Clear warning signs had been ignored
After the turbine was recommissioned, the vibrations measured in the turbine rotor were only just below the maximum permitted by the manufacturer. However, in the following weeks and months, these vibrations did not stabilise, but instead increased steadily, presumably exceeding the permitted maximum by June 2009. Nevertheless, the turbine remained in operation. Fatigue cracks appeared in the retaining bolts. The bolts sheared as soon as the water pressure was sufficiently high to cause residual forced rupture. The turbine cover with turbine rotor and generator weighing around 2,000 tonnes lost its anchorage in the foundation and led to the accident.
Catastrophe court case
Even today, it is unclear why neither the plant management nor the operators halted the turbine which had been vibrating strongly for many months. Many documents are still in the hands of the judiciary. Others were reputedly washed away by the water. After the water had been pumped out of the turbine hall, 49 of the 80 retaining bolts holding the turbine cover in place were subjected to metallographic analysis. Six of them did not even have a nut. They may have been forgotten when the turbine was last serviced. Investigations by the public prosecutor are still ongoing. One year after the accident, charges were filed against the people responsible in the plant operating company and in the maintenance companies. The plant’s operator plans to completely replace all ten turbines between 2011 and 2014.
Improper plant operation
"Professional risk management can help prevent such catastrophes. But regular maintenance and proper use of machinery are indispensable, the more so towards the end of a machine's originally planned life span", Bernd Richter, an engineer and Claims Manager in Munich Re's Europe and Latin America unit, and Klaus Wenselowski, head of the Property Claims Management unit at Munich Re's Global Clients/North America division explain. "To prevent such major losses from occurring, we assist our clients in setting up risk management programmes and attach great importance to compliance with agreed measures and guidelines."