The initial version of this procedure was published several years ago by me. Since then, a large amount of feedback has been accumulated. The most recent reflection appeared in the March 2012 issue of Pumps & Systems with discussion on how the thermal effects of pipe growth influence the supports, anchors and other restrictions. The 10 steps outlined in this article reflect modifications, corrections, your questions, challenges and practical considerations and limitations.
Piping issues directly affect a 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 difficult 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 place and rough aligned. The final alignment will be a free bolt condition, and no come-alongs would be needed, which may be a surprise to some readers. With an initial, common-sense investment and proper attention to details, the pumps will last longer, with fewer failures of seals, shafts, bearings and couplings. More equipment uptime and less lost production will result in significant cost savings and fewer headaches.
Note: This step is only for cases in which NO thermal growth is experienced—otherwise skip to Step 2.
At this point the pipe should be securely anchored just before the last spool, to prevent future growth toward the pump’s flanges. The 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 drawings are received, the final isometrics can be completed and the piping takeoff can be performed.
|Figure 1. Occasionally, anchors (only if NO thermal growth, which is rare) can be used for the pump piping.|
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 ensure 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 before the construction team needs it for installation. Preparations must be made for long-term storage. Using oil mist lubrication is customary to keep the equipment in as-shipped condition while it is stored. 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. In ad- dition, early delivery of equipment to the site allows for the verification of the actual measurements.
When the location of the equipment is set, the baseplate can be put in place, leveled and rough-aligned, with the equipment mounted. Rough alignment should happen prior to building the grout forms. To avoid stresses caused by the thermal expansion of pipes, expansion loops should be installed in the suction and discharge lines. The “sliding” pipe supports near the pump suction and discharge are required to eliminate the weight loads of piping on the pump, which can cause excessive loads and misalignment, leading to seal, bearing and coupling failures.
However, anchors (three dimensional restraints) should not be used because they could cause significant stresses and casing distortions from thermal expansion. Consider, an example (Figure 2, Example C) of an incorrectly placed anchor (restraining growth in ALL directions, not simply a vertical, sliding support), even 2 feet away from the pump suction, and the case of pipe expansion by only 30 F (morning to afternoon):
For the pipe, the area of contact between the pump and pipe flanges depends on the pipe size. Assume, for example, a 20-square-inch contact area (or use the pipe/flange number). The resultant force on the pump will be:
This is high and will distort the pump casing, feet, shafts, etc., and cause problems. If, in addition to that, the pumped product is hot, the piping expansion could be worse. However, even the daily fluctuations of ambient temperature alone could cause problems, as shown in the calculation above.
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)
A. Correct configuration—Sliding support does not keep the piping from sliding up/away.