Semi Lean Pumps Description Semi lean pumps circulate lean solution in the closed purification loop. They take the suction from D-2515 flash vessel and discharge the solution to mid of absorber. Following pumps are used to circulate semi lean solution in the loop Pump P- 2503 P-2503A P-2503 B
In normal operation at 100% FEL load, semi lean solution flow requirement is around 7100 GPM so only two out of three pumps are operational. PHT-2503A and MP-2503B are normally operational while PHT/TP-2503 is standby.
Sequence of Events At about 1300 hours on November 09, 2014 abnormal sound, FRC-125 flow, discharge pressure variation and high amperes of MP-2503 were observed. Normal amperes are around 250-260 while before changeover 285 amperes were observed. The load was immediately shifted to TP-2503, TP-2503 was previously on slow roll. After about half an hour of operation, TP-2503 I/B bearing temperature was observed high, ~220 oF. Vibrations were found normal, ~0.23 ips. Bearing oil was changed twice and 02 air hoses were provided. Temperature reduced to ~170 oF. P-2503 B strainer was inspected and found ok. Pump was manually rotated and was found rotating freely. Go ahead was given to start P-2503 B. However it was instructed to shut the pump immediately in case of any abnormality. At about 2100 hours High temperature, abnormal sound and high vibrations in OB bearing of PHT-2503 were observed. Normal vibrations are ~ 0.20ips. The observed vibrations were up to 0.38 ips. Since the sound and vibrations were on the rise, pump changeover to MP-2503 was decided. MP-2503 B was started in presence of FM section in-charge, abnormal sound was observed. Pump was immediately shut down. Owing to high vibrations and abnormal sound of PHT-2503, it was decided to shut this pump down as well. Both pumps (P-2503 B, P-2503) were shut down and FEL was reduced to 70%. Semi lean circulation load was shifted to P-2503A alone. HIC-193 was opened to 55% Pumps were handed over to Field maintenance for comprehensive overhaul.
Issues in P-2503 P-2503 suction strainer was inspected. 06 Paul rings found inside the strainer Thrust bearing clearances were increased Thrust bearing journal area of shaft was found heavily pitted Radial side of impeller hit the pump casing and impeller edge was heavily damaged Nonmagnetic debris was found in suction elbow Pitting on inner race of journal bearing was found
Issues of P-2503B Impeller and casing wear rings were found damaged. Minor cracks on impeller were observed. Apparently the impeller wear ring broke and got stuck with pump casing
Incident Proceedings The probable reasons of pumps malfunctioning are Pumps cavitation as paul rings were found in suction strainer. This could have resulted into chocking of flow to pump. The discharge pressure was fluctuating heavily. This is another indication of cavitation. Carbamate crystals ingression to pump casing as powdered material has been found at suction flange Mechanical failure of pumps (Wear rings, Bearings Seals damaging etc.)
The pumps overhauling took around four days and then were taken back into operation. Since the incident resulted into heavy production loss, the matter needs serious consideration. Failure of backup pump at hour of need is a serious issue and needs serious attention. Investigation team has been made for detailed investigation of the incident.
