Seal replacement scenarios
Seal replacement is a reality. Whether needed once, twice or repeatedly due to failure or a fixed schedule of planned system checks for safety, service, quality or economy such replacements involve unit and downtime costs. We have identified four seal-replacement scenarios to gauge the impact that the choice of sealing solution can have on total system cost:
- Seals that last for the life of process equipment;
- Replacement once or twice due to failure;
- Repeated replacement; and
- Maintenance by replacement on schedule.
In the first scenario the seals dont have to be replaced as they last for the life of the pump or other process equipment (Figure 3). Strictly on a cost basis, the use of perfluoroelastomer parts isnt justified. Seal selection is driven by cost alone.
Figure 3. An expensive material offers no advantage if a seal lasts for the life of the equipment.
Price isnt the controlling factor for the second scenario (Figure 5). Seals are replaced due to failure or for maintenance reasons once or twice during the life of the equipment. Failure incurs the expense of unplanned downtime. Using perfluoroelastomer seals could be the most-cost-efficient solution.
Figure 4. Using a more expensive perfluoroelastomer material pays off if it avoids unscheduled downtime.
In the third scenario, the seals need to be replaced several times. Perfluoroelastomers should offer substantial savings because in process environments involving elevated temperatures and aggressive chemicals they should last longer than conventional sealing materials.
When seal replacement is regularly scheduled for reasons of safety, service, quality or economy, the downtime cost incurred in replacing existing seals is usually constant (Figure 5). The added expense of switching to perfluoroelastomer seals should be offset by doubling, tripling or even quadrupling the periods between overhauls.
Figure 5. Longer time between overhauls should offset the added cost of a perfluoroelastomer seal.
Take the long view
Each plant has a unique seal replacement rate and downtime cost. In addition, a site must consider its chemical environment and risks when evaluating the potential savings of integrating perfluoroelastomer seals in assembly. However, concentrating mainly on purchase prices can do your plant a costly disservice. Consider the total system cost, and factor in the price of unproductive time and problems such as leakages. This may well show that a premium sealing solution can lead to significant savings. At the very least, devoting time and thought to longer-term factors will be invaluable from a strategic standpoint.
Additional information is available at http://www.dupontelastomers.com/Products/Kalrez/optimize.asp.
Russell Schnell is an applications engineer for DuPont Performance Elastomers, Wilmington, Del. E-mail him at email@example.com.