PUMP LINERS AND A METHOD OF CLADDING THE SAME

Abstract: A method of cladding an internal cavity surface of a metal object is disclosed. The method includes the steps: a) applying a powder metal layer on said internal surface, the metal powder including metal oxide or oxides, borides and carbides, b) filling a pressure transmitting and flowable grain into said cavity to contact said layer, c) and pressurizing said grain to cause sufficient pressure transmission to the powder metal layer to consolidate same.

Description: This invention relates generally to cladding or coating cavities of metal objects, and more particularly to mud pump liner cavities. Internal cavities of metal objects frequently require a cladding, or a coating, that is more corrosion, oxidation and/or wear resistant than the metal object itself. This need may arise in some cases due to high temperatures created within the cavity, exposure to a corrosive or abrasive liquid, and/or to rubbing action of an internal machine member such as a piston. An example of such a metal object is the liners in mud pumps used in oil field drilling. A mud pump is a part of the oil or gas well drilling fluid circulating system, one of five major components of a rotary drilling operation. The other components are the drill string and bit, the hoisting system, the power plant and the blowout prevention system. Drilling fluid, usually called the "mud", in most cases consists of a mixture of water, various special chemicals including corrosion inhibitors and solid particles such as Barite to increase its density. Such fluid is continuously circulated down the inside of the drill pipe, through the bottom of the bit and back up the annular space between the drill pipe and the hole. The driving force is provided by a mud pump. A mud pump liner is basically a heavy wall pipe section with one or two retaining rings at its outer diameter. It is the wear resistance of the inner surface that determines the liner service life. Consequently, the internal surface of the liner is desirably clad with a wear resistant material. The internal cladding layer is subjected to sliding wear by the rubber piston which can wear and cause metallic structure supporting the rubber to contact the liner cladding, thus accelerating the wear process. The cladding material is also subjected to corrosion from the drilling fluid, and metal fatigue caused by cyclic loading, especially at areas where the direction of the piston motion suddenly changes. Further, micro regions of cladding may experience sudden pressurization and depressurization. These operating conditions impose stringent metallurgical requirements on the cladding materials. An ideal cladding material should, therefore, possess high hardness and high resistance to corrosion, impact and metal fatigue. Such properties are desirably achieved by a uniform, fine grained microstructure, which has been the goal of pump liner makers of many years. The outer, heavy wall portions of the commercially available mud pump liners typically consist of either a carbon steel, or a low alloy steel; and the liner cladding is, in most cases, a cast sleeve of iron - 28% chromium alloy. The sleeve can be centrifugally cast into the steel pipe section or cast separately as a pipe, and shrink fitted into the outer pipe section, then machined to a smooth finish. These manufacturing procedures are lengthy and costly, while providing only a cast metal microstructure which is known to be chemically monuniform, since in castings the solidification process results in natural segregation of the elemental species contained in the alloy. Furthermore, the cladding thicknesses are kept undesirably large to allow casting processes to be used. The claddings within metallic objects other than pump liners can be similarly characterized and most likely be prone to the same deficiencies. Our earlier European Patent 0169 718 discloses a method of cladding the irregular exterior surface of a metal object, in which method a powder metal layer is applied on the surface and consolidated by pressurisation within a body of flowable pressure-transmitting material. A cladding layer made of powder metals consolidated to near 100% density and bonded to the outer steel shell appears to provide the most desirable metallurgical microstructure, due to its chemical uniformity and high ductility emanating from its grain size. Existing methods of application of such powder metal layers, however, are grossly inadequate in that they either produce a porous, oxide contaminated layer which is only mechanically bonded to the outer