Ball valve with wear-resistant polyimide coating of the shut-off element

Abstract

This utility model relates to pipeline valves and is intended for use in the oil, gas, and chemical industries. The ball valve comprises a body, a control element, and a spherical steel shutoff element that engages sealing seats. The working surface of the shutoff element is coated with a wear-resistant polyimide film coating 80-120 μm thick. The technical result consists of increasing the service life and maintaining the valve's tightness in the temperature range from minus 269°C to plus 400°C due to a low friction coefficient of 0.15-0.25 and high adhesion of the coating to the metal surface of the shutoff element. 2 ill.

Description

[0001] The utility model relates to pipeline fittings, in particular to ball valves used as shut-off or regulating devices for controlling the flow of working fluid in the oil refining, gas, chemical and other industries, including in conditions of extreme temperatures.

[0002] One of the key components determining the performance of a ball valve is its shut-off element—the plug. In the "open" position, the opening in the shut-off element aligns with the pipeline, allowing the working fluid to pass freely through the valve. When the control element is turned, the shut-off element rotates and closes the passage, completely blocking the flow. When transporting aggressive media, corrosion of the shut-off element's working surfaces occurs, gradually reducing wear resistance and compromising the ball valve's seal.

[0003] Ball valve tightness is achieved by tightly fitting the shutoff element to the pre-compressed sealing seats. The hardness and wear resistance of the plug surface plays a significant role in ball valve tightness, as it is subject to friction with the sealing seats, valve body, and spring supports. Maintaining a tight seal is especially important when operating under temperature fluctuations or at high temperatures, where materials are subject to change and deformation.

[0004] Ball valves are known in the art for their increased wear resistance by using various types of coatings that can extend the service life of the shut-off element. For example, protective galvanic (RU No. 2142520, RU No. 20231011), metallic (RU No. 2104434), ceramic (RU No. 46065, RU No. 20190311), and aluminum oxide (RU No. 2347126) coatings are known. Polymers are also used to extend the service life of ball valves, as these materials exhibit high strength, a low coefficient of friction, a wide temperature range, and a low coefficient of thermal expansion.

[0005] A ball valve (RU patent no. 20130520) is known. It comprises a body with inlet and outlet ports, a ball plug with a bore, seats, and a ball plug control spindle. The working surfaces of these seats are coated with a 4-20 nm thick fluorinated oligomer layer. A disadvantage of this alternative is the low heat resistance and strength of the oligomer coating, which reduces the durability and wear resistance of the structure under high loads compared to a polyimide coating.

[0006] RU Patent No. 2681605 describes a ball valve with a body comprising inlet and outlet sections separated by a working chamber containing a shut-off ball and seals. The valve features a heat-insulating coating made of a polymer binder filled with a porous ceramic material (particle size less than 1 μm), in a ratio of 70-30% binder and 30-70% filler. The seals are made of a polymer material with a coefficient of thermal expansion matching that of the ball and body, thanks to the addition of micro- or nanoceramic powders (10-70% volume content). Polyurethane, epoxy resins, and fluoropolymers are used as binders. The disadvantage of polyurethane coating is its poor resistance to high temperatures, since the melting point and operating temperature range of polyurethane usually does not exceed 160°C. In addition, polyurethane has lower resistance to hygroscopicity compared to polyimides.

[0007] A ball valve (patent RU 2003905 C1) is known, containing a rotary stem with a ball plug interacting with two polymer seats. The internal surfaces of the inlet and outlet ports and the body are equipped with a polymer lining with flanges along the ends of the ports. The plug is made of a high-strength composite material based on high-strength chemical-resistant fiber 0.01-110 mm long and a chemical-resistant polymer binder. The plug is coated with a material containing polytetrafluoroethylene (PTFE) 0.025-0.08 mm thick. A disadvantage of PTFE is its high coefficient of thermal expansion (cold flow) and a tendency to deform under prolonged static loads, which leads to a loss of tightness.

