Robert X. Perez - Pump Wisdom

In the size range up to about 1.5 m × 2.5 m, conventional grouting procedures, although briefly mentioned in this text, are being phased out in favor of baseplates prefilled with an epoxy resin or grout [3]. These standard material prefilled steel baseplates then represent a solid block (the “monolith”) that will never twist and never get out‐of‐alignment.

The process includes five successive stages, all done under controlled conditions before shipment to the site:

1 Baseplate fabrication. (No pour holes are needed for prefilled baseplates)

2 Stress relieving

3 Pregrouting (primer application) in preparation for prefilling. (If there are large pour holes, the inverted baseplate must be placed on a sheet of plywood, Figure 3.7)

4 Fill with epoxy grout and allow it to bond and cure

5 Invert and machine the mounting pads to be flat; then verify flatness before shipment ( Figure 3.8). Protect and ship ( Figure 3.9) – possibly even with pump, coupling, and driver‐mounted and final‐aligned.

The advantage of prefilling is notable. Jobs with pumps in the 750 kW (1000 hp) category and total assemblies weighing over 12 000 kg (26,400 lbs) have been done without difficulty on many occasions. A conventionally grouted baseplate requires at least two pours, plus locating and repair‐filling of voids after the grout has cured. Prefilled or pregrouted baseplates travel better and arrive at the site flat and aligned, just as they left the factory. Their structural integrity is better because they do not require grout holes. Their installed cost is less and their long‐term reliability is greatly improved.

Figure 3.7 Underside of a baseplate after a prime coat has been applied. It is ready to be filled with epoxy. The large pour holes identify it as an old‐style “conventional” baseplate being converted to prefilled style.

Source: Stay‐Tru ®, Houston, TX.

Figure 3.8 Flatness and level measurements determine if the now‐machined‐prefilled baseplate has been properly machined. It is then ready to be installed on a foundation at site.

Source: Stay‐Tru ®, Houston, Texas.

Figure 3.9 Epoxy prefilled baseplate fully manufactured by a specialty company, shown ready for shipment.

Source: Stay‐Tru ®Company, Houston, TX.

If a specialist firm is not available or if upgrading is done at a field location, ascertain that the baseplate's underside is primed with high‐quality epoxy paint. In general, baseplates are specified with an epoxy primer on the underside. This primed underside should be solvent‐washed, lightly sanded to remove the glossy finish, and solvent‐washed again. For inorganic zinc and other primer systems, the bond strength to the metal should be determined; expert instructions will be quite helpful. There are several methods for determining bond strength, but, as a general rule, if the primer can be scraped off with a putty knife, the primer should be removed. Sand blasting to an SP‐6 finish is the preferred method for primer removal. After sand blasting, the surface should first be solvent‐washed and then pregrouted (i.e. epoxy‐filled) within eight hours.

By its very nature, pregrouting a baseplate will greatly reduce problems of entrained air‐creating voids. However, because grout materials are highly viscous, proper placement of the grout is still important to prevent air pockets from developing [4]. The baseplate must also be well supported ( Figure 3.7) to prevent severe distortion of the mounting surfaces due to the weight of the grout.

Once the pregrouted baseplate has been fully cured, it is turned right‐side‐up and a complete inspection of the mounting surfaces is performed ( Figure 3.8). If surface grinding of the mounting surfaces is necessary, then a postmachining inspection must also be performed. Careful inspection for flatness, coplanarity, and relative levelness (colinear) surfaces should be well documented for the facility's construction or equipment files. The methods and tolerances for inspection should conform to the following:

Flatness: A precision ground parallel bar is placed on each mounting surface. The gap between the precision ground bar and the mounting surface is measured with a feeler gauge. The critical areas for flatness are within a 2–3″ radius of the equipment hold‐down bolts. Inside of this area, the measured gap must be less than 0.001″. Outside the critical area, the measured gap must be less than 0.002″. If the baseplate flatness falls outside of these tolerances, the baseplate needs to be surface ground.

Coplanarity: A precision ground parallel bar is used to span across the pump and motor mounting pads in five different positions, three lateral and two diagonal. At each location, the gap between the precision ground bar and the mounting surfaces is measured with a feeler gauge. If the gap at any location along the ground bar is found to be more than 0.002″, then the mounting pads will be deemed noncoplanar and the baseplate will have to be surface ground ( Figure 3.8). Outsourcing baseplate design, fabrication, and prefilling with epoxy grout has often been found economically attractive. Figure 3.9shows it ready for shipment.

Relative level (Colinearity): It is important to understand the difference between relative level and absolute level. Absolute level is the relationship of the machined surfaces to the earth. The procedure for absolute leveling is done in the field and is not a part of this inspection. Relative level is an evaluation of the ability to achieve absolute level before the baseplate gets to the field.

Conventional grouting methods for nonfilled baseplates, by their very nature, are labor and time intensive [5]. Utilizing a pregrouted baseplate with conventional grouting methods helps to minimize some of the cost, but the last pour still requires a full grout crew, skilled carpentry work, and good logistics. To further minimize the costs associated with baseplate installations, a new field grouting method has been developed for pregrouted baseplates. This new method [6] utilizes a low‐viscosity, high‐strength epoxy grout system that greatly reduces foundation preparation, grout form construction, crew size, and the amount of epoxy grout used for the final pour.

Use ultrastiff, epoxy‐filled formed steel baseplates (“StayTru®” method or an approved equivalent) on new projects and on optimizing existing facilitiesProceed by first inverting and preparing the baseplate; use recommended grit blasting and primer paint techniques.Fill with suitable epoxy grout to become a monolithic block. Allow to cure; after curing, turn over and machine all mounting pads flat and coplanar within 0.0005 in./ft (0.04 mm/m).Next, install complete baseplate on pump foundation. Anchor and level it within the same accuracy.At final installation, place epoxy grout between the top of the foundation and the space beneath the monolithic epoxy prefilled baseplate.

On welded baseplates, make sure that standard thickness steel is used and that the welds are continuous and free of cracks.