shell as in sprayed coatings, or they are superficially and only mechanically bonded to the outer shell as in brazed-on coatings. For these, and other reasons, present powder metallurgy techniques for such products have not been considered adequate. One object of the invention to enable powder metal cladding of the internal cavity surface of metal liners and objects in a manner which overcomes the above problem and deficiencies. In addition, the invention provides various material combinations for the production of pump liners and internally clad pipe segments for use with oilfield mud pump fluids. There are many other products that can benefit from this processing technique. In accordance with the invention we now propose a method of cladding an internal cavity surface of a metal object, which includes the steps: a) applying a powder metal layer on said internal cavity surface, the metal powder including a metal compound selected from metal oxide or oxides, borides or carbides, b) introducing the metal object having said powder metal layer on said internal cavity surface into a first chamber of a die and applying pressure-transmitting and flowable particles (grain) into contact with said layer within said chamber said die having a second chamber containing particles and communicating with said first chamber, the second chamber having a cross-section less than the cross-section of the first chamber, and c) applying a force to the particles in said second chamber so as to cause the particles in said first chamber to transmit sufficient pressure to consolidate the powder metal layer, said powder metal layer being disposed about and spaced from the axis along which said force is applied whereby force is transmitted along said axis by the particles in said second chamber and is transmitted away from said axis and against said metal powder layer by the particles in said first chamber. As will appear, pressurization of the flowable particles referred to as grain is typically carried out by transmitting force to the grain along a primary axis, the layer extending about that axis and spaced therefrom, whereby force is transmitted by the grain away from the axis and against said layer. The die has a first chamber receiving the said object, and a second chamber containing grain communicating with grain in the cavity, pressurizing of the grain in the cavity being carried out by pressurizing the grain in the second chamber, as for example by transmitting pressure from the grain in the second chamber to only a medial portion of the grain in the first chamber everywhere spaced from said layer. Further, the metal object is typically cylindrical, the layer being applied on an internal cylindrical surface of said object, the latter for example comprising a mud pump liner. These and other objects and advantages of the invention, as well as the details of an illustrative embodiment, will be more fully understood from the following description and drawings, in which: Fig. 1 is a vertical section showing a mud pump liner; Fig. 2 is a vertical section showing a "green" coated mud pump liner placed in a double chamber die; Fig. 3 is similar to Fig. 2, but shows hot grain filled into the die and liner cavity, and pressurized; and Fig. 4 is a magnified section taken through the wall of a steel tube clad in accordance with the invention. Referring first to Fig. 1, an alloy steel mud pump liner 10 comprises an elongated tube 11 having an outer flange 12 on one end portion. The tube axis appears at 13, and the tube inner cylindrical surface at 14. Tube 11 may be considered to represent other metal objects having interior surfaces (as at 14) facing internal cavities 15. Internal surfaces of the tube or metal object to be clad are first cleaned to remove any oxide layers, grease or dirt; then, using a slurry of the cladding metal powder and a suitable fugitive binder, these surfaces are coated with the slurry, the coating appearing at 16. As shown, the "green" coating is generally cylindrical, and has an outer surface 16 a containing the tube surface 14. The coating process can be accomplished by spraying, dipping in the slurry, brush, or spatula painting, or if the internal cavity is cylindrical, as is the case for pipes, the slurry may be centrifugally spread onto the internal surface by high speed spinning of the part. The thickness of the "green", weakly held together, powder metal-binder mixture can be controlled to some degree by controlling the total weight of the slurry used. Localized surfaces where cladding is not desired can be masked using adhesive tapes (see