Session: MF-16-01 Creep and Creep-Fatigue Interaction

Paper Number: 84126

84126 - Development of Life Estimation Method for Nozzle Welds in Large Scale Piping of Modified 9Cr-1Mo Steel -Part II: Analytical Study- 

Creep strength-enhanced ferritic (CSEF) steels are widely used in fossil power plants operated in many countries and life management for the components made of these materials are of critical importance for plant operators.  In particular, failures in welded joints in softened heat affected zone (HAZ) categorized as type IV failure have taken place widely in piping and boiler headers and prediction of such failure became a urgent requirement to be addressed.  Many failures have firstly occurred in longitudinal welded joints due to the application of high hoop stress normal to the welded line and the approach for their life prediction essentially based on comparison of hoop stress and failure life of small round bar cross-weld specimens has been made.  Weldments used for attaching various nozzles to main piping or boiler headers followed them as a portion susceptible to type IV failure, stimulating the needs for prediction of their lives also.  As a result, it turned out that a more sophisticated approach which can deal with complicated geometries involved in these weldments needs to be developed.

 

With such a background, the authors carried out an internal pressure creep test at 650 °C using the large-diameter pipe made of P91 steel.  Outline of testing condition as well as the results including the periodic damage inspection by several methods is presented in the accompanying paper whereas related analytical efforts will be described in this paper.  Detailed finite element analyses were performed on nozzles with different geometries, incorporating creep deformation properties of each continuant of welded joint.  Moreover, failure criterion based on inelastic strain energy density has been developed for softened HAZ, taking into account of the dependency on temperature, creep strain rate as well as stress triaxiality factor.  Results obtained using these properties were compared with the test results in terms of the location and extent of cracking due to creep damage accumulation.  They showed reasonable agreement, demonstrating the soundness of the developed approach.

Presenting Author: Yukio Takahashi Central Res Inst Elec Pwr Ind

Presenting Author Biography: Graduated the doctor course in University of Tokyo in 1983. Have been engaged in the researches related to structural integrity of various power plant components for nearly 40 years.

Authors:

Yukio Takahashi Central Res Inst Elec Pwr Ind
Haruhisa Shigeyama CRIEPI
Masatsugu Yaguchi CRIEPI