RU2570277C2 - Multistage rotary downhole pump stage and method of its production - Google Patents

Abstract

FIELD: engines and pumps.

SUBSTANCE: set of invention relates to machine building and can be used in downhole electrically driven rotary pumps for oil extraction. Impeller and guide vane of this pump are moulded from cast iron of the following composition, wt %: carbon - 3.2-3.9; silicon - 0.2-1.0; manganese - 0.5-0.8; chromium - 0.1-0.5; copper - 0.8-1.5; aluminium - 1.7-4.0; titanium - 0.0-0.2; phosphorus - not over 0.2; sulphur - not over 0.02, iron making the rest. Surfaces of impeller and guide vane have low-temperature nitrated 50-300 mcm-deep ply.

EFFECT: higher reliability, lower costs, increased MTBR.

3 cl, 1 dwg, 1 tbl

Description

The invention relates to mechanical engineering and can be used in installations of submersible electric centrifugal pumps for oil production.

A known stage used in submersible electric centrifugal pumps, including a guiding apparatus and an impeller made of ligated nirezist cast iron (Vikhman R.G., Filippov V.N. Submersible centrifugal wear-resistant pumps for oil production / Express information: TSINTIKHIMNEFTEMASH, No. 6, 1989). The disadvantage of this stage is the high cost and lack of wear resistance in reservoir fluids with a high content of abrasive particles.

Known step submersible multistage centrifugal pump and method of its manufacture, where the part is made of cast iron billets and subjected to hardening to increase its wear resistance (see RF patent No. 2116515, F04D 1/06, 07/27/1998).

The disadvantage of this step is that the hardening treatment, which consists in quenching a billet of pearlite or pearlite-ferrite cast iron, modified with rare-earth metals, on a martensitic structure with subsequent low tempering, does not provide a comprehensive increase in the reliability and durability of the stage due to increased protection against scaling, corrosion and abrasion resistance and ensuring high operational and technical characteristics of a submersible centrifugal pump.

Known borehole electric centrifugal pumping unit for oil production, containing the impeller and the guide apparatus of the pump stage. (Application for invention 2004126782/2 from 09/08/2004).

The disadvantage of the impeller and the directing device of the pump stage of this utility model is that the friction pairs of the impeller - the directing device and graphite in its composition when working with reservoir fluids with a high mass concentration of solid particles have an increased tendency to scuff, which leads to low loads jamming a pair of impeller - guide vane. This can lead to the destruction of steps, splined joints of shafts, shaft breakage and a decrease in the reliability of the pump installation.

The objective of the group of inventions is to increase the reliability of a submersible multistage centrifugal pump, reduce its cost and increase the overhaul period.

The technical result is achieved by the fact that the step of a submersible multistage centrifugal pump, comprising an impeller and a guide apparatus, made of cast iron of the following composition, wt.%: Carbon - 3.2-3.9; silicon - 0.2-1.0; manganese - 0.5-0.8; chromium - 0.1-0.5; copper - 0.8-1.5; aluminum - 1.7-4.0; titanium - 0.0-0.2; phosphorus - not more than 0.2; sulfur - not more than 0.02; iron is the rest, and the surfaces of the impeller and guide vane contain a layer nitrided with low-temperature nitriding with a thickness of 50 to 300 microns.

A method of manufacturing the impeller and guide vane of a submersible multistage centrifugal pump stage, which provides a solution to the above problem, involves introducing aluminum under the surface of the melt at a temperature of 1400-1470 ° C, subsequent heating to a spill temperature and modifying the alloy in this period by introducing ligatures to obtain the following composition, wt.%:

carbon - 3.2-3.9

silicon - 0.2-1.0

Manganese - 0.5-0.8

chromium - 0.1-0.5

copper - 0.8-1.5

aluminum - 1.7-4.0

titanium - 0.0-0.2

phosphorus - not more than 0.2

sulfur - not more than 0.02

iron - the rest,

pouring the melt into the mold, knocking out the casting and chipping the casting gates, heat treatment of the castings with heating to a temperature of 550-600 ° C with air cooling, machining of the castings to the final dimensions of the impeller and guide vanes, and low-temperature anticorrosive nitriding of their surfaces is carried out at temperature no more than 600 ° C.

The drawing shows the impeller and guide vane stage submersible multistage centrifugal pump.

