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Retubing small fire tube boiler

Lester Bowman

Hot Rolled
Joined
Apr 9, 2011
Location
Modesto california USA
This is a little boiler I picked up intending to use it with the "Virginia City" steam engine... http://www.practicalmachinist.com/vb/antique-machinery-and-history/post-civil-war-small-box-bed-steam-engine-320612/

It is very small..12" diameter with an overall fire tube length of aprox 24" ( from tube sheet to tube sheet ) I have removed the leaking flues and the rest of the boiler looks pretty good although as an added precaution I am having it tested ultrasonically.

Please..I am aware of safety issues here and understand both the shell and tube plates need careful testing to determine if this boiler can be repaired safely.

I post the only stamping in the shell and am curious what it means. Can anyone dissect the information explaining it to me? I will be operating this boiler no higher than 30 psi. Thank you!

Also I need at least nine 2" od boiler tubes 24" long. Wall thickness is .125 . Could anyone suggest a source in California for these tubes? I thought perhaps someone here may have some "cut offs" that could be trimmed and used ?

The tube plates have holes 2.062 in diameter. So the two inch tubes must have been expanded enough to fit these existing holes. I also know the ends of the new tubes need annealing. So between the O.D of the tubes and the I.D of the tube plate holes is .062 clearance. Does this sound right?

Also does anyone have a 2" tube roller I can buy beg or borrow? Thank you :)
 

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I've no wish to be picky or a smartass, but before I laid out for retubing that, in fact before anything I'd have it looked at by a boiler inspector.

If the shell is okay? .he will be able to guide you on tube sizes and specs.

PS, in the UK ''WP'' stands for working pressure which in your case I only assume to be 100PSI

The TS 55,000 stands for the tensile strength of the material again in you case I assume it to be PSI

The other marks could mean anything.
 
We've discussed old boilers and old pressure vessels many times on this 'board. A small vertical fire tube boiler is simply an old boiler with an unknown history at this point. The UT will tell you a lot. Before you get any further with that boiler, I would check your local and state boiler codes and regulations as to whether you will be allowed to put that boiler into steam service. Granted, it is a historic old boiler. However, it does have a lapped longitudinal seam on the barrel. Lapped seams are prohibited in most states. The lapped seam raises a red flag for me. Before you invest time and money into the boiler, be sure that- assuming it were otherwise sound- it could legally be put into steam service with that lapped seam.

If you find there is no code or legal issues with the lap seam, then the next step is to do a thorough visual inspection on the boiler. With today's fiberoptics and miniature video cameras, a person can get a look inside of parts of boilers that previously required cutting an inspection opening. Your boiler is simple enough so that by looking through the tube holes, you should be able to see most all of the internal surfaces. If nothing jumps out at you (such as an area that is visibly wasted or thinned, or cracks in the flue sheets or excessivley wasted rivet heads), then the UT is done. Once you have the UT in hand, it is a matter of interpreting it. The "beam" from a UT transducer can often be reflected back when it finds "laminations" (slag inclusions in the steel plate, there since the plate was rolled at the mill). A lamination will give a false reading, showing a much thinner spot. Those laminations usually never hurt anything, and prior to UT, no one knew they were there. Interpreting the UT so as to recognize anomalies vs legitimately thin or pitted areas takes a little doing.

Once you have the UT in hand, and determine the thinnest areas of each of the boiler sheets, you can then run a set of calculations on the boiler. Based on as-found dimensions, including riveted seam layouts, the "minimum thickness required" for a given maximum allowable working pressure is determined. When you have an old boiler such as this one, I would simply take the thinnest readings on each sheet of the boiler and run a calculation to determine what the maximum allowable working pressure is. Use the tensile stress value stamped on the boiler, and use a minimum factor of safety = 5.


I would suggest getting in touch with the shop at the California State RR Museum in Sacramento. I had a contact there name Dennis Daugherty, for whom I did some engineering relating to various steam locomotives. They have a good sized back shop. 2" diameter fire tubes were commonly used in locomotive boilers. Possibly, they will have some extra 2" tube material and be able to loan/rent you a tube roller. Another place would be the Big Trees and Roaring Camp RR in Santa Cruz, or the Skunk Train up in Fort Bragg. I did some engineering for the Skunk Train years ago as they had a crack in the boiler backhead on a Baldwin steam locomotive. I designed the repair and submitted the Form 19 (Alteration and Repair Report) to the Federal RR Administration. Any of these historic railroads should have tube rollers for 2" tubes and possibly some extra or cutoff 2" tube material.

