Wenzhou Unique Valve Co., Ltd.
High Temperature and High-pressure Wear Resistant Ball Valves (Part One)
Mar 26, 2021
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Abstract: The design and manufacturing key points of a high temperature and high-pressure wear resistant ball valve for harsh working conditions are introduced in this article. Special processing technology and equipment for cold and hot alternating cyclic tests provide a reference for more high-end valves being made in China.
1. Overview
In the processing of inferior crude oil such as residual oil and heavy oil, special processing equipment is required to maintain the octane number of gasoline due to its high viscosity and sulfur content. Special processing devices such as fluidized bed hydrogenation, slurry bed hydrogenation and suspended bed hydrogenation are used for refining heavy and inferior oil. Among them, the fluidized bed hydrogenation process is currently the most effective method for processing heavy and inferior oil. A solid catalyst is required to be added in this process, with hardness of 60HRC, a diameter about 50μm, an operating temperature between 400°C and 460°C and operating pressure of 18 to 22MPa. The high temperature and high-pressure wear resistant ball valve used in the fluidized bed residual oil hydrogenation unit not only needs to adapt to the gas, liquid and solid three-phase working conditions, but also withstands the scouring, abrasion and corrosion of the catalyst under the conditions of high temperature and high pressure. Under the condition of frequent changes of temperature and pressure, the peeling of wear resistant coatings and fatigue alternating should be avoided.
2 Structural design
2.1 Floating ball structure
Generally, metal sealed ball valves are mostly of fixed ball structure. The medium in the fluidized bed residual oil hydrogenation unit system contains solid particles. In order to prevent particles from entering the spring cavity, the valve is designed as a floating ball structure. The inlet end is a floating valve seat, and a pre-tightened disc spring is installed. The outlet end is a fixed valve seat with double-sided sealing, which is fixed inside the valve body by a pressure ring (Figure 1). The front of the valve seat is a concave spherical surface, which forms a sealing pair with the sphere. There are two structures behind the valve seat: one is a plane seal, which forms a sealing pair with the hard plane of the inner hole of the valve body's outlet end, and the other is a spherical seal (Figure 2). The back of the valve seat is a convex spherical surface, and the inner hole of the outlet end of the valve body is processed into a concave spherical sealing surface. The two form a sealing pair, which is beneficial to the grinding and matching of the super-hard sealing surface.
1. Valve bodies 2. Front valve seats 3. T-shaped sealing rings 4. Disc springs 5. Valve bonnets 6. Balls 7. Stems 8. Pre-tightened combination springs 9. Micro-leakage combination packing 10. Anti-friction pads 11. Pressure rings of valve seats 12. Back valve seats
Figure 1 Wear resistant ball valves for fluidized bed residual oil hydrogenation units
1. Overview
In the processing of inferior crude oil such as residual oil and heavy oil, special processing equipment is required to maintain the octane number of gasoline due to its high viscosity and sulfur content. Special processing devices such as fluidized bed hydrogenation, slurry bed hydrogenation and suspended bed hydrogenation are used for refining heavy and inferior oil. Among them, the fluidized bed hydrogenation process is currently the most effective method for processing heavy and inferior oil. A solid catalyst is required to be added in this process, with hardness of 60HRC, a diameter about 50μm, an operating temperature between 400°C and 460°C and operating pressure of 18 to 22MPa. The high temperature and high-pressure wear resistant ball valve used in the fluidized bed residual oil hydrogenation unit not only needs to adapt to the gas, liquid and solid three-phase working conditions, but also withstands the scouring, abrasion and corrosion of the catalyst under the conditions of high temperature and high pressure. Under the condition of frequent changes of temperature and pressure, the peeling of wear resistant coatings and fatigue alternating should be avoided.
