Патент USA US2405859код для вставки
' Aug. 13, _1.946.A - , . H. E. sQMEs> _TUBULAR « 2,405,859 STRUCTÚRAL MEMBER . - ¿Filed Deo. 20. 1941 @Gl _ j ` Jëlcfi I .By v ATTORNEY Patented Aug. 13, 194s 2,405,859 UNITED STATES PATENT oFFlcE 2,405,859 TUBULAR STRUCTURAL MEMBER» Howard E. Somes, Detroit, Mich., assignor, by mesne assignments, to Edward G. Budd Manu facturing Company, Philadelphia, Pa., a, cor poration of Pennsylvania Application December 20, 1941, Serial N0. 423,739 2 Claims. (Cl. 166-4) 1 This invention relates to tubular articles and 2 In the drawing which illustrates a suitable em more particularly to an axial assemblage of tu bular articles such for example, as oil well cas bodiment of the invention: ings. tion of a casing section undergoing a heat treat An axial assemblage of tubular articles is fre quently subjected to unusual stress conditions, ing operation; and one of the most common examples of which is an Figure 1 shows a fragmentary sectional -por Figure 2 is a fragmentary elevational view of an oil well casing string. I attain the objects of the present invention oil well casing. An oil well casing, commonly by employing certain heat treating operations to known as a string, is comprised of a plurality of steel tubes axially connected together and ex 10 provide the casing sections with an internal an» nular zone or layer extending from end to end tending many thousands of feet into the earth, it being not uncommon to set oil well casings to and to create within the inner and outer zones certain predetermined residual stress conditions v depths of between 9,000 and 12,000 feet. In a few instances, casings have been set to a depth which combine with the hardened zone to in of 18,000 feet. The casing string is suspended at crease the strength of the casing sections, the sections to be used for the upper portion of `the its top and frequently is sealed at its lower end casing string being provided with stress condi with concrete or other suitable material, and is supported at such lower end. Due to the great tions different from the stress conditions existing in the casing sections employed for the lowe11 por weight of the string, at least the upper sections tion of the casing string. thereof are subjected to severe tensile stresses The casing sections are ñrst subjected to a acting in an axial direction especially during in heat treating operation similar to that described stallation when the string is being supported from the top. At the bottom of the string, many of in my Patent No. 2,281,331, April 28, 1942, where in there is disclosed a method and apparatus for the lower casing sections are subjected to axial compressive stresses which arise out 0f the fact 25 progressively hardening:A an internal layer of a that the elongation and more particularly the tubular member by- generating heat in the in ternal layer through magnetically induced heat weight of the upper sections imposes an axial ing currents. compression load on such lower sections especially In accordance with the method disclosed in my after installation. In addition, the hydro-static pressure existing externally of the lower casing 30 copending application aforesaid, an electro-mag netic induction heating head “H” and a quench sections exerts severe external pressures radially head “Q” are arranged in coaxial relation with against the Walls thereof which set up compres the casing section to undergo the heat treating sive stresses in the casing wall tending to col operation and in such manner that relative axial lapse the same. Oil well casings are being set deeper and 35 movement can be effected between the casing sec tion Il on the one hand and the heatingv and deeper and this means that the tensile stresses in quenching heads on the other hand while prefer the upper sections and the compressive stresses ably effecting relative rotation. The coil I2 of in the lower sections are becoming greater and the heating head is connected to a high frequency greater, it being well known that the hydrostatic pressures increase as the depth of the casing set 40 source of alternating current and is provided with a laminated iron core i3 threading its center in ting increases. order to assist in the concentration of heating From the foregoing it is clear that whereas ten energy at a high rate inthe internal layer or sile strength is of greater importance at the top of the string, compressive strength is of greater Zone which is to be hardened. The quench head and major importance at the bottom of the 45 Q is preferably provided wtih an annular oriñce Q-lß arranged as closely as possible to the trail string. The aim, therefore, of the present in ing end of the coil l2 to discharge an annular vention is to provide an oil well casing string or stream of quenching medium against the heated similar structure of improved construction where internal surface. in the casing sections forming the upper part The construction of the heating and quenching of the string and those forming the lower part r heads H and Q, respectively, may be substantially of the string, respectively, with respect to a the same as that disclosed in said copending ap standard oil well casing of the same dimensions plication and of course may be of any other suit and composition, have increased resistance to able design and construction, such as shown in axial tensile failure and increased resistance to Figure 1, and capable of producing the same collapse from the exertion of axial and radial compressive forces. rapid heating and quenching results. With the above and other objects in view, the present invention consists of certain features to be hereinafter described with reference to the The heat is generated annularly at a desired shallow depth in the internal zone within a period of a very few seconds and this heated 'zone is accompanying drawing, and then claimed. immediately quenched before any of the heat 2,405,859 3 „ generated in the same can drift to the metal of the outer zone in. any consequential amount, thus providing an inner hardened layer I4 of metal and an outer unhardened or less hard annular layer I5 of metal. By reason of the rapid generation of heat in the inner layer I4 and the rapid quenching of the same, a state of trapped stresses is set up> in which the inner hardened layer I4» is placed under residual compression and the outer less hard layer I5 is placed under residual tension, that is, when the tubular structure is under an unloaded condition. The outer