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Why users must update design contractors’ understanding

10.01.2013  |  Bloch, H. P.,  Hydrocarbon Processing Staff, 

Keywords: [EPC] [pumps] [standards] [start up] [pumps] [base plates]

In early 2012, a rotating equipment engineer was involved in a machinery quality assessment (MQA).1 Located halfway around the globe, this engineer’s new job was to oversee the engineering, procurement and construction (EPC) company and to ensure that the multinational owner-operator’s 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-
  focused users.


Protecting the client’s interest

Representing the owner’s 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 books—among them Pump User’s Handbook and Machinery Component Maintenance and Repair, both of which have argued against the vendor’s and design contractor’s 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 owner’s 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 baseplate’s 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 engineer’s 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.  


Lessons learned

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

LITERATURE CITED

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.

The author

Heinz P. Bloch resides in Westminster, Colorado. His professional career began in 1962 and included long-term assignments as Exxon Chemical’s 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. 




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Ed K
10.18.2013

I usually appreciate the insight of your articles. However, I don't appreciate your smear of those of us on the EPC side of the relationship. We don't show up for work every day trying to figure out how to best screw over our customers. We are professionals looking to provide the best designs that we can.
The initial quality that leads to long term operational savings isn't free and unless the owner operator who puts a project out for bid considers the savings of long term reliability as a factor in the total cost of a project, then they are going to get what their EPC can afford to produce and still survive.
Further, the example you give is way too late to achieve the desired objective. Reliability folks need to be in the loop at the beginning of the design effort when the EPC's proposed details for the project are offered to the client for comment and approval.
I do agree that this is going to have to be driven by the owner's side as they are the ones best positioned to gather the intelligence on long term reliability and to disseminate it to the community. Those of us on the EPC side just don't get the opportunity to see what happens to a unit after we turn it over - the client is kicking us out the gate and closing the checkbook, and we're scrambling to move on to the next project and keep the lights on.

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