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Why Align?
The Importance of Proper Pump Alignment
Nicolas Ganzon, Manager – Field Services, PRO Services - Goulds Pumps,
ITT Industries
Why should a company embark upon a campaign of quality alignment? One
word: Money. In the best case scenario, poor alignment will slowly and
continuously suck money from your bottom line. In a worst case scenario,
a catastrophic failure will cut your operations day short and cost more
in repair and lost production.
The most common manifestations of poor equipment alignment are increased
vibrations, reduced equipment reliability, or outright failure. Any of
these reasons are good enough to justify proper alignment since, what is
the use of having equipment if it is broken? If these reasons were not
enough, the following
list should help:
Increased vibrations
Shaft failure
Bearing failures
Mechanical seal leaks
Noise
Poor alignment can seek its revenge anytime, and usually at the most
inopportune time.
Operating Cost
The reasons for alignment are most often centered on equipment
reliability, and for good reason. Poor reliability is closely associated
with equipment downtime; the bain of a process industry. But while
equipment reliability is the poster child for proper alignment, there is
still a darker side: power consumption. Depending upon the severity of
misalignment, increases in power costs between 2% and 9% may be seen. In
some cases, it has been reported the power consumption may increase as
much as 17% . The math is simple…A 2% impact on power consumption on a
20 horsepower pump translates into $154 per year in operating costs. A
9% impact is worth $692 per year. These costs affect the bottom line and
can be quite significant in a typical process plant with hundreds, if
not thousands, of pumps.
Equipment Alignment
Steps
1. Installation quality – Good alignment is predicated upon a quality
installation. This means proper foundations, base-plate installations
and piping. Before mounting alignment equipment, check for the following:
Foundation soundness – Overall condition of the foundation should be
monitored and considered as equipment is aligned. Foundations can change
over time, and this can affect the equipment alignment. Compare the
quality of the foundation to the alignment records to determine if any
problems correlate.
Baseplate installation – There are a couple of checks that should be
performed that may directly impact the alignment: Baseplate-foundation
separation, corrosion on the mounting pads, and broken welds or cracked
castings.
Pipe Strain - The ideal condition should be where the piping can be
maneuvered into place by hand and axial separation is no more than the
gasket thickness ± 1/32". Additionally, the piping should be inspected
for proper support during operation.
2. Soft Foot checks - Soft-foot is a condition where the pump or motor
feet do not contact the baseplate properly. To check for soft-foot place
a dial indicator on the contact foot of the equipment, and tighten the
holddown bolts. The indicator reading should not change more than .002".
Repeat the process for all the other feet.
3. Alignment - There are several methods for aligning equipment: dial
indicator [rim-andface], reverse dial indicator, and laser. The Pros/Cons
of each method are outlined in Table 2. For general process equipment,
alignment is attained when the alignment criteria of Table 1 are
achieved. As with every rule, there are exceptions:
•For electric motors, the motor shaft initial (cold) parallel vertical
alignment setting should be 0.05-0.10 mm lower than the pump shaft. Pump
manufacturer should be contacted for more specific information.
•For other drivers (e.g. steam turbines, engines, etc…) follow the
driver manufacturers’ recommendation.
4. Documentation - Thorough documentation of the installation checks,
final alignment values, and special findings should be made after each
alignment. Equipment will move after initial alignment and operation.
This information will help trend the movements to help identify any
unusual occurrence and its cause.
An Alignment Program
When to align
The ability to properly align equipment is a skill that must be
continually practiced. Suffice it to say, purchasing the dial indicators
or laser alignment equipment does not make one capable of aligning
equipment. In general, equipment alignment should be checked after the
pump is installed or any changes have been made to the pump, motor, or
coupling. This would include repairing the pump, re-tightening loose
hold-down bolts, or reconnecting piping to the pump. There are some
additional periods in which to perform an alignment check:
Before grouting baseplate - Occasionally a new pump and driver cannot
be aligned. Motor feet may become "bolt-bound" when there is not enough
clearance between the hold down bolt and the foot-hole to allow movement
for alignment. Equipment should be aligned after positioning on the
foundation, but before grouting to ensure that they can be aligned
properly.
After connecting piping and grouting baseplate - Excessive flange
loads can distort the pump and/or pumps pedestal and alter the equipment
alignment.
Hot Alignment - After the pump and the piping system have reached
their normal operating conditions, alignment should be checked to ensure
that thermal expansion has not altered the alignment. Equipment should
be aligned to hot conditions.
Periodically - As mentioned earlier, even though equipment may be
rigidly tied down, movement over time does occur and this will alter the
alignment.
Before removing pump from system - If a troublesome pump needs to be
removed for repair, checking the ending alignment will assist in
identifying the cause of the problem. If equipment is continually found
to be out during these checks, it could mean improper tie-down of the
pump/motor, or excessive flange loads.
While it may be a tedious task, proper equipment alignment benefits the
reliability and cost effectiveness of a pump installation. Repair costs
are reduced as less stress is placed on the equipment, and overall
efficiency is improved, as less energy is lost. <<
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