layer may be placed under a state of residual tension in an amount approximately that of its yield strength. , It is well known, of course, that the tensile strength of a layer of metal is increased by hard ening the same and that this increase in strength increases with the hardness. For the lower sections B of the casing string illustrated in Figure 2 wherein compressive strength is of major importance the casing sec tions treated in the manner just described are employed, these sections being provided with an outer unhardened layer I5 under residual ten sion and an internal layer i4 under residual compression and hardened to such hardness as to increase its ultimate strength to a strength manifoldly greater than that of the unhardened layer I5» which, for example, may be three times thatof the unhardened layer. For example, the ultimate strength of a metal hardened to 60 4 section is placed under axial compressive load ing the external unhardened layer I5 being under considerable tension in opposition to the com pression stress of the internal layer I4 assists the section in resisting axial compressive loading by the amount of the residual tension stress, since the axial loading must ñrst neutralize this re sidual tension stress. It is obvious that in such heat treated cas ing sections B in which the internal layer is hard ened the yield point or yield stress to which it may be carried exceeds the yield strength of the unhardened material and therefore, the internal layer may, when the casing section is subjected to an axial compressive loading, be stressed to a much higher point than the outer layer and still remain within the yield point of the material. For the casing sections A in the upper portion of the casing string A--B wherein tensile strength is of greater importance, the present invention contemplates the embodiment of casing sections having the internal annular layer I4 hardened substantially the same as in the lower sections B but in which the internal layer is placed under a. state of residual tension and l5 is placed under a state of sion, that is, when the casing unloaded condition. In such a structure, it will the external layer residual compres sections are in an thus appear that with the metal of the internal hardened layer I4 having a tensile strength far in excess of the strength of the external unhardened layer I5 and at the same time being under tension while the on the Rockwell C scale may be as high as 311,000 outer layer is under compression, an axial ten~ pounds perv square inch whereas the same metal sion load exerted on the casing section will ñrst prior to hardening might have had an ultimate neutralize the compressive stress in the outer strength of 93,000 pounds per square inch as layer and at the same time increase the tension suming it had an original hardness of Rockwell stress of the internal hardened layer I 4. The C 10; This strength of 93,000 pounds per square metal of this internal layer due to its hardness inch is considerably above the yield strength which would probably be in the order of 60,000 40 however, is of manifoldly greater strength than pounds per square inch. ' the metal of the external unhardened layer. Con sequently, the metal of the hardened internal Assuming for example, that the yield strength layer and the metal of the external layer combine of the unhardened layer of the casing section is and assist each other in resisting axial tensile two-thirds of the ultimate strength and that the loading and thus the axial tensile strength of outer layer is under a residual tension substan tially equal to its yield strength, it will thus ap the casing section is increased, the initial assist ance of the external layer being the amount of pear that an external radial load such as arises its residual or> trapped compression stress. from the hydro-static pressures existing exter In order to bring about the stress reversal in nally of the lower sections of the casing strength changing the residual stress of the external layer must ñrst neutralize the tension stress in outer I5 from a tension to a compression stress con layer I5, this, in the present case, being an dition and of the internal layer I4 from a corn amount equal to two-thirds of the ultimate pression-to a tension stress condition, the internal strength of the outer layer. It thus will be seen layer I4 is expanded, but not beyond its elastic that the outer layer is still capable of withstand limit, an amount suiiicient to expand or stretch ing a compressive load equal substantially to its the metal of the external layer beyond its yield ultimate strength, and therefore, that since the point whereby to upset the same. Upon con strength of the hardened layer is in the order traction of the internal layer the external layer is of three times that of the unhardened layer, the placed under compression and the internal layer, two layers combine and assist each other in re due to the resistance of the external layer to com sisting the compressive loading, at least‘to the pression, isv placed under tension. extent of the strength of the outer unhardened It must> be borne in-mind, however, that the layer, Actually, however, the casing will with total strength 0f the hardened layer must be stand an external loading greater than the sum greater than the total strength of the unhardened of two-thirds the ultimate strength (the residual layer so that the upsetting of the external layer tension stress) of the outer layer I5V and the is accomplished before the internal layer reaches strength of such loading because of the increased its elastic limit. strength of the internal layer I4. It thus is seen The reversed stress may be brought about me that the resistance of the» casing section to col chanically or by longitudinally stressing the same lapse is materially increased. through the application of opposed tension-exert It will, of course, be obvious that the axial com ing forces at its ends, or by closely confining the pressive strength of such casing section will be peripheral surface thereof throughout its length materially increased by the treatment described. and subjecting the same to high internal hy The residual tension stress of the external layer draulic pressure. The stress reversal also may exerts itself not only circumferentially but also be brought'about in accordance with the disclo axially of the section and consequently, when the 2,405,859 5 sure of my Patent No. 2,315,558, granted April 6, 1943, wherein