For many years, pump manufacturers have used metal parts as spigots, bushings, bushings, single-stage and multi-stage petrochemical process pumps for API pumps. Because of wear between the metal part and the metal part, there is a possibility of bite or seizure between the wear part and the pump. In a corrosive working condition, this is even more serious - since the stainless steel part is used more at this time, More bite. At this time you need to increase the gap between the mouth ring to ensure that the pump rotor and stator will not be killed. Despite the warnings, the problems of abrasion and bite still plague the pump user. Abrasion wear components for many reasons, including: ◆ Radial bearing failure Pump radial bearing failure, it will make the rotor runout, contact between wear components increased intensity, which often leads to serious occlusion, eventually leading to the pump bite death. ◆ Products vaporization pump by traditional cavitation, will certainly be produced by the fluid film and reduce the fluid has been the support, so the rotor rotation is too large, wear the contact surface. ◆ Deflection of the axis of the Shaft deflection is caused by wear pieces of another contact with each other another reason. When the centrifugal pump is operated away from the optimum efficiency point, a relatively concentrated radial force causes the shaft to bend, which can result in one or both of the rotating parts (such as the mouth ring or the mechanical seal) coming into contact with the stationary part. Steam Turbine Driven Pump Low-Speed ​​Startup This problem often occurs in large, multi-stage horizontal pumps whose rotors must reach a certain speed for proper support, or the wear parts in the pump come into contact with each other. ◆ Lack of Radial Bearing Support Table 1. API Recommended Radial Operation Gap and Radial Running Gap with WR Material This problem is common in older double suction pumps and two-stage reciprocating pumps. Originally these pumps were designed with a packing seal so that it could provide a radial bearing support for the shaft. However, due to strict leakage standards, many pumps have switched to mechanical seals. This lack of packing bearing support role. Making the shaft deflection greater mechanical seal life reduction and the mouth ring bite. Although there are many ways to reduce the possibility of pump occlusion and seizure, there is a way to think about using non-occlusive, non-seizure abrasive materials. High-performance thermoplastic composites match the steel without bite and do not bite to death, even under dry-running, high-load friction conditions. The role of this composite material is as a sacrificial part. In the worst case, such components will wear or surface melt before the rotor and pump casing can be killed. In recent years, thermoplastic composites have been used in dynamic and static wear parts, matching parts or steel. Thermoplastic composites increase the stiffness and degree of wear between wear parts - the composite material acts as a wear part. Like other materials, thermoplastic composites also have their limitations, which are not obvious in most applications, but the benefits are particularly significant. Back-flow problem API pump in the design and manufacture, to consider how to control from the exit of the impeller back to the inlet of the impeller direction of the backflow phenomenon, this seal refers to the mouth ring. Mouth rings are usually used in pairs, one mounted on a rotating impeller (impeller mouth ring) and the other on a pump casing (pump shell mouth ring), all of which stabilize the rotor. In the past, the mouth ring are made of different grades of steel, the rotation, the friction between the steel parts is large, in order to ensure that the rotor does not engage the stator, the mouth ring gap needs to be increased. Moreover, many steel parts are prone to bite when they come into contact with the fitting, requiring a greater clearance. While the API 610 gives us the minimum radial clearance standard for the split ring, many agencies also have their own clearance standards. People have been trying to reduce the occlusion of the pump. Large gaps can cause backflow inside the pump, with some disappointing consequences: Loss of efficiency - Large gaps can cause more internal fluid to flow back and directly affect pump efficiency. Back-flow cavitation - cavitation can occur due to excessive mouth ring clearance, and cavitation can also occur in backflow. Increasing the clearance of the mouth ring that exits to the suction port affects the fluid flow properties and also increases the NPSHR of the impeller. High vibration - If the fluid velocity is too high, the fluid will disturb the rotor when it flows through the surface of the orbital ring. Composite Wrist Ring WRTM thermoplastic composite material is a non-occluding, low coefficient of friction material, in the non-slurry has a very good wear resistance. Its mechanical properties are more competitive with metals due to the addition of carbon fiber reinforcement, so this material has been used as a port ring for some pumps instead of part of a ferrule. This material reduces friction and bite, to a large extent reduce the mouth ring gap. Table 1 lists the API 610 recommended radial clearance specifications. For cast iron, copper, and chromium with similar hardness of 11-13%, Table 1 also lists some radial runs with WR material gap. Reducing the radial running clearance of wear parts in the pump allows the pump to work at maximum efficiency, reducing internal back flow and reducing horsepower, as well as reducing the chances of pump back-flow cavitation and pump vibration frequency. This performance improvement will soon translate into tangible returns. As an example, a pump OEM repair team updated a nine-stage horizontal split-boiler feed pump to replace stainless steel impeller rings and bushings with thermoplastic composites containing continuous carbon fiber. As a result, pump efficiency increased from 81.2% to 83%. The cost of electricity in the area is $ 0.12 / kWh, saving $ 57,248 annually, bringing the total cost of shipping, maintenance and reloading up to $ 30,000, so users will be able to spend within 6.3 months Cost recovery.
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