Steam turbine work on the international stage can have its challenges, but also its successes.
Mechanical Dynamics & Analysis (MD&A) was contracted to inspect, analyze, and then straighten a Toshiba® steam turbine rotor in Abu Dhabi, United Arab Emirates. MD&A launched its team into action for full analysis of the issues followed by resolution of the most cost-effective and technically sound solution for the owner/operator.
MD&A experts arrived in Abu Dhabi and immediately established all support systems and protocols necessary for an efficient state-of-the-art response.
Initial assessment and engineering analysis showed heavy scale buildup but no significant rub on the covers. Runouts of the steam turbine rotor showed a total indicator runout reading (TIR) of 0.0324 in., confirming that the rotor was bowed and must be straightened.
All options, including rotor machining, thermal straightening, and mechanical straightening, were considered and discussed with the owner/operator in detail. MD&A’s technical expertise, experience, and recommendations were critical factors in the final decision.
The decision was made to keep the rotor horizontal through the entire process. Thermocouples, heating pads and insulation were prepared. Scaffolding was erected for electric wire control. A custom fixture was designed to check rotor location during turning.
The rotor was first inspected (including non-destructive examination), cleaned and prepared for initial stress relief to remove any stresses imposed by the bending. Initial post-stress-relief runouts showed the TIR now reduced to 0.0247 in., improved but not sufficient for full-service, long-term operation.
Controlled and precise thermal applications at well-defined points would follow.
A series of hot spotting, runouts and stress relief followed. Progress was monitored as hot spots were applied and stress relieved.
Three iterations of hot spotting would be applied along with runouts, blast cleaning and NDE/hardness testing, and axial measurements.
After the third iteration of hot spotting and stress relief, MD&A experts determined the maximum TIR to be 0.009 in. Then, in consultation with the owner/operator and with careful review of data from a companion unit, all parties agreed to terminate the hot spotting. MD&A confirmed that limiting the number of hot spotting iterations and thus reducing the metallurgical impact is the ideal goal in any steam turbine rotor thermal straightening project. With this agreement, the rotor was again cleaned and inspected, and prepared for proper low-speed balance.
With the TIR measurement greatly reduced and low speed balance achieved, the unit was successfully placed back in full operation.
This project exemplifies many of the experience-based benefits brought to a project by MD&A:
- Responsive communications
- Solid in-depth analysis
- Strict attention to detail
- Ability to develop and perform “out of the box” repairs to support continued, reliable operation
- Project management skills and coordination of multi-disciplined operations
- Focus on the end goal
- Consideration for the owner/operator’s long-term use of the equipment
- MD&A’s commitment to steam equipment as part of our gas turbine/steam turbine/generator portfolio of expertise and experience
- Global commitment to the power industry
MD&A invites you to discuss any steam turbine, gas turbine or generator rotor issues with us today. Call our Turbine-Generator Repair Facility at (314) 880-3000.
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