US2178141A

US2178141A - Method for straightening oil-well casings or the like

Info

Publication number: US2178141A
Application number: US156289A
Authority: US
Inventors: William M Frame
Original assignee: Nat Supply Co
Current assignee: National Supply Co
Priority date: 1937-07-29
Filing date: 1937-07-29
Publication date: 1939-10-31
Anticipated expiration: 1956-10-31

Description

W. M. FRAME Oct. 31, 1939.

METHOD FOR STRAIGHTENING OIL-WELL CASINGS OR THE LIKE Filed July 29, 1957 4 Sheets-Sheet l INVENIOR.

BY @nmfb uewwv 4 M A 0 ATTORNEYS.

W i TNESSES Oct. 31, 1939. w F M v 2,178,141

METHOD FOR STRAIGHTENING OIL-WELL CASINGS OR THE LIKE Filed July 29, 1957 4 Sheets-Sheet 2 k; ATTORNEYS.

Oct. 31, 1939. w, M 2,178,141

METHOD FOR STRAIGHTENING OIL-WELL CASING S OR THE LIKE Filed July 29, 1937 4 Sheets-Sheet 3 W I TNESSES: INVENTOR- LLG ATTORNEYS.

Patented Oct. 31 1939 UNITED STATES PATENT OFFICE METHOD FOR STRAIGHTENING OIL-WELL CASINGS OR THE LIKE Application July 29, 1937, Serial No. 156,289

11 Claims. (Cl. 29-156) The invention relates to methods of cold- 10 used prior to my invention, well casing has certain characteristics that materially lessen its resistance to collapse, which is quite undesirable because one of the prime requisites of casing for the deep wells that are now being drilled is that 1') it possess a satisfactory high resistance to collapse.

Well casing has been cold-straightened largely, if not entirely, by one or the other of two forms of straightening apparatus, one a cross-roll 20 straightener used extensively, if not exclusively, for the straightening of seamless well casing, and the other a die-pressing straightener used to some extent for the cold-straightening of electrically welded casing.

25 In the operation of a cross-roll straightener, casing is rotated about its axis and fed forwardly by pairs of cross-rolls, and is concurrently and progressively deflected transversely of its, axis by a pressure roll or rolls positioned between the 30 pairs of cross-rolls. I have found that this action of cross-roll straighteners results in the formation of residual compression stresses in the inner and residual tension stresses in the outer wall fibers of well casing. That such peculiar 35 residual stresses diminish the resistance of casing to collapse appears from a consideration of the stresses to which casing is subjected when under external fluid pressure in awell. It'is known that when a hollow. cylinder is subjected to external fluid pressure-the compressive stress is greater in the inner than in the outer fibers of the wall. casing are under residual compressive stresses, as are those of easing which has passed through a cross-roll straightener, and when the casing is subjected to externally applied fluid pressure such as encountered in a well, the compressive stress due to the applied had is added to the residual inner compressive stress with the result 50 that collapse of the casing occurs at a lower applied load than if no residual stress were present in a casing which was otherwise the same.

Aside from these residual stresses being unfavorable and prejudicial for the reasons just ex- 55 plai'ned, they are objectionable because they are Also, when the inside fibers of well frequently not uniform around the circumference of easing. Due to variations in the structure of commercial steel, variations in wall thickness and other dimensions of easing arising from manufacturing methods, and also to other causes, 5 the residual tension or compression, or both, may so vary circumferentially of casing, and with relation to each other, that they distort the casing from its desiredcylindrical form when subjected to cross-roll straightening. By reason of such distortion, as well as by reason of its unfavorable residual stresses, the resistance to collapse of casing which has passed through a crossroll straightener is materially lowered. 4

Die-pressing straighteners, mentioned above, comprise two cooperating dies, each provided with a casing-engaging cylindrical groove of about 180 degrees, and mounted for relative lateral reciprocation to and from a casing to plastically compress it, the casing being fed longitudinally into these dies without rotating it on its axis between pressing operations. By testing casing that has been so die pressed, I have found that the metal was not uniformly cold worked throughout the circumference of the casing. The cold working was greatest in the portions of the casings that were at and adjacent to the lines of joinder of the two-part dies, and at least in the portions of the casing that were at and adjacent to the medial portions or valleys of the dies. For 80 example, impact tests on specimens out from the first-mentioned portions of such casing, namely, those that were at the lines of joinder of the dies when the casing was compressed, showed impact resistances materially below those of specimens cut from the second-mentioned portions of the casing, which is another way of stating that the portions of the casing at and adjacent to the lines of joinder of the dies had less ductility than the portions at and adjacent to the valleys of the dies;

