Page 324 - Improving Machinery Reliability

Life Cycle Cost Studies 293

Pump impellers have a mean time to failure of 12 years. When impeller failure
occurs, 8 hours of downtime is also lost production time. Maintenance crew costs are
US$lOO/hr. Impeller replacement costs are US$3,000/impeller plus US$1,800/inci-
dent for seal and bearing replacements that occur as good maintenance practice
while the pump is disassembled. Impeller, seal, and bearing transportation costs are
expedited and cost US$750 per incident.
Annual impeller costs are (1 yeadl2 yeardfailure) * {US$(3,000 + 1,800 + 750) +
(US$lOO/hour) * 8 hours + (US$4,000/hour * 8 hours)) = US$3,171
Pump housings (scroll end) have a mean time to failure of 18 years. When hous-
ing failures occur, 14 hours of downtime is also lost production time. Maintenance
crew costs are US$lOO/hour. Housing replacement costs are US$3,000/housing plus
US$l,800/incident for seal and bearing that occur as good maintenance practice
while the pump is disassembled. Housing, seal, and bearing transportation costs are
expedited and cost US$1,150 per incident.

Annual housing costs are (1 yeadl8 yeardfailure) * (US$(3,000 + 1,800 + 1,150)
+ (US$lOO/hour) * 14 hours + (US$4,000/hour * 14 hours)} = US$3,519
Pump bearing sets (a set = two bearings) have a mean time to failure of four years.
When bearing failure occurs, eight hours of downtime is also lost production time.
Maintenance crew costs are US$lOO/hour. Bearing replacement costs are
US$300/bearing plus US$l,500/incident for seal replacement that occurs as good
maintenance practice while the pump is disassembled. Bearing and seal transporta-
tion costs are usually expedited and cost US$300 per incident.
Annual bearing costs are (1 year/4 yeardfailure) * { US$(300 + 1,500 + 300) +
(US$lOO/hour) * 8 hours + (US$4,000/hour * 8 hours)} = US$8,688
Motors have a mean time to failure of 12 years considering all causes. (Motors
have many parts and can fail for many reasons. A thorough analysis would be more
accurate than this overview approach taken by lumping all details into one MTBF
number.) When motor failure occurs, eight hours of downtime is also lost production
time as the motor is swapped for a similar unit in stores. Maintenance crew costs are
US$lOO/hour. Motor replacement costs are US$3,000/motor. Motor transportation
costs for expedited delivery use US$500.
Annual motor costs are (1 yeadl2 yeardfailure) * [US$(3,000 + 500) +
(US$lOO/hour) * 8 hours + (US$4,000/hour * 8 hours)} = US$3,025
Couplings have a mean time to failure of eight years considering all causes. When
coupling failure occurs, eight hours of downtime is also lost production time. Main-
tenance crew costs for labor, incidental materials, and expense are US$lOO/hour.
Coupling replacement costs are US$400. Coupling transportation costs for expedited
delivery are US$300.
Annual coupling costs are (1 yead8 yeadfailure) * [ US$(400 + 300) +
(US$lOO/hr) * 8 hours + (US$4,000/hour * 8 hours)] = US$4,188