Another thought: on firetube boilers with hard firing such as on locomotives and some Scotch Marine Boilers, it was common practice to "bead" the ends of the firetubes at the entry of firebox end. Beading consisted of flaring the tube ends and then running around them with a "bootleg" shaped tool in a riveting or chipping gun. The bootleg tool doubled over the tube wall, kind of like rolling up the cuffs on the legs of jeans. The doubled-over tube wall was driven down so it met the tube sheet. A seal weld was then run around the doubled over tube end, and a final rolling was done to insure no leakage. The seal weld was to prevent hot gasses and cinders from cutting or eroding the end of the tube where it projected from the tube sheet, and the doubled-over end and slight flare made a much smoother entry for hot flue gas which often contained fine cinders (or sand if on an oil fired boiler, where "sanding out the tubes" was often done to get rid of carbon soot. For your little boiler, my own druthers on this are to roll in the tubes, and try to get a roller which also flares the ends. Just that much more insurance that the tubes are well set in the sheets, and a much better entry for the flue gasses. Flaring up at the smokebox end also makes sliding in the turbulators that much easier.

Word to the wise: You do not know how many times that boiler has had new fire tubes rolled in, or how many times the fire tubes had to be re-rolled to deal with leaks. The result is the tube holes in the tube sheets can often be considerably larger than original diameter. When this happens, rolling in the new tubes can result in excessive rolling to expand them to meet the enlarged hole in the sheet, with some localized thinning of the tube walls and possible cracking or splitting. What the boilermakers did in this sort of situation was to use copper ferrules on the tubes. The ferrules took up for the oversized holes in the sheet. The other plus side to using ferrules is they are a bit more forgiving as far as keeping the tubes leak-tight in the sheets. Some firetube boilers were ferruled from the git-go, with one sheet figured as the "fixed" sheet (usually the sheet at the smokebox end of the barrel), and the other sheet (usually the firebox tube sheet) as being the more likely sheet to flex a bit. The fire tubes were ferruled in the firebox tube sheet from the git go on a lot of locomotive boilers.

Your boiler has no wet leg nor submerged upper tube sheet. It is as simple a boiler as it can possibly be. My own concern is the fact that the longitudinal seam is made as a lap seam rather than a butt joint. Lap joints are prohibited in most states, even on historic boilers. The reason for this is the lap seam puts the rivets in the seam into a combined loading condition: shear plus bending. Inspecting that seam is a whole other matter. UT will tell you how much of the boiler barrel sheet is left. Sounding each rivet with a hammer and inspecting rivet heads inside the boiler for wastage (reduction in material) is a start. The seam is a very high stress area, and you have a small old boiler with an unknown history. Whether water treatment was ever used is anyone's guess, so I'd be looking for signs of oxygen pitting and loss of material down where the bottom flue sheet meets the barrel from corrosion/mud accumulation.

The type of boiler you have was often used in stores which did steam pressing of clothing, usually in conjunction with tailoring and dry cleaning. These were basic vertical firetube boilers with no wet leg nor submerged upper tube sheet. Steam was a once-through proposition as it was used to run/heat a clothes pressing machine or used to steam the clothes to take out wrinkles. Another place where this sort of small boiler might have seen use would have been in a small creamery.

The ultrasonic thickness testing is a start. A visual inspection made by a competent person such as a boilermaker used to working on riveted firetube boilers is a must.

The pipe plug in the middle of the tube sheet raises another flag. If that plug is in the lower (firebox) tube sheet, it might be plugging a hole formerly used for a fusible plug. A vertical firetube boiler of this type usually came with a "dry" firebox/base. Tailors and cleaners used these boilers in storefront type operations, and usually fired them on gas from the mains (if in a city or town with gas supply). If the boiler was fired with coal, then a base with firebrick lining, grates and ashpit was used. Up on top, there was usually a conical "smoke hood", which fitted onto the barrel and reduced to whatever size smoke pipe was used. On this type of boiler, the hot flue gasses tend to rush right through the firetubes and a lot of heat is lost up the stack. To address this and try to capture more of the heat from the burning fuel, "turbulators" were often used on this type of boiler. These are strips of thin-gauge sheet steel, just wide enough to slide into the fire tubes, and cold twisted. The turbulators are inserted in each firetube from the top flue sheet, and have tabs to keep them from falling thru the tubes and into the firebox. Turbulators are easily made, and being thin sheet steel, are probably long done to rust or removed and thrown in the scrap when the boiler was removed from its installation.

