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Thread: Power station outage part 2.

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    Power station outage part 2.

    In the last part I focused more on the nice high end stuff that everyone seems to want to get into doing, in this post I'll be focusing more so on the down and dirty part of working in a coal fired power station boiler, there's a bit of pipe and tube welding here, but mostly I want to emphasise that if you want to work in power stations and make that sweet shut down money, you have to be able and willing to do a lot more then just but a golden hand pipe welder.

    So in my last post I was welding the secondary super heater tubes back into the header, the less glorious side of that is that this boiler has to be as close to airtight as is possible, each tube had a sleeve that if a very close fit around it slid over it before the tube is welded in, then that boiler skin is to be welded around it, the disadvantage of welding the tubes is that every single weld is shot, the advantage is that except for the close out you have a bit of room to move, for the skin caseing there is no such advantage, all the tubes are in and there is VERY little room to get in to weld the skin on.

    This is the access to the secondary re-heater skin I worked on.



    This picture shows how the re-heater tubes go through the boiler wall, the wall tubes are offset to allow enough space for the re-heater tubes to pass through.



    This is the "skin" we have to weld on around the tubes to seal the boiler, the boiler has to be as sealed as possible as it is run at a slight vacuum to keep the fire contained inside the boiler, the intake air for the combustion is heated to over 400C (900ish F) so every bit of un heated air is a small efficiency.

    here you can see the scallop plate that are welded around the sleeves on the tubes.



    We are using Kempii minarc mig 200 evo MIG machines, they run off os 15 amp 240 volt power, here 240 volt is the standard wall outlet power, but most homes use 10 amp, 15 amp allows us to run small MIG machines like these.

    one of my co-workers in the position.



    and a view from where we are actually working, it is pretty tight, and there is only one access to this space in the middle of the boiler, so you have to army-crawl your way to the work front as well as bring in any tools, equipment or materials like this as well.



    The next job we were put on was the new platten header which I mentioned last post, I wasn't involved in the demolition of the old platten header and tubes, but I was involved in installing the new parts, this is one of two sections of the new platten header ready to be dogged into the header box.





    lifted into the header box with chain hoists, pullers and man power, each section is around 3 tons.



    and very close to being in position.



    The prep on the end of the header section, the header is around 50mm or 2 inches thick, there are 33 platten header elements with 9 tubes each, so that makes 594 welds to get the new platten header all hooked up to the platten elements, the tubes are 2 inch OD with a 5/8th inch wall thickness, material is B3 cro-moly.


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    Re: Power station outage part 2.

    tacked together with bullets.



    We got the root, hot pass and a few fill runs in on the first shift, the header is B3 creep resistant steel welded with ER90s-B3 TIG root and hot pass, and E90-B3 stick fill and cap using the "temper bead" technique, temper bead is the idea that each run tempers the previous one and has very strict heat input, weld size and interpass temps, we are allowed a maximum run width of 6mm (1/4 inch) with the stick fill.



    the night shift finished the weld, and I have to say they did a fine job of the cap, to bad it will be ground off and polished to a 600 grit finish to remove any stress risers which could cause cracks.



    and the space in the platten header all welded in ready for the new tubes, you can see here on the right where the tubes go through the wall into the boiler.



    And this is inside the boiler, the upper bank of tubes you see are the secondary super heater element you may have seen me welding in my last post (I was on the other side of the wall welding the new elements to the header) the lower bank you see are the platten tubes that need to come out.



    we're cutting them rough with the oxy, then cutting them to final length with the grinder and prepping with a pneumatic prep machine.



    and this where the elements go back through the boiler wall, the other tubes you see there are the hanger tubes, they hang from the top of the boiler and support all of the horizontal heating elements in the boiler from the roof down to the platten (the platten is the lowest bank of heating element, they are filled with water at around 400F (remembering the boiler runs at 2000 PSI, so the boiling point of water is much higher than at ambient pressure) the cool water (or hot depending on how you look at it) keeps the hanger tubes from overheating and turning to dust, there are also over 1000 crack repairs to be made on these hanger tubes, the hanger tubes are just carbon steel, exactly what grade of carbon steel I'm not sure, but we weld it with ER70S-4.



    however I was pulled off of the platten job, it is arguably the easiest job that we have going atm as it is welding new steel to new steel, or new steel to existing B3 which doesn't get affected by the heat and high carbon environment anywhere near as much as the carbon steel the wall tubes are made of.

