RU2748009C1 - Module-section of submersible multistage centrifugal pump with integrated wear-resistant plain bearings - Google Patents

Abstract

FIELD: petroleum engineering.

SUBSTANCE: invention relates to petroleum engineering; it can be used in submersible multi-stage centrifugal pumps for lifting reservoir fluid from wells with a high content of abrasive particles and free gas. The module-section of the submersible pump contains a case with a set of stages, a shaft, a head and a base with radial shaft bearings mounted in them. Each shaft bearing consists of a case and a protective shaft sleeve forming a friction pair. The stages consist of open-type impellers and collapsible guide devices with removable upper disks. Bearing cases and protective shaft sleeves, impellers and guide devices are made of high-strength aluminum alloy and have a wear-resistant anti-friction ceramic-polymer coating on their surfaces. Radial and axial plane bearings in the module-section are integrated in the design of the pump section parts, and at least one sliding contact surface of the bearing is made directly in the case of the rotating or stationary part itself. The sliding surfaces of the bearings of both the shaft and the stages are formed by a ceramic-polymer coating.

EFFECT: invention is aimed at increasing the abrasive resistance of bearing units in the pump module section, increasing the reliability and service life of the module-section and the pump as a whole, as well as reducing the cost of manufacturing the module-section and reducing costs during its operation.

4 cl, 2 dwg

Description

Technology area

The invention relates to petroleum engineering and can be used in the manufacture and operation of submersible multistage centrifugal pumps for lifting formation fluid from oil wells with a high content of abrasive particles and free gas.

State of the art

Submersible multistage centrifugal pumps are currently operated mainly in conditions complicated by the presence of mechanical impurities and free gas in the well fluid.

A high concentration of solid abrasive particles in the produced fluid (the hardness of the quartz particles present in the mechanical impurities reaches HV 1100-1200) causes erosive wear of the stage parts and accelerated abrasive wear of the contacting sliding friction surfaces. Indeed, when a submersible pump is operating, it is the pumped borehole fluid that serves as a lubricating medium for friction pairs. Due to the wear of the rubbing surfaces and the increase in the gaps in the tribo-pairs, increased vibrations occur in the pump, leading to its failure. Also, vibrations of pumping equipment are caused by the presence of gas accumulations in the pumped liquid.

The decline in the resource of submersible centrifugal pumps in recent years is largely due to the ineffective operation of sleeve bearings. Taking into account the tendencies in the oil industry to intensify oil production by increasing the rotational speed of the pump rotors and at the same time reducing the outer diameter of pipes and bearings, the task of increasing the performance of bearing assemblies in submersible centrifugal pumps is extremely urgent.

With an increase in the wear resistance of pump parts, the main importance is to improve the friction pairs of radial and axial plain bearings both in the stages and in the pump itself, since friction pairs are primarily subject to increased wear during forced fluid withdrawal modes.

To increase the efficiency of sliding bearings of submersible pumps, new design solutions and new materials with high tribotechnical characteristics are required.

Today, for oil production in conditions complicated by mechanical impurities in the pumped liquid, submersible pumps with sleeve bearings made of monolithic wear-resistant materials are used, the hardness of which exceeds the hardness of quartz sand particles. These are hard alloys or technical ceramics.

Known submersible multistage pump (patent RU 2520797 dated 09/07/2010), containing a shaft, a head and a base with radial shaft bearings located in them and a housing with stages installed in it and additional intermediate shaft bearings. Each radial bearing consists of two carbide bushings, one in the bearing housing and the other on the pump shaft. These bushings form a sliding friction pair.

Known submersible multistage modular centrifugal pump (patent RU 2317445 from 22.05.2006), in which each module-section has a housing with steps installed in it and a base screwed into the housing of the module-section. At the base, a radial plain bearing is installed, consisting of a stationary carbide bush pressed into the base, and a rotating bushing fixed to the shaft using a keyed connection.

