According to statistical reliability data, as much as 65% of the life cycle costs are determined during the design, procurement and installation phases of new machinery applications [Ref. 1]. While design and procurement are important aspects for any application, the installation of the equipment plays a very signifi cant role. A superb design, poorly installed, will give poor results. But, a moderate design, properly installed, will give good results.
Baseplate designs have become less rigid over time. Attention has been focused on the pump end of the baseplate to provide enough structural support to contend with nozzle load requirements. The motor end of the baseplate is generally not as rigid as the pump end. Consequently, the process of shipping, lifting, storing and setting the baseplate can have a negative impact on the motor mounting surfaces. While these surfaces may have initially been fl at, experience shows that there is work to be done by the time the baseplate reaches the field.
The other issue of mounting surface distortion comes from the grout itself. All epoxy grout systems have a slight shrinkage factor. While this shrinkage is very small, typically 0.0002″/in (0.2 mm/m), the tolerances for fl atness and level of the mounting surfaces are also very small. A chemical reaction occurs when the epoxy resin is fi rst mixed with hardener (to which the aggregate is added a little later, so as to form what is commonly termed the epoxy grout). This reaction results in a volume change that is referred to as shrinkage. Chemical cross-linking and volume change occur as the material cools after the exothermic reaction. Epoxy grout systems cure from the inside out, as shown in Fig. 1. The areas closest to the baseplate-to-grout interface experience the highest volume change.
To achieve a proper installation, the reliability team will have paid attention to many requirements: good foundation design, no pipe strain and proper alignment are important, just to name a few. All of these issues revolve around the need to reduce dynamic vibration and prevent component deflection in the machinery system.
Great design effort and cost is expended in the construction of a machinery foundation. Reduced vibration severity and the long-term success of a proper installation are determined by how well the machinery system is joined to the foundation system. The baseplate, or skid, that supports the machine must become a monolithic, virtually integral, member of the foundation system. Twisting of a machine frame or casing must be prevented and machinery vibration should ideally be transmitted through the baseplate to the foundation and down through the subsoil. Failure to achieve such transmission will result in the machinery resonating on the baseplate, as shown in Fig. 2, very often causing consequential damage. Proper machinery installation will give long-lasting benefi ts by signifi cantly increasing mean time between failures (MTBF), extending the life of mechanical seals and bearings and reducing overall life-cycle costs.
Field installation problems of conventional units…
Grouting a baseplate or skid to a foundation requires careful attention to many details. A successful grout job will provide a mounting surface for the equipment that is fl at, level, very rigid and completely bonded to the foundation system. Many times, these attributes are not obtained during the fi rst attempt at grouting, and expensive fi eld correction techniques have to be employed. The most prominent installation problems involve voids and distortion of the mounting surfaces.
Void and bonding issues of conventional units…
The presence of voids at the interface between the grout material and the bottom of the baseplate negates the very purpose of grouting. Whether the void is one inch or onethousandth of an inch in depth, the desired monolithic support system has not been achieved. Voids prevent the foundation system from suppressing resonant and shaftgenerated vibration (see Fig. 2).
Mounting surface distortion of traditional units…
Another field installation problem with costly implications is distortion of the baseplate’s machined surfaces. Distortion can be induced prior to grouting as a result of poor field leveling techniques, or it can be generated by the grout itself.
Hidden budget impact of conventional units…
Correcting the problems of voids and mounting-surface distortion in the field is a very costly venture. Repairing voids takes a lot of time, patience and skill to avoid further damage to the baseplate system. Field-machining the mounting surfaces also involves two resources that are in short supply: time and money.
The real concern with correcting baseplate installation problems on site is that repair-related issues are not refl ected in the construction budget. Every field correction is a step backwards, both in time and money. On fixed-cost projects, the contractor must absorb the cost, whereas on costplus projects, the user/client must pay the bill. Either way, there will be extra cost, accompanied, all too often, by controversy and blame-placing.
Pre-grouted baseplates: a better method.
A pre-grouted (or pre-fi lled) baseplate is shown in Fig. 3. In the late 1990s, a Houston, TX-based service company developed a highly effective method that assists in minimizing fi eld installation costs and improving the reliability of pump baseplates [Ref. 2]. Using a pre-grouted baseplate in conjunction with the service provider’s proprietary pre-grouted baseplate procedure accomplishes these worthwhile goals and is able to provide a superior fi nished product. When OEM pump sets are delivered to plant site on pre-grouted baseplates, the pump train arrives 60% mechanically complete.