My guess is this boiler was probably like the proverbial red-headed step child. It was in some installation where no one was a real stationary or marine engineer, and they just fired it to make steam for some process or equipment (such as a clothing press). It got minimal maintenance, likely little or no water treatment, and may have been steamed at some much lower pressure than the original MAWP (maximum allowable working pressure) of 100 psig.

You have to start at "square one" with this boiler, and you will need to determine if you will be allowed to steam a lapped-seam boiler. If you clear that hurdle, then you move to doing a thorough inspection, UT, and full set of calculations before you start chasing down new tubes and a tube roller.
 
1/8 plus/minus wall tube would put this as an No. 11 gauge tube - a little unusual.

More usual in this diameter (96.2 percent of firetube boilers) is No. 13 gauge (0.095 wall)

Check out Boiler Tube Expanders - Reference Chart - Tube Wall Thickness of Wall in Birmingham Wire Gauge

More to see on tube expanders and expanding at the site.

And for tubes, this is what you want and while I haven't done business with them they could set you up.

http://www.atube.com/anderson_tube_inventory.pdf

I have a 2" "flare" type tube roller aimed at a 13ga tube. (most are) You can borrow it for the shipping - but your needs (and your hobby) might be better served with watching Ebay and picking up a used roller for (usually) less than $100. I paid $75 with shipping for mine. New, even on Ebay is still pretty pricey - but do a search on "most recent first" and do it day by day and you may find a used tube roller.

And to be truthful - companies like TC Wilson get BIG BUCKS for tube rollers which doubtless are made in China, and imported to this country "on demand" (usual delivery from TC Wilson is 6 weeks - a clue to where their roller/expanders are made.) And this kind of frosts the heck out of me. BIG TIME markup simply because you're buying an expander from an American name?

Sorry - pet peeve.

While you're at it, look for the beading tool. Commonly called in the day a "boilermakers thumb" (out of emulation of the shape of the hand with the thumb outstretched,) the beading tool can be either hand driven or (better) sized to fit a common air gun (IIRC, the usual muffer air hammer socket is 0.490 - or something like that.) I have a small traditional D handled air chipping hammer - Chicago Pneumatic or some other lesser brand (Ingersoll Rand is STILL the name to look for) but have yet to find a thumb to fit. Low on my list I guess.

tube-installation-tool-beading-1459128.jpg


images


Heh - on the other board I mentioned Joe Mastroberti of Worcester, MA who re-tubed my VFT. Joe was a school teacher in real life - but re-tubed boilers on weekends for spare cash - and continuing the family name and business.

When it came time to put the beads on the tubes in the firebox Joe got positioned on his side with the boiler laid down and stuck both head and shoulders in the firebox - about 20" inside diameter - the airgun right at his head. BAM-BAM-BAM-BAM-BAM one tube after another as he turned "circles" around the beads on those tubes. And NO earplugs or earmuffs.

After he had finished I inquired "Joe - Can you hear me now?"

"Barely" he said.

I truly wondered how he could be a teacher the rest of the week after the auditory assault he endured on the weekends.

Alas, I see from a 1999 obituary that Joe Mastroberti is now passed (age 66 then) and was listed as "Science Teacher" http://www.capecodtimes.com/article/19991112/Obits/311129973 2/3rds way down the page.

VERY generous with sharing what he knew of firetube boilers. One could tell he enjoyed the lesson as much as the student. I learned at the knee of a master.

And one of those people you remember.

Joe in NH
 
Re Joe Michaels #3

A positive treatise on the subject, from a man who has forgotten more about steam boilers than I will ever know and can put in to words far better than I.

