For transferring superheated steam from the tur-bine heat exchanger, the pipes are used which are currentlyundergoing long-term working temperature and mechani-cal stresses. Such pipeline performance depends not onlyfrom the load and from the temperature but also from thesuperheated water vapour content (aggressive hydrogeneffect), diffusion processes in metals. Transferring techno-logical parameters of superheated steam is very high: oper-ating pressure in the pipe elbow ?219 then the wall thick-ness changes in tensile zone from 28 and compression zoneto 42 mm is 13.2 MPa. These pipe elbow are also affectedby thermal stresses, by the weight of pipes elbow (includ-ing insulation), by the vibrations caused by the steam pres-sure variation and dynamic loads from the unbalancedpump rotor [1]. Working environmental parameters alongthe pipe elbow is the same. Pipe elbow during the manu-facturing process is mechanically processed and at someregions the wall become thicker and at some regions be-come thinner. We modelled manufacturing process withspring back strains. Since this kind of strains is always dueto residual strains. In such a state where residual stress-strain resides there is a big possibility to develop crack,since in the pipe working pressure rises residual stressvalue. In this work has been given a great attention to thickpipes elbow in which during the manufacturing processemerged residual stresses [2-4]. To simulate the process ofpre stress-strain conditions the finite element method soft-ware LS-Dyna were employed. In this work the attentionwas focused on the working pipe elbow which operatedonly half of the potential work resource. There were de-termined all mechanical properties along the pipe elbowsand by given data there were designed identical finite ele-ment model (FEM). The results obtained from finite ele-ment analysis (FEM) compared with the results obtainedfrom the static tensile tests.
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