Ansicht eines Kernkrraftwerkes

Partial stress-relieving annealing of a circumferential weld on a high-pressure preheater

It is necessary, in all partial heat-treatment operations, to take account of possible obstructed expansion and its effects on the component. Special attention must therefore be devoted to questions of expansion and contraction.

Particularly in this case, where a 446 mm thick pipe bend with a shell section and a hemispherical head of 85 mm wall thickness were located only 400 mm from the annealing sites (circumferential weld, D = 2,600 x 35 mm wall thickness). A stress analysis, which specified the axial and radial plots of temperature, was drafted in order to keep the stress exposure of the HP preheater within permissible limits during heat treatment. It was also necessary to bear in mind that the HP preheater’s supports (fixed and floating bracket) were located only 150 mm from the annealing site. The deadweight of the shell section of the HP preheater had caused it to deform during stress-relieving annealing. For this reason, 85 t of the HP preheater had to be suspended at above 300 °C using the machine shop crane. The residual load on the fixed and floating brackets was thus only 5 t. The crane’s load was continuously reset to 85 t during heat treatment, in order to compensate for the axial expansion caused by the heat.

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