Mechanical conditioning

Metal surfaces in a well-designed, well-operated cooling water system will establish an equilibrium with the environment by forming a coating of protective corrosion product. This covering effectively isolates the metal from the environment, thereby stifling additional corrosion. Any mechanical, chemical, or chemical and mechanical condition that affects the ability of the metal to form and maintain this protective coating can lead to metal deterioration. Erosion-corrosion is a classic example of a chemical and mechanical condition of this type. A typical sequence of events is ... 

The retention efficiency of membranes is dependent on particle size and concentration, pore size and length, porosity, and flow rate. Large particles that are smaller than the pore size have sufficient inertial mass to be captured by inertial impaction. In liquids the same mechanisms are at work. Increased velocity, however, diminishes the effects of inertial impaction and diffusion. With interception being the primary retention mechanism, conditions are more favorable for fractionating particles in liquid suspension. 

While an increase or a decrease in amplitude may indicate degradation of the machine-train, this is not always the case. Variations in load, operating practices, and a variety of other normal changes also generate a change in the amplitude of one or more frequency components within the vibration signature. In addition, it is important to note that a lower amplitude does not necessarily indicate an improvement in the mechanical condition of the machine-train. Therefore, it is important that the source of all amplitude variations be clearly understood. 

All machinery with moving parts generates mechanical forces during normal operation. As the mechanical condition of the machine changes due to wear, changes in... 

Three basic types of vibration transducers that can be used for monitoring the mechanical condition of plant machinery are displacement probes, velocity transducers, and accelerometers. Each has limitations and specific applications for which its use is appropriate. 

Broadband analysis techniques have been used for monitoring the overall mechanical condition of machinery for more than twenty years. The technique is based on the overall vibration or energy from a frequency range of zero to the user-selected maximum frequency, Fmax Broadband data are overall vibration measurements expressed in units such as velocity (PK), acceleration (RMS), etc. This type of data, however, does not provide any indication of the specific frequency components that make up the machine s vibration signature. As a result, specific machine-train problems cannot be isolated and identified. 

Broadband analysis techniques, which are used to monitor the overall mechanical condition of machinery, are based on the overall vibration or energy from a frequency range of zero to the user-selected maximum frequency (Fmax)-... 

The system should be able to establish the norm based on trends developed over time. However, the analyst must establish the level of deviation that triggers the alarm. The level of deviation in rate depends on the mechanical condition of each machine-train. For a new machine in good operating condition, the limit is typically set at two... 

Examine apparatus for general mechanical condition, including guards and other safety devices. 

This method provides the means to quickly monitor the mechanical condition of critical machine components, not just the overall machine condition. This technique provides the ability to monitor the condition of gear sets, bearings and other machine components without manual analysis of vibration signatures. 

The first method used for wear particle analysis is routine monitoring and trending of the solids content of machine lubricant. In simple terms the quantity, composition and size of particulate matter in the lubricating oil is indicative of the mechanical condition of the machine. A normal machine will contain low levels of solids with a size less than 10 microns. As the machine s condition degrades, the number and size of particulate matter will increase. 

As an example of the importance of process parameters monitoring, consider a process pump that may be critical to plant operation. Vibration-based predictive maintenance will provide the mechanical condition of the pump and infrared imaging will provide the condition of the electric motor and bearings. Neither provides any indication of the operating efficiency of the pump. Therefore, the pump can be operating at less than 50 per cent efficiency and the predictive maintenance program would not detect the problem. 

Acquiring accurate vibration and process data will require several types of transducers. Therefore, the system must be able to accept input from as many different types of transducers as possible. Any limitation of compatible transducers can become a serious limiting factor. This should eliminate systems that will accept inputs from a single type of transducer. Other systems are limited to a relatively small range of transducers that will also prohibit maximum utilization of the system. Selection of the specific transducers required to monitor the mechanical condition, i.e. vibration, and process parameters, i.e. flow, pressure, etc., will also deserve special consideration and will be discussed latter. 

The purpose of predictive maintenance is to minimize unscheduled equipment failures, maintenance costs and lost production. It is also intended to improve the production efficiency and product quality in the plant. This is accomplished by regular monitoring of the mechanical condition, machine and process efficiencies and other parameters that define the operating condition of the plant. Using the data acquired from critical plant equipment, incipient problems are identified and corrective actions taken to improve the reliability, availability and productivity of the plant. 

The systems that use dynamic alert/alarm limits base their logic on the rate of change of vibration amplitude. Any change in the vibration amplitude is a direct indication that there is a corresponding change in the machine s mechanical condition. However, there should be a maximum acceptable limit, i.e. absolute fault. 

Often, the main cause of catalyst losses is a change in the mechanical condition of the unit. Examples are ... 

Changes in Operating Conditions Changes in Catalyst Properties Changes in feedstock Properties Changes in Mechanical Conditions of the Equipment... 

The regenerator dense phase temperature (see Figure 8-7) can be adversely affected by the feed quality, the condition of the catalyst, the operating variables, and the mechanical conditions of the unit ... 

True conversion is affected by feed quality, catalyst, operating variables, and mechanical conditions (Figure 8-11 A). 

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