Thank you Joe, :)
 
I think Wicksteed Eng in Kettering still make tube ex panders. Amen to all the good advice above. Here's a tale that gives me a shiver to this day,I think you'll probably agree! I grew up with Burrell 3555 "The Busy Bee",it was sold out of the family after over fifty years after Fathers passing. Father religiously kept it in ticket,steam test annually. Lagging off every ten yrs and hydraulic test to 1 1/2X working pressure plus 50psi. Here's the scary bit...about Nov 1971 we had a very pleasant evening outing to a pub in St Neots market square...plenty of beers throngs of people keeping warm by the engine,perfect evening. When the pub was closing up(as it had to by law in those days)Father noticed a slow but regular drip coming out from the lagging near the smoke box. We steamed back next morning(!!!)and removed the lagging. When cooled right down,Father probed a damp patch on the lap joint at bottom of boiler barrel and stuck a screwdriver right through! The previous evening the engine was in the middle of a crowd with 200 on the clock!
 
I've got a book Modern Steam boilers their construction care and operation with questions and answers
Calvin F. Swingle published by frederick J Drake and co Chicago copyrighted 1905 and 1912
I saved it as a kid when cleaning a great uncle's house. Whole sections on how to rivet and how to build the brick fireboxes for max efficiency.
Find a copy if you can its a great read.

Here is a free on line copy!
Steam boilers, their construction, care and operation, with ... - Full View | HathiTrust Digital Library | HathiTrust Digital Library
 
I think Wicksteed Eng in Kettering still make tube ex panders. Amen to all the good advice above. Here's a tale that gives me a shiver to this day,I think you'll probably agree! I grew up with Burrell 3555 "The Busy Bee",it was sold out of the family after over fifty years after Fathers passing. Father religiously kept it in ticket,steam test annually. Lagging off every ten yrs and hydraulic test to 1 1/2X working pressure plus 50psi. Here's the scary bit...about Nov 1971 we had a very pleasant evening outing to a pub in St Neots market square...plenty of beers throngs of people keeping warm by the engine,perfect evening. When the pub was closing up(as it had to by law in those days)Father noticed a slow but regular drip coming out from the lagging near the smoke box. We steamed back next morning(!!!)and removed the lagging. When cooled right down,Father probed a damp patch on the lap joint at bottom of boiler barrel and stuck a screwdriver right through! The previous evening the engine was in the middle of a crowd with 200 on the clock!

Nasty :eek: ...reminds me of one day public running Sunday afternoon at The Norwich Model Engineers track in Eaton Park, ........one of the clubs own locos (5'' gauge Double Dyak) in the hands of a know it all, .......who hadn't kept the boiler water level up, just as well it was still on the steaming bay and well away from the public! ......................................................................................................................................................................................................................................................................................................................................Loh and behold, it came to pass that said loco blew the crown sheet fusible plug, ...........and even a boiler with 1/2 gallon of water in goes with a fair old whoosh :eek: ..............said know it all nearly jumped out of his skin, then walking ''very awkwardly'' made his excuses and left for home ;) ............................................. he'd had an involuntary movement :D )
 
Bless his dear departed soul, my Dad came home one day to find me building steam in a hot water heater tank that I had nabbed from the dump. I had a broom handle in the outlet, so when the steam made up, it would expel the handle a fair distance up the hill. Dad, who was a steam engineer, nearly swallowed his cigar when he saw it vent. I was only 10 or 11 years old, so when he put out the fire, he very calmly explained to me how dangerous my "boiler" was. Regards, Clark
 
Bless his dear departed soul, my Dad came home one day to find me building steam in a hot water heater tank that I had nabbed from the dump. I had a broom handle in the outlet, so when the steam made up, it would expel the handle a fair distance up the hill. Dad, who was a steam engineer, nearly swallowed his cigar when he saw it vent. I was only 10 or 11 years old, so when he put out the fire, he very calmly explained to me how dangerous my "boiler" was. Regards, Clark

My Dad was a steam engineer too. I have his Massachusetts 1st Class Operator's License (No. 623) on my wall - next to my own. (No. 1233)

He made a similar discovery on me when I was about 10 years old - and mine a boiler made up of wrot iron pipe fittings and nipples.

"But Dad, even Babcock & Wilcox tells of the safety advantages of water-tube boilers in their book" (my copy from 1922!)

"No matter" he says. "You're not a steam engineer - heck you're not even an engineer."

