Our locos routinely have their tubes replaced at every 10-year overhaul, and they are expected to last until the next one. When tubes leak like this, it is a matter of expanding the ends where they pass through the tube plates until the metal fits and cures the leak. One of the drawbacks of locos with relatively short fireboxes is that whenever the firebox door is open for shovelling coal, cold air enters and does not get the chance to warm up sufficiently before it reaches the tube plate. The result is that the relatively thin tubes cool down and shrink faster than the more bulky tube plate which retains heat much better, the consequence of which is leaking around the tubes.
Having re-expanded the tube ends a number of times, Rob Houghton, our Chief Engineer, bit the bullet and decided to remove the offending ones to replace them with spare ones we had in stock. This was when he discovered that both the original and our spares were standard 1 ¾ inch tube whereas the tube plate could accommodate the next Imperial size up, namely 1 7/8 inch. The extra expansion needed to get the 1 ¾ inch tubes to fit was adding to the problem as the wall thickness was getting thinner, thus less material on which to ‘bite’. Obviously, thicker tube was needed and after phoning around all the tube suppliers, we discovered why we had used 1 ¾ inch tube rather than 1 7/8 as nobody stocked that size. But we could get 1 15/16 for some strange reason (neither size works out at a round figure in metric either)!
However, this larger tube was 0.6mm too big so we were stuck until one of the suppliers, Salem Tube whom we have used before, suggested swaging down one end and expanding the other, which is exactly what we did and they even supplied us in about half the time quoted. So whilst George B sat out July, he/she is now back in service with new and hopefully less troublesome tubes.