Discussion on the causes of failure in circulation pumps in metal processing plants
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1. Operating conditions of the plant circulation pump: Medium: plant circulation water, pH value of 6.0 (slightly acidic), chloride ions at 400 mg; there are also small amounts of plastic lumps (about 1 cm in length) as well as floating debris. Solid particles are less than 1%. 2. The height difference between the water pump mounting base and the water inlet and the water surface of the pool is +1.7 meters (the water level is higher than the pump mounting surface). 3. Currently in use is a split-case double-suction pump: a high-speed 2P pump with 3000 revolutions per minute, a head of 120 meters, and a flow rate of 550 cubic meters. The pump casing is made of ductile iron, while the other components are made of 304 material; the net positive suction head is 6.7 meters. 4. Problems encountered during use: After less than a year of operation, dents and damage appeared on the lower pump casing, while the upper pump casing remained intact. The pump shaft showed minor cavitation-induced spots (which are tolerable), the impeller was in good condition, but excessive wear of the 304 wear-resistant ring led to an increased gap and a decrease in the pump’s efficiency. Help and discussion: 1. The main reasons for short operating time and large holes appearing on the pump casing ； 2. Is a center-open double-suction pump suitable for this industrial application? ； 3. Without changing the pump type, by upgrading the material of the water pump to 316 stainless steel and replacing it with a 1500-rpm 4P low-speed pump, can it be possible to resolve the issue of damage to the pump body caused by cavities, as well as the problem of wear on the wear-resistant rings? This approach could potentially extend the operational life of the pump to around 3 years. Friends, teachers, experts who are interested are invited to participate in the discussion and offer their suggestions!
1. Motor damage: Motor damage may be caused by voltage fluctuations or prolonged operation under high load, or it may result from faults in the stroke mechanism and capacitors. 2. Pump body damage: Damage to the pump body may be caused by improper use, such as pressures exceeding the specified flow rate, or operating for extended periods at flow rates above the rated value. 3. Seal failure: Seal failure may be caused by prolonged flow at high volumes, excessively high external temperatures, or an abundance of external oxidizing agents, impurities, and contaminants. 4. Wear of pump internal components: Wear of the internal parts of a pump can be caused by poor wear resistance of the materials used for these parts, excessive pump speed, or improper scaling. -
It’s mainly the pump casing that’s damaged; everything else is fine!
The possible reasons for damage to the pump casing are as follows: 1. Improper material selection: The material chosen for the pump casing is not suitable for the medium used in the plant’s circulating water; for example, the casing material cannot withstand the corrosiveness of that medium. 2. Unstable system operation: This may be due to excessive water flow in the system, which exceeds the capacity of the pump, resulting in damage to the pump’s casing. 3. Improper installation: The height difference between the water pump’s mounting base and the water inlet relative to the water surface of the tank is +1.7 meters (the water level is higher than the pump’s mounting surface). This type of installation can lead to cavitation, which may cause damage to the pump. 4. Poor pump operation condition: If, during operation, the pressure at the pump outlet is abnormally high or if foreign objects enter the pump outlet, this can lead to damage to the pump casing. To address the above possible causes, it is recommended to take the following measures to solve the problem: 1. Replace the pump casing material: Choose a material suitable for the circulating water medium in the plant. 2. Check system flow: Ensure that the pumping capacity of the water pump meets the system’s requirements. 3. Adjust the installation method: Change the way the water pump is installed to prevent cavitation. 4. Regular inspection and maintenance: Regularly inspect and maintain the water pump to prevent it from operating under abnormal conditions and to address any faults promptly. -
1. Do you mean that the water pump inlet is at the same level as the pump base, or is the water depth insufficient? 2. The water pump was operating beyond its rated flow rate, by up to 20%, and was not running at the designated operating condition. 3. The issue that cannot be completely avoided under operating conditions is the presence of plastic lumps in the water; there are small amounts of them, but they cannot be entirely eliminated, and sometimes they get trapped between the wear ring and the pump casing.
Based on your description, the main cause of the pump casing damage is the presence of some hard particles in the water. Additionally, what exactly do you mean by those plastic nodules? Does it have a certain degree of hardness? Suggestions: 1. Choose a motor with a low speed ； 2. Consider filtering and settling the raw water quality before feeding it into the pump.
By reducing the rotational speed, the net positive suction head of the pump decreases significantly; damage to the impeller caused by cavitation is eliminated or reduced. As for the material, duplex steel can be considered for the impeller.