Boiler shutdown, waterwall burner tube replacement.

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I have a pretty decent haul from this outage (around 100 good pics I can tell a story with) and I'm not sure weather to just update this thread as I have to time to upload and explain what's happening, or if I should make a new thread for each "parts", let me know what's easiest for everyone.So this is a 375 Megawatt Brown coal fired boiler, this year I'm on the burner crew, replacing water wall offset tubes that go around the coal burners which create opening into the boiler for the coal to be blown into.The way this work's is first the boiler get's a wash down to remove the bulk of the soot and clinker, then they build the internal boiler scaffold, then the burner's are sand blasted to remove scale and coal residue and MAG particle and thickness tested to find crack's and pitting deep enough to warrant tube replacement..

This is just the firebox scaffold, the floor of this is still 40 feet from the bottom of the boiler, where the flat bottom deck of this is, is where the wall starts to slope inwards to a point to collect the ash.

There are 24 burners per boiler, 2 burner units per wall, each unit consists of a lower, upper and inert burner, the inert burner burns the volatile compounds that offgas from the coal as it dry's in the drying shaft's and each burner has a floor and a roof, making 48 work fronts on this job, some requiring a lot of tubes to be replaced, some only needing a few.. this is my first job, one of the lower burner floor's and only need 3 partial tube replacements so is a good candidate for a step by step.Starting the the workfront after inspection, tubes to be cut out are marked with red paid on the cut lines, minor defect's for repair (pad welding) are marked in red pencil

Old tubes are cut out with a 120 amp hypertherm plasma, way overkill for what the job is, but it does make it nice a fast, and the plasma will eat the dirt and soot caked in behind the tubes, where as an oxy will redirect the oxygen flow which can cause damage to adjacent tubes that are to be left.



once the tubes are cut out an Escotool Millhog Mongoose Air powered tube beveling machine is used to prep the tubes.


The tube is slowly taken down to size, since the original boiler tubes were sand bent, and the new tubes are mandrel bent the bend radius is often different, so it's a case of taking it nice a slow to get the new tubes to fit.My offsider and I both like a nice tight gap, especially because the bottom of the root run is easiest to put in vertical down with the TIG running nice and hot, around 160-170 amps.

vertical down root from the inside.


Reply:And from the outside.

I'm on the outside for this one, so nice and tight.

Caps finished.


Once the new tubes were put in we had to re weld the fin bar back together from the inside, on this burner we used 1/8th ESAB OK 48.00 7018 rods.


but we for some reason are also using .035 E71T-11 self shield flux core with C25 gas, the question was asked and we got told to just use it so don't shoot the messenger, but it does come up pretty nice.Flat with the self shield.

And a vertical


Reply:Another thread makes a guy tired to look at,,, hawww.urkafarms.com
Reply:Wow! I've never seen the inside of a boiler like that.  I think that a visit there should prepare you for work as an astronaut!
Reply:Ttoks, totally amazing!  Thank you for the pics and explanations..   Amazing skill!Lincoln Precision TIG 185.Flex-Loc 150 torch.Super-Flex hose.Lincoln MIG 180.Victor Oxy/Act torch set.DeWalt Bandsaw with SWAG stand
Reply:I can’t do that well sitting in a nice chair and lighted shop.  Excellent workmanship!Miller 350 DynastyMiller TrailblazerMiller 625 Plasma Lincoln Power MIGVictor oxy/acetyleneHyperthem 85
Reply:I've welded in some tight places and used a stinger on a 4ft. broom handle but after seeing what ttoks does, I'm not worthy. Outstanding skills!!!
Reply:Love your threads ttoks,  the self shield wire with mixed gas is an interesting  combination,  agreed it does lay down nicely!
Reply:Outstanding work you do Sir!!!!!!Weld like a "WELDOR", not a wel-"DERR"

MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:We are running UNIMIG/Razor/Jasic (depending on where in the world you are) 200 amp DC high frequency start TIG welders, last outage we used Lincoln 170 TPX machines, but they're had to much trouble running with long extensions leads with voltage fluxuations, we couldn't weld for hours at a time sometimes, the Unimig machines are a really nice machine, nice adjustment range on the arc force and hot start for stick and a good strong HF start on TIG with a smooth stable arc even with the wide input voltage fluxuations we get.

.For the MIGs we're running Kemppi Minarcmig EVO 200's, they're expensive for a 200 amp MIG that only does MIG at around 2.5k, but these things are tough as all hell and reliable, these machines just burn wire day in, day out and don't seem to break.


So a lot of the tubes to be replaced have they're cut line right where there's an 18 inch universal beam buck stay outside the boiler that holds the tubes where they're meant to stay while the boiler is running which means we only have access from one side of the tube, that means we have to do window welds.first run a 7" grinder through the cut line from inside the boiler, these Metabo 7 inch grinder's are great as they have excellent depth of cut line a 9 inch without the huge size and weight, they're alot safer to use in awkward positions.

on the bottom cut line we have access to both sized of the tubes, so cut as far through as we can with the grinder without nicking the adjacent tubes, then nip the last bit with an OXY

once the bottom is cut all the way through we slide a piece of sheet metal in the cut to prevent slag/dross from falling down the tubes, then cut out the front of the tubes on the top cut line to get access to the back of the tube, and nip the last bit at the back with an oxy where the grinder doesn't quite reach.

Then you prep the tubes with an internal bevel with the Mill hog, mark the center of the tubes and put a center pop 8mm (3/8") up from the prep to mark the top of the window, and use a straight oxy hed with a circle cutter to cut the window from the tube, the window are oval shaped so the center pop is off center from the weld line and then you just take the last bit out on the sides with a grinder to get a nice smooth half oval on each tube.


Then clean up the slag and remove scale from inside the tube trying to get to nice shiny metal without thinning out the tubes to much.

Then you do the same process of slowly take the new tubes to length to make sure they fit nice without being short, internal prep, mark and cut the windows making sure the window is oriented correctly with the cutout in the old tube, and tacked in ready to weld the back.


Reply:my offsider welding a window root.

and a look at it.

and the outside of the root.

On the root run of the window you start in the center and weld out towards the tangents, for the fill and internal cap you go the other way, start at the tangents and weld in towards the center, at least that's how I find it easiest to weld them

Stringer caps, they like a 3/8" max bead width, so these pretty much all end up with stringer caps.

Then the saddle is installed, it usually takes a bit of grinding to get a nice even gap all the way around as the window is full penetration as well, a nice fit makes life easy, before welding the saddle in the back of the root is x-rayed and mag particle tested, however the saddles themselves can't be tested, from what I understand it's near on impossible to determine if there are defects in the shot due to angles, so we usually have an inspector supervise welding thesaddles, unless they trust the welder.

Then once all of the tubes are installed, new fin bar has to be fabricated and installed, it takes a fair bit of pattern making, heat's and bending to get the fin to fit nicely, and then there's a good few shifts just in welding it out on the inside, later on we will go outsde the boiler and weld it outside as well.