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A method is presented for the inspection and repair of fatigue cracks that occur in the bottom tension flanges of crane runway girders. The date of first inspection and the interval of inspection are determined from fatigue crack initiation and propagation tests, respectively. The toes of the welds should be finished by rotary grinders to increase the crack initiation life. A wet‐type magnetic test appears to be the most promising tool for crack inspection. Methods of repair by welding are also presented.

The pulsating tensile fatigue tests have been carried out on the butt welded specimens using a Vibrophore fatigue testing machine. The microscopic examintion of these specimens has revealed the presence of small notches or grooves which have a sharp root radius and exist mostly at the periphery of the deposited metal near the welded toe. In any case, fatigue crack is initiated at these notches which are exceedingly small, not more than 0.03 mm in root radius and less than 0.1 mm in depth.In case of fatigue cracking at the periphery of the deposited metal, the smaller the root radius and the deeper the notch, the shorter becomes the fatigue life. Therefore fatigue strength increases as the periphery of the deposited metal becomes very smooth and the root radius of the nocthes becomes large, even if an undercut may be present. The fact that the fatigue strengths of welded materials with different static strengths show nearly similar values can be explained by the presence of such a sharp notch and not by the marcoscopic notch effect. Besides the marcoscopic stress concentration due to the geometrical effect of the welded toe, another microscopic stress concentration caused by these small notches has been confirmed, and such notches influence the fatigue strength of welded specimen.A conspicuous improvement of the fatigue strength of the welded joints can be attained if the welded toe and the periphery of the deposited metal in the vicinity of the toe are smoothed by some method of welding or post treatment after welding.