Inspecting an ejector is something that should be done annually, although it’s understood that this might not be possible if the unit has infrequent shutdowns. An ejector’s internals can be inspected by removing the steam chest, shown as (3) in the above figure. Removing the steam chest provides access to the motive nozzle and diffuser. Remember, always isolate and lock out an ejector before opening it.
Once the ejector is open and accessible the following are issues you might encounter:
- Motive Nozzle Blockages – Debris, like piping scale, can lodge in the ejector’s motive nozzle, item (1) shown in the ejector diagram above. If this happens it will restrict the motive flow. Visually checking for debris in the nozzle can be easily done during an inspection. Some ejectors are set up with an inspection/clean out plug on the motive inlet allowing this check to be performed without opening the ejector. Installing a Y-type strainer close to the motive inlet of each ejector can help prevent debris from entering a nozzle.
- Motive Leaks – Ejectors are often supplied with a threaded motive nozzle and those threaded connections, identified as being between parts (1) and (3) above, can develop motive leaks. A leak would add an artificial load to the ejector hurting performance. Visually checking these connections for signs of bypass should be done during the inspection. If found, these joints can be seal welded shut or the parts replaced. Note that nozzles can be supplied in a welded design which reduces this issue but doing so makes replacing the motive nozzle more difficult.
- Inspection of Motive Nozzle and Diffuser Throats – The motive nozzle throat, part (1), and diffuser throat, Part (7), are the most prone to wear. It is recommended that these throat measurements are taken and compared to design. Graham suggests that they are replaced if the cross sectional area is worn by more than 7% or 3.5% by diameter. Note that the diffuser throat diameter does not need to be taken on ejectors that are longer than about 12 feet in length.
- Wet Steam Impingement – If an ejector is being operated with wet motive, that steam will be accelerated through the motive nozzle and exit at very high speeds. This will cause damage in the inlet diffuser of the ejector in the form of pitting / gouging. This changes the geometry of the diffuser and hurts the ejector’s performance. With time the wet steam will eat a hole through the side of the diffuser causing an air leak. One should verify that the motive piping is well insulated and the steam piping is installed with a cyclonic steam separator.
- Process Build Up – At times process can build inside of the ejector, especially if the ejector was not operated consistently. During an ejector inspection the air chamber and diffuser should be checked for any process build up that could hinder flow. Any build up should be removed prior to putting the ejector back in service. If the ejector is found to have process build up, the upstream and downstream piping should also be checked.
- Corrosion & Erosion – The ejector internals should also be visually inspected for signs of corrosion or erosion. Specific attention should be given to the ejector diffuser and the nozzle and extension. Parts should be replaced as needed.