According to many sources, maintenance cost avoidance can be
built into a compressor specification.13
Maintenance cost avoidance should be confirmed during the
pre-purchase machinery quality assessment (MQA). At all times,
specifying, purchasing, installing and operating reliable
compressors makes more sense than buying compressors based on
faith, past reputation or the lowest bid.
When purchasing new compressors, the best available
solutions are minimizing risks as part of the process to
specify, design, build and install the machines. It is possible
to design out the need for frequent or specific
types of maintenance. Remember: The most
desirable compressor is designed for uptime extension, low
failure risk and the lowest possible lifecycle costs. On
equipment that is already in service, maintenance must seek the
next-best available solution. Such approach mandates that every
maintenance intervention is viewed
as an opportunity to upgrade. If upgrading is feasible, it
should also be a cost-effective solution. An upgrading program
would result in the systematic reliability improvement for
previously weak links in facility-wide operating
1. Compressor overhaul activities.
Photo courtesy of Julian Hanks, PE.
A prominent source attributes that 13% of all
turbocompressor failures are due to errors or omissions in
condition monitoring and maintenance.3 With advances
made in monitoring technology and modern operating and
maintenance practices, we would assume that this general number
is lower with time. What are good monitoring and maintenance
practices around turbocompressors? Compressor condition
monitoring has these components:
- Proper response to supervisory instrumentation, such as
alarms and trips
- Periodic observation and evaluation of operating
parameters, such as the compressors physical condition
and its performance efficiency. This would include measuring
and judging the rate of deterioration of mechanical and
performance conditions for input into maintenance plans.
Vibration analysis and aerodynamic performance calculations
are conducted. Daily visual inspections are done by operators
and are structured on the principles of operator-driven
- Evaluation of operating trends. This should include
auxiliary systems, such as lubrication and seal-oil consoles,
compressor online washing facilities and dry-gas seal
- Periodic testing of lubrication and seal oils. Six basic
analyses and testing are: appearance, dissolved water
content, flashpoint, viscosity, determining the total acid
number (TAN) and additive content.3
- Periodic testing of emergency safety and shutdown devices
(ESD) and other fail-to-danger components, such as exercising
the compressors surge control valve loop and the trip
and throttle (T&T) valve on steam-turbine-driven
- Data logging and automated record-keeping, such as the
number of unplanned trips per train per year as a basic
indication of compressor reliability
- Diagnosis of problems, rating the severity of the problem
and remedial action applied
- Remedial action and execution planning
- Corrective measures that should preferably be applied
onstream to reduce the impact on compressor availability.
Online flushing (washing) is a good example.
In general, turbocompressors have maintenance inspections,
overhauls and repairs (MIO&R); these are also known as
inspection and repair downtime (IRD). These terms are used
interchangeably with turnarounds. MIO&R or IRD events are
scheduled in periodic intervals ranging from 2 years to 10
years, depending on the service. For clean services in the
hydrocarbon processing industry (HPI),
maintenance intervals of 6 years to 10 years are not uncommon.
The extent of MIO&R efforts ranges from simple bearing
inspections to opening the compressor and replacing the rotor
with a spare rotor. Used rotors are examined for rubs at
labyrinth seal locations and for fissures and cracks located
around the impeller eyes on radial compressors. On axial
compressors, moving and stationary blades receive thorough
attention. In all cases, nondestructive test (NDT) procedures
As the scheduled compressor turnaround approaches, it is
best practice to carefully review the machines operating
and maintenance history. If there are any defects noted at
inspection, these questions should be asked:
- Are any of these defects repeat occurrences?
- If so, can they be expected at the next turnaround?
- What steps can be taken to eliminate them?
- What action should be taken at this time?
A thorough pre-turnaround review should be done to plan the
work required. The review should consist of:
- An assessment of the compressors mechanical
condition, solidly backed up by data
- A diligent review of the machines past history
- A well-documented performance check, with findings and
recommendations accepted by operations, maintenance-technical
Preventive and predictive maintenance programs
Good- and poor-performing compressors must be maintained.
The prevailing maintenance strategies applied are preventive
maintenance (PM) or predictive maintenance (PdM). PM is
time-based, whereas PdM has the goal of operating the
compressor until defects start to develop and are discovered.
For PdM, detection requires high-quality monitoring methods;
these tools have a cost factor. Qualified personnel are needed
to perform ongoing monitoring efforts with great precision.
Management expects PdM to determine when a failure will occur
and then plan an outage accordingly.
Certain state-of-the-art predictive routines can be used to
minimize the impact of a premature failure, or to understand
when a machine drifts into off-design operation. But cost
savings always come back to the knowledge factor. None
of the various PdM judgments can be made without experience.
Real depth of experience and wisdom is needed when several
seemingly minor deviations occur and converge.