The disadvantage of these solutions is the use of bushings in plain bearings made of hard, but relatively brittle materials - hard alloys based on tungsten carbide with cobalt or nickel binder or sintered ceramic materials (SiC, Al2O3, ZrO2). Low thermal conductivity and a relatively high coefficient of friction (more than 0.12 in water) at high pump rotor speeds lead to overheating of such bushings, cracking and failure. A significant difference in the coefficients of linear thermal expansion of carbide and ceramic elements and the metal material of the bearing supports during heating of the friction units often leads to their falling out of the press-fit points.

Structures of friction units are complex and low manufacturability. Carbide and ceramic elements should only be subjected to compressive loads while maintaining a stable gap in the friction pair under all pump operating conditions. Pressing elements into metal cages with the required tightness requires the manufacture of high-precision seats.

The disadvantages of these pump designs also include the imperfection of the design of the radial shaft bearings. Radial shaft bearings installed in the section housing, head or base, consist of a bearing housing with a pressed-in sleeve and a shaft protecting sleeve. The bearing housing is a disc with a central hole and hub and several axial peripheral holes for the pumped liquid to flow through the pump section. The need to press in the sleeve (liner) increases the radial thickness of the hub and reduces the cross-sectional area of the axial holes, which leads to an increase in the hydraulic resistance to the fluid flow and a decrease in the pump efficiency. In addition, when assembling the radial shaft bearing by pressing the support sleeve into the bearing housing, due to its uneven rigidity and deformation, misalignment of the shaft and the pump section housing may occur, which will lead to shaft vibrations and reduce the pump's performance.

The sliding bearings of the stages themselves (radial and axial) are also equipped with insert elements made of hard alloys or ceramics. In the known designs of steps with an open wheel (utility model patents RU 59752 from 05.07.2006 and RU 74174 from 11.02.2008), insert parts made of hard alloy or ceramics are installed as elements of sliding bearing assemblies.

A radial bearing centering sleeve is installed between the pump shaft and the guide vane, and an axial bearing support in the form of a ring is installed between the end surfaces of the impeller and the guide vane, located in a precisely bored annular groove in the guide vane.

The disadvantage of these structures is their low manufacturability and increased cost. The manufacture of ring bushings from hard alloy or ceramics requires laborious diamond grinding on all surfaces, which significantly increases the cost of the product. In addition, as noted above, parts made of such brittle materials are susceptible to cracking and fracture from thermal and dynamic loads during pump operation.

A more promising way to increase the service life of submersible centrifugal pumps is to use parts of stages and plain bearings with a wear-resistant anti-friction coating. This makes it possible to obtain an advantageous combination of high surface hardness and structural strength of the support, as well as to improve heat transfer from the friction surface into the body of the parts.

Known elements of a submersible centrifugal pump (patent for a useful model RU 106689 dated 12/17/2010) with an anti-salt wear-resistant polymer coating, which contains a hardening additive in the form of fine ceramic particles (up to 20%).

The disadvantage of the described coating is its uneven thickness, which reduces the accuracy of the mates between the pump parts and requires an increase in the tolerance field for the manufacture of mounting holes, which in turn causes an increase in the flow in the pump and reduces its performance and efficiency. In addition, the polymer coating with a hardening additive works satisfactorily in wells with an increased content of mechanical impurities in the produced fluid, but it wears out quickly if it contains solid abrasive particles. When the friction unit is operating under the action of load and elevated temperature, the polymer matrix softens and deforms, exposing hard particles that are weakly bound to the matrix material, which are easily pulled out without being completely worn out.

The closest to the claimed invention in terms of the combination of features is a submersible multistage centrifugal pump, described in the invention RU 2580611 dated 06/19/2014 and adopted as a prototype. The pump contains a housing, a shaft and stages, consisting of an impeller and a guide vane. Impellers and guide vanes are made of cast iron and contain a nitrided layer on their surfaces. The contacting surfaces of the impellers and guide vanes, which form friction pairs of axial sliding bearings of the stages, are additionally coated with a wear-resistant sprayed hard-alloy coating based on tungsten carbide.

The disadvantage of this technical solution is the large number of technological operations in the manufacture of steps, which increases the complexity and cost of manufacturing steps. It should also be noted that there is a fairly high coefficient of friction between the hardened contacting surfaces in the absence of any solid lubricant.

