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Epoxy-Filled Baseplates

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Fig. 3: Steel baseplate ---epoxy pre-filled or conventional---with anchor bolt shown on left and leveling screw on right. A chock (thick steel washer) is shown between leveling screw and foundation (Ref. 2).

AuthorHeinz P. Bloch, P.E.

Baseplates pre-filled with epoxy and precision-machined in the shop are rightly considered monolithic blocks (Ref. 1). They are much preferred over conventional “hollow” baseplates with mounting pads that will rarely remain flat and coplanar.  Hollow baseplates will likely twist and get out-of-true co-planarity and parallelism if left untouched for years. In contrast, monolithic pre-filled baseplates are ready for installation on a rough-chipped foundation, as previously described in my previous article – “Why pumpsets should not be installed in ‘As-Shipped’ Condition“.

If a specialist firm is not available or if work is done at a field location, ascertain that the baseplate’s underside is sand-blasted and 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. Don’t try to substitute inappropriate materials.

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 pre-grouted (i.e., epoxy-filled) within 8 hours. After that, it has to cure for 24 hours.

Fig. 1: Underside of a base plate 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” base plate being converted to pre-filled style (Source: Todd Monroe, Stay-Tru®, Houston,TX)
Fig. 1: Underside of a base plate 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” base plate being converted to pre-filled style (Source: Todd Monroe, Stay-Tru®, Houston,TX)

 

By its very nature, pre-grouting 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 (Ref. 2).  The baseplate must also be well supported to prevent severe distortion of the mounting surfaces due to the weight of the grout. Use a written procedure and resist doing things from memory or based on anecdotes passed down by others. Be as professional as an airline captain. Even after 5,000 take-offs and landings, he or she still insists on using a procedure. Nobody in his right mind would prefer it if a medical or airline professional did all things from memory.

 Fig. 2: Flatness and level measurements determine if the now machined pre-filled baseplate has been properly machined. It is then ready to be installed on a foundation at site (Source: Todd Monroe, Stay-Tru®, Houston, Texas)
Fig. 2: Flatness and level measurements determine if the now machined pre-filled baseplate has been properly machined. It is then ready to be installed on a foundation at site (Source: Todd Monroe, Stay-Tru®, Houston, Texas)

 

Once the pre-grouted base plate has been fully cured, it is turned right-side-up and a complete inspection of the mounting surfaces is performed (Figure 2).  If surface grinding of the mounting surfaces is necessary, then a post-machining inspection must also be performed.

Now the baseplate is ready for installation on a roughed-up surface (see Figure 3 at the very top of this page). Careful inspection for flatness, co-planarity, and relative levelness (co-linear) 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” to 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.
Co-Planarity. 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”, the mounting pads will be deemed non-coplanar, and the base plate will have to be surface ground.

Relative Level (Co-Linearity). 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.

A good contractor will work with you and agree on the superiority of epoxy-prefilled baseplates. But not all contractors are good contractors, especially if they must survive in a work environment where the owner-operator unduly emphasizes cost and schedule. For reliability and safety, accept nothing today that’s known to deprive an installation of reaching its long-term reliability goals (Ref. 3). How would you feel if a medical professional did stuff that solves an issue for days, but will harm a patient for years to come? Be on a par with other pros. Resolve to become and remain a reliability professional!

Remember that grouting a baseplate (pre-filled or not) to a foundation requires careful attention to many details.  A successful grout job will provide a mounting surface for the equipment that is flat, level, very rigid, and completely bonded to the foundation system.  Many times these attributes are not obtained during the first attempt at conventional grouting, and expensive field correction techniques have to be employed.  Predominant installation problems involve voids and distortion of the mounting surfaces. In fact, the most frequently overlooked foundation and pipe support problems are related to foundation settling.  All of these issues are avoided with pre-filled baseplates. An added bonus can be that the entire installation job using monolithic pre-filled baseplates may actually cost less than doing it the “old way.” Conventional installations all too often allow hollow spots and out-of-true mounting pads. These compromises then reduce the life of pumps and their components for decades to come.

 

References

 

  1. Bloch, Heinz P. and Allan Budris; “Pump User’s Handbook: Life Extension,” 4th Edition, (2014), Fairmont Publishing, Lilburn, GA, ISBN 0-88173-720-8
  2. Bloch, Heinz P.; “Pump Wisdom: Problem Solving for Operators and Specialists”; (2011), Wiley & Sons, Hoboken, NJ; ISBN 9-781118-04123-9
  3. Bloch, Heinz P.; “Petrochemical Machinery Insights,” (2016) Elsevier Publishing, Oxford, UK, and Cambridge, MA, ISBN 978-0-12-809272-9

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