American Oil and Gas Reporter - March 2016 - 56

SpecialReport: Gas Industry Strategies

Valve Monitoring Maximizes Efficiency
By Scott Bassett
KNOXVILLE, TN.-Driven by operational, economic and regulatory factors,
more emphasis is being placed on the reliability and health of the intake and exhaust valves on natural gas compressors.
When a valve begins to exhibit signs
of leakage, compressor efficiency can be
lost. Reciprocating compressors are designed to last a long time on the job site,
but the health of individual valves needs
to be assessed and addressed continually
in order to maintain maximum compressor
efficiency, optimize the overall performance of gas-producing assets, and prevent
lost production.
Valve failures can occur as a result of
numerous problems. Proppant flowback
and fracturing fluid flowback are particularly hard on the valves in reciprocating
compressors. However, even in clean gas,
valve degradation will occur over time
as a result of normal wear and tear. With
any amount of valve wear comes a significant decrease in sealing capacity.
Whether valve damage occurs as a result
of liquid intrusion, or is simply caused
by normal wear, it is essential that operators maintain an awareness of valve
functionality.
Unfortunately, in many companies,
valve maintenance comes well after efficiency and production quality losses have
already begun to occur. By the time pressure and volume curves and temperature
readings have signaled a problem in a
valve, valuable product delivery has been
delayed because of produced gas recirculation.
Continuous monitoring is the key to
managing valve health in reciprocating
compressors. By continuously monitoring
the vibration and temperatures on a valve,
a rate of degradation can be established,
allowing the operator to predict the ideal
time to schedule a valve replacement.
This can be beneficial whether the organization is monitoring groups of valves
regionally, or more ideally, continuously
monitoring individual valves at each compressor location.
Monitoring Approaches
One common setup involves groups
of valves monitored continuously through
cumulative data collection on the compressor head. In this regional monitoring
56 THE AMERICAN OIL & GAS REPORTER

setup, the primary value comes from the
improved efficiency associated with predictive maintenance. Instead of relying
solely on lagging indicators from pressure/volume calculations and temperature
variations, monitoring valves using vibration data will alert maintenance to
issues well before they would have been
detected in volumetric calculations. This
means less time where horsepower is
being wasted recirculating gas because
of a leak in a valve.
In addition, by switching from periodic
monitoring to continuous monitoring,
maintenance teams no longer have to
worry that an issue will arise shortly after
a periodic maintenance check, leaving
machines running at low efficiency for
an extended time. This prevents situations
where a problem begins the day after a
check, and continues to impact production
for an entire week or month until the
next pressure, volume or temperature
check.
In addition to increasing efficiency,
switching to continuous monitoring of
valves in reciprocating compressors means
decreasing costly downtime. Letting a
valve run to failure means adding the
cost of lost production to the already undesirable cost of repairs. In pad developments where a single compressor is
serving multiple wells, the lost production
costs are compounded significantly.
Continuous monitoring enables equipment failures to be predicted. The value
of this predictive data is in the ability to
schedule and shorten the duration of
maintenance on essential equipment. This
avoids not only the cost of lost production
during emergency repairs, but also the
risk of added rework cost from having to
make do with hasty repairs.
Monitoring individual valves brings
the same benefits as regional monitoring,
but with the added benefit of greatly decreasing repair times. When fully implemented, continuous monitoring of individual valves allows maintenance teams
to pinpoint the particular valve in a compressor that is failing. This allows the
maintenance team to schedule a replacement for only one valve, which could
easily save six to seven hours over replacing all the valves in the compressor,
as well as avoiding the rebuild cost for
multiple valves in a system.
In addition, monitoring individual

valves shortens unavoidable downtimes.
It is far easier to schedule a two-hour
repair than one that will take eight hours.
Should downtime related to valve repair
or replacement be necessary, being able
to accurately diagnose the problem valve
can save thousands of dollars in maintenance costs and lost production.
Case Study Application
Needing a solution for high valve failure rates on reciprocating compressors
that were handling wet gas, an oil and
gas company operating in the Midwest
decided to take advantage of the predictive
maintenance benefits of continuous monitoring. Monitoring specialists helped implement technology that would cut through
the complexity of machinery analysis to
provide a simple, reliable indication of
equipment health through a single trend
by filtering out traditional vibration signals
to focus exclusively on "impacting."
In addition to needing to simplify the
monitoring process, the organization
wanted to expand its monitoring to encompass all of the crossheads and to
take an axial reading on each throw, in
order to more easily detect the looseness
and/or impacting that occurs when some
of the mechanical components begin to
wear.
The compressors were outfitted with
a high-frequency (10 millivolts/g) accelerometer mounted on one of the
studs/bolts that held the valve cover in
place. Standard accelerometers also were
mounted vertically on the crosshead section, and axially on the head. Being able
to determine the phase angle of the occurrence is essential so that other signatures
present in a given valve reading can be
related to other events happening on the
compressor.
The user also had the option to utilize
dual-purpose, high-frequency/temperature

Coming In April
The Kansas Independent Oil &
Gas Association will hold its 2016
midyear meeting April 20-22 in
Great Bend, Ks., Expo Complex. See
the Official Convention Section in
the April issue of The American Oil
& Gas Reporter.

American Oil and Gas Reporter - March 2016

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