The failure of the pump led to a drop in output of more than 40 percent, which affected the local grid and company profits.
Thermal power plants rely on boiler feed pumps to supply large volumes of pressurised water to create the steam that drives the turbines. Keeping these vital assets in good order requires personnel to follow detailed operating procedures and planned maintenance programs. Following on from the failure of the first pump in this particular power station, the worry of a second pump suffering from the same problem and ensuring overall reliability meant root cause analysis was as important as getting the facility back to full capacity.
The power plant has two boiler feed pumps that have been in service for approximately 10 years without any issue. However, recently, the operator noticed a problem with the mechanical seals. Sulzer responded with specialist field service personnel on site the next day. Further investigation revealed that the pump was seized as a result of not following the correct start-up and maintenance procedures.
While the boiler feed pump was out of action, productivity from the plant was reduced. Although the lost output from the power station was covered by other sites, the profit loss ran into multi-millions of Euros for every week the pump was out for repair.
Claudia Calies, service centre manager at Sulzer, said: “The first task was to explain to the plant management how the project would be delivered and the timeframe involved. Clearly, the pump was required back in service in the shortest time possible and we have to manage this expectation and provide an accurate timeline for the work to be completed.”
Due to the high water pressures involved, the pipe connections to the pump are welded, requiring a specialist to disconnect the 10-tonne pump. Once this was complete, the pump was removed and transported to Sulzer’s service centre in Jänschwalde to enable the necessary repairs to be completed.
The initial investigation found that the balance piston and sleeve were welded together, and this would require the shaft to be cut off and drilled out to separate the parts. The piston was replaced while a boring machine was used to bore out the sleeve to its original dimensions and complete the repair.
The Jänschwalde service centre staff worked two shifts per day to minimise the time required to get the pump back up and running.
The plant operator had a stock of spare parts, including a new pump rotor, which had been ordered at the time of the pump’s installation. It was sent to Sulzer to be inspected and to confirm its suitability for installation after 10 years in storage.
The repaired balance piston was then fitted together with the spare rotor, which had passed its inspection. All the additional spare parts required for the repair were also on-hand having been ordered for urgent delivery.
“Due to the important role of the pump, the power plant needed to have extensive documentation completed detailing all of the work carried out. This included independent checks and x-ray inspection of the new welds when the pump was reinstalled. The complex details involved in the repair of key pieces of equipment go far beyond the physical repair work, but Sulzer’s experience in maintaining all rotating equipment means that every aspect is covered in a turnkey project.”
With the power plant running two of these pumps, the operator was interested in identifying the root cause of the initial problem to enable any additional preventative measures to be taken. During the inspection, there was evidence that a steam bubble was present in the area around the balance piston, indicating a lack of cooling and lubrication, which led to a massive rise in temperature.
Some information that was missing during the initial investigation was that the plant suffered an unexpected shutdown two or three days before the pump failure took place. Once the reason for the shut-down was resolved, the pump was restarted, however, during this process a procedural issue was determined as the root cause of the subsequent pump failure, confirming the operational reliability of the pump.
As a result, having reinstated the pump and recommissioned it, Sulzer offered additional training for the plant personnel to try and prevent any reoccurrence in the future.
In total, from the initial stoppage of the pump to recommissioning, the whole project was completed in nine and a half weeks. In contrast, the alternative would have been to order a new pump, but typically such an engineered asset would have considerably longer lead time.
Once the pump was reinstalled and operational, a review meeting was held to assess the performance of Sulzer’s team and the results achieved during the project. Although the operator had initially suspected that the pump might be at fault, it was concluded that the incorrect start-up procedure was responsible. The additional training and the checks that were carried out on the second pump have ensured that the scenario will not be repeated and that both pumps will continue to deliver reliable service.
Calies concluded: “We regularly support the plant with annual shutdowns and communication between us is open and transparent, which is essential for a rewarding relationship.”
Following the successful completion of the project, the original rotor will be refurbished by Sulzer with a new balance piston being fitted along with refurbished impellers. This will enable the power plant to restock the spare part in case it should be needed in the future.