2 Structural design
2.1 Floating ball structure
Generally, metal sealed ball valves are mostly of fixed ball structure. The medium in the fluidized bed residual oil hydrogenation unit system contains solid particles. In order to prevent particles from entering the spring cavity, the valve is designed as a floating ball structure. The inlet end is a floating valve seat, and a pre-tightened disc spring is installed. The outlet end is a fixed valve seat with double-sided sealing, which is fixed inside the valve body by a pressure ring (Figure 1). The front of the valve seat is a concave spherical surface, which forms a sealing pair with the sphere. There are two structures behind the valve seat: one is a plane seal, which forms a sealing pair with the hard plane of the inner hole of the valve body's outlet end, and the other is a spherical seal (Figure 2). The back of the valve seat is a convex spherical surface, and the inner hole of the outlet end of the valve body is processed into a concave spherical sealing surface. The two form a sealing pair, which is beneficial to the grinding and matching of the super-hard sealing surface.
1. Valve bodies 2. Front valve seats 3. T-shaped sealing rings 4. Disc springs 5. Valve bonnets 6. Balls 7. Stems 8. Pre-tightened combination springs 9. Micro-leakage combination packing 10. Anti-friction pads 11. Pressure rings of valve seats 12. Back valve seats
Figure 1 Wear resistant ball valves for fluidized bed residual oil hydrogenation units
1. Valve bodies 2. Valve seats 3. Balls 4. Pressing plates
Figure 2 Valve seats with double-sided spherical surfaces structure
2.2 W-shaped hyperboloid gaps
In order to reduce the scouring of the medium to the valve seat at the moment of opening and closing of the ball valve and reduce the flow rate of the medium, a W-shaped gap is designed in the orifice of the ball. W-shaped gaps are also designed for some products in China, but they are only ground. Replace the W-shaped gap with a hyperboloid (Figure 3 to Figure 5). The hyperboloid gap can make the connection between the inner hole channel of the sphere and the outer spherical surface of the sphere have a tangent smooth transition, avoiding the transition of intersecting sharp corners. Even if it is ground, the tangent effect cannot be achieved. Both the spherical hole and outer spherical surface need to be hardened, and the W-shaped hyperboloid gap has a good effect on preventing partial stress concentration and the peeling of the hardened layer. At the same time, the hyperboloid gap increases the complexity of its machining process, and it needs to be programmed by installing edgecam software on the five-axis machining center.
Figure 3 W-shaped gaps of the sphere channel
Figure 4 Figure 3A-A sectional views
Figure 5 Sectional views of the Figure 3B
2.3 T-shaped pressure self-tightening sealing rings
Because the medium has high temperature and high pressure and its temperature alternates between cold and heat, the sealing gasket at the connecting end of the valve body and bonnet has high requirements. The sealing surface of flanges is designed with two seals: the outside is the tongue-and-groove connection surface plus the spiral wound gasket, and the inside is a T-shaped self-tightening sealing ring. The outer side of the self-tightening seal ring has 15° inclined planes in order to form a sealing pair with the corresponding inclined planes of the valve body and valve bonnet. The sealing pair at this place is required to have poor hardness. The T-shaped sealing ring adopts F347H. After solid solution and stabilization treatment, its hardness is low. The sealing surface of the valve body and bonnet is build-up welded with STL hard alloy, which can meet the requirements for poor hardness. The T-shaped self-tightening sealing ring has another function, that is, when the medium pressure increases, the sealing ring will be deformed and attached to the sealing surface to achieve a self-tightening sealing effect.
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2.4 Hardening treatment for surfaces
According to the different processing conditions of the sphere and valve seat, supersonic spraying (the HVOF process), flame powder remelting technology (the SP process) and laser cladding technology can be chosen to improve surface hardness and scratch resistance. Supersonic spraying WC or CrC has a coating thickness of 0.3 to 0.6mm and hardness greater than 65HRC; the bonding strength is about 100MPa and the transition layer is mechanically bonded. The transition layer of flame powder remelting and laser cladding is a metallurgical combination, and the peeling resistance is more ideal. The inner cavity, channel and spherical hole of the valve body are all sprayed with wear resistant alloy by supersonic spraying to improve the scouring resistance. The hardness of the sprayed hardened layer is 64 to 68HRC; the bonding strength is greater than 69MPa, and the effective thickness of the coating is 0.2 to 0.5mm.