The procedure referred to includes a comprehensive pre-grout plan that calls for a detailed inspection of the primer system used on the underside of the baseplate, proper preparation of this primer for grouting, inverting and then fi lling the baseplate with a suitable epoxy grout, post-curing of the grout material and a detailed post-grout inspection of the baseplate mounting surfaces. If the mounting surface tolerances fall outside of the API 686 specifi cations for fl atness, co-planar and co-linear dimensions, precision grinding or machining is performed to restore or achieve the necessary tolerances. The use of shims is thus avoided and much future grief thereby eliminated. The service provider mounts and aligns pump and driver.
Calculating the value of pre-grouted baseplates…
It has been demonstrated that utilizing the combined hardware and procedural approach spearheaded by a leading provider of pre-grouted baseplate technology will save 30% of the cost associated with traditional machinery grouting methods, and provide a superior fi nished product. It can be inferred that superimposing the somewhat more elusive value of the resulting reliability improvement will substantially lower the life-cycle cost of pump installations that make use of this methodology. (For more details, see Table I that follows this case history.)
New fi eld-grouting method for pre-grouted baseplates…
Conventional grouting methods for non-fi lled baseplates are, by their very nature, labor- and time-intensive. Utilizing a pre-grouted baseplate in conjunction with conventional grouting methods (Fig. 4) 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 pre-grouted baseplate. This new method 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.
New grout-forming technique for pre-grouted baseplates…
With the smooth concrete shoulder of the foundation still intact, a very simple “2 x 4″ grout form can be used, (See Fig. 4). One side of the simple grout form is waxed, and the entire grout form is sealed and held in place with caulk. While the caulk is setting up, a simple head box can be constructed out of dux seal. Because of the flow characteristics of the low-viscosity epoxy grout, this head box does not need to be very large or very tall. The low-viscosity epoxy grout is mixed with a hand drill, and all the grout is poured through the head box to prevent trapping air under the baseplate.
This new installation method has been used for both ANSI and API-style baseplates with excellent results. With this technique, fi eld experience has shown that a pre-grouted baseplate can be routinely leveled, formed, and poured with a two-man crew in three to four hours. The proof of benefi ts can be readily seen in rigorous fi eld installation cost comparisons. This comparison applies realistic labor costs; it does not take credit for the elimination of repair costs associated with fi eld installation problems, such as void repair and field machining. It is shown on page 19.
It should be noted that industry experience shows eight men typically involved
in the average size conventional grouting job. Using 2003 data, an actual labor cost of $45 per man-hour was assumed in U.S. installations. Here, employee benefits and overhead charges were included.
Using this information, a cost comparison can then be developed, based on the installation of a typical API baseplate, using epoxy grout, for the conventional two-pour procedure, and a pre-grouted baseplate, using the new installation method. The following conditions apply:
In 2003, a baseplate with the listed dimensions could be pre-grouted for $2,969. This expenditure included surface preparation, epoxy grout, surface grinding and a guaranteed inspection. The essential results of following this experienced service provider’s well-defi ned baseplate installation procedure were found to include:
- Void-free grout installation
- Proper surface preparation of baseplate underside
- All machine surfaces fl at, co-planar and co-linear, in accordance with API-686
- Elimination of the need for costly and less effective field machining
- 30% cost-savings over the traditional field installation procedure
In conclusion, then, Table I shows a realistic accounting of time and labor for the installation of a typical API baseplate. The total installed cost for a conventional two-pour installation is $6,259. The total installed cost for a pre-grouted baseplate, installed with the new installation method, is $4,194. Aside from the obvious cost-savings, the long-term reliability impact of this void-free and fully co-planar installation is of great importance to reliability-focused pump users.
This is one of the rare occasions where a longer-life, less-failure-risk-inducing product actually costs less than its more maintenance-intensive predecessor alternative. The payback is, thus, instantaneous and the benefi t-to-cost ratio could be called “infinite.” What more could we ask?
- Stay-Tru® Corporation, Houston, TX
- arringer, Paul, and Todd Monroe, 1999, “How to Justify Machinery Improvements Using Reliability Engineering Principles,” Proceedings of the 16th International Pump Users Symposium, Turbomachinery Laboratory, Texas A&M University, College Station, TX.
Contributing editor Heinz Bloch is the author of 17 comprehensive textbooks and over 340 other publications on machinery reliability and lubrication. He can be contacted directly at: email@example.com