| Pumps, reducers, castings
(1) Electrochemical corrosion
Electrochemical corrosion refers to an electrochemical process in which a contact surface of a heterogeneous metal forms a battery due to a difference in potential between the electrodes, thereby causing corrosion of the anode metal.
Measures to prevent electrochemical corrosion. First, the flow path of the pump is preferably made of the same metal material. Second, the sacrificial anode is used to protect the cathode metal. For example, a small piece of consumables is made of a low-potential metal, and as an anode, an important part of a large part is made of a high-potential metal. As a cathode, the anode metal is first corroded to protect the cathode metal.
(2) Uniform corrosion
Uniform corrosion refers to the occurrence of uniform chemical corrosion of the entire metal surface when the corrosive liquid contacts the metal surface. This is the most common type of corrosion type and the least hazardous type of corrosion.
Measures to prevent uniform corrosion are: take appropriate materials (including non-metal) and consider sufficient corrosion margins in pump design.
(3) Intercrystalline corrosion
Intergranular corrosion is a type of local corrosion, mainly referring to the phenomenon of precipitation of chromium carbide between stainless steel grains. Intergranular corrosion is extremely corrosive to stainless steel materials such as stainless steel submersible pumps or stainless steel self-priming pumps. The material in which intergranular corrosion occurs is almost completely lost in strength and plasticity.
Measures to prevent intergranular corrosion are: annealing stainless steel or ultra-low carbon stainless steel (C < 0.03%).
(4) Pitting corrosion
Pitting corrosion is a type of localized corrosion. This phenomenon is called pitting corrosion due to the local failure of the metal passive film causing a certain partial area of the metal surface to rapidly form a hemispherical pit. Pitting corrosion is mainly caused by Cl.
To prevent pitting corrosion, M0-containing steel (usually 2.5% Mo) can be used, and as the Cl content and temperature increase, the M0 content should also increase accordingly.
(5) Crevice corrosion
Crevice corrosion is a type of local corrosion. It refers to the corrosion caused by the partial destruction of the passive film of the metal due to the decrease of oxygen content in the gap and/or the decrease of pH value when the gap is filled with corrosive liquid. Stainless steel often undergoes crevice corrosion in CL-solutions. Crevice corrosion and pitting corrosion are similar in formation mechanism. Both are caused by the action of Cl- and the local destruction of the passive film. As the Cl content increases and the temperature rises, the possibility of crevice corrosion increases.
The use of metals with high Cr and M0 content prevents or reduces crevice corrosion.
The order of resistance to crevice corrosion is as follows: 12% Cr steel <17% Cr steel < austenitic stainless steel < austenitic 316 stainless steel.
(6) Stress corrosion
Stress corrosion refers to a type of local corrosion caused by the combination of stress and corrosive environment.
Austenitic Cr-Ni steel is more susceptible to stress corrosion in C1-medium. With the increase of Cl content, temperature and stress, stress corrosion is more likely to occur. Usually 70, -80. Stress corrosion does not occur below C. The measure to prevent stress corrosion is to use austenitic Cr-Ni steel with high Ni content (Ni; >25% to 30%).
(7) Erosion corrosion
Refers to a scouring corrosion of a metal surface by a high velocity fluid. Fluid Scour Wear Corrosion is different from the abrasion caused by solid particles in the medium. Different materials have different wear and corrosion resistance properties. The anti-wear corrosion performance is from poor to good: ferritic Cr steel <austenitic-ferritic steel <austenitic steel.
(8) Cavitation corrosion
Corrosion caused by cavitation of the pump is called cavitation corrosion. The most practical and convenient way to prevent cavitation corrosion is to prevent cavitation. For pumps that often cavigate during operation, to avoid cavitation corrosion, use cavitation resistant materials such as cemented carbide, phosphor bronze, austenitic stainless steel, 12% chrome steel, or pneumatic diaphragm pumps or other diaphragms. Pump products can avoid the occurrence of cavitation.
How to prevent corrosion problems in the pump?
Corrosion in the centrifugal pump can affect the wet surface or a small portion of its internal components, which are general or highly localized. Typically, pump failures are caused by highly localized and affected components. Therefore, it is very important to find a solution that reduces the effects of corrosion.
Let's take a look at the different ways to reduce corrosion! Not only will this save you millions of dollars, but it will also extend the life of your pump.
1, material selection
When solving corrosion problems, material selection should be considered first. This not only handles corrosion problems, but also selects the best material to reduce the rate of degradation based on the operating conditions of the centrifugal pump.
Cast iron has a relatively low corrosion resistance and can quickly reduce pump performance. Therefore, pump manufacturers use stainless steel to avoid corrosion.
Please note that the correct material selection is ultimately the responsibility of the user. Only the user can control the liquid being pumped relative to the concentration, temperature, and the like. It is the responsibility of the pump manufacturer to provide the materials of choice under physically good conditions and to provide the correct chemical composition while meeting specified hydraulic requirements. In practice, a trusted pump supplier will provide guidance based on his experience with previous applications involving similar services.