[0008] The closest technical solution (prototype) is a ball valve according to patent RU 140065, comprising a body with inlet and outlet ports, a ball plug with a bore, a seat, and a ball plug control handle. The working surfaces of the ball plug are coated with a metal-fluoroplastic material 0.1-0.4 mm thick. Metal-fluoroplastic is a polymer composite, as it contains PTFE.

[0009] The disadvantages of the prototype are:

[0010] 1. Limited operating temperature range (up to plus 200°C), due to the properties of the fluoroplastic matrix.

[0011] 2. Shrinkage and insufficient dimensional stability of the coating at cryogenic temperatures due to the difference in the thermal expansion coefficients of the metal and metal-fluoroplastic.

[0012] 3. Relatively low adhesion and mechanical shear strength compared to polyimides, which leads to coating peeling during temperature cycling.

[0013] The technical challenge is to create a ball valve that can operate reliably and maintain tightness over a wide temperature range from minus 269°C to plus 400°C, as well as ensuring an increase in the service life of the shut-off element.

[0014] The technical result consists of increasing the operational reliability of the ball valve over a wide temperature range (from minus 269°C to plus 400°C), as well as extending the service life of the shut-off element. This result is achieved due to stable adhesion and increased wear resistance of the shut-off element coating, achieved through its high corrosion resistance and low friction coefficient, which reduces abrasive wear. According to the utility model, this technical result is achieved by applying a polyimide coating 80-120 μm thick to the spherical working surface of the shut-off element, which contacts the sealing seats, in a ball valve comprising a body, a control element, sealing seats installed in spring-loaded supports, and a metal shut-off element with a through bore.The shutoff element can be shaped as a sphere, equipped with upper and lower coaxial cylindrical projections in the form of support trunnions for fixation in the housing. The shutoff element can be made of stainless steel with a roughened surface prepared by mechanical treatment and chemical activation before application of a polyimide coating. Kapton® XD (DuPont) or Upilex®-S (UBE Industries) can be used as the polyimide coating—an example of polyimide materials operating in the temperature range from -269°C to +400°C.

[0015] The proposed utility model is illustrated by drawings, in which:

[0016] Fig. 1 shows a general view of the ball valve in section;

[0017] Fig. 2 shows an example of applying a polyimide coating to the surface of a ball valve plug.

[0018] The following designations are used in the drawings: 1 - valve body; 2 - control element (stem); 3 - shut-off element (plug); 4 - spring-loaded supports; 5 - sealing seats; 6 - polyimide coating; 7 - through hole of the shut-off element (plug); 8 - trunnions of the shut-off element (plug); 9 - technological hole.

[0019] Implementation of a utility model

[0020] The ball valve comprises the following key components: a body 1 with inlet and outlet ports, made, for example, of steel or cast iron, capable of withstanding the required operating pressure and temperature ranges. Sealing seats 5, preferably made of a fluoroplastic material (e.g., PTFE, FEP), are mounted within the body 1 in spring-loaded supports 4. These seats provide the necessary pressure against the shut-off element 3 and compensate for wear.

[0021] The choice of fluoroplastic is justified:

[0022] high chemical inertness to aggressive environments;

[0023] low friction coefficient (0.04);

[0024] high contact tightness.

[0025] A shut-off element 3, made of stainless steel and shaped like a sphere with a through hole 7, is installed with an interference fit between seats 5. Shut-off element 3 can be equipped with upper and lower trunnions 8 for centering within the body, which reduces the load on the seals. They are fixed in corresponding bores of the valve body, ensuring precise positioning of the ball and the ability to rotate it with minimal effort. The upper trunnion is connected to the actuator via a stem. A hole 9 is made on the surface of shut-off element 3 to equalize the pressure in the cavities of the valve when the ball is in the closed position. This reduces the force required to rotate it and prevents excessive pressure on the seals. Rotation is controlled via control element 2.

[0026] In a particular implementation case, the shut-off element 3 is a high-precision processing sphere (for example, accuracy class not lower than IT6-IT7) with the following design elements:

[0027] Shut-off body: made of stainless steel (for example, grade 12X18H10T), which provides corrosion resistance, mechanical strength and dimensional stability under temperature changes.

