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When would certain flush systems be better than others? It is necessary that one has to pre-select mechanical seal and flush system design during the pre-FEED project phase, based on plant, company and/or industry experience, to optimize mechanical seal MTBF. Use plant, company and industry lessons learned to properly select a flush system that will result in optimum seal life – in your plant!
Frequently, the flush system is selected by the process licensor or the EP&C (contractor) and does not reflect actual plant conditions. Be proactive early in the project design (pre-FEED phase) to convince project management of the proper flush systems to apply for all pump services.
The use of the following flush system components where they are not warranted has resulted in low mechanical seal MTBFs and has exposed plants to safety issues:
There are a few parameters required for a reliable flush source. Mechanical seal flush must possess the following qualities for optimal seal life – it must be cool, clean and approximately 345 kPa (50psi) above vapor pressure (psia), and most importantly it must be cost effective. Therefore, if you can say that the flush system for an application can provide all the qualities (most important is cost effectiveness), then you have selected the optimal flush system.
Different seal flushing scenarios have considerations that are specific to each. In general, the points that can aid flush plan selection are:
Flush line strainers can expose plants to seal failure and safety issues, since they are not monitored in the control room and can result in flush line blockage, which will fail the mechanical seal and can expose the plant to significant safety issues in hydrocarbon applications.
This best practice has been used since the mid-1970s, from the time that prohibiting the use of flush line strainers and cyclone separators has resulted in optimum mechanical seal safety and reliability during field mechanical seal reliability optimization audits for all projects.