New developments and guideline updates for HFMI treatment for improving the fatigue strength of welded joints

High-frequency mechanical impact (HFMI) has established itself as a reliable, effective, and user-friendly method for a post-weld fatigue strength improvement technique for welded structures. HFMI can be implemented as an important element of lightweight design for new structures and as a tool for the rehabilitation of structures in service. The first IIW recommendations for HFMI treatment were developed over several years and published in 2016. An abundance of new research and test data confirms the important elements of that guideline. However, it also demonstrated that certain portions of those recommendations need to be clarified, expanded, and improved. These include:The scope of the guidelines for steels with yield strengths from 960 to 1300 MPaRelaxing the fatigue geometry requirement of the weld profile prior to HFMI treatment and the groove dimension following treatmentPresenting fatigue strength modification factors also numerically as an alternative to modifying the fatigue classIncorporating the updated thickness correction factors from the newest IIW Fatigue Design RecommendationsAdding a series of tables that summarize the rules for defining the appropriate fatigue strength for different combinations of material strength, load ratio, stress range, and assessment methodProvide guidelines on HFMI treatment of prefatigued structuresPresent a methodology for verifying the effectiveness of HFMI devices based on documentation and experimental data This paper presents details of this new information that is being incorporated into a revised IIW recommendations for HFMI treatment for improving the fatigue strength of welded joints.