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Suitable Seals Lower the Total Cost
It is no secret that the cost of fixing pumps and related seal failure are among the highest recurring expenses in a maintenance budget. A recent study showed that one facility had repair costs of $1,600 for an ANSI overhung process pump every three to four months. At a minimum, this equates to $4,800 annually and $96,000 for the projected 20-year life of the pump. Consider the number of pumps in a typical process plant and this number grows exponentially extremely fast. The same study also found that the user of another pump reported a much higher repair bill for a single repair of $4,500; however, this pump needed repairs only every five years. This equates to $22,500 for the 20-year life, a savings of $73,500 as compared to the first pump with frequent, albeit less expensive, repairs.
Obviously, significant savings can be achieved by extending the amount of time between repairs or maintenance, referred to as MTBR or MTBM, and thus lowering the total cost of ownership. However, looking at the total cost of ownership does represent a change in mindset. And, because maintenance and operations are prime targets for cost savings, strategies for extending MTBM are focused primarily on maximizing reliability. Operated within their design limits, seals run for their designed life. However, when seal leakage and failure occur, it is normally a symptom of something else gone wrong.
- Mechanical difficulties – improper installation or other conditions that create irregular motion affecting the seal, or system operating problems that push a pump outside of optimal performance conditions, such as upsets, dry running orpressure/temperature fluctuations.
- Problems with the process itself – when the properties change in the fluid being sealed.
- Poor assembly and installation –are common causes of seal failure, especially with conventional, liquid-lubricated seals. Dirt or grease contamination of the seal faces can also affect performance. The Universal Cartridge seal has proven to alleviate such problems.
Beyond addressing common sources of pump failure, increased MTBM also can be achieved with integration of recent innovations in sealing technology. Mechanical seal manufacturers have increased the reliability of both liquid-lubricated and non-contacting gas-lubricated seals. The latter, inherently reliable because they address some of the common operating and mechanical problems discussed above, eliminate the conditions that negatively affect cooling and lubrication at the seal faces, such as loss of seal flush, dry running, startups without venting, low NPSH and cavitation. Further, since the seal faces do not contact, there is little heat generation or wear.
One new tool that promises to assist the industry in properly estimating the Life Cycle Cost (LCC) of mechanical seals and their associated systems is the LCC Estimator. Offered by the Fluid Sealing Association (FSA) and developed by its member companies, the free tool enables users to identify opportunities to significantly reduce energy, operating and maintenance costs; reduce energy consumption, emissions and waste; gain a greater understanding of the components of sealing system LCC; and increase productivity. It is designed with the intent that the LCC Estimator will help the sealing industry establish a LCC standard. For more information, visit http://65.215.75.3/fsa/seallife.asp
MTBR is defined as the average time between repairs. It’s either based on historical data or estimated based on experience and serves as a point of reference for determining reliability. The equation for computing MTBR is simple and universally accepted: The general idea is to divide the number of machines, N, by the number of repairs, R, in a given period of time. |
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