How To Achieve World Class Pump Reliability
In 2004, a refinery in North America was struggling with pump reliability
. The MTBR (mean time between repair) for pumps was stuck at 39 months, which was about the same level as the plant had achieved in 1996. In a dramatic turnaround, by the end of 2011, the refinery MTBR for pumps had improved to 85 months.
This is the story of how they did it.
A Simple Program
There were two aspects to the program: better repair practices and reduced internal clearances using Vespel CR-6100. Over the 7 years of the program, more than 400 pumps were upgraded using Vespel CR-6100 wear componentsnearly half the refinery pump population.
The Repair Practices
One of the core issues the refinery faced before 2004 was a repair schedule dictated by Operations. Pump repair was based on timeliness, not quality. Operations would put pressure on Maintenance because they did not want to run without a spare pump in place. Most pumps were repaired as is or to the original specification without systematically implementing root cause failure analyses or
best practices. Many pumps were repaired with pump cases left in the field. The refinery had all the necessary personnel and skills; they simply needed to use their resources effectively.
In 2004, the Maintenance department began to change the repair process such that every repair was viewed as an opportunity for improvement.
The first step was to gain more time to execute a proper pump repair. The plant used the existing condition monitoring program to verify that the running spare pump was healthy. This information was communicated to Operations and over time they became more comfortable with pumps running for longer periods of time without the spare pump in place.
With enough time to perform a thorough inspection and repair, the Maintenance department was able
to implement a much more thorough procedure. Some of the changes implemented were as follows:
Pulling all pumps and cases into the workshop for repair. No more field repairs (except seal changes on deep well pumps not showing signs of internal wear).
Root cause failure analysis of the pump and seal for each pump repair
Measurement and correction of fits, concentricity, and squareness of all pump componentswhether new from the OEM or used
Improved lubrication practices to ensure clean lube oil
Correcting of seal flush plans, and bringing piping within the pump flanges so the whole assembly could be tested prior to leaving the shop
Installation of Vespel CR-6100 wear components : wear rings, throat bushings, throttle bushings, and vertical pump shaft bushings with clearance of wear rings set to 50% of the API minimum for metal parts.
After assembly, but before mechanical seals were set, pump rotor turned by hand to ensure there were no internal rubsverifying that the fits and concentricity were good
Air testing of the pump before being sent to the field for installation
Vespel CR-6100 with reduced clearance
A major catalyst for the program was the use of Vespel CR-6100 for the stationary wear components in the pumps. Vespel CR-6100 components can be installed with much tighter clearance than metal wear componentstypically 50% of the API minimum values for metal wear rings. The tighter clearance provides the impetus for better fits, superior concentricity, and improved squareness of mating surfaces. Furthermore, Vespel CR-6100 does not gall or seize like metal parts, giving mechanics the courage to reduce the internal clearances, knowing that the pump will not stick during alignment or start up and return to the shop.
Vespel CR-6100 is a composite material with exceptional dimensional stability. It is chemically compatible with all of the typical process fluids and chemicals in a refinery with a temperature range from cryogenic to 260 C. This broad application window made it an ideal choice for a standard repair material. By standardizing on one material for upgrades, the plant was able to have one set of installation and machining procedures and one material on the shelf.
The Vespel CR-6100 was installed as the stationary wear componentswear rings, throat bushings, throttle bushings, and vertical pump shaft bushings. In general, wear ring clearance was reduced to 50% of the API minimum, throat bushing clearance was set to function with the mechanical seal flush plan., and throttle bushing clearance and vertical pump shaft bushing clearance were set to 50% of the API minimum plus 0.002 (0,05 mm).
The small change of reducing internal clearance is a major reliability upgrade. Reduced clearance increases hydraulic damping and stiffness, reducing vibration and shaft deflectionmechanical seals and bearings last longer. Reduced clearance also reduces NPSHR, reducing the potential for cavitation. Because internal leakage is reduced, pump performance and efficiency are improved, reducing energy consumption or boosting throughput. And even in the case where a pump suffers from an off-design process event such as running dry or running blocked in, Vespel CR-6100 has proven that it can withstand significant abuse, helping the pump to survive these events with minimal damage.
The results at this plant are just one more data point in a growing list of plants which have derived very large reliability gains from the use of Vespel CR-6100 with reduced clearance combined with superior repair practices.
Over the 7 years of this program, the refinery was able to reduce their annual pump repair costs by 30% and save millions of dollars in maintenance cost.
Nearly all of the original Vespel CR-6100 wear components remain in service today
by: Robert Aronen
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