The Lavender Line
Yvonne’s boiler was inspected on Friday 13th February by an independent boiler inspector, who has given all the plate-work a clean bill of health. Sample thickness readings around all over the boiler and firebox inner showed that the material is all in good condition and there is no more than minimal wastage anywhere in the boiler, which is really good news. The main flue, was the area most likely to be at risk due to it being exposed to higher temperatures and being partially in the water space and partially in the steam space. In order to inspect it properly, we had to cut out the liner which was installed within the flue to protect the flue from the hot exhaust gases from the fire. Behind the protective tube was a layer of sand, which also had to be scraped out to expose the metal. After application of an angle grinder to clean up the surfaces, we were able to get sample readings over the length and circumference of the tube, from which we were pleased to note that the wall thicknesses were still around 13mm thick, which puts it in good stead for another 10 year ticket.
Unfortunately not all the news was quite as good as this. When inspecting the firebox, we found that a welded seam was showing signs of cracking and it was not possible to see the effect of this cracking below the surface. Obviously, with a pressure vessel, this is a significant concern, so the boiler inspector requested that we arrange a full Non Destructive Test (NDT) of the weld. This was arranged for Friday 20th February and consisted of a Magnetic Particle Inspection (MPI) and an Ultrasonic Inspection. The MPI test involved spraying the weld with a special white coating and putting black iron filings along the length of the weld. An electromagnet was then run along the length of the weld and the particles are attracted to any cracks. From this initial test, evidence of a very fine crack in the weld was observed. This was further investigated with an Ultrasonic test that permits “seeing” below the surface of the steel in the same way as an ultrasonic scan is used to look at a baby during pregnancy. From this, it was determined that there were hairline cracks of varying depths along the length of the weld, but that there was no damage to the plates themselves.
The conclusion was that the weld needs to be ground out and prepared, then a new seam will need to be welded by a coded welder. The weld is about 1.5m long in 13mm thick steel, so will take quite a lot of grinding out and a sound set of skills to rebuild.
As well as attending to the faulty weld, the boiler makers will be replacing all the studs that are used to attach fittings to the boiler and will also be installing the new boiler tubes.
Meanwhile, back at home, I have been starting to clean up valves and fittings ready to re-unite them with the boiler when the time comes. They have been exposed to years of accumulated soot, scale and oxidisation, so they are going through a process of de-greasing, wire brushing, mild abrasive cleaning and polishing to bring them back to a nice condition. I am also replacing seals and gland packing in the valves and gauge frames as well as installing new glasses in the gauge frames.