But the main disadvantages of a pump with these stages are the disadvantages inherent in all cast-iron stages: the low accuracy of heavy cast wheels of a closed type leads to imbalance and vibrations during pump operation, the high roughness of the cast surfaces of the flow channels of the stages increases the hydraulic resistance to the flow of the pumped liquid and enhances the processes of scale deposition and clogging. channels with mechanical impurities.

Disclosure of the essence of the invention

The objective of the present invention is to increase the abrasive resistance of the bearing assemblies in the pump module-section, to increase the reliability and service life of it and the pump as a whole during operation in wells complicated by a high content of abrasive particles and free gas in the formation fluid, as well as to reduce the production cost of the module-section and operating costs.

The technical result achieved by the implementation of the invention consists in:

- in increasing manufacturability and reducing the cost of manufacturing bearing assemblies in the pump module-section by simplifying the design;

- in reducing abrasive wear and vibration loads in the friction units of the module-section due to the use of a wear-resistant anti-friction coating on the parts and increasing the accuracy of assembly of mating surfaces;

- in reducing the operating temperature of friction units in the pump module-section and in the pump as a whole by reducing the sliding friction coefficient and improving heat removal from the contact zones by making bearing parts and stages from high-strength aluminum alloy with high thermal conductivity;

- in increasing the efficiency of the pump module-section, reducing energy consumption by minimizing friction losses, reducing the mass of rotating impellers (350-600 pcs. in the pump) by 2.9 times and, in connection with this, a significant reduction in vibrations, which will increase reliability and life time

- reducing the total mass of the module-section by 2.9 times: the shaft bearing housings, shaft protective sleeves, impellers and guide vanes (350-600 pcs. in the pump) are made of aluminum alloy.

The module-section of a submersible multistage centrifugal pump, ensuring the achievement of the above technical result, contains a shaft, a head and a base in which radial shaft slide bearings are located, consisting of a shaft bearing housing and a shaft protecting sleeve, and a housing with a set of stages consisting of an impeller open type and collapsible guide vane with a removable top disc.

Shaft sleeve bearing housings, shaft protecting sleeves, impellers and guide vanes are made of high-strength aluminum alloy, and a wear-resistant antifriction ceramic-polymer coating is formed on their surface.

Radial shaft slide bearings, radial and axial slide bearings of the stages are integrated in the design of the module-section parts, when at least one sliding contacting surface of the bearing is made directly in the body of the rotating or stationary part. In this case, the supporting inner cylindrical surfaces of the shaft bearing housings, with their ceramic-polymer coating, contact the ceramic-polymer coating on the outer cylindrical surfaces of the protective shaft sleeves, forming friction pairs of the radial shaft sliding bearings; the supporting flat surfaces of the annular protrusions on the ends of the guide vanes with their ceramic-polymer coating contact the ceramic-polymer coating on the end surfaces of the impellers, forming friction pairs of the axial sliding bearings of the stages; the supporting inner cylindrical surfaces of the hubs of the guide vanes with its ceramic-polymer coating contacts the ceramic-polymer coating on the outer cylindrical surfaces of the elongated bushings of the impellers, forming friction pairs of the radial sliding bearings of the stages.

The stages consist of open-type impellers (diskless) and collapsible guide vanes with a removable upper disc. Stages with open impellers are most effective when pumping formation fluid with a high content of solids and free gas. When the pump is running, open impellers disperse both gas bubbles and dirt inclusions, homogenizing the pumped liquid.

The design of the stage with an open wheel and a guide vane with a removable top disc is highly technological. The absence of closed cavities in the details of the step simplifies their machining and makes it possible to form smooth ceramic coatings of uniform thickness on the surfaces of the details.