The step of a submersible multistage centrifugal pump consists of an impeller 1 and a guide apparatus 2. The impellers 1 consist of an upper main disk 3 with an upper axial support 4, a hub 5, a lower cover disk 6 with a lower axial support 7, and blades 8 fixed between the upper disk 3 and the lower disk 6. The hubs 5 of the impellers 1 are fastened to the pump shaft 9 by means of dowels 10. The guide device 2 comprises a blade cover disk 11 with a supporting surface 12, a hub 13, a cylindrical ferrule 14 with an annular wall 15, atki 16, the support shoulder 17.

To increase the wear and corrosion resistance of the stages and the pump as a whole and reduce the specific axial load on the impeller 1 and on the guide device 2, the upper disk 3 of the wheel can have an axial support 19 from the side of the sinus 18, which can be supported by the axial support 20 of the hub 13 of the guide device 2, forming a couple of friction.

Submersible multistage centrifugal pump operates as follows.

During the operation of the pump, due to the rotation of the impellers 1 located on the shaft 9 and fastened by means of the hubs 5 relative to the stationary guide vanes 2, the pumped liquid enters the base (not shown conditionally) of the pump section, passes through the base and is sent to the pump stage. The pumped liquid enters the paths between the blades 8 of the rotating impeller 1 and moves from its center to the periphery. In this case, the impeller 1 creates a pressure head of the pumped liquid both due to the circulation forces and due to the Coriolis forces. Next, the fluid enters the channels of the guide apparatus 2, in which the rotation and flow direction to the impeller of the next stage are carried out. Passing through the stages of the pumps, the head (not shown conditionally) of the pump section, the pumped liquid continues to move up.

During the passage of formation fluid with a solids content in the paths between the blades of the impeller and the guide vane, mechanical and corrosion wear occurs in the zones of passage of the reservoir fluid of the channels of the impellers and guide vans. With an increase in the content of chemically aggressive components in the reservoir fluid, the corrosion and mechanical wear of the stages and the pump as a whole increases. Moreover, the impellers and guide vanes are subjected to especially intense wear when they are exposed together when the pump is operating with a high content of mechanical impurities and aggressive components of the reservoir fluid.

A method of manufacturing the impeller and guide vane of a submersible multistage centrifugal pump stage, which includes introducing aluminum under the melt surface at a temperature of 1400-1470 ° C, subsequent heating to a spill temperature and modifying the alloy in this period of time by introducing ligatures to obtain the following composition, wt.%: carbon - 3.2-3.9, silicon - 0.2-1.0, manganese - 0.5-0.8, chromium - 0.1-0.5, copper - 0.8-1.5, aluminum - 1.7-4.0, titanium - 0.0-0.2, phosphorus - not more than 0.2, sulfur - not more than 0.02, iron - the rest, pouring the melt into the mold, knock out the taste of the casting and chipping of the sprues of the castings, heat treatment of castings with heating to a temperature of 550-600 ° C with air cooling, machining of castings to the final dimensions of the impeller and guide vane and low-temperature nitriding of their surfaces to a depth of 50-300 microns at a temperature of not more 600 ° C.

The addition of alloying elements of aluminum, titanium, chromium to the composition of cast iron in the above proportions, where each of the listed chemical elements occupies a niche in the iron crystal lattice, while nitriding increases the rate of nitriding in the depth of the part and significantly increases the hardness of the nitrided layer. The melt is poured into the mold through a sprue bowl. After cooling, the casting is removed from the mold, the gate system is separated, the flash is removed and the castings are heat treated with heating to a temperature of 550-600 ° C. After heat treatment, the step parts are machined in accordance with the dimensions of the drawing. Finished impellers and stage guiding devices arrive at the low-temperature nitriding section. During nitriding, the process of diffusion saturation of the surface layer of the impellers and guide vanes with nitrogen occurs during heating in a nitrogen-containing medium. In this case, there is an increase in the surface hardness of the product, endurance and wear resistance, resistance to cavitation effects, an increase in corrosion resistance in water-containing environments, in the atmosphere, in acid and alkaline environments. The process of low-temperature nitriding is carried out mainly in gaseous media - a mixture of nitrogen and ammonia, dissociated ammonia. To activate the process, oxygen or air is introduced into the saturated medium. Also, to accelerate the process of saturation of the surfaces of the stage parts with nitrogen, nitrogen-saturated media are supplemented with carbon-saturated media, i.e. in addition to dissociated ammonia, natural gas, luminous gas, endogas, alcohol vapor or kerosene are present. The temperature of the nitriding process does not exceed 600 ° C and is usually 540-600 ° C. Heating to 600 ° C does not cause structural and geometric changes in the details of the steps made by the above method. The above method of manufacturing the impellers and guide vanes of the stages of a submersible multistage centrifugal pump gives the parts of the stage high surface hardness and strength that does not change when heated to 400-450 ° C.