While this variation in ductility is objectionable in itself, particularly when the portions of the casing at and adjacent to the lines of joinder of the dies is so brittle that the casing may break under service conditions, the residual stresses in the casing arising from the non-uniform plastic flow of its metal are particularly objectionable because they ultimately result in a distortion of the casing to such out-of-roundness as to mate- 5o rially lessen its resistance to collapse. In such a die-pressed casing its inner wall fibers are under residual tension and its outer wall fibers under residual compression stresses, but the residual tension and compression stresses in the portions of the casing that were at and adjacent to the lines of joinder of the dies are materially greater than those in the other portions of the casing, namely, those that were at and adjacent to the valleys of the dies. The result of this is that when the casing is freed from the dies the unequal residual stresses so distort the casing that it is of a general elliptical shape, its major axis being in the direction of the casing that extended from one to the other of the portions of it that were at the lines of joinder of the dies. It is well understood that out-of-roundness of a tubular body materially diminishes its resistance to collapse.

5 In addition to the foregoing objectionable characteristics of well casing that has been subjected to cross-roll straighteners, it is well known that in the operation of cross-roll straighteners there can be no straightening of the end portions of cylindrical articles that are passed through them. This results in a material endcropping loss of well casing that has been passed through cross-roll straighteners. Also, I have found that casing which has been subjected to die-pressing straighteners of the type explained lacks longitudinal straightness to an objectionable extent.

Objects of my invention are to provide a method of and apparatus for so straightening well casing that it is substantially free from such unfavorable and objectionable residual stresses that its resistance to collapse is lessened, and that it is axially straight and of such roundness that it is highly resistant to collapse, and to provide cold-straightened casing that is round,

straight and highly resistant to collapse.

In the practice of my invention well casing, of the seamless, welded, or any other type, is coldstraightened by reducing it in diameter in such a way that the plastic flow of its metal may result in imparting to the metal residual stresses that increase the resistance of the casing to collapse, and in all events avoid imparting objectionable residual stresses thereto. This reduction in diameter is effected by subjecting the casing, increment after increment and progressively from end to end, to repeated radial pressure applied solely to the exterior of the casing and substantially uniformly about its circumference. The pressure is preferably applied to the casing by a die formed of not less than three complemental members mounted for repeated lateral reciprocation to and from closed position. The uniformity of the application of pressure to a casing may be effected by increasing the number of complemental members forming the die, but is preferably effected by repeated compressions of small increment of the casing accompanied by turning the casing on its axis between repeated applications of pressure. So that the pressure will be applied solely to its exterior, the interior of the casing is not provided with a mandrel or any other pressure-applying or wall-supporting instrumentality or medium. 5 This repeated diameter-reducing pressure causes the metal of the casing to flow plastically in a substantially uniform manner around the casing.

While thus subjected to this plastic flow, the successive increments of the casing are molded to uniform-diameter cylindrical form, each in axial alignment with increments that have been previously molded to such form. This molding is effected by the shaping of the interior casingengaging portions of the complementai die members. Preferably, each untreated increme the casing is first molded to tapered form, and this is preferably done in a plurality of pressureapplying steps between each of which the casin is turned on its axis an angular amount equal to one-half of the arcuate extent of each complemental die member, but it may be turned more or less than this amount. Immediately following the tapering of each increment, it is further compressed to plastically mold it to cylindrical form, preferably in a portion of the die immediately adjoining its taper-forming section, and when each increment is thus reduced to cylindrical form, it is advanced in the cylindrical portion of the die where it is elastically compressed in the next pressure-applying operation. The effect of this is to axially align with each elastically compressed increment the succeeding tapered increment that is being plastically reduced to a cylindrical form of the same diameter, which action proceeds progressively from end to end of the casing.

As a result of this manner of straightening well casing, I have found that it is axially straight and circumferentially round within the commercial contemplation of these terms. It is straighter and more truly cylindrical than well casing that has been cold-straightened on any commercial straightener known to me. In addition to this, I have found that the metal of casing may have, throughout, substantially uniform residual tension stresses in its inner and substantially uniform residual compression stresses in its outer fibers. These residual stresses increase the resistance of the casing to collapse, as compared to casing not so stressed and otherwise the same. When the casing is subjected in service to external fluid pressure, the compressive forces so imparted to it must first relieve the residual tension stresses in the inner wall fibers of the casing before such fibers become subjected to the compressive collapse-producing stresses produced by the applied fluid-pressure load, which manifestly results, as stated, in increasing the resistance of the casing to collapse. In addiiton to this favorable action of the residual stresses, their uniformity c-ircumferentially of the casing maintains the casing in its cylindrical straightened form. Hence, well casing that is cold-straightened according to my invention has, by reason of its shape and the residual stresses of its metal, collapse-resistingcharacteristics materially superior to prior coldstraightening well casing.

