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Aftermarket precision – lasting performance
16
Application
WORLD PUMPS
April 2018
Operating & maintenance
Aftermarket precision – lasting performance A
major oil refinery in Illinois was experiencing repeated issues with its BB5 Heater Charge Pump. Repeated repairs proved not to be the answer, so an independent aftermarket assessment from Hydro Inc gave the refinery a viable solution to the chronic failures.
A major oil refinery in Illinois was experiencing repeated issues with its BB5 Heater Charge Pump. The pump operated between 700 and 750 Fahrenheit, which is a major challenge to the metallurgy. Certain metals expand when heated and shrink when chilled. This heater charge pump is designed with special material selections, with metals that can handle the high temperature and abrasive environments that pumps
like these (charging, jet, decoker, etc) endure daily. Due to the heat, many special considerations are required for its setup, and it also must have dynamic running clearances that enable the pump to function at the different temperatures employed. As the temperature changes, the clearances tighten or loosen during operation. The impellers shrink fit for pumps
with two stages or more in this high temperature service usually is analyzed via finite element analysis, to evaluate the impact in thermal growth of the impeller and shaft. Unfortunately, due to a latent defect the pump was given little consideration to its’ special configurations, such as metal expansion, needed to the handle the heat.
Inadequate clearance The dynamic running clearance was inadequate to give the pump a viable MTBF. During operation, there would be several different events that catastrophically shut down the pump. Repairs were performed under the warranty, but as more and more problems arose, the plant was persuaded to look at independent aftermarket solutions to give them a viable solution to their chronic failures and Hydro Inc was given the task.
The pump as received.
www.worldpumps.com
Many times, major factories and plants are challenged by their equipment. Most equipment is under warranty and this gives a user the illusion that the item they just bought is ‘sound’ enough- no one would offer a full-service warranty on a failing product. However, many original contracts have clauses that make it easy
WORLD PUMPS
Application April 2018
Shaft failure near the thrust collar. The vibration spectrum depicts hydraulic instability.
to come and patch ‘band-aids’ to make the pump run a bit longer, but only extending the MTBF long enough to give the illusion that the pumps were fixed. When this occurs, it not only damages the pump further, but it also leads towards the pump failing for good, requiring the hefty purchase of a new pump. During Hydro’s root cause analysis, several critical issues arose. First and foremost, there was a failed shaft at the thrust collar location. When a shaft ‘fails’ near the thrust collar, it is because the weight of torque on the shaft exceeds its radial bearing load. Additionally, the impellers were found to be severely damaged on its suction eye, and the back-hub side. The rotor failed due to hydraulic instability as the rings and bushings became displaced.
Impeller exhibits severe contact damage.
A full rotor condition analysis uncovered an expansion of the impeller on the last stage, which caused the rotor to displace. This means the shaft is bending. In some pump nomenclature, this is called a ‘bow’ in the rotor. Along with the rotor issues, the channel ring vane tips had been severely eroded. The wear components were severely damaged due to extremely high vibration issues. Finally, the hydraulic balance disc was found to be severely damaged. This was all caused from the last catastrophic failure.
Forensic analysis
The full BB5 rotor.
After performing a full rotor condition analysis of the pump and a subsequent complete forensic analysis of its failed components, Hydro created a full work www.worldpumps.com
17
18
Application
WORLD PUMPS
April 2018
scope that addressed the root causes of the pumps failure, and upgraded elements to the hydraulic design. The client supplied key vibration signatures that were analyzed by Hydro and taken into consideration when creating the work scope. Hydro created an initial analysis and work scope and reviewed all their findings and future work with the customer, which received positive feedback. Hydro instilled the trust by creating detailed plans that addressed every foreseeable issue with the pump. The detailed work plans with drawings were released to production. During production, there was a consistent detailed inspection of all upgrades and modifications. Hydro needed to disassemble the rotor and diffuser assembly. Then, they physically and dimensionally inspected the components. The rotating element was to be balanced and meet or exceed Hydro’s 1W/N residual unbalance requirements. Previously hot rolled material had been used to create its components, Hydro had upgraded to forged material which is much harder and tolerable of heat.
Balancing the rotor to 1W/N.
No grain flow and no directional strength.
Rolled material versus forged material.
Directional alignment yielding maximum strength, which increases resistance to impact and fatigue.
Forging offers uniform structure and composition. Forging results in metallurgical recrystallization and grain refining because of the thermal cycle and deformation stage. This strengthens the resulting steel product most notably in impact and shear strength. Forged steel is generally stronger and more reliable than castings and rolled steel because the grain flows of the steel are manipulated, conforming to the shape of the piece. All impellers and diffuser channel dimensions were brought back to OEM specifications, apart from the wear ring diametrical clearances. Hydro increased the wear ring diametrical clearance on the suction side to maintain the backside hub wear wrings clearances. Alignment of the bearing houses and centering of the rotating element within the barrel was witnessed by the client. The pump was returned to the client including all new parts. The element assembly was completed and precision rollers were used to centralize the rotor to the channel rings, which simulate the shaft within Babbitt bearings. The customer installed the pump without any issues. The barrel pump started right up, and performed above expectations.
