621
![[IMAGE]](logos/redball.gif) Major Rehabilitation 2007 / 2008
Then Loco Manager Ian Johnston has compiled a detailed list of tasks undertaken in 2007 /2008 on tasks leading up to the loco test runs and the its return to service on the 17th August after a lengthy period of maintenance. Click HERE to download Ian's report (in PDF format)
A small number of tasks were attributable to damage incurred in a minor derailment near Gemmells; a bent draw bar, broken speed recording sender unit and some minor dings to wheel rims and brake rod supports under the tender. All other work performed was due to normal wear and tear along with the age of our equipment requiring some routine heavy maintenance.
The description of the tasks does not indicate the time spent which can vary from a few hours to a number of weeks. Hopefully the list will give "non mechanical" volunteers some appreciation of the scope of the work we undertake with very limited resources and why the maintenance of such "old" machines, which includes everything we operate, is a large task fraught with difficulties due to the age and condition of many bits and pieces.
The loco returned to service by operating trains from Mt Barker to Victor and Strathalbyn on Sunday August 17th 2008 This was a success and we now plan to use the loco to run the Southern Encounter and Cockle Train on the first and third Sundays until late November, the October School Holiday Cockle Trains and the Highlander to Strathalbyn on the second Sunday of September and November.
A Rust Problem - September 2008
The loco team were looking forward to a busy fortnight of steam Cockle Train running when they lit up the loco on Saturday 27th September in preparation for taking it to Goolwa Depot. However the dark clouds descended when it was obvious there was a serious steam leak from the regulator and no more than 10psi could be raised!
Here are some words from Ian Johnston on what then eventuated.
"We have had some rotten luck with 621 today (Saturday 27th Sept) during its preparation to transfer to GD for the forthcoming CTs. Once boiler pressure began to rise, a significant steam leak from the regulator (via the release cocks) became very obvious to such an extent that from 10 psi, no more pressure would accumulate easily due to the leak. A number of "tests" were undertaken to try and work out what the problem might be but nothing at all showed up.
Ron Williams and I delved into 621's regulator first thing on Sunday morning and found a good reason for the heavy steam leak - No. 3 valve was stuck open at least 1/16 inch. Doesn't sound much but on a 3 inch diam valve, it leaves an awfully big gap. The reason for this appears to be our old enemy - a slow build up of a small amount of galvanic corrosion around the balancing piston, mostly on No.3 valve because it is the last one to sequentially open and hence does not open very often during normal running.
Some more pertinent info revealed itself on Monday morning when the superheater header had cooled down. The bottom chamber of the header is what is called a balancing chamber which is in communication with steam once the regulator has been opened but steam only flows to it (not through it) to apply an equal steam pressure to the underside of the valves to "balance" them so that very little physical effort is required to open them against the boiler pressure
We found a significant amount of corrosion products accumulated in this bottom chamber, so much so that under No. 3 valve, the pile of rust and scale made contact with the base of the regulator valve and prevented it from seating fully.
The amount of corrosion around the balancing piston and its bore was minimal and I was curious how this alone might have impeded the valve closing. The reason for this large amount of rubbish could well be linked to the fact that for 3 months the boiler sat completely idle full of treated water and that the pH in the header could not be monitored and adjusted as could the boiler water itself. So during that 3 months a significant amount of corrosion would have taken place as nature dropped the pH for us. What we will need to do in the future is monitor the corrosion process inside the header on a fairly regular basis until we are satisfied as to what has just happened was more of a one off due to the 3 months of wet storage."
Attached is Ian's photo of about two mugs full of corrosion products found in 621's header although the height of the pile does not show all that well. This stuff, representing about 90% of the total, was removed from the bottom balancing chamber of the header with most of it piled up under the No. 3 regulator valve, this being the prime reason for impeding the closure of that valve and hence the problem last Saturday.
The loco was steamed up again on Tuesday morning and ran light engine to Goolwa where it took over from DE507 to run the final Cockle Train of the day.