The design of a radial shaft bearing consists of only two parts: the shaft bearing housing, which is tightly mounted in the head or base, and the shaft protecting sleeve, which is secured to the shaft with a key. The exclusion from the design of the main element of the traditional plain bearing - a sleeve (liner) made of a monolithic solid material made it possible to simplify the design and reduce the labor intensity of manufacturing the friction unit. In addition, the installation of bearings has been simplified, the alignment accuracy and alignment of the bearing surfaces of the bearings and the shaft have increased. Also, the absence of a pressed-in sleeve made it possible to increase the cross-sectional area of the axial peripheral holes in the bearing housing by 20-25%. This, in turn, makes it possible to significantly reduce the hydraulic resistance to the flow of the pumped liquid at the inlet and outlet of the pump module-section and to increase the efficiency of the pump.

Shaft bearing housings, shaft protecting sleeves, impellers and guide vanes are made of high-strength aluminum alloy with a yield strength of at least 400 MPa. The strength of such an alloy is twice that of "ni-resist" nickel cast iron. A wear-resistant ceramic-polymer coating with a thickness of 45-65 microns and a hardness of HV 1400-1900 is formed on the surfaces of light aluminum parts of the section.

Strong and hard oxide-ceramic coatings, 1.5-2 times superior in abrasive wear resistance, are created on the surface of aluminum parts by the method of plasma electrolytic oxidation (PEO). The PEO method is the most effective way to harden aluminum alloys.

The new high-frequency version of PEO allows for a short time (0.5 hours) to form coatings with a thickness of 45-65 microns on the surface of aluminum parts, while the original dimensions of the parts remain within the tolerance field (patent RU 2681028 dated 01.17.2018 and Eurasian patent 012825 dated 02.04. 2007).

Aluminum parts with such a coating successfully resist abrasive and erosive wear and vibrodynamic loads.

The introduction of a fluoropolymer into the micropores of a ceramic coating leads to a significant improvement in its protective properties. The presence of polymer on the surface of the ceramic-polymer coating reduces the coefficient of friction in water to 0.04-0.06, which is half that of hard alloy and ceramics. The low coefficient of friction minimizes the operation of friction units and reduces the energy consumption of the pump. The hydrophilic properties of the ceramic-polymer coating prevent the deposition of salts and ARPD on it. The friction pair "ceramic-polymer coating over ceramic-polymer coating" provides stability of tribotechnical characteristics due to self-lubricating properties. The wear pattern of such surfaces is fundamentally different from the wear pattern of surfaces with a protective polymer coating described in the above utility model patent RU 106689. When a tribo unit with a ceramic-polymer coating is operating, a strong and hard ceramic frame (micro protrusions of a ceramic layer) perceives the mechanical load, and the polymer , located in the micropores of the coating, acts as a solid antifriction lubricant.

With an increase in temperature in friction pairs under conditions of boundary lubrication (with a free gas content in the pumped liquid above 40%), heat is intensively removed from the friction zone due to the high thermal conductivity of aluminum supports and steps.

Thus, a comprehensive improvement in the operational characteristics of the module-section sliding bearings is achieved due to the maximum reduction in the coefficient of friction, increase in the hardness and abrasive wear resistance of the contacting surfaces, and intensification of heat removal from friction units.

Known technical solutions for the use of pump stages made of aluminum alloys with a ceramic coating. This is the stage described in the patent WO 2008069702 dated 06.12.2008, and the guiding device described in the patent RU 2387881 dated 09.02.2009. The main disadvantage of these technical solutions is the low manufacturability of the step structures, which does not allow using the advantages of the new structural material to the full. In the above patents, the stage parts are traditionally made in one piece. Cast closed-type impellers and guide vanes have narrow deep cavities, the surfaces of which are located close to each other. It is difficult to apply a high-quality ceramic coating using the PEO method on such surfaces, since they shield each other. In addition, cast aluminum alloys (silumins), due to their chemical composition, also impede the production of high-quality ceramic coatings. Silicon crystals are present on the surface of these alloys, which poorly conduct electric current, which complicates the passage of plasma discharges during oxidation. The coatings are porous with reduced hardness.

Therefore, the application of the described technical solutions has no practical perspective.

Also known is the stage of a submersible electric centrifugal pump, described in Eurasian patent 029187 dated 03.26.2015. The stage consists of an open wheel and a collapsible guide vane and is made of a heat-resistant aluminum alloy with a protective ceramic coating impregnated with a polymer.