tape 17) which are removed after slurry coating is applied. The green coating is then dried at or near room temperature and heated to a temperature between 871°C and 1260°C (between 1600 °F and 2300 °F) where the coated metal powders are easily deformable under pressure. For most materials the furnace atmosphere should be either inert or reducing to prevent oxidation of the powder. Such a furnace is indicated at 18, and it may contain inert gas such as argon or nitrogen. Referring to Figure 2, the next step in the process is to place the liner containing the green now lightly sintered layer 11 a within a step die 19 where the liner fits into the large cavity (i.e first chamber 19) in the die as shown in the figure, and having inner cylindrical walls 19 a and 19 b . The die second chamber 20 throat diameter D₁ should be equal to or smaller than the "green" internal diameter D₂ of the mud pump liner 11 a . This assures relatively shearless pressing of the green powder metal cladding 11 a under largely lateral pressure during the pressurizing step. Chamber 20 has a bore 20 a . As seen in Fig. 3, pressurization takes place in a press 21 after filling both the die and the pump liner cavities with a refractory powder 22 already at a temperature near or above the consolidation temperature of the cladding powder. The pressure from ram 23 is transmitted to the liner by the horizontal forces created within the refractory powder grains. In this regard, the second chamber 20 is in axial alignment with the first chamber 19, the second chamber having a cross section less than the cross section of the first chamber, whereby pressure is transmitted from the grain 22 a in the second chamber to only a medial portion of the grain 22 b in the first chamber which is everywhere spaced from layer 11 a . Therefore, lateral pressurizing of the grain in the cavity 19 is effected by grain pressurized longitudinally in the second chamber, and no destructive shear is transmitted to layer 11 a . Consolidation of powder metal into substantially solid objects through the use of refractory particles (grain) has been disclosed in previous U.S patents No. 3,356,496 and No. 3,689,259 by R W Hailey. This invention, therefore, can be regarded as am improvement over those of the two patents, the invention providing a novel die design and a unique provision for horizontal pressurization transformed from a vertically applied load. The critical factor which prevents the powder cladding layer from being stripped (due to shear forces created when a vertically applied force is directly transmitted by a refractory bed of grain) is the die shape which moves the "shear" region away from the cladding. A number of experiments using steel tube segments measuring 3.81 cms (1.5 inches) long having 5.075 or 8.25 cms (2 or 3.25 inches) O.D's and 0.635 cms (0.25 inch) wall thickness were conducted to establish and verify the above described process. The objective was to clad the tubes with metal powder without distorting the tubes in any way. This was accomplished utilizing the die configuration shown in Figures 2 and 3. In a typical procedure the cladding material consists of 98.5% by wt. powder mixed with 1.5% by weight cellulose acetate and acetone in an amount to establish sufficient fluidity to the mixture. This mixture is spun at 500 rpm to provide a thin (approximately 0.254 cm - 1/10th of an inch) green coating inside a 3.81 cm (1.5") long X 8.25 cm (3.25") O.D. X 0.635 cms (0.25") wall tube. The tubing is allowed to dry at room temperature overnight and heated to an elevated temperature for about 14 minutes, the furnace atmosphere being substantially hydrogen. Immediately after the tube is placed in the die cavity, the refractory grain which heated to 1260°C (2300°F) in a separate furnace is poured and the press ram allowed to pressurize the grain. After a peak pressure of 695 MN/m² (45 tons per square inch) is reached for about 10 seconds, the pressurization cycle is considered complete and the pressure released. The die is then moved to a location where its contents can be emptied. In a modified procedure a furnace atmosphere of 100% nitrogen can be used instead of hydrogen. A consolidated mixture of 40% Deloro 60 - 60% tungsten carbide powder (item 4 in Table 1) can be bonded to a steel tube at a temperature of 1037°C (1900°F) under 695 MN/m² (45 tsi) pressure to produce a typical cladding microstructure at the steel tube cladding interface as shown in Figure 4. Other applications utilizing various cladding materials to clad internal cavities of other metal objects such as valves, tubes, rock