And then another problem during the October Running
On stabling the loco at Mt Barker after a very busy and fruitful SE/CT day on the 5th October , the customary listen in the firebox revealed an ominous loud hissing noise, usually associated with a cracked/broken crown stay or a leaky element. It turned out to be the former but instead of the "normal" slow bubbling of steam and water from the stay telltale (leakage) hole, it was running water. This indicated the stay was well and truly broken and because of the amount of water flowing into the firebox, it was impossible to determine if any other suspect stays might have been contributing. Consultation with the boiler inspector confirmed 621 was a no go until the extent of the leak had been investigated and if relatively minor, the leak could be temporaily plugged.
The stay was plugged once the loco had cooled down, but still in a hot but bearable environment with a simple tapered steel plug hammered home hard. This normally works as a temporary stop gap until a window presents itself to remove the broken stay and replace it with a new one. Among all the thousands of stays around 621's firebox, there are 3 rows of 24 flexible crown stays on each side of the firebox (144 total) located along the radius of the inner firebox in the transition from the flat crown sheet to the vertical sides. These stays carry most of the load when the firebox is at its hottest and hence fully expanded. Unfortunately these stays are fairly old - most date back to the 1950s and hence are prone to cracking and sometimes breaking. Once this has happened it is desirable to replace the stay as soon as practicable so as not to overload adjacent stays resulting in the same fate. And if any two adjacent stays play up, it is instant withdrawal of the boiler - and hence the loco. We have previously operated for short periods with one stay plugged and this is acceptable provided frequent monitoring of the situation is maintained - again for obvious reasons.
Ian Johnston's photos shows the results of the leak first up and then the same thing after a bit of a clean up and the plug hammered into the tell tale hole. We will be closely watching that this plug remains in place and no other stays start to leak. The reason the stay head immediately to the left of the crook stay looks different is that it is an earlier replacement stay and rather than rivet the heads over, we now run a fillet seal weld around the head - much quicker, easier and safer than using a rivet gun in a confined space. The 3 blobs across the top of the photo are the "button head" ends of the crown sheet stays - a different type of stay but does the same thing.
The loco was returned to Goolwa to resume duties after a break of just a couple of days.
Much Bigger Problems - December 2008
The Initial Assessment (18th December 2008)
Our hardworking Mechanical Services team had a Christmas present that they did not deserve when routine inspection of the loco in preparation for summer Cockle Train workings revealed water in the smoke box which was traced to an 8mm crack in one of the 20 year old flue tubes.
It was initially thought this could be welded up but removal of the flue confirmed a much more serious and major problem, which resulted in the boiler inspector condemning all flues and boiler tubes. This will unfortunately mean 621 will not be available over summer, and we will have to rely on DE507 and railcars
Apart from an indicative cost of around $50000 for new flues and tubes alone, procurement of material and consequent fitting will be a massive task taking into account our limited resources and based on previous experience other unpredictable maintenance work inside the boiler could well be required.
Here are a few more details at this early stage
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Removal of the flue revealed a stress corrosion problem in the end of the flue tube, hence the crack, hence the leak. Based on the age of the flues, it is believed the metal has crystallised and because of that and the thinness of the flue walls plus a few other factors, BD has had no hesitation in condemning all flues - no good even for reuse as they have been in the boiler for 23 years and are already second hand. Then based on all of the above, the same reasoning has been applied to the tubes. So to cut a long story short, all flues and tubes require replacement; not suprising - they have had an extremely long life.
- We have 16 flues purchased for 520 in 1994 which can be used in 621. We will need to purchase a minimum of 6 new flues. We have no spare tubes and will need to purchase over 100
- We hope to have a more accurate view as to where we are heafing within a couple of weeks so watch these pages, and if anyone feels they wish to contribute financially or in any other way to this unexpected setback - please contact us.
- Obviously work on retyring Rx207 will be put back for the moment - speeding up this work rather than putting resources onto 621 was considered by BOM but was not a realistic option.
Work Assessment 16th January 2009
Since November deciding in requirement to replace all 22 flues and 102
boiler tubes, a reasonable amount of physical work has been undertaken and
seemingly an equivalent amount of time spent on measurements and
calculations to determine the exact state of the firebox and smokebox
tubeplates, both 50 years old having been fitted as part of the last general
boiler overhaul by the SAR in 1959.