2.5 Valve stems
The opening torque of the floating ball valve is very great, and the design of the valve stem must not only adopt corrosion resistant, high temperature resistant and high-impact materials, but also can withstand an operating torque that is 2.5 times higher than the calculated torque. The outer surface of the lower end of the valve stem and upper plane of the boss should be build-up welded with cemented carbide, and the surface in contact with the packing should be sprayed with a hardening layer by supersonic spraying. The hardened layer should be finely ground and polished, and its surface roughness value Ra should be less than 0.1μm.
2.2 W-shaped hyperboloid gaps
In order to reduce the scouring of the medium to the valve seat at the moment of opening and closing of the ball valve and reduce the flow rate of the medium, a W-shaped gap is designed in the orifice of the ball. W-shaped gaps are also designed for some products in China, but they are only ground. Replace the W-shaped gap with a hyperboloid (Figure 3 to Figure 5). The hyperboloid gap can make the connection between the inner hole channel of the sphere and the outer spherical surface of the sphere have a tangent smooth transition, avoiding the transition of intersecting sharp corners. Even if it is ground, the tangent effect cannot be achieved. Both the spherical hole and outer spherical surface need to be hardened, and the W-shaped hyperboloid gap has a good effect on preventing partial stress concentration and the peeling of the hardened layer. At the same time, the hyperboloid gap increases the complexity of its machining process, and it needs to be programmed by installing edgecam software on the five-axis machining center.
Figure 3 W-shaped gaps of the sphere channel
Figure 4 Figure 3A-A sectional views
Figure 5 Sectional views of the Figure 3B
2.3 T-shaped pressure self-tightening sealing rings
Because the medium has high temperature and high pressure and its temperature alternates between cold and heat, the sealing gasket at the connecting end of the valve body and bonnet has high requirements. The sealing surface of flanges is designed with two seals: the outside is the tongue-and-groove connection surface plus the spiral wound gasket, and the inside is a T-shaped self-tightening sealing ring. The outer side of the self-tightening seal ring has 15° inclined planes in order to form a sealing pair with the corresponding inclined planes of the valve body and valve bonnet. The sealing pair at this place is required to have poor hardness. The T-shaped sealing ring adopts F347H. After solid solution and stabilization treatment, its hardness is low. The sealing surface of the valve body and bonnet is build-up welded with STL hard alloy, which can meet the requirements for poor hardness. The T-shaped self-tightening sealing ring has another function, that is, when the medium pressure increases, the sealing ring will be deformed and attached to the sealing surface to achieve a self-tightening sealing effect.
2.4 Hardening treatment for surfacesAccording to the different processing conditions of the sphere and valve seat, supersonic spraying (the HVOF process), flame powder remelting technology (the SP process) and laser cladding technology can be chosen to improve surface hardness and scratch resistance. Supersonic spraying WC or CrC has a coating thickness of 0.3 to 0.6mm and hardness greater than 65HRC; the bonding strength is about 100MPa and the transition layer is mechanically bonded. The transition layer of flame powder remelting and laser cladding is a metallurgical combination, and the peeling resistance is more ideal. The inner cavity, channel and spherical hole of the valve body are all sprayed with wear resistant alloy by supersonic spraying to improve the scouring resistance. The hardness of the sprayed hardened layer is 64 to 68HRC; the bonding strength is greater than 69MPa, and the effective thickness of the coating is 0.2 to 0.5mm.
2.5 Valve stems
The opening torque of the floating ball valve is very great, and the design of the valve stem must not only adopt corrosion resistant, high temperature resistant and high-impact materials, but also can withstand an operating torque that is 2.5 times higher than the calculated torque. The outer surface of the lower end of the valve stem and upper plane of the boss should be build-up welded with cemented carbide, and the surface in contact with the packing should be sprayed with a hardening layer by supersonic spraying. The hardened layer should be finely ground and polished, and its surface roughness value Ra should be less than 0.1μm.