PM encompasses periodic inspections and applying remedial
steps to avoid unanticipated breakdowns and production
stoppages and to prevent detrimental machine, component and
control-function failures. PdM, and to some extent PM, is the
rapid detection and treatment of equipment abnormalities before
they cause defects or losses. This is evident from considering
lube oil changes. This routine could be labeled preventive if
time-based, and predictive if done only when testing shows an
abnormality in the lubricant. Without strong emphasis and an
implemented PM program, plant effectiveness and reliable
operations are greatly diminished.
In many HPI facilities or organizations, the maintenance
function does not receive proper attention. Perhaps because it
was performed as a mindless routine or has, on occasion,
disturbed well-running equipment, the perception is that
maintenance does not add value. This may lead management to
conclude that the best maintenance program is the least-cost
maintenance. Armed with this false perception, traditional
processing plants have underemphasized preventive, corrective
and routine maintenance. Many facilities have neglected to
properly develop maintenance departments, pursue proper
training programs for maintenance personnel, and optimize PdM
programs. Many unforeseen compressor failures and safety
hazards have resulted from not understanding what this is
really all about.
Correctly executed, maintenance is not an insurance policy or a security blanket. It is
a requirement for success. Without effective PM, equipment is
certain to fail during operation. To be effective, maintenance
must be selective. Note: Selective PM results
in damage avoidance, whereas effective PdM allows existing or
developing damage to be detected in time to plan an orderly
Maintenance in best-practices plants (BBPs)
Four levels of effective compressor maintenance exist.
Although there is some overlap, the levels of maintenance
- Reactive or breakdown maintenance. This
type of maintenance includes repairing equipment after it has
failed, or, in other words, run-to-failure. It is
unplanned, unsafe, undesirable and expensive. If the other
types of maintenance are performed, usually it is
- Selective PM. This maintenance approach
includes lubrication and proactive repair. For example, the
onstream lubrication of the admission valve control linkage
on certain steam turbines should be done on a regular
schedule. In this instance, anything else is unacceptably
risky and inappropriate.
- Corrective maintenance. This
includes adjusting or calibrating equipment. Corrective
maintenance improves either the quality or the performance of
the equipment. The need for corrective maintenance results
from PM or PdM observations.
- PdM and proactive repair. PdM predicts
potential problems by sensing operation of equipment. This
type of maintenance monitors operations, diagnoses
undesirable trends and pinpoints potential problems. In its
simplest form, an operator hearing a sound change made by the
equipment can predict a potential problem. This leads to
either corrective or routine maintenance. Proactive repair is
a repair based on a higher level of maintenance. This higher
level determines that, if the repair does not take place, a
breakdown will occur.
PdM instrumentation is available for both positive
displacement and dynamic compressors. It has many forms and can
be used continuously or intermittently. It is available for
every conceivable type of machine. PdM instrumentation schemes
range from basic, manual and elementary, to totally automatic
and extremely sophisticated. Recommended instrumentation
depends on the compressor size and the owners sparing
philosophies. For example, a facility may opt to install three
50% machines, two 100% machines or perhaps only one 100%
machine in a given service. Moreover, unless the value of
downtime avoidance is quantified, it will not be possible to
make firm recommendations for the most advantageous level of
monitoring instrumentation, shutdown strategies, etc.
There are many competent manufacturers of manual monitoring
equipment. Also, manual monitoring is often used on small air
compressors. Advanced PdM onstream systems are used with large
process compressors to continuously monitor vibration behavior.
By gathering vibration data and comparing these data with
normal operating conditions, both manual and continuous systems
can predict and pinpoint the cause of a potential problem. The
trouble is that detecting vibration is different from
An intelligent but highly selective PM program may lead to
actions that prevent bearing distress and thus prevent
vibration from occurring in the first place. A selective PM
program may be more cost-effective than other strategies to
detect defects before failures occur. This fact establishes
that sweeping management edicts that disallow all manner of
PM on compressors do not harmonize with the principles of
asset preservation and best practices. Traditionally, industry
has focused on breakdown maintenance, and, unfortunately, many
plants still do. However, to minimize downtime and equipment
unavailability, maintenance programs should focus on levels 2
Emergency repairs should be minimized
Plant systems must be maintained at their maximum
performance levels. To assist in achieving this goal,
maintenance should include regular inspection, cleaning,
adjustment, and repair of equipment and systems. Repair events
must be viewed as opportunities to upgrade. In other words, the
organization must know if upgrading the failed
components and subsystems is feasible and cost-justified.
Conversely, performing unnecessary maintenance and repair
should be avoided. Breakdowns occur because of improper
equipment operation or failure to do basic preventive
functions. Overhauling equipment periodically when it is not
required is an expensive luxury. Upgrading where the economics
are favorable is absolutely necessary to sustain
Regardless of whether or not PdM routines have determined a
deficiency, repairs done on an emergency basis are three times
more costly in labor and parts than repairs conducted on a
preplanned schedule. More difficult to calculate, but high
nevertheless, are costs that include shutting down production
or time and labor lost during the event. Bad as these
consequences of poorly planned maintenance are, much worse is
the negative impact from frequent breakdowns on total
performance, including the subtle effect on worker morale,
product quality and unit costs.