The main activities were;
-
all flues (5 1/2 ins. diam) were removed first and this has never been
an easy task. First the welded flue ends were tediously ground from the
firebox tubeplate then the expanded flue ends in the smokebox slit with an
oxy torch and partially collapsed to release that joint. This was followed
by the hardest part, slogging the firebox end of the flue with a sledge
hammer while cramped in the firebox until that expanded joint released
itself and the flue moved forward about 100 mm.
- with the each flue released, a shackle was attached to the smokebox
end of the flue and the hydraulics of the Leyland truck used to drag the
flue from the boiler. It was then a task for at least 3 chaps to transfer
the flue to the tray of the Leyland - the flues are that heavy.
- the removal of the 102 tubes (2 1/4 ins. diam) required the same
process, except the hydraulics, and was easier due to their much smaller
size.
- the condition of all flues and tubes was fairly good corrosion wise
but together with their by now relatively thin walls and age , the boiler
inspector considered their use by date was up.
with all flues and tubes out, it was time to clean the scale from the
interior surfaces of the boiler including the barrel sides, tubeplates, feed
water tray, palm stays, internal pipes etc. Although the interior was
considered to be reasonably clean, a number of buckets of scale resulting
from many years of water boiling, were removed. What was very heartening was
the effective layer of iron tannate deposited on all surfaces from the
tannin treatment to the boiler water. The tannin also assists in removing
scale and sludge via the blowdown valve.
Ian's photo caught young
volunteer Oliver Lukins hard at work descaling the boiler.
- a few weeks was then spent grinding excess weld from the tubeplates,
cleaning and deburring all flue and tube holes and cleaning the water side
of both tubeplates (required needlegunning as well) - all these tasks being
pretty dirty affairs.
- at this stage the "bible" of pressure vessels, Australian Standard
1210, was being consulted and calculations started to determine how the
tubeplates measured up against the AS with regards to the specified pitch of
all holes, minimum ligament widths between holes, maximum permitted hole
diameters and tubeplate thickness.
- a number of sets of AS based calculations were carried out to see how
the tubeplates compared with their original drawings, tolerances permitted
by the AS, the current tubeplate thickness and hole diameters and finally
the repair options proposed by ourselves.
Fitter
Ron Williams
accurately
measuring the
smokebox
tubeplate
Photo:
Ian Johnston
- the calculations showed the condition of the firebox tubeplate was
such that it could probably be used without any major work required on the
plate itself but that the diameters of the swaged ends of both the flues and
tubes would need to be increased to allow for the increased diameter of all
holes.
- the same calculations applied to the smokebox tubeplate showed that
the plate required some major work or even partial replacement. The main
deficiencies were related to oversize and oval flue holes resulting in
undersize ligaments plus oversize tube holes although the ligament widths
were still acceptable. After much discussion, our final proposal was to
reform the flue holes by welding followed by machining back to drawing size
and to "bell" out the ends of the tubes to more closely match their
respective holes. This is much more preferable than over expanding tubes out
to the oversize holes. The AS allows holes to be no more than 0.100 ins.
larger than its corresponding flue or tube and that is one of the limits we
have to work within.
- a meeting was held at Mt Barker on 14/01/09 with our boiler inspector,
Bernie Dickinson, and SteamRanger's Ron Williams, Ian Johnston, Bob Sexton
and a number of interested volunteers to discuss all aspects, calculations,
current corrosion wastage of tubeplates (minimal at about 0.060 ins.) and
our proposed repair methods. Bernie confirmed our calculations and
interpretations of AS 1210 to be correct and endorsed the welding repairs to
the smokebox flue holes. The holes will be machined after making mods to our
magnetic based drill to adapt it to use more as a borer.
- however before any of this takes place, there are two more critical
and major determinations to be carried out on both tubeplates - magnetic
particle tests for cracks in holes and ligaments on both sides and ultra
sonic testing of the thickness of the entire plates to ensure their
compliance with the AS. Until the plates pass these tests we cannot
conclusively say that either plate is still suitable for use.
So for the next week or two, the outside faces of each tubeplate need to be
cleaned back to bare metal followed by the crack testing of both sides of
both plates then if no major issues arise from that, ultrasonic thickness
testing of both plates. If at this stage both plates can be used, albeit
with a fair bit of welding and machining on the smokebox plate, new flues
and tubes can be ordered with some hunting around for someone to swage and
bell the ends of both as required.