We recommend that you carefully consider the choice of materials, which is one of the most effective ways to improve the corrosion resistance of your pump.
Sources of information that can be referenced for material selection include:
(1) First-hand in-plant experience;
(2) Similar applications in other locations;
(3) Corrosion diagram of hydraulic research institute;
(4) Recommended drawings of mechanical seals;
(5) The experience of the pump manufacturer;
(6) Appropriate literature, texts and similar references.
Normally, no data available will specifically satisfy the conditions, especially if a solution containing several concentrations of several chemicals is pumped. When the temperature is increased by 10 ° C, the corrosion rate can be doubled.
The presence of dissolved air or other oxidant in the liquid may cause the corrosion rate to accelerate separately, otherwise it is considered acceptable. In some
Water is closely related to our lives. Once the water supply equipment fails, it will affect the normal life of the residents. If the problem is not eliminated in time, it may increase the possibility of other hardware damage. This article gives a brief introduction to common faults and solutions for water supply equipment.
First, the fault description: the system can not hit the water
1. Check if there is water in the pool, whether the motor is running, the motor is turning, and the inverter may be redirected;
2. If the check valve is at the front end of the motor, if there is water at the front end of the check valve, the water in the motor is drained;
3. Disassemble the water pump and check if the welding impeller is broken. This kind of situation is generally louder.
Second, the fault description: the pump starts to pressure very much
1. Check if there is any obstruction in the pipeline, causing a sudden change in pressure (because the flow becomes smaller), check the pipeline for water leakage, and the pressure cannot be maintained;
2. Generally speaking, the water supply unit is automatic, and its automatic action is to control the switching action of the unit by pressure. The flow rate of the pipeline will also have a great influence. The flow will automatically become smaller, which will cause the pump to start. The pressure at the outlet to the blockage will suddenly increase, causing the pressure control to malfunction and the start will be frequent (water leakage will also occur);
3. The water hammer is generated instantaneously when the water pump is started;
Third, the fault description: the switch often jumps or can not close the fault
2. The switch selection is wrong.
3. Pump jam or motor circuit problem
4. Line aging, short circuit, too small or missing phase.
Solution: Turn off the power of the control system, and then use the winding motor to check whether the three phases of the circuit are short-circuited or grounded. (Note when measuring: Remove the inverter output to avoid burning the inverter output module during testing. Bad); turn the motor by hand to see if there is a jam; replace the switch if necessary.
Fourth, the fault description: When the user uses water, there is a lot of noise, and the pressure of the water is not very stable. What is the cause of this?
1. When the user uses water, the water pressure fluctuates drastically, and the variable frequency pump is always in the frequency conversion state;
2. Pipeline resonance caused by water pressure fluctuation caused by frequent frequency conversion of user water and variable frequency pump;
3. The frequency of the frequency conversion part may be close to the mechanical vibration frequency of the pump to cause resonance;
4. Check for cavitation (whether the pump is fully charged) and air accumulation in the outlet line.
Vibration is an important indicator for evaluating the operational reliability of pump units. The hazards of excessive vibration are mainly caused by vibration, which can cause the pump unit to fail to operate normally; cause vibration of the motor and pipeline, causing damage to the machine; causing damage to bearings and other parts; causing loose connection parts, base cracks or motor damage; The pipe or valve connected to the pump is loose and damaged; vibration noise is formed.
The causes of pump vibration are manifold. The shaft of the pump is generally directly connected to the shaft of the drive motor, so that the dynamic performance of the pump and the dynamic performance of the motor interfere with each other; the high-speed rotating parts have many, the dynamic and static balance can meet the requirements; the components that interact with the fluid are greatly affected by the water flow condition; The complexity of fluid motion itself is also a factor limiting the stability of pump dynamic performance.
1 Analysis of the causes of pump vibration
The structural parts of the motor are loose, the bearing positioning device is loose, the iron core silicon steel sheet is too loose, and the bearing stiffness is reduced due to wear, which may cause vibration. Mass eccentricity, uneven rotor mass distribution caused by rotor bending or mass distribution problems, resulting in static and dynamic balance exceeding the standard. In addition, the squirrel-cage motor rotor has a broken cage cage, which causes the magnetic force of the rotor and the rotational inertia of the rotor to be unbalanced, causing vibration, the motor is out of phase, and the power supply of each phase is unbalanced. Due to the operational quality problems of the installation process, the stator windings of the motor cause an imbalance in the resistance between the windings of the respective phases, resulting in a non-uniform magnetic field generated, resulting in an unbalanced electromagnetic force, which becomes an exciting force to cause vibration.
