surrounding Christmas tree wall, one of said separate flow openings being in communication with said flow tubing and the other of said flow openings being in communication with" the conduit between said flow tubing and said larger tube.

6. Oil well apparatus of the character described for use in an oil well having a casing and oil well flow tubing therein, comprising; a casing head having a hanger seat therein, a Christmas tree mounted on said casing head, a pair of tubes arranged one within the other providing an inner conduit and an outer conduit between said tubes, said tubes being attached to and depending from said Christmas tree through said casing head, said Christmas tree having a pair of flow openings therein, means to seal off the upper end of the outer of said tubes in communicating relationship with one of said openings and to seal oil the upper end of the inner of said tubes in communicating relationship with the other of said openings, a coupling having a first fluid way extending therethrough communicating the inner conduit with the flow tubing and having a second separate fluid way therethrough connecting the outer conduit with a separate piping system extending down into the well, said outer of said tubes having a polished exterior with a hanger mounted thereon adapted to he landed in said hanger seat, said hanger having a stuffing box therein surrounding the polished portion of said outer of said tubes whereby the flow tubing may be vertically adjusted in the performance of operations incident to the completion of the well.

7. Oil well apparatus of the character described for an oil well having a casing and an oil well fiow tubing therein, comprising; a casing head having a hanger seat therein, a, Christmas tree mounted on said head and having a. pair of flow openings with flow lines extending therefrom, a pair of tubes depending from said Christmas tree and arranged one within the other forming inner and outer flow conduits, said Christmas tree having means to seal off around the upper end of each of said tubes to establish separate channels of flow between one of said openings and one of said conduits and the other of said openings and the other of said conduits. and a hollow coupling carried at the lower ends of said tubes having means for attachment to the flow tubing to establish communication for flow between the upper end of said flow tubing and said inner flow conduit, said coupling having a second separate fluid way therethrough in non-communication with said flow tubing and in communication with said outer flow conduit, means connected to said coupling and in communication with said second separate fluid way therein for establishing communication 01 flow between said second separate fluid way and the lower end of the flow tubing.

8. 011 well apparatus of the character described for use in an oil well having a casing and oil well flow tubing therein, comprising; a lower coupling attached to the flow tubing adjacent the lower end thereof and having a fluid way extending therethrough in communication with the flow tubing, said coupling having a second fluid way therein with a separate inlet which communicates with said flrst fluid way for injection of treating fluid into the flow tubing, an upper coupling for attachment in the flow tubing adjacent the upper end thereof and having a first fluid way therethrough communicating with the flow tubing, said upper coupling having a second fluid way therethrough non-communicating with said first fluid way for downward passage of the treating fluid, a pipe section smaller than the flow tubing having means for attaching the same to the outer wall of the flow tubing and for connecting the same to said upper and lower couplings to establish communication between the respective second fluid ways of each, and well head equipment comprising a well head having a hanger seat therein, a hanger supported in said hanger seat above said upper coupling to seal off the upper end of the well casing, said well head equipment having means providing a conduit connected to the upper coupling for upward passage of oil from the flow tubing and a separate conduit extending from above said hanger to the second fluid way in said upper coupling to convey the treating fluid downwardly into said pipe section.

ROBERT L. CRADT.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 404,397 Geiser June 4, 1889 1,500,400 Larsen July 8, 1924 1,944,573 Raymond et al. Jan. 23, 1934 2,148,327 Smith et al. Feb. 21, 1939 2,177,164 Baash Oct. 24, 1939 2,207,469 Roye July 9, 1940 2,241,288 Yancey May 6, 1941 2,241,333 Smith May 6, 1941 2,244,684 Foran June 10, 1941 2,247,023 Humason et al June 24, 1941 2,293,442 Montgomery Aug. 18, 1942 2,335,355 Penick et a1 Nov. 30, 1943 2,445,249 Sproull July 13, 1948

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