The photos above speak for themselves. The close up of the water sides of
both plates (smokebox (L) and firebox (R) )shows the degree of cleaning required
for crack testing - back
to bare metal. It also gives some idea of the spot corrosion on the plates -
in most cases looks worse than it is.
Latest News 7th February 2009
There is not a lot to see visually (except for the crack testing white paint) as to what has gone on with 621 tubeplates since the 14 January report but there have been a fair amount of time consuming tests and some repair work started.
- Ron Williams spent a few days undertaking the magnetic particle crack testing of both sides of both tubeplates including the flue and tube seats in each hole. Both tubeplates showed minor but fixable cracks, the most significant being a "shower" of surface cracks on the water side radius between the very bottom tube hole of the smokebox tubeplate and the barrel. It is intended to grind the cracks until they have completely disappeared (as indicated by MP testing) then build up the plate with pad welding - a slow process to prevent any undue heat stresses being set up. A few tube holes in both plates have small radial cracks which will be similarly ground out and welded.
- Boiler Inspector Bernie Dickinson has kindly loaned us his ultra sonic thickness meter to measure the tubeplates' thicknesses at dozens of spots. The probe requires perfectly flat and smooth surfaces to yield accurate results so many spots were prepared on both plates and these correspond to the numbers seen on this photo. While there is some thickness wastage of both plates, a bit more than we had theorised, Bernie considers that there is still adequate thickness in both plates.
- Some time has been spent in developing and perfecting techniques to weld all smokebox tubeplate flue holes due to their being oval in shape and oversize, plus four tube holes with the same problems. As a means of providing a full and clean weld edge on the back (water side) of the tubeplates, a number of firebrick "pavers", as used in slow combustion heaters, were purchased. These will be clamped to the water side of the tubeplate with the welding rod being run against the paver from the smokebox side. A "flue hole" was cut into a vertically mounted steel plate on the bench and our magnetic base drill was adapted to run a cutting tool to machine the hole, before and after a welding run had been applied. After some fine tuning by Ron Williams, this technique has worked a treat and provides a very easy and cheap way of reforming the holes.
- As well as the above hole repairs, two tube holes in the firebox tubeplate and ten in the smokebox tubeplate have ovalities exceeding 0.040" - one at 0.086". The higher the ovality, the more difficult it becomes to expand a round tube into an oval hole using a circular expander. Previous experience in SR and elsewhere has shown the holes with ovalities over 0.040" can be leakers on the first (and subsequent!) hydros. The two firebox tube holes have already been bored using the magnetic base drill set up as a borer.
- All the holes (22 flue, 10 tube) to be welded have been "centred" and "circled" so that when the cutting tool is set up to machine the welded holes, the scribed circle, based on plotting the hole centre, around each hole is used to centralise the cutting tool. Don't need a newly machined hole to be offset from its centre.
- Calculations and measurements showed that most tubeplate minimum ligament widths satisfied AS 1210 except for a few around the flue holes in the smokebox tubeplate. However the repair work on those holes effectively makes them smaller thus increasing the ligaments to acceptable widths.
- The question of swaging and belling of the new flues and tubes as required is being actively pursued but not with a lot of luck at this stage. Ideally it would be nice if this work could be done in Adelaide but a number of firms we have approached either are not set up to do it or don't want to do it. There are firms capable of the work interstate but it will be a costly exercise to transport flues and tubes across the border and back. The firebox end of the flues and tubes need to be swaged down in diameter while the smokebox end of the tubes need to be belled up in diameter - all to non standard sizes because of the necessity to have all flues and tubes as close as possible to their respective existing hole diameters.
- A 16 page report has been drafted covering all aspects so far; what we found, what was considered to be why, options of replacement or repair, loads of calculations as required by AS 1210, final repair proposals and why, and the boiler inspector's endorsement of everything being proposed.
- So far so good for the existing tubeplates but the writing is certainly on the wall that both plates will more than likely need to be renewed at the next major internal inspection, maybe 10 years time.
Updated to 7th February 2009
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