Does anyone have any comments on whether regular descaling of a kettle
causes surface damage that can make it more susceptible to limescale
in the future?

Oddly enough, it is more likely that _using_ it has that effect. For
the scale to form the minerals (normally calcium/magnesium carbonate
plus a touch of silica) need a nucleation site to begin to form their
crystals on. once a seed crystal is formed, it will continue to grow as
long as there is available saturated solution. I have not got my
reference book to hand, but I think all three minerals have a positive
solubility coefficient i.e. they are more soluble in hot water than
cold. If the kettle cools with boiled water in it further
crystallisation will take place This is how Travertine marble (really a
limestone) is formed by hot springs. The buff squiggly stone on the
front of a certain very litigious burger chain is this rock. But I
digress.

When you boil water it cavitates i.e. a bubble forms and collapses. The
collapse is violent, so violent in fact that it can damage metal.
Eventually the bottom of the kettle will be microtextured, with myriad
nucleation points. If the cavitation is bad enough, it can, over time,
erode metal. If you try to put too much shear stress on water
cavitation occurs. I once the impeller of a Francis turbine
(hydrelectric use, water powers the turbine) which had been in service
for 20 years. A quite staggering amount of bronze (15%?) had been
removed. Cavitation also affects ships propellers, which keeps bronde
foundries in business. If the propeller is run grossly too fast the
cavitation can get to the stage where almost the entire propeller is a
cloud of cavitated water and the efficiency is greatly reduced.

Finally, should you wish to see nucleation points in action, buy
yourself a pint of fizzy cider or lager. When it was settled examine
the liquid near the side of the glass. Do you see a stream of little
bubbles heading to the surface? They are all coming fron the same
point. That is a nucleation point.

John Schmitt