This second edition presents a substantially expanded and refined set of IIW Recommendations, delivering updated and clarified design rules supported by extensive new data for engineers working with HFMI‑treated welded joints. It introduces relaxed weld‑geometry requirements prior to treatment, revised thickness‑correction factors consistent with the 2024 IIW Fatigue Design Guidelines, and greatly enlarged tables covering fatigue strength across material grades, load ratios, stress ranges, and assessment methods. The scope has been broadened to include steels with yield strengths up to 1300 MPa, alongside refined limits for variable‑amplitude loading. New chapters provide guidance on retrofitting and life‑extension of existing structures, as well as methodologies for assessing HFMI devices based on experimental evidence. With clearer procedures, expanded applicability, and rigorously updated technical content, this edition serves as a comprehensive, practice‑oriented reference for the design, verification, and upgrading of welded structures using HFMI treatment.

Gary B. Marquis is a professor of applied mechanics at Aalto University, Finland. Within IIW, he served as a chair for Commission XIII: Fatigue of welded components and structures for eight years, chair of the IIW Technical Management Board and as IIW president for three years.

Zuheir Barsoum is a professor of lightweight structures at KTH Royal Institute of Technology, Stockholm, Sweden. Within IIW, he has served as chairman for XIII-WG2: Techniques for improving the fatigue strength of welded joints for 8 years, vice chairman for Commission XIII for 6 years and member of IIW TMB (Technical Management Board) for 3 years.

Martin Leitner is a professor of structural durability and railway technology at Graz University of Technology, Austria. Within IIW, he is currently chair of Sub-Commission XIII-SC-B: Fatigue Improvement Techniques.