Benifeld Regenerator inspection interval (Probable damage mechanism)

[Inspengrmm]

I am interested in knowing about the probable damage mechanisms that may render a benfield regenerating column at risk. The current interval at which these beds are being inspected is 8 years. Historically, this particular column has had no instance of any thickness loss, however, what I am actually curious to know is whether this interval can, in anyone's opinion, be stretched to perhaps 10 years or even (more than the codes standard) 12 years.
The only factor affecting this interval is the apprehension of some nascent mechanism initiating right after its inspection, 8 years ago, and its aggravation into something alarming by the end of our current interval.