This manufacturing method does not require significant energy and material costs. Low temperature nitriding can be carried out in gas nitriding furnaces using gas inlet control units.

The wear levels of steps made of cast iron, made by the above method, and niresist, the most commonly used alloy for corrosion-resistant submersible multistage centrifugal pumps, are shown in table 1.

Table 1 No. p / p Stage The initial mass of samples, g The mass of samples after 40 hours of testing, g Mass wear, g The amount of wear,% one A step made of cast iron by the claimed method 119,776 119,615 0.152 0.1269 2 The stage made of cast iron nresist 153,397 153,198 0.199 0.1297

It follows from the table that the wear values are almost the same, the wear of a nresist stage is even slightly greater than that of a step made of cast iron by the claimed method.

The maximum nitriding depth of 300 μm with the maximum titanium content is fulfilled for the most difficult working conditions: for work in reservoir fluids with a high content of solid particles with high hardness, the mass concentration of solid particles is up to 1.0 g / l or more with a hardness of up to 7 points on the Maoss scale , and with high wheel speeds, wheel speeds of up to 15,000 rpm. Alloying additives of chromium (0.1-0.5)%, aluminum (1.7-4.0)%, titanium (0.0-0.2)% are nitride-forming, in the surface layer with low-temperature nitriding of cast iron with the above composition and method, they form highly solid chemical compounds at a depth of up to 300 microns: chromium nitrides, aluminum nitrides and titanium nitrides, as a result of which the hardness of cast iron after nitriding rises by about 2 times compared to the initial one before nitriding and reaches up to HV equal to 850-1000 kg / mm ² , also increased the corrosion resistance of the surface layer z and by increasing the density of the surface layer of the part, which makes it difficult for oxygen and other aggressive elements to access the elements of cast iron. The above cast iron with low temperature nitriding has a surface layer hardness at a depth of up to 300 μm that is 2-2.5 times greater than the most commonly used alloyed cast iron niresist, corrosion resistance is not inferior to niresist, at a price cheaper by about half.

The implementation of the pump stages in this way improves the reliability of a submersible multistage centrifugal pump, reduces its cost and increases the overhaul period.

Claims (3)

1. The step of a submersible multistage centrifugal pump containing an impeller and a guide apparatus, made of cast iron of the following composition, wt.%:
carbon - 3.2-3.9
silicon - 0.2-1.0
Manganese - 0.5-0.8
chromium - 0.1-0.5
copper - 0.8-1.5
aluminum - 1.7-4.0
titanium - 0.0-0.2
phosphorus - not more than 0.2
sulfur - not more than 0.02
iron is the rest, and the surfaces of the impeller and guide vane contain a layer nitrided with low-temperature nitriding with a thickness of 50 to 300 microns. 2. A method of manufacturing the impeller and guide vane of a submersible multistage centrifugal pump stage, comprising introducing aluminum under the melt surface at a temperature of 1400-1470 ° C, subsequent heating to a spill temperature, and modifying the alloy in this period of time by introducing ligatures to obtain the following composition, mass. %:
carbon - 3.2-3.9
silicon - 0.2-1.0
Manganese - 0.5-0.8
chromium - 0.1-0.5
copper - 0.8-1.5
aluminum - 1.7-4.0
titanium - 0.0-0.2
phosphorus - not more than 0.2
sulfur - no more
0.02 iron - the rest,
pouring the melt into the mold, knocking out the casting and chipping the casting gates, heat treatment of the castings with heating to a temperature of 550-600 ° C with air cooling, machining of the castings to the final dimensions of the impeller and guide vane and low-temperature nitriding of their surfaces to a depth of 50- 300 microns. 3. The method according to claim 2, characterized in that the low-temperature nitriding of the surfaces of the impeller and the guide apparatus is carried out at a temperature of not more than 600 ° C.

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