الخلاصة:
To ensure the integrity of a tubular exchanger, tubes to tub sheet assembly has seal plates,
positioning the tubes to absorb the different loads and increase the rigidity of the assembly.
These functions are performed by an optimized maximum pressure expander choice, by
geometrical, mechanical and thermal characteristics of tubes and plate. Often when in service,
the sealing assemblies is lost because of the loss of the residual contact pressure, produced by
the manufacturing process, as the effects of creep and relaxation, or due to the emergence
cracks in the tubes at the transition zone due to mechanical and thermal loads, under the effect
of stress corrosion cracking (SCC). The vibrations generated by the fluid flow could also
introduce a mechanism of additional rupture.
At first, the research was interested in the expansion process, and then they were oriented
toward the axial resistance and it was only later that they were oriented to the residual stresses
and degradation mechanisms of the assembly.Several models have been developed to predict the residual contact pressure at the end of the
expansion process: one based on an assumption that the assembly model is elastic perfectly
plastic, another taking into account the hardening materials by a constitutive bilinear law, etc.
All these models have their strengths and weaknesses.
Recently a new analytical model has been developed introducing the effect on the creep on
the relaxation of the residual stress and its effect on the residual contact pressure at the end of
the expansion process and in service.
