By Dr. Lev Nelik, P.E., APICS, Pumping Machinery, LLC www.PumpingMachinery.com
Aligning your pump and piping correctly can have a big impact on the successful operation of the pump.
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 levelled in place and rough aligned. Then, the final alignment will be a “free bolt condition”, and, as may come as a surprise to some, no “come-alongs” would be needed. As an ultimate investment 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 significant savings in dollars, and fewer headaches.
This applies only in cases where there is NO thermal growth – otherwise see Step 2
At this point the pipe should be securely anchored just before the last spool, to prevent future growth towards the pumps flanges.
The final piping lay out should not be finalized until certified elevation drawings are received from 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 completed.
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 mean 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.
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. To avoid stresses caused by thermal expansion of pipes, expansion loops should be installed in suction and discharge lines. The “sliding” pipe supports near pump suction and discharge are required to eliminate weight loads of piping on the pipe, which can cause excessive loads and misalignment, leading to failures in seals, bearings, couplings and so on. However, “anchors” (three dimensional restraints) should not be used, as these could cause significant stresses and casing distortions due to thermal expansion. Consider, an example (Fig. 2C) of incorrectly placed “anchor” (restraining growth in ALL directions, i.e. not simply a vertical “sliding” support), even 2 feet away from the pump suction, and the case where the pipe expands by only 30 degrees F (morning to afternoon):
For the pipe you use, the area of contact between the pump and pipe flanges depends on the size of the pipe. Assume, for example, a 20 in2 contact area (or use your pipe/flange number). The resultant force on the pump will be:
F = 6000 x 20 = 120,000 lbs – very high. It will distort the pump casing, feet, shafts, etc., causing problems. If, in addition to that, you are pumping hot product, the piping expansion problem could be so much worse. But even the daily fluctuations of ambient temperature alone could cause problems, as shown in a sample calculation above.
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.
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.
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.
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.
Reinstall the pump and the motor on the baseplate. Rough align the equipment again, using reverse indicator or laser alignment or similar accurate techniques.
It should now be 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.
Make up the final spool pieces for the suction and discharge spaces. Bring the piping to the pump now.
Warning! –if the “anchor” is placed erroneously – it will restrain the pipe thermally moving away from the pump free: the pipe will expand from the anchor into the pump! (see step 2).
As a final alignment step, bring the piping to the equipment, take final measurements and 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.
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 indicators of 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.
Place an 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
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2. API 610 Standard for centrifugal pumps, 8th Edition, American Petroleum Institute, Washington, DC, August, 1995
3. API 676 Standard for rotary pumps, 2nd Edition, American Petroleum Institute, Washington, DC, December, 1994
4. Equipment Testing Procedure for Centrifugal Pumps (Newtonian liquids), 2nd Edition, AlChE, New York, 1984
5. AlChE Equipment Testing Procedure for Rotary positive displacement pumps (Newtonian liquids), Second printing, New York, 1968
6. Nelik L., “Centrifugal and Rotary Pumps: Fundamentals with Applications”, CRC Press, Boca Raton, FL, March, 1999
7. AlChE Equipment Testing Procedure, 1999, New York, NY
8. L. Rizo, L. Nelik, “Piping-to-Pump Alignment”, Pumps & Systems, April 1999