And the last cutting blow - "You take that BOMB apart this instant. Yes, did you hear me - a BOMB."

I usually paid attention when Dad said anything a SECOND time.

Joe in NH
 
I recommend "historic boiler explosions"by Alan McEwen,Sledgehammer Press. Mainly boilers in textile mills . Lester,I have a similar size engine to yours made by Tidman of Norwich-I think I might just run it on air but it's well known a steam engine runs better on steam! Limy,I imagine that loco owner was given a wigging by his club later on!
 
Joe Michaels..thank you VERY much for the information you have provided and the suggestions you have made. I appreciate all this very much. Also profuse thanks to Joe K who not only approached it from a similar safety perspective you both share...but also from a historical stand point of boiler repair and testing procedures. Joe K. also provided a copy of the 2010 Boiler Code which may be found here.. https://law.resource.org/pub/us/code/ibr/asme.bpvc.i.2010.pdf https://law.resource.org/pub/us/code/ibr/asme.bpvc.i.2010.pdf

I spent a good part of yesterday wire brushing the outer shell trying to find any additional stamping,a date or manufacturer to no avail. I also removed all the frozen plugs and fittings remaining in the shell then chasing up their threads. These all seem pretty good although the fittings were pretty corroded inside where they met the steam/water.

Some of the fittings are so close to the bottom tube sheet that I can reach in and feel where the scale has filled the outer edge of the bottom tube sheet. I'll be removing this today using gentle "pecks" with a long small diameter pinch bar. It will fit through the holes in the upper tube sheet down to the inner edge of the bottom tube sheet. This will allow me to gently chip away the shell.

Next I plan to "brush blast" the inside rather than just blast the hell out of it leaving as clean a shell as I can. Oh! Yesterday I "rang" tested the rivets inside and out using about a one pound ball peen. Everyone sounded crisp and tight transmitting the blows to the shell. I tested them individually from the outside. I went back and checked the inside upsets. Then I checked each one from outside head to inner upset. They all rung consistently sounding the same. Is this the correct way to "sound" rivets?

So after the sandblast I will ultrasound the boiler. Holidays have been here and none of the tank builders seem to be open. I'll approach that after the first of the year. Also I have a camera at work which can reach down far enough to view the attachment of the tube sheets.

So all these things will take place. Thank you all very much not only for safety procedures but for the proper steps in repair. Ok..out to chipping away scale :)
 
So all these things will take place. Thank you all very much not only for safety procedures but for the proper steps in repair. Ok..out to chipping away scale :)

PSSSS wanna make that easy on yourself and not damage the boiler? ......it's only a littlun so boil it in vinegar - ordinary dirt cheap vinegar at near boiling point will eat away the scale nicely, and without attacking the shell.

FWIW I use it for cleaning the fragile steam injector nozzles on my 5'' gauge steam loco, ........no damage and perfectly clean.

Obviously best done outside a camping stove or Barbie (it stinks) but it beats scraping and chipping any day.
 
When you blast the interior, hit the lap seam "obliquely" and in the direction of lap. (think rain falling off the roof shingles.) Or perhaps "head on" such that sand/abrasive won't find its way between the lap.

It is possible to drive particles of sand between the laps and "open" what might otherwise be a "caulked" joint.

Caulking is normally done using an intentionally "dull" cold chisel, and creating an indent in the outer plate which tends to "close" the any gap at the seam if done gently. If caulked too much, it is possible to drive the plates apart and create a worse leak than you might have. And NEVER caulk under pressure - that "eccentric" loading of the lap seam mentioned by Joe M. See Sumatechnology: RIVETS AND RIVETED JOINTS

Well, given the small ID of this boiler shell, one imagines the inside NOT caulked - hard to swing a hammer. But the same precaution applies regarding grit between the plates.

Given that you have a lap joint which was probably tight - and I expect the majority of this seal a "rust joint" - you don't want to do anything which might upset this rust - like boiling in vinegar (sorry LS - vinegar is a "penetrant") or doing the electrolytic method of cleaning. (which came to mind an an alternate to vinegar - but a second thought rejected.)

Joe in NH
 
Lester:

I am glad you appreciated what I had to say. You are going about the matter of evaluating and getting the little boiler ready for steam service in the right way.

