The Turbine end shaft end was bent and found to have a 0.007” total indicator runout (TIR) at the coupling outer diameter. The generator end shaft end was bent and found to have a 0.053” TIR at the coupling outer diameter. MD&A was able to straighten both shaft ends to within 0.0015” TIR using a combination of thermal and machining straightening processes. Then, MD&A completed the final high-speed balance and final machining of the shroud covers.

Shaft End Thermal Straightening
The rotor thermal straightening process included an initial rotor stress relief and multiple thermal straightening iterations. MD&A expert technicians performed detailed visual, dimensional, and non-destructive examination (NDE) of the rotor forging before and after each thermal process to confirm that no issues were present. Rotor NDE inspections consisted of both hardness testing and wet fluorescent magnetic particle testing.

Based on the amount of shaft end distortion and the experience and expertise of MD&A technicians, it was recommended carrying out an initial stress relief of the rotor and additional thermal straightening iterations of the shaft ends to further reduce the shaft end runouts.

The initial stress relief of the rotor forging was performed on both shaft ends to relieve any internal stresses and determine the final relieved state of the shaft end runouts. This involved removing all installed blades and seal strips, stress relieving the rotor, blast cleaning, NDE, hardness checks, and runout checks along the length of the rotor.

Additional thermal straightening iterations were also performed on the generator end of the shaft to further reduce the amount of runout. This involved thermally moving the shaft end, stress relieving the rotor, blast cleaning, NDE, hardness checks, and runout checks along the length of the rotor.

Due to the high temperatures of both couplings during the stress relief processes, a vertical stress relief was not possible. As a result, the stress reliefs were performed in the horizontal orientation while rotating the rotor periodically 180° during the heating process so as not to set a thermal bow into the rotor.

DFLP Rotor Machining
Based on results of the thermal straightening iterations, machining straightening of both shafts was performed. The work involved final straightening machining of both shaft ends and final dimensional, NDE, and runout checks along the length of the rotor.

The thermal straightening operations reduced the Turb End shaft end TIR from 0.007” at incoming to 0.003” after completion. The Turb End shaft end straightening machining included final machining of the steam gland diameter, all steam gland seal grooves, all transition radii, and the coupling to remove any remaining runout.

The thermal straightening operations reduced the Gen End shaft end TIR from 0.053” at incoming to 0.015” after completion. The Gen End shaft end straightening machining included final machining of the journal, oil deflector, steam gland diameter, all steam gland seal grooves, all transition radii, and the coupling to remove any remaining runout. Also, the coupling holes were line bored to set the bolt circle pattern back on center.

High-Speed Balance
In parallel to the blading and seal strip installation, MD&A produced a new stub shaft in support of performing the high-speed balance.

The balance work involved the installation and aligning of the new stub shaft, installation of the rotor in the high-speed balance facility, balancing the rotor at operating speed, and performing an overspeed test of the rotor.

The rotor work was completed on schedule and returned to the owner.

For every repair job, large or small, the speed and effectiveness of our response team is matched only by the depth and breadth of our engineering expertise.

Have us look at your bowed rotor today. Call our Turbine-Generator Repair Facility at (314) 880-3000 or use our Contact form.

The post DFLP Rotor Straightening and Machining appeared first on MDA Turbines.

Motoring is the mode of turbine-generator operation during which the generator acts as a synchronous motor, taking energy from the grid to drive the turbine at operating speed. Motoring can be problematic, however, because the rotor blades are moving at a high velocity without the steam to keep the last stages of the LP rotor cool. MD&A’s engineering and technical expertise provided cost-effective solutions for a power plants after such damage.

The power plant customer expected to find damage in the LP section because of the motoring event. MD&A performed an on-site steam path damage assessment. Damage to the DFLP rotor was noted, and the customer sent the rotor and inner cylinder to the MD&A’s Turbine-Generator Repair facility in St. Louis.

During the rotor inspection, both the governor end and generator end L-2 blades were found to be twisted. A governor end L-1 blade had a large crack emanating from the admission edge just inside of the lashing lug. Multiple covers were missing from the generator end L-1 blades. This caused heavy foreign object damage to both the generator end L-1 blades and tenons, and L-0 blades.

This damage led to reliability concerns with the L-0, L-1, and L-2 blades so the best solution to ensure the rotor’s future reliability was to replace all six blade rows.

Roundness and horizontal joint gap checks were performed as part of the LP inner cylinder inspection, and the bore was found to be elliptical. MD&A machined the horizontal joint to decrease the out of roundness and close up the horizontal joint gaps, as well as, machined the bore to increase clearance.

Once the LP rotor repairs were completed, the rotor was balanced in MD&A’s high speed balance facility. During the balance, a sudden shift in the rotor imbalance occurred. It was determined that the coupling shifted when the rotor was tested at 110% of its rated speed. After consulting with the customer, MD&A removed the coupling and performed a full inspection.

MD&A experts found that the rotor did not have a hole for the coupling radial pin. In fact, the pin was making contact with the outside of the shaft. Once the coupling keys were removed, the coupling was found to have shifted.

The evidence suggested that the coupling was subjected to a large amount of torque during the motoring event and that this caused the coupling to shift. If it were not high speed balanced in a controlled environment, these coupling issues would not have been identified until the unit was reassembled and put back into operation, at which time the customer would have experienced extensive delays and costs to fix the issues.

The coupling was then re-installed onto the rotor, a hole was drilled into the shaft for the radial pin, new keys and a new pin were manufactured and installed, and the coupling face, rabbet fit, and outer diameter were re-machined. This allowed for the proper balancing of the rotor.

This project is just one of the many examples of MD&A’s expertise to fix difficult rotor issues.

Have MD&A look at your turbine rotor today, call our Turbine-Generator Repair Facility at (314) 880-3000 or use our Contact form.

The post Turbine Blade Replacement appeared first on MDA Turbines.