Upgraded Replacement Gearbox by Philadelphia Gear Helps Nuclear Power Plant Avoid Expensive Engineering Changes
The Primary Challenge
A Michigan nuclear power plant that generates enough electricity to serve a city of 1 million people experienced excessive noise in the gearbox of its diesel-driven fire pump. The noise was caused by two issues: a bevel set with an outdated design and debris created from excess wear in the cast-iron ramps of the backstop that prevents the unit from operating backwards. While not operated continuously, the fire pump and its gearbox were, and remain, critical components of the facility’s fire protection plan required by the U.S. Nuclear Regulatory Commission (NRC).
“The plant experienced this same issue a few years prior,” says Chris Hanes, senior service center engineer – Philadelphia Gear. “At that time, the gearbox had been repaired by an aftermarket machine shop because the original equipment manufacturer didn’t offer repair services. In addition, the OEM still manufactured its replacement parts using cast iron, meaning that they were likely to have the same issues as the original parts did.”
The replacement backstop ramps installed by the machine shop wore out a second time. Debris was once again introduced into the gearbox. The greatest risk associated with the damage was potential lack of access to fire protection water in the event of a plant fire – a catastrophic event that could result in loss of life, loss of revenue and environmental concerns.
The plant’s system engineer considered two alternatives. The first was to purchase a new pump gearbox and engine. This would have required a significant engineering change (EC) because the original gearbox provider could not provide a like-for-like gearbox; therefore, a new engine would have been required to accommodate the new gearbox’s gear ratio. The second was asking another gearbox OEM – Philadelphia Gear – to successfully repair the existing unit using a different approach. However, this wouldn’t solve the issue that the nuclear facility didn’t have a spare gearbox to use when the unit needed maintenance again
Philadelphia Gear suggested a third alternative: repair the existing unit as a short-term solution, and build an all-new, like-for-like replacement unit as a longer-term solution. The proposed new unit would include design upgrades to extended gearbox life and improve performance over the original gearbox. The customer accepted the recommendation due to their confidence in Philadelphia Gear’s reputation for excellence in gearbox design, manufacturing and service.
The original gearbox was repaired using a combination of replacement parts from the OEM and new components manufactured by Philadelphia Gear. The existing backstop ramps were repaired by Philadelphia Gear using information the customer acquired during the previous repair.
At the same time, Philadelphia Gear engineers worked closely with the customer’s Plant System Engineering team to customize the new gearbox that met regulatory requirements and could easily be integrated into the application’s existing design envelope and footprint. This included:
- A 14 FP right-angle configuration Philadelphia Gear gearbox with the same input (2200 RPM) and output (1800 RPM) speeds as the original to accommodate the existing diesel engine’s available torque and fire pump.
- Design customization to allow easier access to the gearbox oil pump. The original gearbox oil pump for self-lubrication was internal to the unit and only accessible by disassembling the gearbox. Philadelphia Gear solved this issue by integrating an inspection cover that is easily removed for pump maintenance – and added an oil filter to filter the oil in the event of contamination. The existing gearbox did not have an oil filter.
- Backstop ramps and pins manufactured using high-quality steel. Improved materials and more modern manufacturing processes make the new components more wear resistant and nearly eliminate the risk of damage and debris.
- Appropriate lubrication to accommodate low operating speeds during routine testing. As a system used only in emergencies, the fire pump is tested occasionally to ensure it remains in proper working order. This entails idling the unit at low speeds and ramping up to full speed a few minutes at a time. Philadelphia Gear adjusted the unit’s lubrication to accommodate varying speeds.
- Standard enclosed factory acceptance testing. This included operational testing for noise, vibration, temperature and water leakage.
- Packaging for long-term storage with the GearLogic℠ Long-term Preservation System. The customer plans to warehouse the new gearbox until the existing unit requires maintenance, which is anticipated to be in several years. The unit was coated in special preservation oil for rust prevention, and a hygroscopic breather element was installed to release air pressure and prevent seal leakage during storage. In addition, desiccant bags and humidity cards were added to prevent water condensation and a plexiglass cover was installed for easy inspection of the desiccant bags and maintenance during storage.
The repaired gearbox was put back in service and is expected to operate as needed for 10 years or more. The new, upgraded “like-for-like” gearbox was delivered to the customer and put into long-term storage as a critical spare.
“Few OEMs understand the complexity of nuclear regulations and can service nuclear plant customers like Philadelphia Gear,” Hanes says. “We were able to use our expertise to offer this customer cost-effective options that saved them from a complex EC and new equipment purchase. We also delivered a new unit that will perform better and longer for them once installed.”
The customer was connected with Philadelphia Gear, a Timken Power Systems (TPS) company, through its existing relationship with TPS company Schultz Electric, a specialist in electric motor and generator repair serving nuclear power plants. “Together, Philadelphia Gear and Schultz Electric offer customers a single source for original equipment and MRO services that support power systems used through a nuclear power facility.”