[0028] Through cylindrical bore 7: The diameter determines the valve's flow capacity. When rotated 90°, the bore aligns with the pipeline direction (open position) or is blocked by the solid wall of the ball (closed position).

[0029] Upper and lower trunnions 8: coaxial cylindrical projections serving as pivot points. They ensure precise valve centering, minimize lateral loads on the seals, and allow free rotation with minimal torque.

[0030] Technological equalizing hole: a small hole on the surface of the sphere serves to equalize the pressure in the cavities of the valve when the shut-off element is closed, which reduces the turning force and prevents excessive pressure on the sealing seats.

[0031] Control element (pos. 2) - a stem connected to the upper trunnion of the shut-off element, provides control of rotation for opening and closing the valve.

[0032] The outer spherical working surface of the shut-off element 3, which contacts the sealing seats 5, is coated with a continuous, wear-resistant polyimide coating 6 with a thickness of 80-120 μm. Suitable coating materials include Kapton XD (DuPont) and Upilex-S (UBE Industries), which feature high heat resistance (operating temperature range: from -269°C to +400°C), high mechanical strength and wear resistance, chemical inertness, dimensional stability, and low shrinkage.

[0033] Specificity of the friction pair "Polyimide-Fluoroplastic":

[0034] 1. The selection of polyimide coating material matches the sealing seat material (fluoroplastic), providing an optimal friction pair with:

[0035] minimum friction coefficient (0.15-0.25);

[0036] maximum contact tightness;

[0037] minimum energy loss when operating the crane;

[0038] minimal abrasive wear of both materials.

[0039] 2. Both materials have a low coefficient of friction and material compatibility, eliminating component migration between the materials. The difference in thermal expansion coefficients creates an optimally distributed contact tension that is maintained at cryogenic and high temperatures.

[0040] The use of polyimide coating provides a reduction in the coefficient of friction and an increase in service life compared to unprotected steel.

[0041] Table 1 - Comparative data of the surface characteristics of the ball with and without coating

[0042] Material Characteristics Kapton XD (DuPont) Upilex-S (UBE Industries) Uncovered Operating temperature range, °C from minus 269 to plus 260 from minus 269 to plus 400 from minus 196 to plus 125 Coefficient of friction at minus 196°C 0,15-0,25 0,15-0,25 0,2-0,5 Cryogenic stability Yes (no cracking) Yes (no cracking) Yes (no cracking) Adhesion to metal at minus 196°C, MPa 20-25 25-30 - Resource at minus 196°C, cycles 50000 100000 <10000

[0043] A polyimide coating is applied to the working surface of the ball valve shutoff element with a thickness of 80-120 µm. The specified maximum thickness of the polyimide coating is determined by the following:

[0044] If the thickness is less than 80 µm, the coating limits the scope of application, since a thin layer of polyimide is less resistant to mechanical stress, which reduces its protective properties. In addition, defects in the coating and incomplete application of the coating are possible, which will not ensure the tightness of the shut-off element;

[0045] When the thickness is more than 120 µm, the wear resistance of the coating decreases due to the increase in plasticity, which does not allow it to be used for ball valves operating in a working environment containing a large number of foreign particles.

[0046] Thus, the maximum polyimide coating thickness values ​​are optimal for ensuring wear resistance and improving the tightness of the ball valve shutoff element. In the range of 80-120 µm, an optimal balance is achieved:

[0047] compensation of micro defects of the base (ensures uniform contact);

[0048] Sufficient rigidity to maintain spherical shape;

[0049] plastic deformations are minimized;

[0050] The friction coefficient remains in the minimum range of 0.15-0.25.

[0051] Creating a high-quality coating requires following four consecutive stages of preparation and application:

[0052] Stage 1 - Mechanical Surface Preparation: The valve surface is mechanically processed (e.g., polishing, grinding, or abrasive blasting) to achieve the desired roughness. The goal is to create micro-protrusions and micro-depressions that serve as "anchors" for the polyimide coating and to eliminate macro-defects (scratches, dents).

[0053] Stage 2 - chemical cleaning and degreasing: removal of process contaminants (machine oil, preservative lubricants), for example, using organic solvents (acetone, alcohol) or alkaline solutions.

