Pumps & Systems, March 2007
Many plants now turn to precast polymer concrete pump foundations to reduce pump installation costs and improve reliability. Here's why.
Precast polymer concrete pump foundation systems provide numerous advantages over conventional means, including savings in installation costs, improved reliability, and superior corrosion resistance for pumps in corrosive service.
Precast polymer concrete systems consist of a foundation and baseplate shell for rotating pumps and motors. The foundations are constructed of polymer concrete in a one-piece shell. The shell replaces the baseplate, foundation, anchor bolts and grouting system of a traditional pump foundation and can be combined with a variety of rotating pump designs, including ANSI and ISO pumps. Additionally, custom-built foundations can meet special pump requirements.
"Often, precast polymer concrete pump foundations are selected for pumps in corrosive service," explains Larry Welch, the industrial products manager for Structural Preservation Systems, a Houston-based provider of precast polymer concrete pump foundations. "These foundations are advantageous in corrosive environments because they are made from inert aggregate filled with inherently corrosion-resistant thermosetting resins, such as novolac epoxy or vinyl ester."
However, many end users are installing these units in non-corrosive services in new construction, as well as repairs or upgrades of existing pump installations, for enhanced constructability reasons alone. Because precast polymer concrete pump foundations eliminate the need for forming and pouring conventional concrete foundations in addition to anchor bolts, separate baseplates and grouting systems, the time and labor necessary in new construction to install a pump package is dramatically reduced.
In the case of upgrade or repair of existing pump installations, it is common to complete the upgrade or repair and have the pump back up and running within one or two days.
Reduced Installation and Life Cycle Costs
Precast polymer concrete pump foundations can drastically reduce the total installed cost compared to conventional fabricated steel baseplates.
For example, with a typical ANSI pump installation, installation time is reduced from a week or more to one or two days. Craft man-hours are reduced 70 to 80 percent. Other savings come from the ANSI pump being mounted prior to installation. Fewer installation steps require fewer skilled craftsmen. Minimal edge forming is used, and expensive acid brick foundations used in traditional foundations are avoided. Instead of expensive grouts, standard 3,000-psi (200-bar) concrete is used. Finally, sandblasting is not necessary for proper bonding.
In addition to providing cost savings during the installation process, a precast polymer concrete foundation reduces overall life cycle costs. The technology improves vibration signatures, which reduces downtime and related maintenance costs associated with fewer seal and bearing repairs. Furthermore, a precast polymer concrete foundation offers excellent corrosion resistance and improved equipment MTBPM.
The Installation Process
Installing a precast polymer concrete pump is a relatively simple process, compared to a traditional pump foundation.
In using precast polymer concrete technology to install a new foundation, a steel rebar cage is doweled into the concrete slab or footing - as would normally be done when forming and pouring a conventional concrete foundation. But then, the precast polymer concrete foundation is placed over the rebar cage and is leveled and filled with standard 3,000-psi concrete.
Installation typically requires only a few hours to complete and saves considerable time in new plant construction. Because of the inherent rigidity of precast foundations, warping of the coplanar pump and motor mounting surfaces (a factor common with steel baseplates) is eliminated.
"Precast polymer concrete pump foundations are used mostly for standard ANSI pumps," says Welch. "For this reason, standard-sized reusable molds are used to precast ANSI standard combination foundation/baseplate units."
Precast polymer concrete allows a further refinement of the technology in formulating removable, single-piece, motor-specific precast blocks, which are bolted onto the motor end of the precast units. These motor blocks have precisely positioned, specially fabricated threaded inserts cast integrally into the polymer concrete body of the block to match the bolt patterns of standard NEMA frame motors. Changing to a different-sized motor for a given pump becomes a mere change out of precast motor blocks.
The unique characteristics of polymer concrete allow greater versatility in designs. One example is the motor adjusting devices, favored by millwrights, which facilitate motor and pump alignment in the field. Polymer concrete also allows cast-in drip catch pans with integral drain fittings to be incorporated at the pump end of the precast unit, so leaks can be collected and piped off to a collection basin or trench.
Less Vibration
Vibration signature testing is commonly used on rotating equipment to diagnose and predict pending failures with pump and motor operation. Readings are typically taken in three planes (horizontal, vertical and axial) and reported as velocity amplitudes in inches per second at various frequencies. It is generally accepted that the lower the velocity amplitudes on a vibration signature for a given pump system, the longer that equipment will operate before maintenance is required.
The vibration signatures observed on pumps mounted to precast polymer concrete foundations indicate that polymer concrete is a vibration dampner for rotating equipment. Velocity amplitudes in the range of 0.10-in/s are considered desirable by rotating equipment engineers, but results as low as 0.005-in/s have been reported on signatures from pump installations on precast polymer concrete foundations. (Pump and motor alignment must still be properly executed - and any pipe strain must be removed - or the signatures will not be acceptable in any case.)
