Читать книгу Pump Wisdom - Robert X. Perez - Страница 28

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 3.9 shows 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.