•
The author, Dave Allard, is V.P. Technical Support at Hydro Inc. The finished product.
www.worldpumps.com
www.hydroinc.com
Application
WORLD PUMPS
April 2018
Operating & maintenance
Aftermarket precision – lasting performance A
major oil refinery in Illinois was experiencing repeated issues with its BB5 Heater Charge Pump. Repeated repairs proved not to be the answer, so an independent aftermarket assessment from Hydro Inc gave the refinery a viable solution to the chronic failures.
A major oil refinery in Illinois was experiencing repeated issues with its BB5 Heater Charge Pump. The pump operated between 700 and 750 Fahrenheit, which is a major challenge to the metallurgy. Certain metals expand when heated and shrink when chilled. This heater charge pump is designed with special material selections, with metals that can handle the high temperature and abrasive environments that pumps
like these (charging, jet, decoker, etc) endure daily. Due to the heat, many special considerations are required for its setup, and it also must have dynamic running clearances that enable the pump to function at the different temperatures employed. As the temperature changes, the clearances tighten or loosen during operation. The impellers shrink fit for pumps
with two stages or more in this high temperature service usually is analyzed via finite element analysis, to evaluate the impact in thermal growth of the impeller and shaft. Unfortunately, due to a latent defect the pump was given little consideration to its’ special configurations, such as metal expansion, needed to the handle the heat.
Inadequate clearance The dynamic running clearance was inadequate to give the pump a viable MTBF. During operation, there would be several different events that catastrophically shut down the pump. Repairs were performed under the warranty, but as more and more problems arose, the plant was persuaded to look at independent aftermarket solutions to give them a viable solution to their chronic failures and Hydro Inc was given the task.
The pump as received.
www.worldpumps.com
Many times, major factories and plants are challenged by their equipment. Most equipment is under warranty and this gives a user the illusion that the item they just bought is ‘sound’ enough- no one would offer a full-service warranty on a failing product. However, many original contracts have clauses that make it easy
WORLD PUMPS
Application April 2018
Shaft failure near the thrust collar. The vibration spectrum depicts hydraulic instability.
to come and patch ‘band-aids’ to make the pump run a bit longer, but only extending the MTBF long enough to give the illusion that the pumps were fixed. When this occurs, it not only damages the pump further, but it also leads towards the pump failing for good, requiring the hefty purchase of a new pump. During Hydro’s root cause analysis, several critical issues arose. First and foremost, there was a failed shaft at the thrust collar location. When a shaft ‘fails’ near the thrust collar, it is because the weight of torque on the shaft exceeds its radial bearing load. Additionally, the impellers were found to be severely damaged on its suction eye, and the back-hub side. The rotor failed due to hydraulic instability as the rings and bushings became displaced.
Impeller exhibits severe contact damage.
A full rotor condition analysis uncovered an expansion of the impeller on the last stage, which caused the rotor to displace. This means the shaft is bending. In some pump nomenclature, this is called a ‘bow’ in the rotor. Along with the rotor issues, the channel ring vane tips had been severely eroded. The wear components were severely damaged due to extremely high vibration issues. Finally, the hydraulic balance disc was found to be severely damaged. This was all caused from the last catastrophic failure.
Forensic analysis
The full BB5 rotor.
After performing a full rotor condition analysis of the pump and a subsequent complete forensic analysis of its failed components, Hydro created a full work www.worldpumps.com
17
18
Application
WORLD PUMPS
April 2018
scope that addressed the root causes of the pumps failure, and upgraded elements to the hydraulic design. The client supplied key vibration signatures that were analyzed by Hydro and taken into consideration when creating the work scope. Hydro created an initial analysis and work scope and reviewed all their findings and future work with the customer, which received positive feedback. Hydro instilled the trust by creating detailed plans that addressed every foreseeable issue with the pump. The detailed work plans with drawings were released to production. During production, there was a consistent detailed inspection of all upgrades and modifications. Hydro needed to disassemble the rotor and diffuser assembly. Then, they physically and dimensionally inspected the components. The rotating element was to be balanced and meet or exceed Hydro’s 1W/N residual unbalance requirements. Previously hot rolled material had been used to create its components, Hydro had upgraded to forged material which is much harder and tolerable of heat.
Balancing the rotor to 1W/N.
No grain flow and no directional strength.
Rolled material versus forged material.
Directional alignment yielding maximum strength, which increases resistance to impact and fatigue.
Forging offers uniform structure and composition. Forging results in metallurgical recrystallization and grain refining because of the thermal cycle and deformation stage. This strengthens the resulting steel product most notably in impact and shear strength. Forged steel is generally stronger and more reliable than castings and rolled steel because the grain flows of the steel are manipulated, conforming to the shape of the piece. All impellers and diffuser channel dimensions were brought back to OEM specifications, apart from the wear ring diametrical clearances. Hydro increased the wear ring diametrical clearance on the suction side to maintain the backside hub wear wrings clearances. Alignment of the bearing houses and centering of the rotating element within the barrel was witnessed by the client. The pump was returned to the client including all new parts. The element assembly was completed and precision rollers were used to centralize the rotor to the channel rings, which simulate the shaft within Babbitt bearings. The customer installed the pump without any issues. The barrel pump started right up, and performed above expectations.
•
The author, Dave Allard, is V.P. Technical Support at Hydro Inc. The finished product.
www.worldpumps.com
www.hydroinc.com