My invention will be further explained with reference to the accompanying drawings, of which Fig. 1 is a side elevation of apparatus which may be used in the practice of the invention; Fig. 2 a plan view of the apparatus shown in Fig. 1; Fig. 3 a longitudinal central sectional View of the preferred form of a die member used in the apparatus of Figs. 1 and 2; Figs. 4 to 10 diagrammatic views of the die member of Fig. 3 illustrating the progressive incremental diameter-reducing action of the die; and Fig. 11 a transverse sectional view of the die member taken on the line Fig. ii but illustrating the three complemental members forming the complete die.

Referring to Figs. 1 and 2, a casing is shown as being passed through a press i having complemental die members, usually three in number and hereinafter described in detail, which are closed around the casing to straighten it. The die members are reciproc'ated radially of the casing, usually the rotation of eccentrics which may be driven in any suitable manner, as by shafts 2. Except for the structure of the die and the general construction and operation of the apparatus in which it is used, the apparatus forms no part of my invention. A preferred form of die-actuating apparatus is that shown in patent application Serial No. 140,635,

filed May 4, 1937, by F. C. Biggert, Jr.

Briefly describing the apparatus, the casing may be supported on each side of the press by mechanisms 3 and 4 which feed the casing forwardly increment by increment between the pressure-applying, diameter-reducing movements of the die members and also for concurrently turning the casing on its axis. Specifically, each of the mechanisms may include a chuck III for releasably gripping the casing during the forward feeding movement only which chuck is rotatably received in a carriage ll slidably mounted on a 20 base I2. To obtain the incremental forward feeding movement of the casing each carriage II .is moved forward and back on its base l2 by suitable means which may comprise a crank and connecting rod drive l3, each of which is con- 25 nected by shafts I4 to a line shaft l5 driven periodically insynchronism with the opening and closing of the chucks Hi. It will be understood that when the chucks III are open the carriages II are returned to the beginning of their feed- 30 ing positions, the chucks are then closed about the casing so that the forward feeding movement of the carriages ll moves the casing an increment into the press. This forward feeding movement of the casing occurs when the die mam-- 35 bers of the press are open and is accompanied .by rotation of the casing about its axis. In the apparatus illustrated the casing is turned about its axis by gearing l6 connected to the shafts l4 and serving to rotate the chucks H].

In Fig. 11, die I9 is illustrated as being formed of three complemental members or parts which are alike in extent, interior configuration and general shape. Each member is provided interiorly with a groove so shaped that when the members are in closed die-forming position the interior of the die is provided at an end with an outwardly flaring bell section for facilitating the entering and centering of a casing in the die. Adjoining the bell section there is a truncated conical section 2| which converges inwardly from the entering end of the die and which serves to plastically compress to tapered form successive increments of a casing. The

axial length of this section is preferably several times the diameter of a casing to be straightened. By way of example, and not of limitation, its length may be about three feet for the straightening of easing eight inches in diameter. The difference between the large and smalldiameter ends of tapered section 2| depends upon the extent it may be desired to reduce the diameter of casing beyond that required for straightening it. In the straightening of casing of plain steel having a carbon content of about .35 per cent to .50 per cent, it is sufficient to re duce its diameter not more than about two per cent. Any additional reduction in diameter serves to increase the hardness and yield point of the metal beyond that ordinarily obtained in straightening the casing according to my invention. v

Immediately adjoining the small-diameter end -of the truncated conical section 2| of the die, there is a cylindrical section 22 in axial alignment with the conical section having a diameter that is preferably the same as that of the inner end of the truncated conical section. The length of the cylindrical section is preferably about the same as that of the truncated conical section, or, in other words, several times the diameter of the casing to be straightened. Specifically, the length of the cylindrical section of the die depends upon the stepped forward feed .of the casing rather than on the diameter of the casing. Preferably the cylindrical section is of the same length in dies of different size capable of operating on casings of various diameters except that in the bigger casing sizes having heavier walls a shorter cylindrical length may be used. The length of the tapered section of the die depends upon the number of reductions required to get uniform cold work circumferentially of the casing assuming a given axial and rotary feed of the casing. Each of the cylindrical and tapered sections of the die should be longer than one diameter of the casing.