Effectiveness of selective PM
When used properly, selective PM can produce considerable
savings. Sweeping, broad-brush maintenance, including the
routine dismantling and re-assembling of compressors, is
wasteful. It has been estimated that one out of every three
dollars spent on broad-brush, time-based PM is wasted. A major
overhaul facility reported that 60% of the hydraulic
pumps sent in for rebuild had nothing wrong with them.
This is a prime example of the disadvantage of performing
maintenance to a schedule as opposed to the individual
machines condition and needs.
However, when a selective PM program is developed and
managed correctly, it is the most effective maintenance plan.
The proof of success can be monitored and demonstrated in
several ways, including:
- Improved plant availability
- Higher equipment reliability
- Better system performance or reduced operating and
- Improved safety.
A plant staffs immediate maintenance concern is to
respond to equipment and system functional failures as quickly
and safely as possible. Every maintenance event must be viewed
as an opportunity to upgrade to avoid repeat failures. Good
maintenance refers to relatively frequently scheduled work.
Systematic upgrading will extend allowable intervals between
Know your existing program
The starting point for a successful long-term selective
maintenance program is to obtain feedback regarding
effectiveness of the existing program from personnel directly
involved in maintenance-related tasks. Such information can
provide answers to several key questions, and these answers
will differ from machine to machine and plant to plant. Your
in-plant data and existing repair records will provide most of
the answers to seven questions listed in Table
1. A competent and field-wise consulting engineer will
provide the rest.
Changes should not be considered in areas where existing
procedures are working well, unless some compelling new
information indicates a need for a change. In short, focus on
known problem areas. To keep focus, continuity of information
and proper activities relative to maintenance programs, some facilities assign responsibility for
well-delineated plant systems to a knowledgeable staff person.
All maintenance-related information, including design and
operational activities relating to such a system, are funneled
through this expert. The maintenance expert is responsible for
refining maintenance procedures and
reshaping the PM program into a selective PM system.
Problems associated with machine uptime and quality output
will affect several functional areas. Many people, from plant
managers to engineers and operators, make decisions and take
actions that directly or indirectly affect machine performance.
Production, engineering, purchasing and maintenance personnel,
as well as outside vendors, use their own internal systems,
processes, policies, procedures and practices to manage
sections for the business enterprise. These organizational
systems are interactive and dependently interact; yet, at
times, these systems constrain efficiency and effectiveness for
the company as a whole. Some constraints are appropriate;
others can have disastrous consequences on equipment
Program objectives must be clearly defined.
Table 2 lists the elements and objectives of
an effective maintenance program. Following these general
guidelines of Table 2 for centrifugal
compressors will provide positive results.
What we have learned?
The main lesson is that one deviation alone might not be
enough to bring on a compressor failure, but, when several more
deviations combine, the failure risk increases exponentially.
So, while it may be possible to avoid more serious failures by
implementing an automatic compressor unloading scheme, or by
adding bells and whistles that annunciate excessive
temperatures and vibrations and seal deficiencies, there will
never be any substitute for the human brain supplying both
logical root-cause failure analysis and upfront failure
Achieving these up-front processes before calamities and
finger-pointing occur requires both training and accepting
accountability. The operator, supervisor or manager accepting a
deviation from established practice should be motivated or
compelled to understand the potential ramifications of
bypassing or not following established guidance as documented
in writing. As documentation requirements are enforced, fewer
deviations are tolerated. Accept the initial incremental cost
outlay needed to do things right. The apparent expenditure of
time and money will ultimately bring rich rewards in safety,
reliability and increased profitability.
If youre stuck with an existing compressor, view every
maintenance event as an opportunity to ask if upgrading is
feasible. If it can be shown to be cost-justified, then DO IT.
Its your professional duty to the stakeholders.
Stakeholders are not just investors; more importantly, they are
employees, families and the community. HP
1 Bloch, H. P. and J. J. Hoefner,
Reciprocating Compressors: Operation and Maintenance, Gulf Publishing
2 American Petroleum Institute, API 617,
3 Bloch, H. P. and F. K. Geitner, Compressors:
How to Achieve High Reliability and Availability,
McGraw-Hill, New York, 2012.
4 Allianz Insurance Handbook of Loss Prevention,
Munich, Germany, 1984.
5 Geitner, F. K., Pipeline and Gas Technology, December
6 Bloch, H. P. and F. K. Geitner, Maximizing
Machinery Uptime, Elsevier-Butterworth-Heinemann,
Stoneham, Massachusetts, 2006.
Fred K. Geitner is a registered
consulting engineer in Brights Grove, Ontario,
Canada, engaged in process machinery consulting. He
retired from Imperial Oil with 20 years of service
that included a position as engineering associate
with Esso Chemicals Canada, Inc. He teaches reliability improvement
courses worldwide. Mr. Geitner graduated from the
Technical University of Berlin, Germany, and has had
extensive equipment selection and upgrading