TWI Industrial Member Report Summary 3/1976
By J Knight
Rotating bending resonance fatigue tests have been carried out using 114mm OD x 8.5mm wall thickness friction welded pipe specimens, fabricated from carbon-manganese steel with a yield strength of 289~/mm2. Although the test results gave considerable scatter, approximately 7% of the results were found to lie fairly close to the lower extreme of the scatterband and it is suggested that this lower extreme of the test results could be used as a design S-N curve.
All specimens failed due to cracks propagating from the inside wall, even when the internal flash due to friction welding was machined off prior to testing. It is suggested that the higher stress concentration factor resulting from the flash blend radius is the predominant reason why cracks initiated at the inside surface of the pipe. Comparison with published data reveals that friction welding produces fatigue strength data comparable with that for pipe joined by manual butt welds, and a comparison is also made with tests carried out on flash welded pipe.