Figure 1.1 Assessing a process machine
The idea for this reference book evolved from the fact that, at the time of inception, we were not aware of a single reference that combined machinery assessment advice with established guidelines for the most commonly used machinery condition parameters, such as vibration, pulsations, temperature limits, and lubrication. Up until this guide was developed, machinery users had to identify, purchase, and maintain an expansive, as well as expensive, library of machinery books and standards to assemble a body of sound evaluation practices. For these reasons, we have endeavored to combine the assessment advice, the most commonly used assessment tools, and helpful references into one compact volume.
The reader must remember that these guidelines should not be considered absolute. Instead, they are relative starting points for machinery assessments. Criticality, machine construction, local standards, and manufacturer’s recommendations should all be factored into your final decisions and actions. By combining various guidelines into one reference, machinery owners can take a more holistic approach to machine evaluations.
We hope you find this resource a useful addition to your machinery reliability library and that it makes your job a little easier.
Robert X. Perez and Andrew P. Conkey
A Brief Introduction to Machinery Monitoring
To survive, a processing facility must be profitable. To thrive, a processing facility must incessantly strive to become more and more profitable in order to sell products for a lower price than their competitors. To maintain a sustainable competitive edge, process owners must always be on the lookout for smarter ways to increase yields while reducing raw material costs, energy needs, maintenance costs, etc. This book is written for those working in organizations that wish to thrive and become industry leaders.
Because maintenance costs represent a significant portion of an organization’s expenses, maintenance budgets are constantly under scrutiny during budget review times. Everyone knows that lowering maintenance costs can have a major effect on the bottom line. However, blindly cutting maintenance efforts without carefully weighing the potential effects can be costly to the overall bottom line and drastically affect the site’s risk profile. Every organization must choose whether they will maintain their process facility proactively or reactively.
Rotating machinery represents a major source of expense to a maintenance organization due to both their complexity and their labor-intensive nature. The machinery maintenance budgets are often seen as having “low hanging fruit” opportunities; therefore, they are targeted for review. Any modifications to a machinery maintenance program must be carefully evaluated and approved by machinery professionals. Poorly managed rotating machinery can devastate a process organization by adversely affecting process availability, safety, and efficiency.
A powerful methodology called Reliability Centered Maintenance, RCM, is aimed at establishing a safe minimum level of maintenance and focusing key maintenance resources specifically toward mission critical equipment, such as process machinery. Reliability centered maintenance is an engineering framework that helps establish a complete maintenance philosophy and organization. It employs a structured framework for analyzing the functions and potential failures for a physical asset (such as a pump, compressor, or gas turbine). Its primary focus is preserving system functions rather than preserving equipment. The promise of RCM is reduced maintenance costs and improved equipment availability.
Some key steps of RCM include:
1.Identifying key machine functions
2.Determining machine criticality
3.Identifying functional failure modes and effects
4.Identifying failure consequences
5.Identifying how failures can be prevented and predicted
6.Identify the causes of failure
7.Selecting maintenance tasks
Once an RCM analysis is complete, there are several principle risk management strategies that are recommended. Some of these are:
•On-condition maintenance tasks, i.e. condition monitoring
•Scheduled restoration or replacement maintenance tasks, i.e. preventive maintenance
•Failure-finding maintenance tasks, for example, checking a steam turbine overspeed trip system to ensure it is functioning properly
•One-time changes to the “system” (e.g., changes to hardware design, operations)
•Run to failure
The approved risk management strategies are then judiciously folded into an integrated maintenance plan that will provide an acceptable level of process reliability, with an acceptable level of risk, in an efficient and cost-effective manner. These scheduled maintenance plans usually include predictive maintenance program definition, such as vibration collection and analysis, and time-based maintenance activities, such as oil and filter replacements.
RCM emphasizes a combination of predictive maintenance (PdM) techniques with applicable and traditional preventive measures. These preventive measures include activities such as cleanings, inspections, oiling, and adjustments. The goal of PdM, or condition-based maintenance, is to assess the condition of equipment by performing periodic inspections—such as vibration analysis, temperature monitoring, oil analysis, ultrasonic analysis—or by using continuous (online) equipment such as vibration or temperature sensors. The primary tenet of the PdM philosophy is that it is more cost-effective to perform maintenance at a scheduled point in time than to risk running equipment until it loses performance capability and adversely affects the process. This view is in contrast to a time-based maintenance approach, where a piece of equipment gets maintained (i.e., overhauled or refurbished) at a prescribed time interval, whether it is warranted or not. Time-based maintenance is usually labor intensive and ineffective in identifying problems that develop between scheduled inspections; it has been proven not be cost-effective.
The purpose of most process machines is to transport liquids and gases efficiently from one point in the process to another. This action typically requires raising a fluid stream’s overall energy state by increasing its elevation, pressure, or velocity—or a combination of these fluid energy forms. Many different designs are utilized in process machinery; each design depends on the fluid being transported, the flow volumes required by the process, or the horsepower required for the task at hand. However, all machines are imperfect. Therefore, they are less than 100% efficient, which means that some of the horsepower provided by the driver (e.g., motor or turbine) is always converted into unusable forms of energy, such as vibration, pulsation, or heat. These tell-tale signs give us clues about the condition of operating machinery.
The majority of this book is dedicated to proven predictive maintenance techniques that can be employed on industrial machines. However, the aim of this book is