In Figs. 4 to 10, inclusive, there is illustrated a series of successive steps performed by the lateral reciprocation of the die members and the rotation and advancement of the casing in the straightening of a well casing C according to the preferred practice of my invention and by the use of the particular die herein disclosed. For simplicity, the successive stages are illustrated in connection with only one of the die members. In Fig. 4 the die is shown in its open casing-receiving position, and the casing is shown as having its first or forward end increment a moved into the die. This and the suceceeding increments may be about one-half the length of the tapered section 2| of the die, as illustrated, although it will be understood that the length of the increments may vary with relation to the length of this section of the die. When the die is closed by inward reciprocation radially of the casing, the first increment a is plastically compressed to tapered form, as shown in Fig. 5. Thereafter, the die is opened, and, during the time that it is not in engagement with it, the casing is moved longitudinally to enter its second increment b, and it is also turned or rotated on its axis an angular amount substantially equal to one-half the a'rcuate extent of the groove of each die member, or, in other words, it is rotated about 60 when three-part dies such as illustrated are used.

In the second closing ,movement of the die, increment a is further plastically reduced, and increment b is plastically reduced the same as was increment a in the stage of the operation illustrated in Fig. 5. In the next stage, shown in Fig. 8, the die is opened and the casing is rotated on its axis and advanced longitudinally to present its next increment c .to the die in the manner explained above. In this stage of the operation increment a lies in the forward end of the cylindrical section 22 of the die. The diameter of this section is sufllciently less than the small-diameter end of increment a that upon the closing of the die the metal of the casing forming this increment is plastically compressed and molded to cylindrical form in the manner illustrated in Fig. 9, which also shows increments b and c as being reduced and molded to progressively smaller tapered form. When -the die is'opened after the molding of increment a to cylindrical form, the elasticity of the metal increases the diameter of this increment somewhat beyond that of the cylindrical portion of the die. In the next stage of the operation, illustrated in Fig. 10, increment a is elastically compressed, without any permanent reduction in its diameter, to the diameter of increment b which is then being plastically compressed to cylindrical form. The stages of the operation that have been described with reference to Figs. 5 to 10 are repeated until the entire casing has passed through the straightener, the casing being advanced increment by increment and turned on its axis between each diameter-reducing and molding operation of the die.

It will be observed that in the cold-straightening of well casing according to my invention, the casing is progressively reduced in diameter an amount suillcient to cause a substantial plastic flow of all its metal, and that while the metal is subjected to such flow it is positively molded to desired cylindrical form in increments of such length that they retain their molded form. Furthermore, each increment is molded to its cylindrical form in positive axial alignment with an adjoining elastically compressed increment that has previously been molded to the same cylindrical form. Thus the entire casing is not only straightened, but is made cylindrical. By turning the casing on its axis between its incremental and progressive reduction in diameter, the pressure is so applied to the metal as to cause itsplastic flow to be substantially uniform around the body of the casing and from end to end. As a. result of this, the cold-straightened casing is free of objectionable residual stresses.

The practice of my invention not only straightens the casing but also sizes it in a single simultaneous operation. Heretofore casing ordinarily has been sized in a sizing mill while still hot, and unless the temperature of the casing is within close limits during sizing it is under or over size According to the provisions of the patent statutes, I have explained the principle and mode of operation of my invention, and have illustrated and described what I now consider to be the best way of practicing it. However, I desire to have it understood that, within the scope of the appended claims, my invention may be practiced otherwise than as specifically illustrated and described.

I claim as my invention:

1. The method of cold-straightening well casing formed of steel, comprising reducing it in diameter substantially without elongation by subjecting it increment after increment and progressively from'end to end to repeated radial pressure applied solely to the exterior of the casing and substantially uniformly around its circum- Ierence, and while thus subjected to plastic flow concurrently molding the increments to axially aligned uniform-diameter cylindrical form.

2. The method of cold-straightening well casing formed of steel, comprising reducing it in diameter without substantiallyany elongation by subjecting it increment after increment and progressively from end to end to repeated radial pressure applied solely to the exterior of the easing and substantially uniformly around its circumference, and while thus subjected to plastic flow concurrently molding the increments first to tapered form and then to axially aligned uniformdiameter cylindrical form.

3. The method of cold-straightening well casing formed of steel, comprising reducing it in diameter without substantial elongation by subjecting it increment after increment and progressively from end to end to repeated radial pressure applied solely to the exterior of the casing and substantially uniformly around its circumference, and while thus subjected to plastic flow concurrently molding the increments to axially aligned uniform-diameter cylindrical form, and turning the casing on its axis between the applications of said diameter-reducing and molding pressure.