The properties of polymer concrete also allow the fabrication of larger custom-made precast pump foundation/baseplate combination units for non-ANSI pumps. In fact, it is possible to fabricate units as large as 4-ft wide and 14-ft long, with stainless steel mounting pads for the pump, and with the motor integrally cast into the top. The pads are first milled flat and coplanar, then drilled and tapped for the specific pump and motor. Pump packages with motors as large as 1,000-hp are successfully operating in the field on custom-made precast units. This technology is also successfully employed with centerline mounted API pumps.
Combining the disciplines of civil engineering and mechanical engineering has resulted in the practical application of polymer concrete technology to provide corrosion-resistant, precast polymer concrete pump foundation systems, which are more cost-efficient and quicker to install. Over time, these new designs may go a long way toward eclipsing conventional pump support systems in refining and petrochemical facilities.
Case Study: Petrochemical Plant Expansion
In 2002, a major petrochemical company located in the Louisiana Gulf Coast region was faced with the challenge of installing 90 ANSI pumps for its plant expansion. The company chose precast polymer concrete pump foundations for their ability to reduce total installation costs.
The company previously relied on conventional pump installations and had experienced numerous problems with the traditional method. For instance, the facility commonly had to remediate the conventional pump installation because of a warped baseplate. In other cases, voids were formed in the epoxy grout during baseplate grouting, and tedious and expensive epoxy injection of the voids delayed pump start-up. Finally, only expensive field machining could salvage some baseplates.
After first inspecting random ANSI precast units from inventory to ensure they met coplanar and parallel flatness requirements, plant managers then analyzed the cost projections of installing the precast polymer concrete pump foundations. When the data demonstrated cost savings, installation of the precast foundations was scheduled.
The pump foundations were then shipped to the pump manufacturer, where the pumps and motors were mounted and factory alignment completed. Next, the pumps, motors, and precast foundations were sent as complete packages to the petrochemical plant's laydown yard until they were ready to be installed.
The plant marked off each place in the new plant where a pump and foundation would be installed. For each pump location, a steel rebar cage was dowelled into the concrete slab, and the foundation with pump and motor attached was set over the rebar cage. At this facility, five to six pumps were installed and leveled at a time. A concrete truck then filled each rebar cage with concrete. After a final alignment was performed and the piping was connected, the installation was complete.
The plant saved more than $1,000 per pump on installation costs alone. Not only did installation go quickly, it also was performed very safely - another key issue for the plant. Using the precast pump baseplate and foundation reduced labor, and with fewer people on site, risk.
Five years after the installation was complete, the petrochemical plant is reaping the rewards of using the precast pump baseplate system. The plant has not had to repair these pump systems as it would have with conventional methods. Vibration signature testing shows the new pumps are vibrating much less than with traditional installations, which means fewer replacement parts and downtime. Results of the testing show the overall velocity amplitudes at half or more than half of that of conventionally mounted pumps in the plant. Overall, the plant has noticed its pumps running quieter, smoother and with longer time between repairs.
Case Study: Paper Mill Repair/Upgrade
In 1999, an Alabama paper mill needed to repair and upgrade five pumps within a very limited timeframe. Within a five-day shutdown, the pumps and many other repairs needed to be performed. The pump repair presented challenges because conventional installation methods generally take two to three weeks, depending on site conditions and how they affect cure times for the concrete and epoxy grout materials used in this method. Instead, precast polymer concrete pump foundations were chosen for the repair.
In this unique installation, workers held each of the five pump foundations in place with crossbars while a rope saw was used to cut the concrete foundations even with the slab while the pumps and motors were running. Then, when the plant shut down, workers removed each pump-motor-foundation system.
Next, the pumps and motors were removed from the existing foundation. Then a rebar cage was placed at the location of each pump and precast polymer concrete pump foundations were set in place. Repairs and upgrades were performed on the pumps and motors within the allotted timeframe, and each pump and motor system was returned on top of its new foundation.
Since installing the precast polymer concrete pump foundations, the paper mill has experienced vastly increased reliability over their traditional foundations. With the traditional foundation systems, work orders were requested on a monthly basis; with the precast polymer concrete pump foundations, only two work orders have been placed. As a result, the plant has saved money not only in labor costs, but also in materials and parts for repairs and lost production due to downtime necessary for repairs.
Conclusion
While many plants choose precast polymer concrete pump foundations to reduce installation costs, time has proven the technology's capacity to continue providing savings in terms of improving maintenance costs.
Whether a plant needs to install a completely new foundation or to repair a damaged existing foundation, precast polymer concrete pump foundations provide a more cost-efficient and faster installation over conventional pump foundations.
Ashley Kizzire is a writer based in Birmingham, AL.