Session: MF-05-01 Fitness-For-Service and Failure Assessment

Paper Number: 62535

Start Time: Wednesday, July 14, 2021, 08:00 PM

62535 - Cumulative Creep Damage Using Advanced Predictive Analysis 

Advanced techniques of evaluating cumulative material damage for power plant components operating in the creep range can enhance life management strategies, especially as power plants transition to more flexible operations.  Power piping creep damage is strongly sensitive to the operating temperatures, operating pressures, and applied stresses. 

Several empirical examples reveal large ranges of operating temperatures and pressures throughout the operating years of power piping systems.  Multiple examples reveal that the operating conditions may be significantly different over the years.  Time and pressure histories for main steam (MS) and hot reheat (HRH) piping systems are provided to illustrate these operational changes, including mean and median annual and monthly plant information data.  Operating temperature and pressure histograms can reveal single modal and bi-modal plant operations.  Examples of mean, median, and upper 95% confidence operating temperature and pressure values are included in this study. 

There may be some instances of operating above design temperatures and design pressures for short periods of time.  Advanced evaluations have revealed that some above design temperature events have occurred with low operating pressures, so coincident operating pressure and operating temperature evaluations are also discussed to determine more accurate estimates of cumulative creep damage.  Accelerated creep fatigue damage can occur from high temperature ramp rates obtained from the detailed temperature profiles.

At specific critical component locations, creep damage algorithms have been utilized to determine the cumulative material creep damage using a life fraction analysis methodology.  The cumulative creep damage has been evaluated using several years of historical 5-minute temperature/pressure data.

Evaluation of the applicable applied stresses in piping system weldments should consider the simulation as-found stresses, redistributed through-wall axial and circumferential stresses, weld residual stresses, and redistributed multiaxial stresses.  The hot and cold piping system walkdowns should compare the actual piping displacements to the predicted design displacements.  Piping walkdown evaluations should identify and evaluate the observed significant field anomalies.  Several empirical examples illustrate that the simulation as-found stress analysis (considering adverse field conditions) can result in piping stresses significantly different than predicted in the as-designed piping stress analyses. 

In the past, the selection of weldment reexamination intervals has been based on standard industry practice.  Advanced predictive analytic evaluations can be used to provide a technical justification for continued plant operation until critical components are reexamined.  Several case studies illustrate that an evaluation of historical operating pressures significantly below the design pressure can result in significantly increased component remaining creep lives and can be used to justify increased component reexamination intervals. 

This study provides several examples of using the actual operating temperatures, operating pressures, field stresses, and cumulative operating hours to estimate the cumulative creep/fatigue damage at critical system components.  Depending on the future expected piping system operations, the remaining useful lives (RULs) for the critical system components can be estimated.  A piping system RUL contour isometric can illustrate the most critical weldment creep damage rankings (these are few lead-the-fleet locations).  If there are no significant fabrication defects in the other weldments (which can be confirmed by a one-time examination), the evaluation can be used to justify that many of the remaining weldments do not have to be examined for the next 30 operating years.

Presenting Author: Marvin Cohn Intertek

Authors:

Marvin Cohn Intertek
Michael Liu Intertek
Michael Cronin Intertek
Nikhil Kumar Intertek
Martin Gascon Intertek