The location on the boiler where I would imagine mud (solids that settle out of the boiler water, whether in the form of silt/clay and similar or in the form of minerals precipitated out by boiler water treatment) would likely be along the circumference where the bottom tube sheet meets the barrel. The tube sheets are flanged, and the flange is turned down (outside the water/steam space) to allow riveting to be done.
The flanged sheets have what is known as a "knuckle" or radius'd corner. As a result, there is a "valley" from where the knuckle radius begins on the sheet, to where it comes tangent to the barrel. This valley is a likely place for mud and scale to accumulate. Boiler blowdowns and boiler washouts help, but in actuality, mud and scale will collect and remain in that "valley". The result is often localized heavy wastage of the sheets (any piece of plate steel going into the making of a firetube boiler is referred to as a "sheet", even if it is anything but flat).

The UT will be of some help here, and the fact the boiler appears small enough to maybe get a finger or two through a tube hole to given an educated feel may also help. Grinding a point on a piece of bronze brazing rod and bending it as needed and dragging it in this area like a "cat's whisker" may also give you a feel for whether there is localized heavy wastage. The mini-cams and fiberoptic snakes used by plumbers to inspect piping internally are a real God-send for these kinds of inspections. The boiler inspectors and boilermakers used to drill/tap inspection/gauging holes in the boiler sheets where it was other wise impossible to gauge the sheet thickness. Starrett made a boiler inspector's micrometer with a hooked/detachable frame. This was a rod bent like a candy cane. It would fit into about a 1/4" or 3/8" hole drilled in a boiler sheet,so that the tip of the return end of the candy cane formed the anvil of the mike. Once snaked into place thru the hole, the shank of the candy cane was projecting out of the boiler sheet. The micrometer head was slid onto the shank of the candy cane and reconnected to it using an index notch or groove in the shank. The inspector or boilermaker could then mike the sheet thickness. Afterwards, the hole was tapped and plugged. On the mudlegs of some locomotive boiler, where it was otherwise impossible to get a real good look-see or sense of the condition, I would ask that an inspection "window" be cut, extending down to the "mud ring" or foundation ring. This would give a representative sample of whether heavy localized wastage had occurred where the inner (firebox side) and outer (wrapper) sheets met the foundation ring. This is a square corner, and we'd often find heavy localized wastage, despite getting good UT readings for thickness immediately near that inside corner. Despite blowdown valve connections and washout plugs in the vicinity of this corner, it seemed like a prime place for wastage to occur. On your boiler, you have the advantage of almost full visibility and with some inventiveness such as using a hooked "cat whisker" to feel the surfaces, you should be able to make a determination.

I'd also look along the inside surfaces of the barrel sheet where the lapped seam is (at the toe of the seam) for localized wastage, and check the rivet heads for pitting or grooving.

What the little boiler has going for it is its simplicity, and the fact that it may never have been steamed hard (fired to get maximum pressure and steam flow) in working service. In a place like a cleaner/tailor shop or similar, the boiler was kept in steam to run a clothes press on an occasional basis, rather than being steamed hard to keep an engine at speed/load. My guess is this boiler came out of a place like a tailor shop or possibly a place where small amounts of steam were needed for things like sterilization or pasteurization.

Keep us informed as to your inspection progress. I am happy to run a set of numbers for you once you have dimensions and UT readings. The rivet sounding sound OK to me. What the next step in that regard is, is to make some kind of template or get the dimensions of the rivet heads. Hopefully, the same shape/size head was used inside and outside the boiler seams. The reason for this measuring and sketching of the heads is to determine the shank diameters. We then use the shank diameter plus an allowance for "swell" or upsetting in the rivet holes in calculating the efficiency and strength of each seam. By looking in old texts, I am usually able to determine the nominal shank diameter of rivets from the "factory made" head shape/dimensions.

I would not be surprised if the boiler were steamable at some reduced working pressure, based on minimum measured thicknesses and a factor of safety of 5.0. PM me if I can be of help.

Best regards for the New Year-
Joe Michaels
 
Given that you have a lap joint which was probably tight - and I expect the majority of this seal a "rust joint" - you don't want to do anything which might upset this rust - like boiling in vinegar (sorry LS - vinegar is a "penetrant") or doing the electrolytic method of cleaning. (which came to mind an an alternate to vinegar - but a second thought rejected.)

