Article #26: Proper
Pump Piping Procedure – 10 steps
By
Dr. Lev Nelik, P.E., APICS
Pumping Machinery, LLC
It
should be realized that piping issues directly affect the pump’s life and its
performance. Bringing the pump to the
pipe in one operation and expecting a good pump flange or vessel fit is a very
difficult, if not impossible, task. When
bringing the pipe to the pump the last spool (suction side and discharge side,
each) should always be left until the pump has been leveled in placed and rough
aligned. The final alignment will be a
“free bolt condition”, and, as may sound like a surprise to some, no
“come-alongs” would be needed. As an ultimate investement in common sense and
proper attention to details, - your pumps will last longer, with fewer failures
of seals, shafts, bearings and couplings. More equipment uptime, and less lost
production, will result in ignificant savings in dollars, and fewer headaches.
Step 1
At
this point the pipe should be securely anchored just before the last spool, to
prevent future growth towards the pumps flanges.
Figure 1 Typical
anchors for the pump piping
The
final piping lay out should not be finalized until certified elevation drawings
are received form the engineering group or from the pump vendor. Once the final certified prints are received
the final isometrics can be completed and the piping takeoff can be done.
The
delivery of the equipment can either be early or it can be late in arriving at
the site. When the equipment is late it
is critical to have certified elevation prints of the equipment. The certified prints that the isometrics
required for the piping takeoffs can be made without impacting the construction
schedule. If the equipment is early, it
will arrive at the site prior to the construction team needing it for
installation. In such cases, early preparations must be made for long term storage. It is customary to use oil mist lubrication
to keep the equipment in as-shipped conditions during the storage. The pressurization of the bearing housing and
the casing with just 10 to 20 H2O pressure prevents moisture and
contaminants from entering the sealed areas and damaging the components. The early delivery of equipment to the site
has the advantage of allowing for verification of the actual measurements.
Step 2
Once
the location of the equipment is set, the baseplate can be put in place,
leveled and rough-aligned, with the equipment mounted. Rough alignment of the equipment should be
done prior to building the grout forms.
Figure 2 Rough
alignment phase (note that the motor and the pump are not coupled yet and the
baseplate is still sitting free, not grouted
Step 3
Once
you are satisfied with the rough alignment, remove all the equipment (pump, motor gearbox, etc) from the
baseplate. Level the baseplate to
maximum out of level of 0.025" (0.06 mm) from end to end in two
planes. Use machined pads as the base
for the leveling instruments. Inspect the foundation for cleanliness, and if
not clean, use solvent to remove grease and oil.
Figure 3 Baseplate
leveling pads and grout location
Step 4
Allow
time for the cleaning substances to evaporate.
Form the base using the appropriate techniques to allow for the weight,
temperature rise and fluidity of the grout material. Grout the base using epoxy grout. Allow the grout to cure, following the grout
manufacturer’s recommendations. This
normally requires 24 hrs at 80° F (27°C). Remove the forms and clean all sharp
residue and edges from the foundation.
Figure 4 Typical
anchor bolt and leveling wedges
Step 5
The
rough alignment step, which we mentioned above, is critical to minimize the
changes that will be required to appropriately fit the piping to the pump. At the last stage, when the final spools are
installed, the final alignment will be achieved with small adjustments. This will minimize the adjustments required
on the motor feet/bolts. Unfortunately
(motor manufacturer’s take heed!), motor hold-down bolts are often too tight
and allow only for small adjustments to the motor before becoming bolt
bound. Motor manufacturers could improve
this situation significantly if motor feet were slotted, by design, rather than
drilled for bolts. Figure 5 shows
the tightness of space available to insert the foot hold-down bolt.
Figure 5 Potential
bolt-bound situation due to tight clearances between bolt, feet and base
This
illustrates once again why good alignment at step 3 can save time and the cost
of having to alter motor feet (a nightmare) by slotting or reaming.
Step 6
Reinstall
the pump and the motor on the baseplate.
Rough align the equipment again, using reverse indicator or laser
alignment or similar accurate techniques.
Figure 6 Rough
alignment after grouting
It
should be now easy to fine-tune the motor movement within the allowable
alignment target without becoming bolt bound.
This is possible because of the rough alignment during the prior step (Step 4) was completed. Note: Never install shims under the
pump feet. If the shims are lost or
misplaced then alteration to the piping may be required to get the pump within
the required alignment specification.
The normal procedure is to place 0.125" (3.2 mm) thick shims under
the motor feet. This allows for
adjustments that will be required during final alignment.
Step 7
Make
up the final spool pieces for the suction and discharge spaces. Bring the piping to the pump now.
Figure 7 Illustration
of the final connection of the suction piping.
Step 8
Figure 8 Final piping
As
a final alignment step, bring the piping to the equipment; take final
measurements, tack weld the spools in place.
At this time the spools can be removed and taken back to the hot work
permit area to finalize the weld. Leave
a square and parallel gap between the flange faces. The gap should be wide enough to accommodate
the size of the gasket required, plus 1/16 - 1/8”, depending on piping sizing.
(This is the only distance over which the piping will be pulled. However,
because it is properly anchored before the spool pieces, this length is
short, and stresses are minimized).
Final align the equipment, taking into account hot and cold operating
conditions, using two indicators on the pump shaft coupling area.
Step 9
Figure 9 Overhead
view of the motor and pump
As
the piping is tightened into place, the shaft shall not be moved more than
0.002" (0.005 mm), otherwise modify the spool pieces until the piping
misalignment is fixed.
Several
clues are common to piping misalignment.
These clues come via the way of mechanical seal and or bearings running
hot, and failures. A quick analysis of
the failed parts can clearly show the evidence of piping misalignment. To make a final confirmation of the symptoms,
unbolt the piping while measuring the movement in the vertical and horizontal
plan. Again, the piping that moves more
than 0.002" (0.005 mm) must be modified to correct the situation.
Step 10
Place
and indicator in horizontal and vertical planes, using the motor and pump
coupling.
Uncouple
the pump and motor, while watching the indicator movement. Start unbolting the flanges, and continue
watching for movement in the indicators.
If the needle jumps over 0.002" (0.005 mm) the piping has to be
modified to improve the pump’s performance.
Figure 10 Piping
alignment verification
References
1.
1) Pump
Standards, Hydraulic Institute publication, ANSI/HI 1.1‑1.5‑1994,
2.
2) API 610
Standard for centrifugal pumps, 8th Edition, American Petroleum Institute,
Washington, DC, August, 1995
3.
3) API 676
Standard for rotary pumps, 2nd Edition, American Petroleum Institute,
4.
4) Equipment
Testing Procedure for Centrifugal Pumps (Newtonian liquids), 2nd Edition,
5.
5) AlChE
Equipment Testing Procedure for Rotary positive displacement pumps (Newtonian
liquids), Second printing,
6.
6) Nelik L.,
"Centrifugal and Rotary Pumps: Fundamentals with Applications", CRC
Press,
7.
7) AlChE
Equipment Testing Procedure, 1999,
8.
8) L. Rizo, L. Nelik, “Piping-to-Pump
Alignment”, Pumps & Systems, April 1999
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