ASME BPVC Fatigue Analysis – Part 5.5: Protection Against Failure from Cyclic Loading

Effective ASME Fatigue Analysis - Predictive Engineering FEA Consulting Services Portland Oregon Section VIII, Division 2

Analysis

ASME BPVC

Objective

Even with an academic and experimental background in fatigue analysis, it is daunting to provide a hard, no-nonsense life-cycle prediction.  It is especially daunting when your fatigue prediction can cost or save your client millions of dollars.  As for seeking an easy way out with “fatigue software”, it can just mean a black-box solution where one off-loads their reputation and hopes for the best.     

Over the years, we have learned that there are three critical components to a quality fatigue analysis: i.) accurate FEA stress results, ii.) accurate FEA stress results and iii.) accurate FEA stress results.  Okay, sad, old, real-estate joke about location, location, and location; but let us just imagine that your stress numbers are good, then what?  Fatigue analysis is all about the protection of structures and systems against failure from cyclic loading.  This is where the ASME Boiler & Pressure Vessel Code (BPVC) provides a tried and true standard that, if your stress numbers are good, then you can be assured that your fatigue prediction will be conservative. 

Besides providing robust fatigue curves, the Code provides explicit guidance on how to treat welds based on type, inspection and surface quality.  For example, if the weld is completely un-inspected and un-finished, then it earns a fatigue-strength-reduction factor of 4.0, which means your FEA stress numbers are multiplied by 4.0 prior to the calculation of fatigue cycles per the ASME curve.  In contrast, if a full penetration weld is ground to smooth profile and then fully-inspected (volumetric and surface examinations) , then the fatigue-strength-reduction factor is 1.0.  The ASME code makes clear that it is not saying that the weld material is as good as the base material, but merely that the ASME fatigue curves are still accurate. 

The ASME fatigue method was recently used to confirm cyclic fatigue damage and to guide subsequent design revisions.  From an engineer’s perspective, it was a very satisfying journey since the Code provided clear guidance on how to treat welded and non-welded sections.  The projects have been completed and now we wait to see what happens.  Nothing is perfect and one never truly knows with fatigue, but at least following the ASME “Protection Against Failure from Cyclic Loading” we are not flying alone.

PDF Download

effective_fatigue_analysis_on_engineered_structures_and_systems_-_predictive_engineering_fea_consultants.pdf (1007.18 KB)
ASME Fatigue Code Application – Non-Pressure Vessel Application
ASME Fatigue Code Application – Power Plants, Hydroelectric, Rotating Machinery, Pressure Vessels, Piping.
ASME Fatigue Code Application – Power Plants, Hydroelectric, Rotating Machinery, Pressure Vessels, Piping, Predictive Engineering FEA Pressure Vessel Services
Fatigue of Welded Structures: Weld Surface Fatigue Reduction Factors
ASME Part 5.5 - Fatigue of Welded Structures Weld Surface Fatigue Reduction Factors - ASME Div 1 and Div 2
ASME Part 5.5 - Fatigue of Welded Structures Weld Surface Fatigue Reduction Factors - Predictive Engineering ASME Div 1 and Div 2 Alternative Rules Consulting Engineers
Weld Quality Levels As-Welded (4x) to Machine Profiled, Fully-Inspected (1X)
ASME Section VIII Design-by-Analysis Fatigue Classification
ASME Section VIII Design-by-Analysis Fatigue Classification Weld Quality Levels As-Welded (4.0) to Machine Profiled, Fully-Inspected (1.0) - FEA Pressure Vessel Consulting Services
Application of ASME Fatigue Code: Effective Total Equivalent Stress Amplitude
Application of ASME Fatigue Code: Effective Total Equivalent Stress Amplitude - Preditive Engineering, Portland, Oregon - ASME Section VIII Code Consultants
Application of ASME Fatigue Code 3-F.1 ASME Smooth Bar Fatigue Curves
Application of ASME Section VIII, Division 2, Part 5.5 Protection Against Failure from Cyclic Loading Fatigue Code 3-F.1 ASME Smooth Bar Fatigue Curves - Predictive Engineering FEA Pressure Vessel and ASME Structures Consultants
Application of ASME Fatigue Code More Than Just Boilers and Pressure Vessels
Application of ASME Section VIII, Division 2, Part 5 Fatigue Code More Than Just Boilers and Pressure Vessels - FEA ASME Services, Portland, Oregon, USA