Joe in NH

Good point Joe, I shall go and stand in the corner.
 
Joe..Thank you again for your observations and excellent explanation of scale buildup and where to look. You wrote.."The flanged sheets have what is known as a "knuckle" or radius'd corner. As a result, there is a "valley" from where the knuckle radius begins on the sheet, to where it comes tangent to the barrel. This valley is a likely place for mud and scale to accumulate. Boiler blowdowns and boiler washouts help, but in actuality, mud and scale will collect and remain in that "valley". The result is often localized heavy wastage of the sheets (any piece of plate steel going into the making of a firetube boiler is referred to as a "sheet", even if it is anything but flat).

This is exactly what has occurred in this boiler. This morning I removed the 3/4" npt plugs in the tube plates leaving the boiler completely stripped. I took a long 5/8" octagon pinch bar which my Great Grandfather made and because it was a somewhat blunt chisel shaped on the end, I used it to remove the buildup you spoke of. I didn't hammer or pound. I simply gently chipped away at it. When I started it had a full radius of scale and rust completely filling this area. When I finished I could see the radius of the flanged tube sheets meeting the outer shell.

So a bit of sandblasting using Joe K's method is next in order. I called a Tank fabricator who was recommended to me ( close by ) and spoke with their Foreman. They have a certified Ultrasound probe and will do the testing for me. He said they can check the thickness of the plates but wherever there is a rust void..the measuring stops. It won't measure the full thickness of two plates riveted together if there is a rust layer between them.

Also he said his ASME inspector who inspects their tanks is also a volunteer at Railtown which is a working steam railroad with several steam locomotives. So he wants this Inspector to take a look at this little boiler being he is involved in servicing and maintaining the steam equipment at Railtown. Terrific!

Joe..can you work with a set of thicknesses from the above description of their testing? I know you'll need the rivet head dimensions as well. If this boiler gets that far I would deeply appreciate you running the calculations for me. Thank you!

I laughed too at the "cat whisker" comment :) Not too many people will see the analogy but I've built crystal radios which used Galena. Touching about with the "cat whisker" for the sweet spot was always "iffy".

Thank you Joe and to everyone who has responded. I'll certainly update the findings but it will be a couple of weeks before this happens. In the meantime I'll continue a gentle cleanup.
 
Hello Lester:

Yes, I can work from UT readings, but will also need a set of dimensioned sketches of the boiler. Basic sketches, nothing fancy, or even a set of as-measured dimensions will work.

What we'll do is to take the thinnest UT readings on each sheet of the boiler and calculate maximum allowable working pressure (MAWP). The sheet with the lowest MAWP determines MAWP for the whole boiler.

The barrel, having a lapped seam, is an easy proposition to run the numbers on. The tube sheets' weakest area is what are known as the "ligaments", the web of steel between adjacent tube holes. Between the effects of cold-working from rolling in of tubes and thermal cycling, the ligaments can develop cracks. The tube sheets, having the flanged circumference riveted to the barrel, are quite stiff at the circumference. Some flexure of the firebox tube sheet in the area of the ligaments is expectable, so you may find some rippling of the firebox end tube sheet. The other flexure point is at the "tangent circle" where the flat portion of the tubesheet meets the knuckle. I've seen a few firebox end flue sheets on locomotive boilers with cracks in this area.

I have this somewhat insane habit of "crawling inside the boiler" I am evaluating, and putting my mind into the various sheets, imagining the forces acting on the sheets and the developed stresses. Flue sheets are an interesting proposition, as the tubes are not so "innocent" in the matter. The tubes are rolled into the sheets, and if this is done right, are essentially locked into the sheets. However, a firetube has hot flue gasses passing through it, and has a temperature gradient over its length. The firetubes tend to want to expand lengthwise, a bit more than the barrel, so the flue sheet takes the brunt of this. The tubes probably buckle or spring slightly off straight since they are effectively restrained at each end by the tube sheets. What is more likely the case is the ligaments in the tube sheets and the area bounded by the tangent circle (where the curve of the knuckling begins) "oilcans" or springs out of flatness as it goes where the tubes take it.

