Fracture Analysis of the Main Valve Stem in the Steam Turbine

The failure analysis of the main valve stem in the steam turbine made of 2Cr12NiMo1W1Vis presented.The failure of the main valve stem in the steam turbine occurred at 11 operating years.Several examinations were carried out to identify the main valve stem failure's root cause: macroscopic inspection, chemical composition analysis, hardness test, metallographic analysis, mechanical properties analysis.It is found that there are multiple cracks in the fracture of the valve stem. From the lines, it can be seen that the cracks develop from the inner wall of axial and radial holes to the outer diameter of the valve stem, and finally break in the outer wall of the four quadrals.The material performance of the valve stem is lower than the reference standard GB/T 8732-2014 and the manufacturer's requirements, which is the internal factors of the valve stem fracture. The axial cross opening of the valve stem and the center of the axial inner hole do not coincide with the valve stem center. Local stress concentration and additional stress are the external (mechanical) factors of the valve stem fracture.It is suggested to contact steam turbine manufacturers to optimize the valve stem structure, to avoid the influence of axial cross orifice stress concentration, and to avoid the factor that may produce additional stress; Check and accept valve stem in strict accordance with manufacturer's standard, including but not limited to valve stem material quality certificate, geometric dimension review, spectrum, etc.