    I was moved into the boiler furnace (or fire box) to do crack repair and tube replacement on the water wall tubes, mostly around the offset tubes of the oil and main coal burners, soot blower offset tubes and gas offtake offset tubes. these are all opening in the boilers for various uses, the oil burners are small burners used to start the boiler when it's cold, they slowly heat the rest of the boiler and once the boiler is pre heated are used to light the coal burners as the coal will not burn in a stable way if the boiler is cold, there are 16 of these, in this pick my off sider is pre heating an offset tubes for one of these oil burners for a crack repair.

    despite these tubes only being carbon steel rather than cro-moly, because they have been heat baked in a carbon rich environment for so long they've absorbed alot of carbon, and so can be very brittle and difficult to weld, everything must be pre heated to 150 degrees C (around 300 F) otherwise it will crack, and sometimes does anyway even with precautions, if the tube cracks after the first repair attempt it will be cut out and replaced.



    the internal boiler scaffold is impressive, it starts at the bottom of the hearth and extends all the way to the top of the furnace/bottom of the superheater elements, where i'm standing here is on the third floor of the boiler, around 10 meters (3ish feet) from the ground, under the deck I'm standing on here is where the boil tapers into the hearth, called the sloping wall, the furnace is 44 meters (144 feet) tall and the boiler totals 84 meters (or 275 feet) from basement to top.



    There is around 3'500 tonne of scaffolding just for the furnace scaffold, not including the safety deck's at the top of the furnace and above the primary super heater, the safety decks are completely sealed decks to prevent objects from falling which allows people to work up in the elements without risking the lives of the people working in the furnace, you can see the trusses that make up the backbone of the safety deck in this picture.


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    Re: Power station outage part 2.

    the soot blowers are scattered all over the boiler, in the furnace they are water blowers that blow boiler pressure hot water (2000 PSI and around 400 degrees F) to remove the accumulated coal ash that sticks to the boiler tubes, the ash is a problem as it is an insulating agent the prevents heat transfer to the tubes and so to the water or steam reducing the efficiency, further up in the steam heating elements superheated steam is used at water blowers would very quickly erode the superheater, re-heater and economizer tubes, there are around 120 soot blowers in total per boiler, the main coal burners are obviously where the coal comes into the boiler, there are 24 of these, 6 per side in two ros with 3 burners per row, pulverised and dried coal are mixed with the hot air I mentioned earlier and blown into the boiler by the coal pulverising mills (of which there are 8 per boiler, each mill feeds one row of 3 burners).

    This is one of the coal burners, the hot air is injected though the tubes you see that are in a cross pattern, these are made of MA253 stainless steel which is incredibly heat resistant, they sustain temperatures of 1100 degree's C (around 2050 F), the coal is blown in by the mills in opening around the air injection tubes.

    .

    The gas offtakes are connected directly to the coal mills via a 4 meter (16 feet) diameter pipe called the drying shafts, there are 8 of these per boiler (one for each coal mill), the mills create a vacuum and suck some of the hot 2000 degree C (3600ish F) oxygen deprived combustion gasses down the shaft and into the coal mills, the coal (which has been pre milled down to around the consistency of gravel) is fed into the drying shafts and the hot gas dries the coal (which has up to 50% moisture content) as it is fed into the mills, the mills pulverise the coal down to the consistency of baby powder before it is blown back up into the burners and introduced the the hot oxygen rich air from in air heaters.

    these are the bends that make up the gas offtake openings.



    our access to the top of the furnace scaffold is through one of the gas offtakes, it is a 40 meter ( 140ish foot) drop down to the ground under this small scaffold.



    We cut out the old tubes with a beast of a plasma, sometimes we use an oxy but the plasma is much faster, this is a more modern boiler design with a "fin tube" style of seal, where every tube is welded together to seal the boiler rather than having a sealed skin outside of the tubes, so there is fin plate between every tube that needs to be cut to remove each tube.



    once the tubes are cut out with the plasma we cut them again with a 5 inch angle grinder or barrel grinder to get rid of the dross/slag from the oxy or plasma, and then prep the tubes with an air powered mill hog.



    these tubes only have access from one side, so we cant do a normal butt weld, so they are are prepped backwards with the bevel tapering to the outside of the pipe rather than the inside in preparation for a window weld, you cut see the reverse bevel here.



    after the reverse bevel is cut with the mill hog, we cut out a window from the tubes so we can weld 2/3 of the weld from the inside of the pipe.



    once the inside is welded wel cut and sit a "saddle" which is also a full pen but weld over the opening we used to weld the inside of the pipe.





