Updating Your Sealing Technology

Last year, I traveled with my wife to Disneyworld in Florida. We spent a week avoiding winter weather in Iowa - a vacation for ourselves this time, not tied to the grandkids. Of course we love our grandchildren, but they wouldn't have been excited to see some of the high-tech attractions three times in a row while skipping Cinderella's Castle altogether. Disney impressed us for reasons based on organization, service and engineering.

We suffered through the minor annoyance of security lines and having to remove our shoes at the Des Moines airport. Although we passed the metal detector, we were reprimanded because our maximum 3.5 ounce (100 gram) liquids were in a one-gallon plastic bag, whereas "the regulations clearly state that they must be in a one-quart plastic bag." Flying to Orlando via Atlanta, our luggage arrived in Florida on a later flight. That, however, was not a problem for Disney's highly efficient in-airport service counter. They scanned the bar code on our itinerary and we boarded an impeccably clean bus waiting to take us to the Disney properties.

As promised, our luggage was later delivered to our room without us having to make any further inquiries. The card key to the hotel room was the same that admits guests and visitors through the turnstiles into the various Disney locations. When using the card key for the first time, guests insert their index finger into a small electronic fixture which, thereafter, links the card key to just that one particular guest. The same card key tracks food and other purchases. Staff at any of the hundreds of the clean and well-run establishments and checkout counters can tell guests what portion of their pre-payment is left, or the total tab accumulated since their arrival.

Cartridge Bearing Seals Photo Courtesy of Isomag

At one of the Disney eateries, we overheard a conversation between two of Disney's multitasking project-maintenance engineers. The two gentlemen seemed knowledgeable and informed in advanced electronics, hydraulics, mechanisms and critically important human interface relationships with others. It was evident that they had adapted new technologies long before their more conservative peers would reach out for the opportunity. Which gets us to the point: Don't knock Mickey Mouse. Learn from the successes of others. As an example, in industries that move fluids, look for advancements in mechanical sealing technology.

Mechanical Seals: Still an Opportunity
Competent manufacturers of mechanical seals have contributed to the uptime extension and component life upgrades realized by acknowledged best-of-class users. In the field of process pumps, canned-motor configurations and magnetic-drive models have occasionally replaced sealed, conventional pumps. Also, seal life has improved and it is thus doubtful whether the total yearly consumption of engineered seals has seen a significant increase. Nevertheless, the future is bright both for innovative seal manufacturers and the knowledgeable, forward-looking seal users (KFSU). Let's examine what should be the business approach for those whom we would anticipate a bright future.

Failure Statistics Prove Revealing
In the late 1990s, the published mean-time-between-failure (MTBF) rates for centrifugal pumps included 13 months at a U.S. pulp and paper plant, 17 months at an oil refinery in Brazil, and 68 months at a U.S. oil refinery in California. In the early 2000s, MTBF numbers in excess of 100 months were occasionally reported.¹ This proves that there is a wide range of MTBFs in industry. It also supports the view that the selection strategies, installation practices and troubleshooting methods of companies who always operate in a business-as-usual approach vary greatly from more progressive types.

At some of the less effective facilities, piping connected to equipment nozzles is pulled into place with chain-falls and other mechanical assistance devices. If a seal now fails as a direct result of this unacceptable installation practice, it is nevertheless assumed to be the fault of the seal. A replacement seal is hastily installed, or an altogether different seal type is tried. But even an advanced technology seal will not survive bad installation practices.

That said, true KFSU companies will position themselves to utilize advanced technology products while paying considerable attention to risky work processes and bad practices. Factors contributing to the unreliability of seals and sealing systems will be emphasized by best-of-class suppliers. The truly best suppliers will assist users with the development of analytical and experience-based data showing the negative impact of bad practices on bottom-line financial performance.

Among the bad practices and unacceptable procedures are ones that disregard judicious installation of piping, baseplates, grout systems and the like. For its part, the user community should view best-practices suppliers as their consulting arm, and partnerships or alliances founded on low-cost supplies alone should become a thing of the past.

Life-cycle Cost Studies
The lack of life-cycle cost data is often responsible for the users' reluctance to upgrade to better seals or superior sealing systems. A business-as-usual attitude prevails in spite of protests to the contrary, and lack of data is typically cited in defense of this attitude.

But, just as a motivated user finds ways to come up with reasonably accurate life-cycle statistics, a good KFSU provides available data and offers requisite calculations to his or her seal supplier(s). Life-cycle comparisons among seemingly identical seals and pumping services will bring installation and operation-related failures cost into proper focus. Life-cycle cost studies will also show if and when conventional centrifugal pumps equipped with properly selected and meticulously installed state-of-the-art mechanical and bearing protector seals exhibit bottom-line cost advantages over many canned-motor and magnetic-drive pumps.

