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Centrifugal pump maintenance method
Abstract: Individually designed and manufactured sophisticated high-quality products, if they are properly maintained, the failure rate during their entire life cycle will increase. Combining engineering application experience, discuss the current situation and future of centrifugal pump maintenance methods, and put forward personal suggestions for oral reference.
If a high-quality product that is well designed and manufactured and fully meets the requirements of on-site operating conditions, if it is not properly maintained, the frequency of failures during its entire life cycle will be greatly increased, and the service life of components will be greatly reduced.
Common maintenance methods
There are three common maintenance methods for centrifugal pumps: reactive maintenance, preventive maintenance and predictive maintenance.
1.1 Reactive maintenance
The equipment has failed, and maintenance is carried out after the accident. Traditional maintenance methods are mostly reactive maintenance.
1.2 Preventive maintenance
Take appropriate measures (such as increasing strength, strengthening testing, etc.) to prevent equipment from malfunctioning. Preventive maintenance also includes various regular maintenance, such as equipment alignment, bearing lubrication, and inspection of instrumentation and control instruments.
1.3 Predictive maintenance
Predictive maintenance refers to the use of data, machine learning techniques and statistical algorithms to predict the most likely failure results of the system. Analyze the equipment data collected by monitoring devices, such as sensors (wired or wireless), in order to provide consistent predictions on when the specified parts should be replaced or maintained, thereby optimizing maintenance costs and downtime .
Predictive maintenance is a branch of state-based maintenance that monitors the state of equipment over time to predict when and where problems may occur and why. Maintaining products before they fail or stop unexpectedly is the ultimate goal pursued by the manufacturing industry.
Determination of maintenance methods
The maintenance methods of pumps used in different industries and working conditions are different.
The maintenance method is mainly determined by factors such as the importance and value of the pump (in the system), user or market requirements. The importance of the pump is usually divided according to the following conditions.
2.1 Important pumps
Usually refers to:
1) If the pump fails, it will cause catastrophic consequences to the equipment, system, and environment or cause major property losses.
2) The consequences of the malfunction are very dangerous and may cause serious irreversible injury or even death.
3) There is no backup pump.
2.2 More important pumps
1) If the pump fails, it may cause certain economic losses, such as shutdown of the production line, damage to some parts of the pump (and/or a long delivery period of spare parts).
2) Unattended or inconvenient on-site (such as pumps for offshore platforms, field oil pumping stations, etc.)
2.3 Non-essential pumps
Pumps used in some unimportant working conditions, such as ordinary agricultural pumps.
For important and more important pumps or pumps (and systems) with special requirements, special attention and special maintenance are usually required; while for non-important pumps, relatively simple maintenance is usually carried out, or even no maintenance is required.
The following will discuss important and more important pumps or pump (and system) maintenance methods with special requirements.
Current status of maintenance methods
3.1 Current domestic situation
At present, there are basically two maintenance methods for centrifugal pumps in my country: reactive maintenance and preventive maintenance. Reactive maintenance is mainly for some ordinary non-important pumps without monitoring devices, such as: ordinary farmland irrigation and drainage pumps, cooling circulating water pumps, etc.
In the actual engineering application of the petrochemical industry, for many important pumps (such as high temperature, high pressure, high speed pumps, the implementation of API 610 standard , hereinafter referred to as the “standard”), usually by improving the strength and reliability, increasing the mechanical protection system , Strengthen the way of regular daily maintenance to achieve preventive maintenance. Specific measures such as:
1) Improve strength and reliability
Standard clause 6.3.3 The pressure pump casing shall be designed as:
Under the worst combination of the maximum allowable working pressure (and the maximum working temperature) and the action listed in Table 5 on each orifice twice the allowable orifice load, it can be operated without leakage or rotating parts There is no contact between stationary parts. Can withstand the water pressure test.
Standard appendix K.1: Provides the judgment principle of the shaft rigidity of OH2 and OH3 cantilever pumps and the relationship diagram between the flexibility coefficient L3/D4 and the pump size factor.
The flexibility coefficient is a measure of the stiffness of the rotor. For a cantilever pump with a certain size factor, if its flexibility coefficient is below the rigid line, it indicates that the pump is a rigid shaft design, which meets the requirements of API pumps and is safe; the smaller the L3/D4, the smaller the rotor deflection. Conducive to improving the reliability of mechanical seals. If L3/D4 is too large, especially when the pump is running close to the dead center position and the hydraulic radial load is too large, it may cause the risk of shaft breakage.
How to improve the reliability of the product? Here are some guiding principles
Try to use proven and mature technology.
Simplify the structure as much as possible and reduce the number of parts.
Use standardized and modular structure as much as possible.
Set up fault monitoring and diagnosis devices.
Give an appropriate design margin.
Use redundant design when necessary.
Fail safe design.
Strengthen the reliability analysis of important parts.
Carry out reliability confirmation tests.
Mechanical protection system
With the development of sensor technology and the collection of equipment operation data, preventive maintenance has become the most common maintenance method at present.
In order to improve operational reliability, some important pumps (groups) are equipped with mechanical protection systems (sensing, measuring, monitoring and displaying machine parameters to indicate their operating status), such as bearing temperature monitoring, bearing housing or pump shaft Vibration monitoring, etc. When a parameter exceeds a predefined limit, indicating an abnormal situation, the system will communicate the event to the operator and/or shut down the system. The goal of this system is to reduce damage to the machine.
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