The main disadvantage of this technical solution is the insufficient strength of the heat-resistant aluminum alloy selected for the manufacture of hardened parts of the steps. This is manifested, first of all, when the steps are operated in harsh conditions of abrasion. When an abrasive particle enters the friction surfaces, it exerts a powerful force on them. Local contact voltages reach high values. If the material of the rubbing bodies is an aluminum alloy with a ceramic coating 50 μm thick, then the behavior of the coating in this case depends on the yield strength of the base alloy. It has been experimentally established that the use of an aluminum alloy with a yield point below 350-400 MPa in tribological assemblies (the high-temperature alloy selected in the analogue has a yield point of 270-300 MPa) leads to plastic deformation of the alloy under the coating in the zone of action of the abrasive particle. This leads to the appearance of cracks in the coating and its subsequent destruction. The use of high-strength aluminum alloys with a yield point of more than 400 MPa in tribo assemblies, in such a case, only leads to elastic deformation of the coating and base alloy in the zone of action of the abrasive particle and its further crushing into smaller fragments. The disadvantage of the known solution is the use of additional plug-in bushings and rings made of hard alloys or ceramics in the friction pairs of the stages.

High wear resistance and tribotechnical characteristics of the friction pair "ceramic-polymer coating over ceramic-polymer coating" made it possible to simplify the design of friction units and to make mating surfaces of plain bearings directly in the body of the parts themselves, that is, to integrate the bearings into the design of the parts. This made it possible to abandon the placement of special bearings in the pump module-section in the form of additional antifriction bushings and rings.

The radial shaft sliding bearing is formed by the supporting inner cylindrical surface of the shaft bearing housing and the outer cylindrical surface of the shaft protecting sleeve.

The design of the stage provides for the presence in each stage of radial and axial plain bearings, made directly in the body of the stage parts. The axial sliding bearing of the stage is formed by the supporting flat surface of the annular protrusion on the end of the guide vane and the end surface of the impeller. The radial plain bearing is formed by the supporting inner cylindrical surface of the guide vane hub and the outer cylindrical surface of the elongated impeller sleeve. To ensure the required bearing capacity and the acceptance of the acting loads, the sleeve length l must be related to its diameter d, as l = (0.6-0.8) d. The light weight of the aluminum wheels and the high precision of their manufacturing ensure balanced rotation of the rotor of the pumping module-section with a minimum level of vibrations.

This allows the use of modern high-speed submersible motors without hindrance and significantly increases the pump performance.

The essence of the proposed technical solution is illustrated by drawings. FIG. 1 shows a longitudinal section of the inventive module-section of a submersible multistage centrifugal pump.

The module-section of a submersible centrifugal pump contains a drive shaft 10, a head 2, a base

3 and housing 1, in which a set of steps is installed. The shaft 10 of the module-section rests on radial shaft bearings located in the head 2 and base 3. The radial shaft bearings consist of stationary, rigidly mounted in the head 2 and base 3, shaft bearing housings 13 and shaft protecting sleeves 11, secured to the shaft with keys and rotating together with the shaft 10. The bearing housing of the shaft 13 is a precision-made disc with a central hole and several axial holes 12 around the periphery for the pumped liquid to pass. The supporting inner surfaces of the bearing housings of the shaft 13, in contact with the outer cylindrical surface of the protective bushings of the shaft 11, form friction pairs of the radial sliding bearings of the shaft 14. Both contacting surfaces have a ceramic-polymer coating.

FIG. 2 shows an element of a module-section with steps (longitudinal section) on an enlarged scale.

In housing 1, a set of stages is installed, consisting of open-type impellers 4 and collapsible guide vanes b. The impellers 4 are mounted on the shaft 10 by means of keys and rotate with it. The guide vanes 6 are fixed inside the housing 1 due to the frictional forces from the interference created by the heads 2 and the base 3 screwed into the housing 1 from both sides. The impeller 4 consists of an elongated sleeve 5 with radial blades placed on it. The length of the sleeve l is related to its diameter d, as l = (0.6-0.8) d. The guide vane 6 consists of a glass, made integral with a thickened lower disk, and an upper removable disk 7. The lower thickened disk has a central hub 8 and channels-blades leading from the periphery to the center. An annular protrusion 9 is made at the end of the lower disc.