4. The method of cold-straightening well casing formed of steel, comprising reducing it in diameter but substantially without elongation by subjecting it increment after increment and progressively from end to end to repeated radial pressure applied solely to the exterior of the casing and substantially uniformly around its circumference, concurrently molding the increments first to tapered form and then to axially aligned uniform-diameter cylindrical form, and turning the casing on its axis between said applications of diameter-reducing and molding pressure.

5. The method of cold-straightening well casing formed of steel, comprising reducing it in diameter without substantially any elongation by subjecting it increment after increment and progressively from end to end to repeated radial pressure applied solely to the exterior of the casing and substantially uniformly around its circumstance, and while thus subjected to plastic flow concurrently molding the increments to axially aligned uniform-diameter cylindrical form, and maintaining cylindrically molded increments in axial alignment with those being molded.

6. The method of cold-straightening well casing formed of steel, comprising reducing it in diameter without substantially any elongation by subjecting it increment after increment and progressively from end to end to repeated radial pressure applied solely to the exterior of the easing and substantially uniformly around its circumference, concurrently molding the increments first to tapered form and then to axially aligned uniform-diameter cylindrical form, turning the casing on its axis between said applications of diameter-reducing and molding pressure, and maintaining cylindrically molded increments in axial alignment with those being molded.

7. The method of straightening well casing from end to end and without substantially any elongation which comprises reducing the casing in diameter between dies increment after increment and progressively from end to end and while unsupported internally, each increment being first reduced in diameter in the entering part of the die and subsequently further reduced in diameter in other parts of the die while concur rently a succeeding increment is reduced in the entering part of the die, the casing being advanced longitudinally and rotated axially between each reduction, and while being reduced in diameter maintaining the increments in alignment with that portion of the casing that has been straightened.

8. The method of cold-straightening well casing which comprises progressively reducing the casing in diameter in a tapered multi-piece die, advancing the casing axially into a smaller part of the tapered die between compressive movements thereof, rotating the casing about its axis approximately one-half the arcuate extent of a piece of the die during the advancing movement of the casing, further reducing the casing in diameter in a tapered part of the die, advancing the casing into a cylindrical part of the die between compressive movements thereof while rotating the casing about its axis so that the pass line of the dies is remote from the previous one with respect to the casing, further reducing the casing in diameter in the cylindrical part of the die, advancing the casing into the cylindrical part of the die betweencompressive movements thereof while rotating the casing about its axis so that the pass line of the die is remote from the previous one with respect to the casing, and

compressing the increment of the casing last reduced in the cylindrical part of the die but within the elastic limit of the metalthereof so as to hold its axis in alignment with the axis of other increments being sized and straightened.

9. That method of sizing and straightening an oil well casing while avoiding and relieving stress concentrations therein which comprises forming a taper on the end of the internally unsupported casing by pressure applied substantially simultaneously over the entire circumference of the portion of the casing tapered so that the taper is visible on the inner and outer surfaces of the casing, turning the casing through a partial are about its longitudinal axis, again but in a separate operation extending the taper over a greater length of the casing by similarly applied pressure, then step by step moving the taper back from the end of the casing by plastically flowing and positioning a portion of the casing at the small end of the taper parallel with the axis of the casing, said portion of the casing positioned parallel with the axis being equal to the distance the taper is moved back on each step from the end of the easing and holding the parallel portion of the casin so that its axis is in parallel relationship with the axis of those portions of the casing being formed.

10. The method of cold sizing and straightening oil well casing which comprises reshaping the entire wall of the end of the casing without internal support and by plastic flow of the cold metal to form substantially atruncated hollow cone the base of which has a diameter equal to the ,original diameter of the casing, advancing and rotating the casing about its axis, extending the length of the cone by inclining more of the wall of the casing by plastic flow of the metal and while maintaining the base diameter of the cone, thereafter advancing and rotating the casing, again extending the length of the cone as last described and simultaneously by plastic flow positioning parallel with the casing axis a length of the casing at the small end of the cone equal to the extension in length of the cone, and repeating the advancing and rotation of the casing and the last-named cone extending and wall positioning steps until the entire length of casing is formed with a reduced diameter and aligned walls parallel to the casing axis.

11. That method of sizing and straightening oil well casing which comprises applying pressure relatively slowly over the outside only of the end of the casing to cause a plastic flow of the metal, controlling the direction and extent of the plastic flow to form a substantially conical taper on the end of the casing both on the inside and outside of the casing and without any appreciable change in wall thickness or elongation of the casing, advancing and rotating the casing about its axis relative to the pressure-applying zone, repeating the application of pressure as before and while the metal at the small end of the taper is flowing plastically controlling the direction and extent of the flow to reposition the casing wall at the small end of the taper parallel with the axis of the casing and to a uniform diameter.