The conscientious pursuit of life-cycle approaches allows KFSUs to counter the greater run-length claims of some manufacturers of seal-less pumps. The initial purchase price and energy efficiency-related operating cost advantage of certain conventional pumps will lead to new opportunities for the traditional product.

Gas-lubricated Seals
The viability of gas-lubricated (dry) seals for certain centrifugal compressor services has been established beyond doubt. For pumps, best-of-class users are taking steps to expand the application of gas seals into some services where conventionally lubricated mechanical face seals have been used previously. The trend toward gas seals in steam turbines, which was started and cost-justified by Exxon Chemicals in the late 1970s is almost certain to accelerate, as is the trend toward using gas seals in some mixer services.²

Again, the function of a competent reliability professional is to acquire an understanding of fluid processes and to delineate and explain the bottom-line merits of available advanced sealing technology. As mentioned earlier, both the user and seal manufacturer will benefit from the consulting relationship that develops along these lines.

Bearing Housing Seals
There is consensus among all reputable manufacturers of rolling element bearings: Lubricant contamination is the most frequent cause of bearing failures in the process industries. Every year, millions of these bearings reach only 10 percent of the calculated life anticipated for the loads and speeds at which they operate. Fully sealed (clean) bearing environments have allowed automotive and home refrigeration systems to perform with high degrees of reliability. In contrast, unreliability is often noted in process pump bearings exposed to dust and water vapor. Avoidable failures thus still abound in many process pumps and their limited uptime has proven expensive to the process industry.

Most centrifugal pumps are considered as simple fluid machines when compared to the complex and highly reliable aircraft jet engine. This fact highlights marvelous opportunities for the KFSU. The use of advanced bearing housing seals for the millions of pump bearing housings alone can create value for both users and manufacturers. Long-term testing by a major manufacturer of centrifugal pumps has confirmed the feasibility and cost-effectiveness of utilizing face-type, narrow-width mechanical seals in lieu of lip seals, stationary labyrinth seals and old-style rotor-stator labyrinth seals.

Consider that if axial movement or operation at speeds below lift-off were to occur in modern, advanced rotating labyrinth seals, the dynamic O-ring would contact a generously dimensioned contoured surface. Tests show that O-rings in these modern bearing protector seals will degrade much slower than the design in which the O-ring contacts the groove. The moral of the story: Envision how parts operate, then buy wisely.

It is also worthy to note that, when used in conjunction with simple sight glasses, best-available-technology bearing housing seals eliminate the need for constant-level lubricators and breather vents. The exclusion of atmospheric contaminants greatly extends lubricant life and makes it economical to use the more expensive, elevated-temperature tolerant polyalphaolefin and diester synthetic hydrocarbon lubricants. ^{1, 3}

Where Seal Users and Manufacturers are Headed
Progressively, more of the leading users of fluid machinery will use life-cycle costing and related analytical methods to determine and establish the relative merits of competing sealing options. Competent seal manufacturers accelerate these moves and assist the smaller, less sophisticated users in performing these evaluations. These seal manufacturers support their efforts with statistics, checklists, installation procedures, operating guidelines, troubleshooting know-how and consulting services.

It has been theorized that the application of state-of-the-art seals and seal flush plans to conventional centrifugal pumps will slow down the rate of growth of seal-less pumps. In any event, the choice between canned-motor and magnetic-drive pumps on the one hand and conventional centrifugal pumps on the other hand must be governed by economics. However, to be valid, these comparisons must be made for conventional pumps with the best sealing technology, not the cheapest seals. Using this approach, conventional pumps with superior seals will often win out against all competition. Think about it, then buy wisely.

Using this logical premise, gas seals and advanced bearing protector seals will undoubtedly take the place of conventional or "just cheap" fluid seals, and the many inadequate attempts at bearing protection will be sorted out.4 Users will seek out the consulting input of competent seal manufacturers and show no reluctance in paying the price justly commanded by high performance. A few high-class manufacturers will understand the shift in thinking and establish themselves as the providers of high value. If progressive companies such as Walt Disney can use these smart-thinking processes, so can the process industries.

About the Author
Heinz Bloch currently works as a consultant for Process Machinery Consulting. He has extensive experience in machine reliability and is widely regarded as an authority on the subject. Heinz 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 which have been used for lectures and consulting assignments internationally. To learn more, visit www.heinzbloch.com.

References

1. Heinz P. Bloch and Alan Budris. "Pump User's Handbook: Life Extension," 2nd Edition Fairmont Press, Lilburn, Georgia, 2006.
2. Heinz P. Bloch and H.G. Elliott. "Mechanical Seals In Medium-Pressure Steam Turbines." Lubrication Engineering, November 1985.
3. Heinz P. Bloch. "Better Bearing Housing Seals Prevent Costly Machinery Failures." World Pumps, December 1993.
4. Heinz P. Bloch. "Counting Interventions Instead of MTBF." Hydrocarbon Processing, October 2007.