Fatigue testing of interlocking Stainless Steel

An interlock tube, usually made of stainless steel, is one of the key structural components for both bonded and unbonded flexible pipes of composite construction. The fatigue performance of this component is an important factor in determining the long term integrity of the entire pipe. This paper presents an experimental technique developed for the establishment of the basic fatigue characteristics of such interlock tubes. Details of the fatigue testing method, the specimen design, preparation and calibration procedures will be described in conjunction with tests carried out on 254 mm interlock tube samples. One of the most important results from this work is that, by careful design and machining of the specimen, the mode of failure seen in full scale pipe samples can be reproduced on small specimens in a laboratory using a fatigue machine. The significance of this is that it is possible to obviate the necessity for expensive full scale composite pipe testing, provided that an accurate description of the loading conditions imposed on components of the composite is available.