|
|
|
|
|
On a condenser tube, the entire tube may not need to be considered. The LAi on a condenser tube may be identified on both inside and outside surfaces and for quite different reasons. Possibly, on the outside surfaces only the locations where the tube interacts with tube supports or with tubesheets are important. On the inside surfaces the entrance to the tube may be prone to erosive damage; if this is a seawater condenser, the inside surface may sustain damage resulting from the growth of sea organisms.
Specific LAi can be selected where the following are particularly intense:
Chemical environments where there are deposits, crevices, electrochemical cells, concentration of species due to evaporation, or aggressive flow.
Stresses due to applied and residual sources are the highest and are tensile. Also, if the stresses are cyclic, locations of relatively low cyclic frequencies, e.g. 1 Hz or less, and high mean stresses accelerate corrosion-related penetration.
Metallurgy like welds or locations of excessive deformation such as bends.
To identify LAi properly it is usually necessary to involve several disciplines such as design, materials, stress, corrosion and fluid flow.
Lifetime Prediction, Roger W. Staehle, Adjunct Professor, Department of Chemical Engineering and Materials Science, University of Minnesota, Staehle Consulting Co.