Don't Tolerate Poor Repair Service

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The full article

Don't Tolerate Poor Repair Service

Costly Turbine Generator Damage

An 18 MW steam turbine generator at a university suffered a loss of lube oil accident in late July. With this type of event, the steam turbine and generator rotors will usually roll to an abrupt stop since there is no oil in their bearings. This causes the bearing areas of the rotors to become hot and may result in bent or bowed rotors. That was the case in this event. The steam turbine rotor remained straight but the generator rotor was bent 0.012 inches from outboard of the fan blades to the end of the exciter.

A Second Opinion

As part of the repair, the generator original equipment manufacturer (OEM) conducted an evaluation of the damaged rotor. In its opinion, there was no hope to repair the 25-year-old rotor, which was not damaged electrically but had only the 0.012-inch bend on one end. Even after discussions with senior OEM management, it was apparent they did not want to do a repair. They preferred to sell a new rotor that could be delivered by Christmas if the customer placed an order within a week.
This was not acceptable to the customer or Hartford Steam Boiler. Today, weld repairs of rotors and large shafts are accomplished successfully by a number OEMs and repair firms. Replacing a slightly bent rotor was not considered appropriate without a second opinion. With customer concurrence, HSB had the rotor moved from the original OEM shop to another OEM repair shop in the same area.

Getting What You Need

The new shop assessed the rotor and the damaged areas on the shaft were machined off. The damaged areas were then weld-built up and re-machined to correct the bent end. This was done at half the cost of a new rotor and reduced repair time by more than three months.
The story does not end there. The rotor was sent back to the original OEM for installation of the remaining parts and balancing, but the OEM had problems with its balancing machine. The customer was in desperate need of the rotor. Again the assembled rotor was moved to the other OEM, balanced, and shipped to the customer in time to meet its re-assembly schedule.

Lessons Learned

If you do not agree with the recommendations of the repair firm or OEM, get a second opinion. Technologies on repairs continue to change. Only after you believe you have exhausted all viable avenues of repair, should long-lead replacements be considered. Also, do not tolerate poor performance by repair firms. Nobody intended to move the rotor out of the original OEM’s shop twice, but to achieve the best repair and get the unit back in service faster, HSB and the customer did what made sense to get results.
Disclaimer statement:

All recommendations are general guidelines and are not intended to be exhaustive or complete, nor are they designed to replace information or instructions from the manufacturer of your equipment. Contact your equipment service representative or manufacturer with specific questions.

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