General

Overview

The author has often wondered how often machines are redesigned and rebuilt or even replaced for reasons that were later found to be incorrect. Based on observations over a considerable number of years, the number might be staggering. Ironically, the incorrect diagnosis sometimes results in a solution that will at least for the time being appear to fix the problem. This type of solution may possibly lead to a future problem because an incorrect symptom-cause relationship is established that will not hold true on another application at another time. All of this is being said to stress the need for proper and careful problem solving that accurately determines the real cause for the problem. It is difficult to address the common sense side of reliability and not make some type of plea for cool heads and calculating minds to overcome the hysteria of the moment on the occurrence of a failure. There are many good problemsolving techniques available, but they must be used in a calm, clear mindset. There certainly is no room for prejudice and "finger pointing." The correct solution to a compressor train problem certainly would do much to aid the cause of reliability.

Today there are many tools available to aid in problem solving or failure analysis. These include the Weibull Analysis, Failure Mode and Effect Analysis, and Fault Tree Analysis, to name a few. One of the most widely accepted is the Weibull analysis. This method can provide an accurate engineering analysis based on extraordinary small samples [1].

This chapter will discuss various reliability issues. The discussion will be kept at a philosophical level rather than getting into a statistical analysis. The statistical analysis is best left to others equipped with the training, tools, and the data. Hopefully, this material will give the reader some "common sense" insight into the various considerations involved in the selection and application of reliable compressors, their drivers, and auxiliary systems.

Reliability for compressors is defined in many different ways, but (he most widely accepted definition states that it is the ability or capability of the equipment to perform the specified function in the designated envt ronment for a minimum length of time [2]. The length of time, "run time," cannot be determined except by operating the compressor for the desired length of time or until it fails. It is not too practical to use this criteria as the lone measure of success. While a historical database can provide valuable information to the later design efforts, this knowledge must be supplemented with other measures to gauge the probability of success.

It is very important right from the start to bear in mind the current axiom offered in the KISS principal, "keep it simple stupid." While this may seem a little offensive, nonetheless, from time to time, one sees systems that give the impression the originators went out of their way to make things unnecessarily complicated. An example of this is controls put on systems that with a litde added thought could have been made self-regulating.

For compressors in general and for some types in particular, the cleanliness of the gas stream is the key factor in a reliable operation. Moisture or liquids in various forms may be the cause of an early failure or in some cases a catastrophic failure. Corrosive gases require material considerations and yet even this may not entirely solve the loss of material issue that can certainly cause early shutdowns or failures and high maintenance cost. Fouling due to contaminants or reactions taking place internal to the compressor can cause capacity loss and the need for frequent shutdowns.

Figure 12-1. Reliability—design of plant and equipment. (Courtesy of Sohre Turbomachinerti

OPERATING PERSONNEL

MAINTENANCE PERSONNEL

OPERATING PERSONNEL

MAINTENANCE PERSONNEL

SPEED—1000 RPM SPEED—1000 RPM

Figure 12-4. Reliability—operation and maintenance. (Courtesy of Sohre Turbomachinerfl

SPEED—1000 RPM SPEED—1000 RPM

MAINTENANCE FACILITIES

gxc*

iletrr

Ate*

UHS

POO

t j

SPEED—1000 RPM

0 iO 20

SPEED—1000 RPM

Figure 12-4. Reliability—operation and maintenance. (Courtesy of Sohre Turbomachinerfl was proposed. It was conceived out of a need to aid in problem solving. The advent of large single train plants took place in the late 1960s to early 1970s. Needless to say, there were many machinery-related problems. Many of the monitoring and diagnostic tools taken for granted at the current time were just being developed. The data being generated tended to overwhelm the analyst's ability to interpret it. There was no baseline for comparison. Diagnostics were strictly based on intuition, which was not always that accurate. With time, the current base of data began to evolve.

If the Sohre approach is taken in a philosophical light, it clearly indicates the need for a robust design. This is true for the basic equipment as well as the installation of foundations and piping. All of the factors were considered in the approach Sohre presented, even if in some cases, they may have been considered subjective. The key to the robust approach can be simplified as low deflection. On a rotor, the shorter the bearing span and/or the heavier the shaft cross section, the lower the deflection. This tends to increase the reliability aspect. On a foundation, heavier sections tend to have lower deflection, which contributes to the ability to maintain train alignment. Better alignment is one of the factors that contributes to higher reliability.

Living Off The Grid

Living Off The Grid

Get All The Support And Guidance You Need To Be A Success At Living Off The Grid. This Book Is One Of The Most Valuable Resources In The World When It Comes To When Living Within The Grid Is Not Making Sense Anymore.

Get My Free Ebook


Post a comment