    That's all I've got for today, the shuts still going so I might have another post at the end, but we'll see how it go's, I hope you enjoyed.

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    Re: Power station outage part 2.

    That is impressive work. Great job and thanks for the detailed explanation and pics. It really helps those of us who don't do this kind of work to understand what you are doing.
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    Re: Power station outage part 2.

    That looks to be the same basic design as the Ahlstrom boiler in the smelter where I worked, we called the the strapping between the tubes "membrane". I always got a kick out of that company, the boiler was supposed to be cooled or heated at a given rate of 100* F IIRC, heck, they would shut it down for a leak & have it at nearly ambient in 8 hours, they'd do the repair and as soon as they got a good hydro it was back online in another 8 hours, if at all possible, management could never get a grip on what "shocking" the boiler meant. They went to the length of re-ducting a large blower to pull ambient air through the boiler to cool it quickly. I always figured the shock they caused cost way more lost production than if they had followed procedure. That boiler grew way more than 6 inches fro cold start to full heat of around 2400*F.
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    Re: Power station outage part 2.

    Thanks for sharing pictures, and the really detailed descriptions of the work too. I'm always fascinated on how things are made , and repaired . Most people have know very little knowledge about how the things they use everyday are made or where it comes from. Food, water ,energy, sanitation, people don't really pay attention until its no there.

    Keep up the good work, we're all counting on you.
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    Re: Power station outage part 2.

    I mostly work nukes now days but I have been in my share of coal fire boilers. I built them for 16 years. All parts and pieces from the burner panels to the steam drums and everything in between. Most average "welders" have NO clue what this kind of welding/work is like. You either love it or hate it. I happen to love it,lol. You learn to do a lot with very little and quickly figure out what is essential and what's just extra weight in your tool bag. A dying breed in the US thanks to low manufacturing and Obama era EPA regs. Reading your post and especially looking at the pics makes me miss me some fly ash and coal fire goodness. Keep up the good work brother.

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    Re: Power station outage part 2.

    Quote Originally Posted by Showdog75 View Post
    I mostly work nukes now days but I have been in my share of coal fire boilers. I built them for 16 years. All parts and pieces from the burner panels to the steam drums and everything in between. Most average "welders" have NO clue what this kind of welding/work is like. You either love it or hate it. I happen to love it,lol. You learn to do a lot with very little and quickly figure out what is essential and what's just extra weight in your tool bag. A dying breed in the US thanks to low manufacturing and Obama era EPA regs. Reading your post and especially looking at the pics makes me miss me some fly ash and coal fire goodness. Keep up the good work brother.
    That's very true, it's actually been highlighted really well on this shut as we have quite a few greenhorns on the job, they've all got a massive tool bag with every imaginable tool, where as the older and more experienced guys have it condensed down to what will fit in a small bucket.

    I personally probably have one of the heavier buckets, I carry this in my bucket

    -Small hammer
    -Half round 1st cut file (that i've cut in half)
    -Flint (to light the oxy/LPG weed burner)
    -Flat blade screw driver
    -Small fox wedge
    -Needle nose pliers
    -Wire brush
    -6 inch and 10 inch adjustable wrench (for changing carbide burr bits and gas bottles)
    -Pen flashlight
    -wire wheel
    -few cutting wheel (.040 and .100 thickness)
    -1 grinding wheel
    -annular cutter box full of tungsten's.
    -welding gloves
    -welding hood (balaclava)
    -3 inch pipe clamp
    -a paint marker (like a texta but writs on hot stuff)

    That all fits into a 2 gallon steel bucket and I have enough room to spare to fit an electric barrel grinder and a 5 inch angle grinder, and that's what I take with me around the place, I keep my main tool bag with all my random crap in my locker in case I need it, but so far I haven't needed any of it, I can think of 1 time in the last 5 years i've needed something more than what's in my bucket.
    Last edited by ttoks; 4 Weeks Ago at 05:43 AM.

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    Re: Power station outage part 2.

    Thanks for all the pics!
    The window cut in to access the back of the pipe answered something that's been rattling around in my head about accessibility.
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    Re: Power station outage part 2.

