Awareness of energy efficiency is
one of the minimum job qualifications for reliability engineers. In the summer
of 1994, Jack Lambley, then an intern at the Imperial Chemical
Industries (ICI) Rocksavage site in the UK, was assigned the
task of quantifying the effects on power consumption for
misaligned process pumps. A surplus pump was overhauled, and
new bearings were fitted. This pump was reinstalled, and water
was recirculated in a suitably instrumented closed-loop
arrangement. Prueftechnik GmbH loaned Lambley a modern
laser-optic alignment instrument.
As an undergraduate student,
Lambley had learned how misalignment affected bearing load, and
how bearing load increases caused exponential decreases in
bearing service life. Following instructions from his
supervisor, Lambley reviewed the engineering sections of
SKFs general catalog, which stated that a 25% increase in
bearing load caused the rated bearing life to be halved.
Lambley investigated the alignment
accuracy and the methods in use at that time. He discovered
that straight-edge methods were inappropriate for refinery pumps. Rim-and-face
alignment methods were judged difficult and unreliable.
Properly executed, reverse-dial-indicator methods required
consideration of the bracket sag, and they would require more
time to apply than modern laser techniques.
From data available at the
Rocksavage site, he calculated that the typical misalignment
consisted of 0.02 in./0.5 mm vertical and horizontal offset and
0.002 in./in. vertical and horizontal angularity. In 1994,
lasers were known to be inherently more accurate than the best
Lambley constructed several graphs
and tabulations, as shown in Figs 14. The resulting
recommendations were to align machinery to within 0.005
in./0.12 mm shaft offsets and to limit deviations in the hub
gap to 0.0005 in./in. of hub diameter. Lambley further
documented that adhering to these recommendations would reduce
ICIs power consumption by about 1%. He confirmed that
laser alignment was faster and superbly more accurate. Lambley
determined that laser alignment technology was bottom-line more
cost-effective; he deserves credit for establishing these facts
instead of repeating the opinions of others.
Fig. 1. Effect of parallel
offset on power
consumption of a pin coupling at 3,000
Fig. 2. Effect of
angular misalignment on
power consumption of a pin coupling
at 3,000 rpm.
Fig. 3. Effect of
parallel offset on power
consumption of a toroidal (tire-type)
at 3,000 rpm.
Fig. 4. Effect of
angular misalignment on
power consumption of a toroidal
coupling at 3,000 rpm.
Using data from a mid-size refinery:
Average demand: 27 kW/pump 3 8,760
hr/yr 3 $0.1/kWh 3 1,000 pumps 3 0.01 = $236,520/yr. And, with
1,000 pumps operating at any given time, this location could
annually save approximately $250,000 in avoided power
The total cost for laser alignment
instruments includes equipment costs plus training costs. The
benefit is 8 man-hours of time-saving credit per alignment job.
For gathering more data, thermography and infrared monitoring
techniques are possible options. These methods have been used
to quantify significant temperature increases in a coupling
located between misaligned pump and driver shafts. You could
compare the energy wasted by the rising temperature of a
coupling to the energy loss, as described by Lambley.
Regardless of calculation method, laser alignment will result
in surprisingly rapid payback. Remember: In
all reliability improvement endeavors,
never let somebodys opinion get in the way of sound
science and facts.
If you are like the majority of
hydrocarbon processing industry facilities in the industrialized
world, your worker and technician resources are probably
stretched to the limit. Understandably, you may be looking for
ways to simplify some of your traditional work processes and
procedures. You may have had an experience that reinforces the
contention in which high-tech tools are not always the answer.
And hold the view that the back-to-basics thinking has
considerable merit. However, decades of well-documented
observation attest to the fact that misalignment has been
responsible for huge economic losses. The more misalignment of
the rotating unit permitted, the greater the rate of wear,
likelihood of premature failure, and loss of efficiency of the
As an inquisitive Lambley proved,
misaligned machines absorb more energy than they consume more
power. So, its always advantageous to update ones
knowledge of shaft alignment and alignment tolerances.
Competent vendors will assist you in illuminating the roadway
to becoming reliability-focused. And indications are that only
the reliability-focused facilities will be around in the
Heinz P. Bloch is Hydrocarbon
Processings Reliability/Equipment Editor.
A practicing consulting engineer with now 50 years of
applicable experience, he advises process plants
worldwide on failure analysis, reliability
improvement and maintenance cost avoidance
topics. He has authored or co-authored 18 textbooks
on machinery reliability improvement
and over 490 papers or articles dealing with related
subjects. For more on alignment, refer to Bloch, H.
P., Pump Wisdom: Problem Solving for Operators and
Specialists, John Wiley & Sons, Hoboken, 2011,