The supporting flat surfaces of the annular protrusions 9 on the ends of the guide vanes 6, in contact with the end surfaces of the impellers 4, form friction pairs of the axial sliding bearings of the stages 16. In this case, both contacting surfaces have a ceramic-polymer coating. The supporting inner cylindrical surfaces of the hubs 8 of the guide vanes 6, in contact with the outer cylindrical surface of the elongated bushings 5 of the impellers 4, form friction pairs of the radial sliding bearings of the stages 15. Both contacting surfaces have a ceramic-polymer coating.

The pumping module-section works as follows. When the section is in operation, the drive shaft 10 rotates in radial shaft slide bearings.

Due to the rotation of the impellers 4 located on the shaft 10 relative to the stationary guide vanes 6, the pumped liquid enters the base 3 and through the peripheral holes 12 in the radial bearing housing of the shaft 13 is directed to the centrifugal stages of the section.

The liquid entering the interscapular cavity of the impeller 4 moves from the center to the periphery. In this case, the impeller 4 creates a pressure of the pumped liquid. Further, the liquid enters the channels-blades of the lower disc of the guide vane 6, in which the turn and direction of the flow to the impeller of the next stage are carried out. In this case, the kinetic energy of fluid movement is converted into potential energy. Passing through the steps of the section, the liquid enters the head 2 and, moving through the peripheral holes 12 in the radial bearing housing of the shaft 13, continues to move upward. During the operation of the module-section, friction pairs of sliding bearings 14, 15 and 16 provide easy balanced rotation of the shaft 10 with the impellers 4 (section rotor).

Thus, the proposed invention makes it possible to create a module-section of a submersible multistage centrifugal pump with integrated wear-resistant plain bearings, which makes it possible with the lowest labor and economic costs to produce and operate submersible oil pumps in wells complicated by a high content of abrasive impurities and free gas in the formation fluid.

Claims (4)

1. Module-section of a submersible multistage centrifugal pump, containing a shaft, a head and a base in which radial shaft slide bearings are located, consisting of a shaft bearing housing and a shaft protecting sleeve, forming a friction pair, a housing with a set of stages consisting of an impeller and a guide device, while the supporting flat surfaces of the annular protrusions on the ends of the guide vanes in contact with the end surfaces of the impellers form friction pairs of axial sliding bearings of the stages, and the supporting inner cylindrical surfaces of the hubs of the guide vanes contacting the outer cylindrical surfaces of the bushings of the impellers are friction pairs of radial sliding bearings of the stages, and the contacting friction surfaces of the radial shaft bearings, axial and radial bearings of the stages contain a wear-resistant coating, characterized in that the impellers are made of an open type, and the guide vanes are disassembled with a removable upper disc, and the shaft bearing housings, shaft protecting sleeves, impellers and guide vanes are made of high-strength aluminum alloy, and a ceramic-polymer coating is formed on their surfaces, radial and axial plain bearings in the module-section are integrated into the design of the section parts when at least one sliding contacting surface of the bearing is made directly in the body of a rotating or stationary part, the friction pairs of the sliding bearings of the section are formed by surfaces with a ceramic-polymer coating, with which they contact each other. 2. Module-section according to claim 1, characterized in that the shaft radial bearing housings, shaft protective sleeves, impellers and stage guide vanes are made of high-strength aluminum alloy with a yield strength of at least 400 MPa. 3. Module-section according to claim 1 or 2, characterized in that the ceramic-polymer coating formed on the surfaces of the shaft bearing housings, shaft protective sleeves, impellers and stage guide vanes is made with a thickness of 45-65 microns and a hardness of HV 1400- 1900. 4. Module section according to any one of paragraphs. 1-3, characterized in that elongated bushings with a diameter d and a length l are made on the impellers of the steps, and the ratio l = (0.6-0.8) d is observed.

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