I proposed to thermally expand the internal layer I4, through the use of the electro magnetic induction heating head l-l shown in» strength, and the lower sections, wherein axial and radial compressive stress is of major im portance, have increased axial and circumferen tial compressive strength, as compared to sec tions of the same size and composition. Other advantages, oi course, are manifold, particularly the temperature of the internal hardened layer in the reduction in weight and saving in cost. to the .desired temperature, for example, such as The number of sections at the upper and lower 400 degrees Fahrenheit. In applying the heat to portions of the casing to be treated in accordance this internal layer almost instantaneo-usly and before any consequential heat may escapethere with the disclosures herein may, of course, vary depending upon the depth of the well, which as from to the external layer l5, the internal layer is well understood is usually determinable in ad which was initially under compression is forced vance to drilling the well. The intermediate sec to expand because of the increase in compression due to thermal expansion resulting from the heat tions may be untreated. However, in any event, generated therein and the consequential tempera 15 the portions of all the sections may be hardened under the threaded end zones to increase the ture rise in the internal layer. The additional strength of the joints to compensate for loss in compressive stress developed in the internal hard Figure 1, by substantially instantaneously raising ened layer through the rapid heating thereof will strength resulting from the cutting of the threads. The production of hardened zones underlying the be suirlcient to stress the cold external hardened layer beyond its elastic limit so that it will take 20 threads 2s is preferably accomplished in the a permanent set. same manner as that outlined in connection with the portions forming the lower casing sections, In practice, tubular members treated in the wherein high collapse strength is desired. manner set forth will be found to have had their axial internal diameter enlarged slightly through Although the invention has been illustrated and described in general in connection with a this treatment, and too because the external layer has been given a permanent setting and stressed speciiic embodiment, it is to be understood that beyond its yield point allowing the internal layer the same is not limited thereto but may be prac formerly under compression to expand, the heat, ticed in various forms and ways. As many changes in the procedure and in the structure however, being such that the inner layer is not expanded beyond its yield point. No quenching 30 evolved therefrom may be made without depart need be resorted to for the structural change in ing from the spirit of the invention, as will be the section takes place immediately upon the de apparent to those skilled in the art, reference velopment of heat and the increasing of com will be had to the appended claims for a definition pressive stresses in the internal layer sufliciently of the limits of the invention. What is claimed is: to force the outer layer to yield. The structure can thereafter be permitted to cool in air or if 1. An elongated tubular metallic structure of the character subject in use throughout portions desired, for rapidity, it may be cooled by place of its length t0 predominating axial compressive ment in a cooling bath, or by quenching it exter nally or internally. stresses and throughout other portions of its The heating of the internal layer to a temper 40 length to predominating axial tension stresses, ature of, for example, 400 degrees F. may not having the wall of each of said portions comprised effect any material change in its hardness and of integral inner and outer layers of metal, said yet the treatment described will materially in crease the internal load strength of the casing section. In some instances, however, it may be desirable to carry the temperature created in the internal layer to a point such as to produce a certain amount of drawing of the original hard ness of this layer, in which case the internal layer may be initially hardened to a much higher de gree than that iinally desired so that the draw ing action will produce an amount of reduction in the hardness of the internal layer such as will inner layers having a yield strength materially greater than that of the outer layers, said inner and outer layers of said ñrst-mentioned portions which are subject to predominating axial com pressive stresses being under residual compres sion and tension stresses, respectively, and said inner and outer layers of said other portions which are subject to the predominating axial tension stresses being under residual tension and compression stresses, respectively. 2. A multi-section oil well casing structure of produce the hardness desired. the character wherein incident to weight and ex While a temperature of 400 degrees Fahrenheit 55 ternal hydrostatic pressure the lower sections has been suggested, the internal layer obviously thereof are subject to circumferential collapsing may be heated to any temperature below the crit stresses and other compressive stresses and inci ical hardening temperature, the temperature dent to the weight of the structure other sec chosen of course being that which is necessary to tions thereoí _are subject to axial tension stresses, produce the desired or necessary upset in the 60 the wall of each section being comprised cf inner outer layer. and outer annular layers of metal substantially The casing sections, as is well known, are coextensive with the length thereof, said inner threaded at their ends, as at 20, for attachment layer being of materially greater hardness than to adjacent sections through suitable couplings the outer layer, each of said lower sections having 2|. its inner layer initially under residual compres It will thus be seen that I have provided an sion stress and its outer layer initially under re improved casing string for use in oil wells, or sidual tension stress, and each of said other sec under conditions wherein similar conditions exist, tions having its inner layer initially under resid by the use of casing sections in which the upper ual tension stress and its outer layer initially un portion of the string, wherein tensile strength is 70 der residual compression stress. of greater importance, have increased tensile HOWARD E. SOMES.