In early 2012, a rotating equipment engineer was involved in a machinery quality assessment (MQA).1 Located halfway around the globe, this engineers new job was to oversee the engineering, procurement and construction (EPC) company and to ensure that the multinational owner-operators long-term reliability interests were understood and carried out.
However, as best-of-class (BOC) owners know, EPC companies are primarily geared to low initial cost and on-schedule plant startups. So, reasonable compromises must be found among the initial cost, safe long-term equipment performance, life-cycle cost (cost of ownership) and project schedules. BOC owner-operators have formalized and institutionalized MQA with the goal of identifying the right compromises.
| Fig. 1. Baseplate flaws, such as out-of-level |
mounting pads, come to light only if the
driver and driven equipment are left off and
leveling procedures can be carried out
with unobstructed access. Note: The fully
embedded hold-down bolts in this
illustration are not acceptable to reliability-
Protecting the clients interest
Representing the owners interest, this engineer was involved in talks with the EPC about acceptable methods of baseplate leveling for centrifugal process pumps. The engineer noted that the pumps at issue did not have adequate access on the mounting pads. Therefore, the machined-mounting surfaces could not be used for leveling without removing the pump. The vendor had suggested using the machined surface of the discharge nozzle instead. However, API RP-686 states that nozzels should never be used for that purpose.
The rotating equipment engineer now consulted a number of relevant booksamong them Pump Users Handbook and Machinery Component Maintenance and Repair, both of which have argued against the vendors and design contractors quick, but risky, approaches. These two books and several other experience-based texts strongly recommend that the pump and driver be removed from the common baseplate. True, the pump and driver had been premounted by the vendor on the baseplate to ascertain bolt locations and fit. Transporting the premounted pump/driver set as a single unit facilitates shipping. However, it should not be considered the best approach to a long-term, reliable field installation.
Full access to machined surfaces will be needed for proper baseplate leveling. This will require removing both the pump and driver until leveling is accomplished.
Does the EPC need technology updates?
From this assignment, the rotating equipment engineer then restated the main points made in those books. These texts always emphasize equipment reliability and caution against making quick installation the primary goal.
In this case, for unexplained reasons, the EPC provider had chosen to specify conventional baseplates for the process pumps on this project. Baseplates prefilled with epoxy would have been viable contenders here.2 Ideally, the owners representative involved in the MQA may have looked into the matter and could have asked to examine cost justification, as well as long-term reliability issues. All parties may have been surprised by the findings.
But even as we sometimes limit ourselves to the more traditional installation methods, let us be sure to keep in mind the linkage between installation details and the ultimate equipment reliability. We must verify that no distortion of baseplate mounting surfaces occurred due to the shipping and delivery processes.
Unless pumps and drivers are removed from their common baseplates, it will not be possible to confirm that all mounting surfaces are coplanar, parallel and colinear. Such confirmations would be needed to make the mounting pad portions of the baseplates qualify as leveling surfaces. Establishing these as reference surfaces would be important to achieve a precise level. Having achieved level allows staff to recheck after completing grouting procedures. At that time, the reliability staff must ascertain that no distortion of the baseplates mounting surfaces has occurred due to grout shrinkage. Allowing grout shrinkage may lead to potential soft-foot alignment issues and, in some instances, resonant vibration.
The reliability engineers understanding of a clause in API RP-686 stating never use nozzles for alignment was correct. Experienced users know that nozzles are not necessarily parallel to fluid machine and driver mounting surfaces. Such out-of-parallelism may make it impossible to achieve precise levels. If there is a lack of parallelism, it prompts installers to use jackscrews and to apply undue force to a baseplate. Result: Another risk will be created. The pump and motor bases may, inadvertently, become distorted, or the pump and motor casings may become slightly twisted. Seals and bearings will no longer run absolutely parallel, and the component life will suffer.
Mechanical seal optimization
Not all design contractors are sufficiently familiar with desirable features found in mechanical seals used in process pumps. Again, the owner-purchaser may have to take the lead in pointing out the desirability of dual seals with superior guide baffle and tapered pumping ring designs as shown in Fig. 2. Some old-style designs are often less efficient and, ultimately, more expensive to maintain.
| Fig. 2. Dual mechanical seal with guide |
baffle and tapered pumping ring for
enhanced movement of buffer fluid. Source:
AESSEAL, Rotherham, UK, and Rockford, Tennessee.
Three lessons are inescapable: 1) Not all EPC companies are knowledgeable about pre-filled baseplates for small- and mid-size process pumps, 2) Reliability focus includes much attention to installation details and 3) Future maintenance cost avoidance requires user/owner input.
Do not let a provider or installers tell you that they have always done it that way. There are instances where the installers have always done it wrong and where the resulting repair frequency has kept an entire plant from ever becoming a BOC performer. HP
1 Bloch, H. P. and F. Geitner, Compressors: How to Achieve High Reliability and Availability, McGraw-Hill, New York, 2012.
2 Bloch, H. P., Pump Wisdom: Problem Solving for Operators and Specialists, John Wiley & Sons, Hoboken, New Jersey, 2011.
Heinz P. Bloch resides in Westminster, Colorado. His professional career began in 1962 and included long-term assignments as Exxon Chemicals regional machinery specialist for the US. He has authored over 520 publications, among them 18 comprehensive books on practical machinery management, failure analysis, failure avoidance, compressors, steam turbines, pumps, oil-mist lubrication and practical lubrication for industry. Mr. Bloch holds BS and MS degrees in mechanical engineering. He is an ASME Life Fellow and maintains registration as a Professional Engineer in New Jersey and Texas.