Regarding my previous note about refurbishing of the UK's National Grid system. I forgot to mention that the refurbishing of the steel towers has been a huge problem, in that the towers, dating from the early 1960s, are all constructed from imperial steel angle shapes. These shapes have long disappeared, and all steel angles are hard metric sizes (150 x 150 x 6, etc). (Rolled steel wideflange beams etc are still in old imperial sizes, even if they are given a metric designation.)
In replacing a newly discovered rusted out angle on these towers, the new metric angle often would not fit, resulting in all kinds of lash-ups and other quick fixes. And they had to be quick - a section of the grid (say one side of a 40 km stretch of line) had a very specific outage window, timed to the minute, with huge penalties if the contractor ran over time (sometimes the crews were working round the clock to stay within the window). Thus there wasn't time to re-engineer the steel angle framing (and new cables could not be strung until the tower WAS fixed) - it was truly a fix-as-you-go solution. One only hopes that the quick fix has an equal or greater degree of structural integrity as the original design.... Of course, if National Grid had conducted a full PSE (pre-sanctioned engineering) survey of every tower on any particular line, instead of the cheap solution of just taking a random sample of towers, these problems could have been avoided. A true case of "A gram of prevention is worth a kilo of cure". John F-L
