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RE: Magnetic Drive Pump Leak at Containment Shell

RE: Magnetic Drive Pump Leak at Containment Shell

RE: Magnetic Drive Pump Leak at Containment Shell

(OP)
thread407-490736: Magnetic Drive Pump Leak at Containment Shell

@jsasada : Did you ever finally figure out the issue with this. I didn't see anyone else comment but something does not look quite right with the picture of the front rotating wear ring. I know that the SiC finish can vary but that axial face looks like it was lapped to a mirror finish and appears significantly more polished than the axial face of the other wear ring or the bushing. The shaft also appears to have some amount of polishing but very difficult to tell from the angle and carbon fiber's naturally ability to look over exposed anytime you use a flash. The bushing appears okay at first glance(I've seen many dry run mag-drivse with a mess of plastic in that annular region). Also I can't tell if ID of bushings is polished or just wet. A polished wet look for SiC generally would indicate limited lubrication.

external damage to containment shell and outer magnet look like collateral damage. I don't think the cause is related to magnetic particles sbased on the little to no abrasion damage on the OD of the impeller magnet. Also given that there is some chipped SiC on shaft and casing ring, that could cause some damage as well as it recirculates inside the pump. If there was a chemical compatibility issue I think there would be blistering or some other symptom with the same material all over unless the metal insert somehow got caught up in the magnetic field and was a localized hot spot.

Is there any entrained gasses in the nitric or a source of turbulence going into the pump? It's below fuming so it shouldn't be NO2 but my experience with thrust balancing from canned motor pumps was that those systems do not function well with dissolved gasses/mixed phase flow.


@BlaineMS : Did you ever figure out the source of your issue? From the cutaway picture in your link(https://files.engineering.com/download.aspx?folder...) I would assume the metal insert is shown in red. It could just be the camera angle but ss there sufficient material encapsulating that metal piece? If there was any material shearing/loss when inserting that shaft that exposed the metal that might explain the issue. Has any extended hydrostatic pressure test been conducted with water prior to going into service(either at factory or in your maintenance shop)? If there is a leakpath through the plastic, water might be able to pass through. If the leakpath is to bare metal, it would probably test fine at the factory but the acid could rapidly dissolve the metal. Do the wear rings normally contact? If there is polishing on SiC then it was likely contacting something and if the containment shell got destroyed/dissolved, that likely would impact the alignment.

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