bits, etc can be accomplished as well. The process, while remaining basically the same, may have some variations. For example, there may be an insulating material positioned between the part (the pump liner in Figure 2) and the die to reduce heat loss before pressing. The insulating material may be a ceramic, high density graphite or a metal which may be heated together with the part. If the insulating material is a metal, a non-bonding refractory powder parting compound may be applied on the insulating material. In addition, the die itself may be a vertically split die to ease the positioning of the part within it when the part shape is more complicated than a simple cylinder. Other minor variations of the process and the die may be utilized as well. Grains used to transmit pressure may have composition as referred to in the two U.S patents referred to above or other compositions that maybe used. Preferably, the lined surface is defined by a mud pump liner having cylindrical shape, said surface at the inner side of the cylinder, the metal powder in said layer selected from the group essentially consisting of: a) Co-Cr-W-C b) Co-Mo-Cr-Si c) Ni-Cr-Fe-Si-B d) Ni-Mn-Si-Cu-B e) Ni-Co-Cr-Si-Fe-B f) Fe-Cr-Co-Ni-Si-C g) Cu-Mn-Ni --Further, said layer may consist essentially of a mixture of 30 to 90% by weight tungsten carbide and remaining metal alloy powder selected from the group consisting of: a) Co-Cr-W-C b) Ni-Cr-Fe-Si-B c) Cu-Mn-Ni d) Ni-Co-Cr-Fe-Si-B e) Fe-Cr-Co-Ni-Si-C--

Claims: A method of cladding an internal cavity surface of a metal object (10), which includes the steps: a) applying a powder metal layer (11a) on said internal cavity surface, the metal powder including a metal compound selected from metal oxide or oxides, borides or carbides, b) introducing the metal object having said powder metal layer on said internal cavity surface into a first chamber (19) of a die (119) and applying pressure-transmitting and flowable particles (22) (grain) into contact with said layer within said chamber said die having a second chamber (20) containing particles and communicating with said first chamber, the second chamber (20) having a cross-section less than the cross-section of the first chamber (19), and c) applying a force to the particles in said second chamber so as to cause the particles in said first chamber to transmit sufficient pressure to consolidate the powder metal layer, said powder metal layer being disposed about and spaced from the axis (13) along which said force is applied whereby force is transmitted along said axis by the particles in said second chamber and is transmitted away from said axis and against said metal powder layer by the particles in said first chamber. A method according to claim 1 wherein said pressure is transmitted to only a medial portion of the particles (22) in the first chamber (19) everywhere spaced from said layer (11a). A method according to claim 1 or claim 2 wherein said object (10) is cylindrical and said a) step is carried out to apply said layer (11a) on an internal generally cylindrical surface of said object. A method according to claim 3 wherein said object (10) is a mud pump liner. A method according to any preceding claim wherein said layer (11a), as applied to said surface includes at least one of the compositions set forth in the following table, admixed with a minor amount of a fugitive organic binder: Nominal Compositions Co-28.5Mo-17.5Cr-3.4Si Co-30Cr-12.5W-2.5C Co-28Cr-4W-1.1C Ni-16Cr-4Fe-3.3B-4.2Si-0.7C, plus up to 92% tungsten carbide Fe-35Cr-12Co-10Ni-5Si-2C, plus up to 92% tungsten carbide Cu-37Mn-10Ni-0.5La, plus Ni-19Mn-6Si-0.5B-4Cu-0.03 rare earth, plus up to 92% tungsten carbide Ni-13Cr-20Co-2.3B-4Si-4Fe, plus up to 92% tungsten carbide. A method according to claim 5 wherein said mixture includes at least about 97% by weight of said composition, and at least about 1.0% by weight of said binder selected from the group consisting of cellulose acetate and hydrocarbon solvent. A method according to any preceding claim wherein said layer thickness is between 1.59 mm and 3.18 mm (1/16 inch and 1/8 inch), when said pressurisation is effected. A method according to any of claims 1 to 4 wherein in addition to said metal compound, the powder in said layer (11a) includes powder selected from the group consisting of: a) Co-Cr-W-C b) Co-Mo-Cr-Si c) Ni-Cr-Fe-Si-B d) Ni-Mn-Si-Cu-B e) Ni-Co-Cr-Si-Fe-B f) Fe-Cr-Co-Ni-Si-C g) Cu-Mn-Ni.

Inventors: ECER, GUNES M.
Applicants: CERACON, INC.
Application year: 1986
Main classification: B22F7
IPC codes: B22F7, B22F5, B22F3, F16J10, C22C29, F04B53