Analytical Approach to Component Lifing
Although basic component lifing can be performed with relatively limited information (such as estimated operating hours, operating temperature, design stress and (assumed) average material properties), such simplified approaches can be useful, particularly if experience-based assumptions (and access to a detailed material database) are applied to improve accuracy.
However, more advanced component lifing approaches require detailed knowledge of stress analysis methods, familiarity with OEM designs used in power plant construction, and a solid understanding of service materials and damage mechanisms that occur in industrial components. Structural Integrity has an experienced team of engineers that knows how to apply advanced modeling and analysis techniques to ensure that component lifing activities provide the highest level of accuracy.
Requirements for Advanced Lifing
As with many analytical practices, methods used in detailed component lifing assessments include applying closed-form equations to specific problems, developing and running finite element stress analyses, incorporating fracture mechanics in cases that require consideration of crack propagation, and consideration of the best available material data for predicting damage rates based on known operating conditions.
Advanced component lifing assessments can be applied to many types of components and systems, including the following:
|Piping Systems||Headers and Drums||Nozzles|
|Turbine Components||Valves and Steam Chests||Boiler Tubes and Assemblies|
|Pressure Vessels||Fittings||Welds and DMW's|
The most important aspect of accurate component lifting involves getting the most accurate values possible for 1) historical service history (time at temperature), 2) the maximum applied stress in the component (based on operating conditions rather than design values), and 3) accurate chemical composition data for the material in use (in some cases, this includes trace elements not included in the material specification). The need for accurate information in these areas often requires on-site efforts to obtain and review historical operating data, review component installations, review and confirm drawings and dimensions, developing computer models to accurately determine stress values based on system condition (e.g., hanger behavior) and component or system geometry, and confirming material properties through either NDE or destructive testing methods (related to material characterization).
For components that are common to power plant systems, specific codes may be used in advanced lifing assessments, These include the EPRI BLESS software for headers and piping, DMW-PODIS for tubing dissimilar metal welds, pc-SAFER for turbine rotors, RRing-life for generator retaining rings, LP-Rimlife for turbine disks, and MPC OmegaPipe for high energy piping girth and seam welds.