You might ask yourself, “Why are these sealing strips so important?” The best way to answer that is by explaining what missing or damaged sealing strips do to the overall performance of a system. If sealing strips become damaged or if they are not replaced when the bundles are pulled, it will allow process load to bypass the condenser bundle. When this happens, some portion of the condensable load entering the top of the condenser will be pulled directly into the downstream equipment. This load would otherwise condense out if it were directed into the tube bundle where it would make contact with the cold tubes. This bypassing acts as an additional load to the downstream ejectors, which causes them to operate at a poorer pressure than they would otherwise. This will generate a higher back pressure at the discharge of the upstream ejector, which can cause them to break performance. In a vacuum distillation system, for example, this could cause the tower top pressure to degrade by as much as 50-75 mmHg. This would be devastating to the process and further emphasizes why it is important to inspect and replace sealing strips.

The best time to confirm good sealing strip installation and condition is when the bundles are pulled and the sealing strips are replaced, although some of you might be thinking, “How can I tell if my sealing strips are in good shape while the equipment is in operation?” When you have sealing strip damage or missing sealing strips, it will result in an elevated outlet temperature from that condenser. In a condenser that is working well, the outlet temperature from the condenser will generally be similar to the saturation temperature at that operating pressure. When load is bypassing the bundle through the sealing strips that load will be hotter than the condenser’s saturation temperature, which elevates that discharge temperature from the condenser. How far elevated that temperature is going to depend on how bad the leaks are and how much load is leaking through the sealing strips. Thermal imaging of the sealing strip area of the condenser can be helpful in identifying a sealing strip failure.

The sealing strip material is normally similar in composition to the condenser tube material, with specific properties to provide better performance for this application. When the condenser tubes are stainless the sealing strips are normally supplied in a 300 grade stainless steel or a 2205 duplex stainless, with the corresponding bolting in a similar material or Monel. In units with copper alloy tubes, it’s not uncommon to see units in the field with brass sealing strips and accompanying brass hardware.

This concludes our discussion on sealing strips. If you are entering an outage, please make sure to pay attention to your condenser sealing strips if your installation includes them. If you have any questions about sealing strips or you suspect a sealing strip issue, please feel free to contact Graham with any questions or concerns.