Part 5: Boiler works—February to April 2001

Detailed investigations have revealed several serious issues with both the frames and the boiler of NM25. New frames, a new cylinder for the left hand side, and a new tube nest in the firebox end of the boiler are the major parts being priced at the moment.

The boiler, which is located at the SteamRanger depot in Mount Barker, is being prepared for its rebuild. The primary reason the boiler is there is to provide ready access to SteamRanger’s pressure vessel welder. Extensive gamma ray photography has been carried out on riveted seams, together with ultrasonic and magnetic particle testing of welds. Unlike the frames, these tests have confirmed that structurally, the boiler is good. However, there is a lot of work being done, and still to do. At present, the surprisingly large number of studs are being removed. These have to be replaced because they are all very, very old, and in most cases very corroded. To add to the complication, there are known to be at least 29 different sizes of studs used on the boiler.

New super heater flues and smoke tubes have to be procured, swaged down and fitted. The tube nest in the firebox end tube plate is being replaced, due to cracking on the water side. Ongoing cracking on other preserved locos, has encouraged us to sort the problem out before returning the loco to service, rather than being faced with patch in a couple of years. At least part of the tubeplate has been replaced in the past, as evidenced by the weld repairs.

However, the major job is the replacement of around 95 of the 124 foundation ring rivets. These hold the inner and outer firebox wrappers together. Most of the rivets have lost their heads on the fire side, due to corrosion since trafficable days. We have arranged the use of a "squeeze riveter" for the insertion process. It is presently at Puffing Billy being prepared for a similar job on the boiler of Garratt G42. We are arranging to send people to Melbourne to assist Puffing Billy, and at the same time learn how to use the machine (they are learning too!). It may well see service on the main frames and bogie frames as well.

The firebox tube nest was cut out, and allowed access for the first time in many years to the inside of the barrel. Having done that, we found that the small remaining piece of steel at the flange between tubeplate and crown of the firebox is very severely stress corrosion cracked all over on the water side. It looks a bit like a dried up claypan—quite horrible really.

The metal appears to be too far gone to weld to, although grinding may help to determine how deep the cracking is (it looks deep). If it is too far gone, we will be faced with the possibility of having to remove it, weld up a look alike, and rivet it in place inside the boiler. This would be interesting as the space is limited, and two people will have to be on the water side to put the rivet in and set up the "holder on" dolly whilst someone else rivets up from below in the firebox. The work may be able to be done with the boiler upside down, but even that will present problems for the people doing the job.

While this has been happening, a new smokebox has been fabricated, due to extensive corrosion in the original. After a successful test fit to the boiler at Mount Barker, it is now back at Panorama for finishing. This will involve seal welding, cutting the hole for the funnel, and fitting items such as marker lamp brackets, handrails, headlight bracket, and the funnel.