Metallurgical Failure Analysis of a Fractured Steam Control Valve Stem
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CASE HISTORY—PEER-REVIEWED
Metallurgical Failure Analysis of a Fractured Steam Control Valve Stem Craig J. Schroeder
Submitted: 5 January 2015 / in revised form: 25 February 2015 / Published online: 1 April 2015 ASM International 2015
Abstract One fractured steam control valve stem was provided for metallurgical failure analysis. The specified material of manufacture for the steam control valve stem was Incoloy 901 alloy. The valve stem was nitrided, but the nitriding process was masked at the location of the fracture. The valve was reported from a throttling type service in a steam turbine subject to steam-induced turbulence while in a free state. The steam was reportedly held at a temperature of 1050F under a pressure of 2400 psig. When the valve was in a closed position, the stem was subject to compression or buckling forces under a seating load of 13,000 lbs. The valve was in a guide bushing with a diameter of 2 in. It was requested that the fractured steam control valve stem could be evaluated to determine potential causes for failure. The scope of the project consisted of visual inspection, scanning electron microscopy with energy dispersive x-ray spectroscopy, tensile testing, hardness testing, chemical analysis, and metallographic analysis. Keywords Bending Complex failures Electron microscopy Failure analysis Fatigue cracking Fatigue striations Metallurgical investigation
process was masked at the location of the fracture. The valve was reported from a throttling type service in a steam turbine, subject to steam-induced turbulence while in a free state. The steam was reportedly held at a temperature of 1050F under a pressure of 2400 psig. When the valve was in a closed position, the stem was subject to compression or buckling forces under a seating load of 13,000 lbs. The valve was in a guide bushing with a diameter of 2 in.
Objective It was requested that the fractured steam control valve stem could be evaluated to determine potential causes for failure. The scope of the project consisted of visual inspection, scanning electron microscopy with energy dispersive x-ray spectroscopy (SEM–EDS), tensile testing, hardness testing, chemical analysis, and metallographic analysis.
Conclusions •
Introduction One fractured steam control valve stem was provided for metallurgical failure analysis. The specified material of manufacture for the steam control valve stem was Incoloy 901 alloy. The valve stem was nitrided, but the nitriding • C. J. Schroeder (&) Metallurgical Engineering Department, Element New Berlin, 3200 S. 166th Street, New Berlin, WI, USA e-mail: [email protected]; [email protected]
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Cracking of the fractured steam control valve stem initiated at a region with the appearance of a pre-crack. The cause of the pre-crack was not clearly evident from this study, but may have occurred during the straightening of the part, or during the installation of the part. The remainder of the cross section cracked due to the application of cyclic stresses that were in excess o
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