Critical components for power generation
Overview
The business of power generation is a delicate balance. The industry is heavily regulated, meaning the only path to higher profits, is reduced operating costs. The more service life a plant operator can get from expensive, critical components, the more profit they can make. One such piece of costly infrastructure is the Boiler Water Circulating Pump. At well over a $1M for a new unit, repairing these has become essential to remaining operational. In this particular instance, a piece of the pump (the thermal barrier) was damaged and should have been replaced. To facilitate the customer’s required timeline and financials, the part was instead repaired.
Challenge
The Boiler Water Circulating Pumps are the third most important piece of equipment in a thermal power plant. The actual boiler takes heat from the fuel of choice, and turns water into steam. The steam then is used to turn a turbine to make electricity. The role of a BWCP is to increase the water feed pressure in the boiler, increasing the temperature at which the water turns to steam. On average, this improves thermal power by over 40%.
In other words, when one of these pumps breaks, the plants can only operate around 60% power. On top of that, due to the aging infrastructure of the world, most power plants are operating beyond they’re planned service life. This means that these pumps (and other components) need to be serviced in ways that was never planned. this particular pump had a 25 year planned service life. When it was sent in for repair, it was over 65 years old. This has lead to fundamental material issues.
Project Approach
The goal was to find a way to return this pump to service. To that end the priorities were:
Provide a safe product.
Maintain the current reliability standard
Get the unit back to the customer as fast as possible.
Make a plan on how to prevent these failures in the future.
Reverse engineering existing pumps
Power plants were built by a mix of companies, and have a huge range in age (oldest we’ve seen was 1918!). The equipment was therefore made by a wide array of companies, most of which have either shut down or lost the IP required to service equipment. The goal then had to be to create a drawing package sufficient to understand how every part of the pump interacted. Then the drawings could be refined to aid in repair. With enough data, these repair drawings could be refined to the point where new unit manufacture is possible.
Project Planning
To get this pump back to service with the customer the following plan was devised:
Develop a fit for service criteria.
Find what information we already had, sifting through all pertinent records the customer could provide.
Reverse engineer the thermal barrier and create a drawing package.
Devise the repair scope and perform.
Prepare plan for how a new thermal barrier could be manufactured.
Fit For Service
Since these power plants are liable for maintaining their own equipment, they have criteria for the performance of each pump. Using this criteria, and industry standards, it was possible to see what was critical to maintaining the pump service life.
Part Archivist, Part Engineer
The customer was able to send in substantial records for the pump to be repaired, however it was all original to the pump from the 1950’s. Translating the code requirements and other specifications took time, but provided a much better understanding of how each piece functioned. This allowed us to begin creating new drawings to start developing repairs from. Using the physical part, and comparing with the archival information, provided a strong enough backbone to proceed.
Repair Scope
The repair to be performed here was a new failure mode, not before seen on one of these thermal barriers. The material had fatigued to the point, that a passage way had eroded between the high pressure boiler water and the low pressure cooling loop. From our drawing package, we had a good idea where the failure would be, and developed weld procedures.
The erosion was excavated to clean metal. A stainless material was then used for filler to maximize repair strength and lifespan. Finally the part was re-machined to ensure all mating/sealing surfaces were restored.
Results
The thermal barrier was reinstalled on the pump and passed its pressure and helium leak test. This meant that the repair succeeded! The customer was then able to reinstall the pump on time and avoid costly shutdown extensions. Getting the power plant back on line was the only successful outcome.
Conclusion
Repairing this pump might have felt like a side project to the greater pump service, however it showed exactly why and how critical parts can be. These ancient artifacts from bygone engineering eras are still essential to keeping the world turning. Finding ways to keep them in service, in turn keeps the world in service.
We did make sure to recommend a replacement be made though to avoid this issue going forward!
We are proud of this result and the way this project turned out. We learned a lot along the way and can’t wait to implement these lessons and practices on our next project.