1.2 Foundation and pump bracket
The contact fixing form adopted between the driving device frame and the foundation is not good, and the basic and motor systems have poor absorption, transmission and isolation vibration, which causes the vibration of the foundation and the motor to exceed the standard. If the pump foundation is loose, or the pump unit forms an elastic foundation during the installation process, or the base stiffness is weakened due to oil immersion blisters, the pump will generate another critical speed with a phase difference of 1800 from the vibration, thereby increasing the pump vibration frequency. The frequency is close to or equal to the frequency of an external factor, which increases the amplitude of the pump. In addition, the looseness of the foundation anchor bolts leads to a decrease in the constraint stiffness and an increase in the vibration of the motor.
The circumferential spacing of the coupling bolts is poor, the symmetry is broken; the coupling is extended with the eccentricity, and the eccentric force will be generated; the coupling cone is out of tolerance; the coupling static balance or dynamic balance is not good; The cooperation between the pin and the coupling is too tight, so that the elastic pin loses the elastic adjustment function, so that the coupling is not well centered; the coupling clearance between the coupling and the shaft is too large; the mechanical wear of the coupling apron is caused by Coupling aprons have reduced mating performance; the quality of the drive bolts used on the couplings varies from one another. These causes vibration.
1 Impeller mass eccentricity. The quality control in the impeller manufacturing process is not good. For example, the casting quality and processing accuracy are unqualified; or the liquid conveyed is corrosive, and the impeller flow path is corroded and corroded, resulting in eccentricity of the impeller. 2 The number of blades of the impeller, the exit angle, the wrap angle, the radial distance between the throat tongue and the exit edge of the impeller are appropriate. 3 In use, between the impeller ring and the pump body ring, between the interstage bushing and the diaphragm bushing, from the initial rubbing, gradually become mechanical friction and wear, which will aggravate the vibration of the pump.
1.5 drive shaft and its accessories
A pump with a long shaft is prone to insufficient shaft stiffness, too large deflection, and poor straightness of the shaft system, causing friction between the moving member (drive shaft) and the static member (sliding bearing or ring) to form vibration. In addition, the pump shaft is too long, which is greatly affected by the impact of the flowing water in the pool, so that the vibration of the underwater part of the pump is increased. If the balance disc clearance at the shaft end is too large, or the axial work movement is improperly adjusted, the shaft will be low frequency and the bearing bush will vibrate. The eccentricity of the rotating shaft causes bending vibration of the shaft.
1.6 Pump selection and variable operating conditions
Each pump has its own rated operating point. Whether the actual operating conditions are consistent with the design conditions has an important impact on the dynamic stability of the pump. The pump runs stably under the design conditions, but when operating under variable conditions, the vibration is increased due to the radial force generated in the impeller; the single pump is not properly selected, or the two models are not matched. in parallel. These will cause the pump to vibrate.
1.7 Bearings and lubrication
The stiffness of the bearing is too low, causing the first critical speed to decrease, causing vibration. In addition, poor performance of the guide bearing results in poor wear resistance, poor fixing, excessive bearing clearance, and easy to cause vibration; and the wear of thrust bearings and other rolling bearings will cause the longitudinal turbulent vibration and bending vibration of the shaft to increase. . Improper selection of lubricating oil, deterioration, excessive impurity content and poor lubrication of the lubrication pipe will cause the bearing condition to deteriorate and cause vibration. The self-excitation of the oil film of the motor sliding bearing also generates vibration.
1.8 pipe and its installation and fixed
The outlet pipe bracket of the pump is not rigid enough, and the deformation is too large, causing the pipe to be pressed down on the pump body, which makes the pump body and the motor have a neutral damage; the pipe is too strong during the installation process, and the inlet pipe is connected to the pump. The stress is large; the inlet and outlet pipelines are loose, the restraint stiffness is reduced or even failed; the outlet flow passages are all broken, the debris is stuck to the impeller; the pipeline is not smooth, such as the outlet has airbags; the outlet valve is off or not opened; the inlet has Intake, uneven flow field, pressure fluctuations. These causes direct or indirect vibrations in the pump and piping.
1.9 Matching between parts
The motor shaft and the pump shaft are out of concentricity; the coupling is used at the connection between the motor and the drive shaft, and the concentricity of the coupling is out of tolerance; the design between the moving and static parts (such as between the impeller and the ring) The wear of the gap becomes large; the gap between the intermediate bearing bracket and the pump cylinder exceeds the standard; the gap of the seal ring is not suitable, resulting in an imbalance; the gap around the seal ring is not uniform, such as the mouth ring is not the person slot or the partition is not the person slot, This happens. These unfavorable factors can cause vibration.
1.10 Factors of the pump itself
The asymmetric pressure field generated when the impeller rotates; the vortex of the suction pool and the inlet pipe; the occurrence and disappearance of the vortex inside the impeller and the volute and the guide vane; the vibration caused by the vortex caused by the valve half opening; due to the limited number of impeller blades Uneven distribution of outlet pressure; outflow in the impeller; asthma