Failure analysis of the low-pressure blade lacing wire in steam turbine

The failure analysis of the low-pressure last stage blade lacing wire in steam turbine made of 0Cr17Ni4Cu4Nb(S17400) is presented. The failure of the low-pressure last stage blade occurred at 7 operating years. Several examinations were carried out to identify the blade lacing wire failure’s root cause: macroscopic inspection, chemical composition analysis, hardness test, metallographic analysis, microscopic examination and inspection of maintenance records. It is found that there is local displacement of the roots of the low-pressure rotor, and the collision between the lacing and the lacing holes is the direct cause and external mechanical incentive of the lacing fracture.the high content of P element and the high hardness reduce the plasticity and toughness of the material which is the intrinsic factor of this tensile fracture, without obvious plastic deformation, the low-pressure last stage blade lacing wire breaks rapidly. It is suggested to find out the local displacement of blade root and fix it in a reliable way, check the strength after eliminating the harmful defects such as cracks, and replace the blade if necessary, strictly according to DL/T438-2016 and the manufacturer’s standard requirements for the inspection of the lacing wire before use.