Istrate Energietechnik GmbH

Many turbines and axial compressors are provided with free standing blades when other designs are provided with partial or continuous blades connections. Each blade apart but also the entire bladed row will be subject of vibrations caused by the rotational speed excitation, the flow excitation, torsional excitations and when those excitations are interfering with the own resonance frequency of the blades or bladed row, the amplitude of the vibrating blade increase dramatically, creating the ground of high cycle fatigue and therefore limiting the blade life. There are many cases when an improper blades or blading activity was causing the blade HCF and therefore the failure of the blade in operation, causing severe damage on the machine flow path and conducting to a forced shut down of the turbine. In a normal case the blades are designed to be the same on the same row, and only the manufacturing differences and installation errors will create a discrepancy in the measured static resonance frequency. A cracked blade or a loose bladed row could be easily detected by the resonance frequency measurement of the blades, this test considered to be mandatory for the designs with free standing blades and tight bladed rows, such as compressor blades and long LP blades.