[0054] Stage 3 - Chemical activation of the surface: removing the oxide layer formed on the surface of stainless steel in air and creating a surface with high surface energy containing active centers for chemical interaction.

[0055] Stage 4 - Application of the adhesive sublayer: A "chemical bridge" is created between the steel and polyimide. A thin layer of 0.5-5 µm adhesive is applied to the activated surface:

[0056] Epoxy resin containing organic groups capable of bonding with metal and polyimide;

[0057] Special silanes / titanates (γ-aminopropyltriethoxysilane) that form covalent bonds with metal oxides;

[0058] Primers based on polyimide oligomers.

[0059] Polyimide coating application methods depend on the manufacturing facility's conditions and resources, as well as the properties and form of the source material. After surface preparation, the polyimide coating (film) is applied using one of three methods:

[0060] 1. The polyimide coating is laminated to the valve element using liquid adhesive or a thermoplastic coating. The material is then pressed under pressure and high temperature, ensuring a uniform bond. After heating and pressing, the valve element is cooled to prevent internal stress and stabilize its dimensions.

[0061] Advantages: large contact area of ​​the coating (film), high reliability, applicable to complex geometric shapes.

[0062] 2. Vacuum deposition: The polyimide material is evaporated or sprayed under vacuum and deposited on the surface of the ball valve. The material is then treated at high temperatures of 200-300°C to improve adhesion.

[0063] Advantages: more uniform distribution, high density, the coating follows the contours without deformation.

[0064] 3. Using adhesives. Apply adhesive in liquid form or as a thin film to the prepared surface of the polyimide liner or ball valve body. The bonded parts are then pressed and exposed to high temperatures (e.g., 180°C).

[0065] Advantages: Flexible choice of adhesive, can be adapted to various equipment, high reliability.

[0066] Case study: A prototype ball valve was manufactured. The plug is made of 12X18H10T steel. The surface is coated with a 100-µm-thick polyimide coating (Upilex-S film). Testing showed:

[0067] the coefficient of friction at minus 196°C was 0.15-0.25 (versus 0.2-0.5 for uncoated steel);

[0068] adhesion to metal at cryogenic temperatures: 25-30 MPa;

[0069] Working life: more than 100,000 cycles without loss of tightness;

[0070] Operating temperature range: from minus 269°C to plus 400°C.

[0071] Thus, the proposed technical solution - a ball valve with a polyimide coating based on materials such as Kapton® (DuPont) or Upilex®-S (UBE Industries) with a thickness of 80-120 µm on the shut-off element and sealing seats - ensures an extension of the operating temperature range to minus 269°C...plus 400°C, increased wear resistance, reduced friction and prevention of plug sticking.

[0072] The coating has high chemical inertness, minimal shrinkage and a low coefficient of thermal expansion, which maintains the sealing gap and tightness during temperature changes.

[0073] This results in a 5-10 times increase in the service life of seals and plugs, stability of control torque after downtime, and prevention of microcracks and delamination.

[0074] Experimental data confirms that the seal remains intact under cryogenic conditions and over multiple operating cycles.

[0075] Overall, the solution increases the durability and reliability of the ball valve in extreme temperature conditions due to improved corrosion resistance and reduced abrasive wear.

Claims

1. A ball valve with a wear-resistant polyimide coating of the shut-off element, comprising a body with inlet and outlet pipes, a control element, a shut-off element with a through hole, compressed with seats installed in spring-loaded supports, characterized in that a polyimide coating with a thickness of 80–120 μm is applied to the working surface of the shut-off element.

2. A ball valve according to paragraph 1, characterized in that the shut-off element is made in the form of a sphere and is equipped with pins for fixation in the body.

3. A ball valve according to paragraph 1, characterized in that the polyimide coating is fixed to the surface of the shut-off element by means of an adhesive layer.

4. A ball valve according to paragraph 1, characterized in that the sealing seats are made of fluoroplastic material.

5. A ball valve according to claim 1, characterized in that the polyimide coating is Kapton XD material.

6. A ball valve according to claim 1, characterized in that the polyimide coating is Upilex-S material.

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