    Quote Originally Posted by CAVEMANN View Post
    That looks to be the same basic design as the Ahlstrom boiler in the smelter where I worked, we called the the strapping between the tubes "membrane". I always got a kick out of that company, the boiler was supposed to be cooled or heated at a given rate of 100* F IIRC, heck, they would shut it down for a leak & have it at nearly ambient in 8 hours, they'd do the repair and as soon as they got a good hydro it was back online in another 8 hours, if at all possible, management could never get a grip on what "shocking" the boiler meant. They went to the length of re-ducting a large blower to pull ambient air through the boiler to cool it quickly. I always figured the shock they caused cost way more lost production than if they had followed procedure. That boiler grew way more than 6 inches fro cold start to full heat of around 2400*F.
    This boiler was built before membrane tubes were a thing, membrane is when the "fin plate" is a solid part of the tube, so the tubes are made with the fin as an integral feature of the tube, these are the same idea but welded onto the the side of the tube, I'm working on one of the two older units at this power stations, units 3 and 4 of this station are actually proper membrane tube boilers and they are far more reliable as a result.

    you are dead right with the run up and down times of the boilers though, this station is bad for it as the water walls (the most likely parts to fail when heat shocked) are carbon steel, they'll bring a unit offline and have it down to ambient in less than 8 hours, and run it back up just as fast, and without a doubt it will be back offline again within 12 hours with a water wall leak, the other large power station in my area is pretty good with it though as they're water walls are made of B2 cro-moly, so they can't get away with shocking the boiler so they usually take it down over 2 days and take 2-3 days to get it back up to full steam.
    Last edited by ttoks; 4 Weeks Ago at 07:28 AM.

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    Re: Power station outage part 2.

    Quote Originally Posted by MinnesotaDave View Post
    Thanks for all the pics!
    The window cut in to access the back of the pipe answered something that's been rattling around in my head about accessibility.

    it's actually a rather interesting procedure in that they cant shoot the saddle covering the window so they always get pretty nervous about it, we always have an inspector watching weld the saddles in which is why I don't have any pic of welding them, however it takes 4-5 times longer per weld than a normal butt weld, it's taken 4 days to cut out, prep and weld 5 tubes (so 10 welds) where as with butt welds with access to both sides that would be a one day job.

    Maybe i should do a post just on how to do a window weld?
    Last edited by ttoks; 4 Weeks Ago at 07:24 AM.

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    Re: Power station outage part 2.

    Quote Originally Posted by ttoks View Post
    it's actually a rather interesting procedure in that they cant shoot the saddle covering the window so they always get pretty nervous about it, we always have an inspector watching weld the saddles in which is why I don't have any pic of welding them, however it takes 4-5 times longer per weld than a normal butt weld, it's taken 4 days to cut out, prep and weld 5 tubes (so 10 welds) where as with butt welds with access to both sides that would be a one day job.

    Maybe i should do a post just on how to do a window weld?
    Dang, that's a lot of money tied up for the 3 extra days

    I'd be interested in seeing the window cut-out

    I've done similar (more redneck style though) on square tube that I couldn't access the back to weld a crack.
    Sliced just inside the corners so I could bevel them out to put the widow back.
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    Re: Power station outage part 2.

    I've enjoyed the installments. That's some kinda job!!

    The word out in the World is that we're gonna be all wind, and solar, within a decade, or less. I don't buy into that. The technology isn't there for such a change yet. Still need fossil fuel to keep the lights on when the wind doesn't blow, and the sun doesn't shine. Although, I've read that Enbridge is partnering with the folks building offshore wind turbines in Europe.

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    Re: Power station outage part 2.

    Quote Originally Posted by farmersammm View Post
    I've enjoyed the installments. That's some kinda job!!

    The word out in the World is that we're gonna be all wind, and solar, within a decade, or less. I don't buy into that. The technology isn't there for such a change yet. Still need fossil fuel to keep the lights on when the wind doesn't blow, and the sun doesn't shine. Although, I've read that Enbridge is partnering with the folks building offshore wind turbines in Europe.
    I see nuclear as the only real solution, you can argue one way or the other if CO2 is affecting the climate so i gonna leave that one alone, but we will be transitioning to less polluting energy one way or the other and wind and solar just can't provide the reliable base load power supply we need, and even for peak load demand its going to need a huge amount of batteries because the sun doesn't shine when the peak load times are, and wind is a complete basket case if it's working or not so I see gas fired gas turbine power stations being a part of the solution for a long time to come as well.

