We have had three failures of a Sundyne pump model LMV-341 running in stripped sour water service. These three failure had a common pattern that we have never seen before. First, a little background may help. We have about 175 Sundyne pumps in our refinery. About 75 of those are gearbox driven pumps running in all sort of services. The particular pump that is giving us trouble has only been in service since September. It has had three complete wrecks during that time. All three failures involved the seal sleeve spinning on the high speed shaft, allowing water to flow under the sleeve and directly into the gearbox. Each time, we thought we found and corrected the problem, but obviously we were wrong.
Failure 1 – The pump had been running for about 3 months since the start-up of the unit. The pump tripped off on low oil pressure. When the operators got out to the pump, they found water shooting out of the gearbox vent. When we opened it up, we found that the inducer had unscrewed, the impeller had dropped and rubbed in the case. We checked all of the likely causes and ruled them out. The motor rotation was correct. The pump was running at the time of the failure. All of the parts were the correct parts. The flow rate from the pump had been stable and just slightly above the BEP flow for the pump. There was no indication of any problem with the source of water they use. We basically felt we eliminated all possible causes except for manufacturing or assembly errors. We filed a warranty claim against the manufacturer. They accepted the claim and paid for all of the repairs.
Failure 2 – The pump had been running for about 3 months again when the operators noted that water was shooting out of the gearbox vent. They shut the pump down. When we opened it up we found that the seal sleeve had spun on the shaft, burning up the o-rings on both ends and allowing water to pass under the sleeve and directly into the gearbox. This time we found a definite machining error. The threaded hole in the inducer was not threaded all the way to the bottom. The manufacturer’s specification states that the hole should be threaded at least 0.800” deep in a 1.0” deep hole. We found approximately ½” of thread. We screwed the parts back together. We found that the inducer stud was reaching the end of the threads at about the point where the face of the inducer contacted the impeller. In other words, it felt like we were tightening it up, but instead we were just bottoming out the stud in the incorrectly threaded hole. It made perfect sense. Even though we had torqued the inducer as per procedure, it was not providing the full clamping force against the impeller, seal face, sleeve, seal face, shaft step stack up. We filed another warranty claim against the manufacturer and they are still evaluating that one.
Failure 3 – The pump shut down on low oil pressure. When they drained the oil out of the gearbox, they found large quantities of water in the bottom. Once again, the sleeve had spun on the shaft allowing water to enter directly into the gearbox. Everything was assembled correctly. The threaded holes in the output shaft and the inducer were the correct depth. The inducer stud had at least 1/4” of extra threads before it would bottom out in the holes. We know from the previous repair that we had torqued the inducer to the correct value and all parts in this high speed shaft assembly were new.
There are two identical pumps in this service. The other pump has run when ever this pump has been out for repair. It has had no problems and has never failed. We obviously have some other problem that is causing these high speed assemblies to loosen up. In all of our other 175 Sundynes, running for the past 20 years, we have never seen an inducer come unscrewed or loosen up before. Does anyone have experience with this type of failure or have any theories that might explain whey this is happening. Thank you in advance for any information you may have to offer.
Johnny Pellin
Failure 1 – The pump had been running for about 3 months since the start-up of the unit. The pump tripped off on low oil pressure. When the operators got out to the pump, they found water shooting out of the gearbox vent. When we opened it up, we found that the inducer had unscrewed, the impeller had dropped and rubbed in the case. We checked all of the likely causes and ruled them out. The motor rotation was correct. The pump was running at the time of the failure. All of the parts were the correct parts. The flow rate from the pump had been stable and just slightly above the BEP flow for the pump. There was no indication of any problem with the source of water they use. We basically felt we eliminated all possible causes except for manufacturing or assembly errors. We filed a warranty claim against the manufacturer. They accepted the claim and paid for all of the repairs.
Failure 2 – The pump had been running for about 3 months again when the operators noted that water was shooting out of the gearbox vent. They shut the pump down. When we opened it up we found that the seal sleeve had spun on the shaft, burning up the o-rings on both ends and allowing water to pass under the sleeve and directly into the gearbox. This time we found a definite machining error. The threaded hole in the inducer was not threaded all the way to the bottom. The manufacturer’s specification states that the hole should be threaded at least 0.800” deep in a 1.0” deep hole. We found approximately ½” of thread. We screwed the parts back together. We found that the inducer stud was reaching the end of the threads at about the point where the face of the inducer contacted the impeller. In other words, it felt like we were tightening it up, but instead we were just bottoming out the stud in the incorrectly threaded hole. It made perfect sense. Even though we had torqued the inducer as per procedure, it was not providing the full clamping force against the impeller, seal face, sleeve, seal face, shaft step stack up. We filed another warranty claim against the manufacturer and they are still evaluating that one.
Failure 3 – The pump shut down on low oil pressure. When they drained the oil out of the gearbox, they found large quantities of water in the bottom. Once again, the sleeve had spun on the shaft allowing water to enter directly into the gearbox. Everything was assembled correctly. The threaded holes in the output shaft and the inducer were the correct depth. The inducer stud had at least 1/4” of extra threads before it would bottom out in the holes. We know from the previous repair that we had torqued the inducer to the correct value and all parts in this high speed shaft assembly were new.
There are two identical pumps in this service. The other pump has run when ever this pump has been out for repair. It has had no problems and has never failed. We obviously have some other problem that is causing these high speed assemblies to loosen up. In all of our other 175 Sundynes, running for the past 20 years, we have never seen an inducer come unscrewed or loosen up before. Does anyone have experience with this type of failure or have any theories that might explain whey this is happening. Thank you in advance for any information you may have to offer.
Johnny Pellin
