We’ll never know if my guess is right, but the pages that have been written about pumps, laid side-by-side, would probably go to the moon and back. After all, only 2.75 billion 11-inch-tall pages would be needed to go that distance. On the other hand, if we counted the people who know all about pumps, we would see zero instead of any real number.
But instead of pondering useless estimates and statistics, we might simply assess the “state of pump knowledge” by reviewing questions asked and opinions voiced. So, this article deals with interesting pump-related issues that arrived in my e-mail in a single month. I will share my answers and conclusions in this article.
Figure 1. In bearing housing protector seals, avoid dynamic O-rings in proximity of sharp-edged O-ring grooves and rotors attached to shafts with only a single O-ring.
Address More Than Oil Change Frequency
One question came from a plant located in the Middle East. The writers sought advice on the number of oil changes to be planned for centrifugal pumps at their ethylene and polyethylene units. The facility is currently running a time-based preventive maintenance (PM) program – essentially, oil changes every six months, irrespective of whether a pump is operating or perhaps waiting to be used as a spare. The plant intended to reschedule oil changes based on actual operating hours and was wondering if this “new PM plan” should be carried out after 2,000 running hours or 4,000 running hours. A specific request was made for supporting explanations or references.
As is so often the case, an answer must point out best practices. In this instance, I had to assume that there are two pumps for each service at the ethylene and polyethylene units. Moreover, I assumed that these units had not availed themselves of oil mist lubrication/standby bearing protection. Oil mist is customary for true best-of-class plants; it both lubricates the bearings of pumps and drivers and protects running and non-running pumps against atmospheric contamination. The importance of this protection is intuitively evident and becomes even more valuable in harsh climates. But for facilities with the more traditional modes of liquid oil application, best practice would include well-defined action steps and procedures. Among them, I would suggest:
- In each service, run the “A” pump in January, March, May, July, September and November, and run the “B” pump in February, April, June, August, October and December. This would be done in the interest of bearing and seal protection for the non-running machine.
- Once a facility has implemented this best practice, it is clear that each pump will operate slightly more than 4,000 hours per year and would stand still close to 4,500 hours per year.
- After these switch-over practices have been explained and accepted, one would (for about one year) assign part of the machinery maintenance workforce to the monitoring of operating pumps. This once-per-month monitoring is for the purpose of identifying potential bearing distress or other signs of defect development (seals, etc.).
- Pumps suspected of incipient failure would be taken out of service and upgraded for uptime extension. The remaining maintenance workforce would be engaged in this well-defined and substantive upgrading work (Reference 1).
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Upgrading for run length extension means any pump taken to the shop would be subjected to a number of action steps:
• It would be retrofitted with advanced bearing housing protector seals. It should be noted that advanced bearing housing protector seals will not incorporate risk-prone design features (Figure 1). To be suitable for use in a reliability-focused plant, bearing housing protector seals must employ two clamping rings to achieve a good hold on the pump shaft. Please note that I would very much caution against older-style bearing isolator seals. Although still prevalent, there are vulnerabilities in the older-style products that often employ only a single O-ring for clamping the rotor to the shaft and use another “dynamic” O-ring perilously close to a sharp-edged O-ring groove located in the stator (shredded O-rings can contaminate the lubricant).
• It would be retrofitted with pressure-balanced constant-level lubricators (Reference 1). The traditional (and still widely used) pressure-unbalanced lubricators would be phased out.
• Only high-quality synthetic lubricants would be used in the upgraded pump bearing housings. Mineral oils would no longer be used after the upgrade.
• Whenever possible, flinger discs would replace the still rather common abrasion-prone slinger rings (Reference 2). - With pure oil mist, the issue of oil changes would no longer apply. With conventional oil lubrication and after implementing the above upgrade measures, the oil would be changed in the A pumps and in the B pumps on the second anniversary date of their upgrading. At that time, an upgraded pump will have accrued close to 9,000 operating hours and 9,000 stand-still hours.
Knowledge Base Must Be Supported by Facts
A question dealing with pump lubrication was sent from the United Kingdom. Its writer commented on an article that had briefly discussed the advantages of using oil mist and synthetic oil for superior bearing protection of pumps and drivers. The protection of standby equipment through the use of oil mist was given special emphasis in books and many articles (References 2 and 3).
The U.K. writer raised two questions, stating first his point of main concern was about using oil mist lubrication in Zone 1 or Zone 2 environments. Claiming that oil mist is categorized as a flammable medium, he feared using this lubrication method in such environments would increase the potential hazard. He went on to say that any failure in an oil mist piping system will release a flammable mixture. This, he opined, may require additional protection and detection equipment which will increase the material and maintenance cost. So, he asked for advice and practical guidance to reduce these risks.
Well, his fears are certainly unfounded and the statement regarding oil mist being a flammable medium is simply incorrect. There have never been, nor can there ever be, such fires. The reason is that the air/oil mixture is several orders of magnitude too lean to sustain combustion.
My answer also quoted, from Reference 3, “The oil/air mixture is substantially below the sustainable burning point. Experiments had shown the concentration of oil mist in the main manifold ranged from 0.005 to as little as 0.001 of the concentration generally considered as flammable.”
With respect to oil mist heaters, the U.K. engineer had further stated and asked: “As far as I know, most of the oil mist systems need air heaters and sometimes also require an oil reservoir heater to control the temperature. … Please advise how much energy is needed for the oil mist heating system?”
A heater (typically 200 watts) is needed only at the point of mixing air and oil. This heater facilitates maintaining a proper proportion of 200,000 volumes of air per one volume of oil at the point of mixing. The heater is built into the small reservoir of the console (see Figure 2) by the oil mist system manufacturer. Once produced, the oil mist will migrate in unheated, uninsulated header pipes to the point(s) of application. It will do so successfully even where ambient temperatures of minus-40 degrees have been encountered.
Figure 2. A Modern Oil Mist Generator Cabinet (Source: Lubrication Systems Company)
Reading and Math Homework
There are really two points I wanted to make in this article. One is to go beyond maintenance whenever possible and to cost-justify. Upgrading and failure avoidance should be the objectives. The second point is to encourage reading and researching the many excellent books and articles that explain virtually every element of equipment technology. Don’t guess. Add value instead.
Suppose we employed six reliability professionals and taught them to view every maintenance event as an opportunity to upgrade (Reference 3). Suppose each of these pros would read two pages a day and finish a 400-page book in 200 days. And suppose that each of the six pros could take credit for even a single pump failure avoided in a year’s time. You do the math and determine the benefits.
References 1. Bloch, H.P., and Allen Budris; “Pump User’s Handbook,” 2nd Edition, 2006. Fairmont Press, Lilburn, Ga. 2. Bloch, H.P.; “Practical Lubrication for Industrial Facilities”, 2nd Edition, 2009. Fairmont Press, Lilburn, Ga. 3. Bloch, H.P., and Abdus Shamim; “Oil Mist Handbook”, 1998. Fairmont Press, Lilburn, Ga.
About the Author
Heinz Bloch works as a consultant for Process Machinery Consulting. He is the author of more than 400 technical papers and similar publications. He has written 17 books on practical machinery management and oil-mist lubrication published by major engineering publishers. To learn more, e-mail Heinz at hpbloch@mchsi.com or visit www.heinzbloch.com.