    I think give it another 20-30 years and there will be nuc stations being built in every developed country.

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    Re: Power station outage part 2.

    That's some hardcore welding, right there. Thanks for posting up.

    I've heard stories about guys welding pipe in nuke boats where it's real cramped with pipes everywhere, and they end up bending stick electrodes to go around corners, and use mirrors to see the puddle, etc. Do you do much of that kind of thing?

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    Re: Power station outage part 2.

    Quote Originally Posted by ttoks View Post
    I see nuclear as the only real solution, you can argue one way or the other if CO2 is affecting the climate so i gonna leave that one alone, but we will be transitioning to less polluting energy one way or the other and wind and solar just can't provide the reliable base load power supply we need, and even for peak load demand its going to need a huge amount of batteries because the sun doesn't shine when the peak load times are, and wind is a complete basket case if it's working or not so I see gas fired gas turbine power stations being a part of the solution for a long time to come as well.

    I think give it another 20-30 years and there will be nuc stations being built in every developed country.
    I love your posts man. You do a great service to humanity.
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    Re: Power station outage part 2.

    That there is some intresting and pretty demanding work, I bet you hurt at the end of the day. I worked a few shutdowns for a small outfit, we tore apart the coal mills and exhausters and fixed what needed fixed and put em back together...greasy dusty dirty grimy and i felt right at home being an old coal miner.

    When we were done I worked sometimes for an outfit doin a lot of the bullriggin for the boiler rats gettin that stuff up and into where they were workin. I watched and helped some of them fellas inside the boilers and was glad I wasnt a real life boiler rat. You guys earn evry penny you get.

    What gets me goin sometimes is people who dont understand what it takes to keep this stuff goin 24 hours a day and bitch piss and moan about the electric bill or the price of gas and so on, they constantly whine and complain, and they dont realize a plant or refinery runs 24 hours a day, repairs add up and gets expensive. Thye usually are the rich bastards doin the most whining as well.

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    Re: Power station outage part 2.

    I don’t bitch and moan about the bill but when the power goes off I cry like a baby

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    Re: Power station outage part 2.

    Quote Originally Posted by Bls repair View Post
    I don’t bitch and moan about the bill but when the power goes off I cry like a baby
    me too

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    Re: Power station outage part 2.

    Those headers require some pretty precision fitting getting all the connections lined up. I worked in a couple vessel shops that could do that kind of precision fitting. It's an art. The most cramped I've ever had to weld was crawling 15' inside an 18" firetube to back weld the 45 deg. cut corner. Cutting both pieces at 45 to make a 90 allows for the the 2 pipes to be closer together than using a forged round 180. I welded half then flipped it over to weld the other half. Welding in between the 2 pipes on the outside was a little tricky too because they were only about 6" apart. I was so glad it passed x-ray. Went in one time and the darn light bulb in the trouble light exploded. Had to crawl out backwards to get a new bulb and then crawl back in. Good thing I'm not claustrophobic.

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    Re: Power station outage part 2.

    We had a company that would come in for some leaks that were inaccessible for welding that used some sort of compound mixed with metal chips, preferably cast iron, then a contour jig was fabbed my the machine shop & then clamped in place over the leak and the compound was pumped in under hydraulic pressure & allowed to cure before doing a hydro and bringing the furnace & boiler back online.
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    Re: Power station outage part 2.

    Quote Originally Posted by CAVEMANN View Post
    We had a company that would come in for some leaks that were inaccessible for welding that used some sort of compound mixed with metal chips, preferably cast iron, then a contour jig was fabbed my the machine shop & then clamped in place over the leak and the compound was pumped in under hydraulic pressure & allowed to cure before doing a hydro and bringing the furnace & boiler back online.
    one of the older stations with low pressure (low pressure being 1000 PSI) boiler's used to use what they called "epoxy sealing" similar to what you described, however it simply doesn't hold up with the newer boilers currently operating around here, this station runs at 2000-2100 psi,they tried epoxy sealing water wall (the lowest temperature part of the boiler water loop) tube leaks on the old hazelwood boilers used to run at 1600 psi and the epoxy just didn't stand up to the pressure and temp unless it was very close to the water wall headers where the temp was under 300F, the most modern station around here runs at 2400 PSI on the oldest 4 and 2500 PSI on the two newest units.

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