Sponsored by Alphatec Engineering
Concrete foundations and grouting for rotating machinery
Alphatec engineering – grouting specialists
Getting the most from your machines and foundations
Industry in general uses an enormous variety of rotating machinery (Generators, pumps, compressors, blowers, fans, presses, mills, mixers, and so on through a long list), the greater number of which are mounted on some type of concrete foundation block, or plinth.
Such a foundation block has the role of positioning and supporting the machine, providing a fixed reference upon which to maintain the machine’s alignment, and acting as an extension of the machine’s structure in controlling its motion under dynamic loads.
The second component in this equation is the grout, which is used to completely fill the gap between a non-precise top elevation of a concrete foundation block and the machined bottom of the equipment base.
The third component is the anchoring system, where highly rigidly, long term integrity is achieved. the anchor bolt must apply sufficient downwards force at the mounting interface to resist (through Coulomb friction only) the highest expected horizontal loads. Anchor bolts need sufficient stretch length to be tightened properly, too.
Frequently, the amount of time and effort spent on the design and construction of the foundations, and on the all-important interface area between machine and foundation, does not seem to be commensurate with the value of the installation as a whole.
In order to ensure the best possible connection between machine and foundation, full-contact grouting is always advised. The base of the machine should be encapsulated in the grout, to ensure good contact on the underside, as well as a measure of lateral and longitudinal restraint.
Associations like the American Petroleum Institute (Ref. API RP 686) or the Gas Machinery Research Council (Ref. GMRC Technology Assessment Report TA-93-1) have represented the industry’s collective wisdom, handing over well-known standards and recommended practices which contain valuable information on foundations and mountings of reciprocating and rotating machinery.
How to detect machinery foundation problems?
Noise and vibration indicate issues that can affect a machine's reliability, such as imbalanced parts, and can even cause machines to fail because of their own damaging effects.
When machines start to show these problems, the first logic step that all engineers and plant managers do is focus on the critic components at the rotating machines as bearing system, but when all the Problem Solving Checklist is reviewed and vibration persists, the next step is to start to look into concrete foundation and grout condition. Many problems directly attributable to the foundation size and shape, or to inherent weaknesses in the concrete material, have been noted over the years. Mechanical problems have arisen from the inability of the foundation to operate as a good vibration damper. Problems related to the use of unsuitable grouting materials are also frequently seen.
Concrete can fail for any of several reasons, ranging from exposure conditions, wearing conditions, and misuse of the structure, to poorly selected ingredients, inadequate mix design and improper placement of mixes (Cold Joints, segregation, among others). Lack of attention to procedures, inadequate training of skilled people, limited knowledge of materials, improper selection of the repairing material to be used, and environmental factors like carbonation or degradation from chlorides are other factors that can contribute to concrete failures. An oil-soaked concrete is also an indicator of concrete fail since oil degrade the particles of this.
Grouting materials provides an inert, impervious barrier between machine fluids and concrete block, and here is where epoxy-based grout surpasses, among other advantages, the cement-based grout, since cement-based grout has less or almost no chemical and oil-resistance compared with epoxy grout.
Machine keepers should periodically monitor occurrences of cracks in the concrete foundation as cracks subject to dynamic loads tend to grow.
If you can't measure it, you can't improve it
It has been stated frequently that a large percentage of the installed base of rotating machinery is operating in a less-than-optimal alignment condition. This percentage could be as high as 70% of all operating machinery. Misalignment causes excessive vibration, increased power consumption, reduced output, and wear and tear on components. But the major cause of misalignment – grout failure – is very rarely diagnosed.
The diagnostics of machine problems have been steadily improving since the electronics revolution, and catastrophic failures are getting fewer every year. The Industry 4.0 has brought amazing capacity of data analysis, where continuous vibration measurements are complemented with advanced symptomatic variables.
A relatively new technology known as Motion Amplification has brought about a new understanding of vibration problems and their root cause. This technology is based on a video processing algorithm that detects subtle motion and amplifies it to a level which is visible by the naked eye; this enhances the understanding of the components and interrelationships creating the motion, allowing simultaneously measuring and quantifying of any structural assets (displacement, velocity and acceleration, as needed, at each critical point).
Yet there is still a gap between the sophisticated diagnosis of vibration and alignment issues, and the understanding of how best to solve intractable and recurrent problems.
When facing a machine with problems of vibration, misaligned, imbalance, or severely degraded grout, consult a grouting specialist expert.
With more than 40 years’ experience, Alphatec Engineering has regrouted and repaired the foundations of thousands of rotating machines in all types of industrial plant. Using the techniques developed and refined in various Alphatec operations around the world, we are able to restore a machine to a condition which is close to its original, or even better in cases where “original” was actually sub-standard.