I remember when I first started doing engineering work on locomotive boilers, I was taught a great deal by boilermakers and mechanics who had worked on repairs and restorations of steam locomotives. My previous experience had been running calculations on a brand-new Chinese steam locomotive boiler for an SY class locomotive (142, originally supplied to the Valley RR, now in service on the Susquehanna). When I got into my first evaluation of an existing boiler, it was a whole new world for me, and I began learning about the effects of steam service on a boiler. Things like a rippled tube sheet initially amazed me as I had thought that the tubes would have restrained the sheet. I am still learning, to say the least.

What I'd suggest is giving the tubesheets a further examination of the ligaments and tangent circle using dye penetrant. A good cleaning with a powered wire brush (aka "wire wheel"), and the a light polishing with some 100 grit discs would be my recommendation. This is to reduce the possibility of "false indications".

UT is a funny thing, not infallible or absolute by any means. I learned early on that the beam can be reflected off things that are not the outer surface of the sheet. I also learned that the beam generally stops and is reflected at any outer face of a sheet, including where a flange laps onto another sheet. On something like the flanged tube sheets, the boilermaker or NDT tech doing the testing should use a small transducer and try to UT through the knuckle.

Back in 2001, I took an ASME 5 day course in "Life Extension and Repair of Pressure Vessels". The presenter was the late Dr. Helmut Tielsch. Herr Doktor Tielsch was a hands-on practical engineer who made a habit of qualifying weld procedures by doing the actual welding himself. He also made a habit of going on the actual repair jobs and working with the crews to get things started or to handle any question or unexpected issues. In class, Herr Doktor Tielsch's teaching style was hardly the stuff of modern "kinder, gentler" ways. He hollered and cussed through most of the presentation as he'd get so worked up about how things could go wrong through stupidity or ignorance or people wanting to rely solely on modern non destructive testing. One tale he told concerned a boiler barrel on a 900 psig water tube boiler. At a five year inspection, the boiler drum was UT'd from the inside out. The UT showed a "dangerously thin" reading in just one single spot. Of course, the plant engineers and insurance company risk minimization engineers all jumped out of their shoes and decided this "problem" had to be addressed posthaste. Tielsch was consulted, and he advised that the "thin" UT reading was a false indication, likely a reflection off a lamination of slag that had been in the steel since it was rolled at the mill. Since the lamination laid along the rolling lines, Tielsch saw no problem and advised everyone to do nothing further. The young plant engineers and insurance guys thought otherwise and sic'd the boilermakers on it. The drum was made of 2 1/4% chrome-moly steel and probably a good 4" thick. Thielsch told them if they attempted to make any kind of repair, they would destroy the boiler drum. He was disregarded. The boilermakers excavated down into this "thin spot" or UT indication and found no cracks nor anything else remarkable. They then had to fill the canyon they had gouged and excavated in the boiler drum using welding. Easier said than done on chrome moly steel in that thickness. Preheat and post heat requirements, and getting boilermakers into a steam drum with a high preheat on the weld zone was only part of it. After doing the weld repair and post-weld heat treatment, the drum was returned to service. Each year after that, inspection of the weld repair would reveal a new crack. More excavation, preheat, welding, postheat and X raying followed. Another year and more cracks propigating. Eventually, the drum was scrapped and replaced. This cost somewhere in the 7 figure range. Herr Docktor Tielsch was almost frothing at the mouth and yelling as he got to this part of the story. He cussed out the people responsible and said that they did not know how to interpret UT testing and knew even less about what would constitute a potential failure point in that steam drum. He hollered that if the ----- so and so's had just left things alone, the boiler drum would have been fine.

So, interpreting UT readings and not hitting the panic button is a bit of an art. Getting a boiler ready for UT requires grinding or sanding small "dots" on the boiler sheets on a grid pattern. These dots are then tied in with a system of coordinates. Lines running Longitudinally on a barrel may be designated with letters (A, B, C, etc) and lines running circumferentially might be designated with numbers. The result is a set of small squares wrapping the barrel, and a grid drawn on the tube sheets, with additional locations on the knuckles and flanges. A sketch of the boiler with a "map" of these coordinates is drawn, and then the tabulated UT readings with coordinates is made up.

You sound like you struck gold with the shop and people you have found. I had a feeling your best bet would be to work through the local historic steam locomotive people as they are about the only people left who know anything about riveted firetube boilers.

I look forward to getting more information so I can run a set of numbers on this little boiler of yours.
 








 
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