Experimental and numerical determination of the creep and relaxation behaviour of high-temperature, flanged pipe joints

The creep-induced deformation behaviour of three near-to-practice flanged pipe joints on a scale of 1:2.5 has been experimentally and numerically examined. The experimental results reveal the curve of plastic (creep) deformation in the bolts or flanged joints as a function of time or location, so that it is possible to assess the integral behaviour of the flanged pipe joints. It is shown that the stress reduction in the pre-stressed bolts describes a similar curve for all the materials examined: After a relatively steep decrease over a short term of about 500 h, the curve flattens and describes a quasi-stable state with only minor changes in velocity. If calculations for modelling of the time-dependent materials behaviour can rely on a sufficiently comprehensive database and if the material laws can be formulated with sufficient accuracy for the entire stress range under examination, the FE calculations will yield a correspondingly accurate description of the time-dependent stress development as a function of degree of deformation of the flanged area (eg. angle between pipe and flange disk). This method in [dition yields information on the entire deformation, the creep-induced deformation, and elastic deformation. (orig./CB)