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  1. #14
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    lol so its like trying to fire a bullet through through a barrel with a bunch of 90's?

    thats crazy, how is the steam released so fast as to accelerate the water that quicly?

    i mean... ive seen steam blow down valves that are like 100-1 ratio with a turn wheel w/ a worm gear on the shaft thats turning a cog to open a little 2" plug valve. idea being it takes you like a full minute to open it up.

    i just assume all other steam components are similar, actuated or otherwise?

  2. #15
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    The reaction is primarily due to the expansion of the water in a confined space. Steam piping design starts with pipe wall thickness calculation. The allowable hoop stress in my experience has always been greater than the allowable stress in bending which explains why the slug travels down the pipe instead of rupturing it in the straight run. The force of impacting with a change in direction is similar in my opinion to the results of a large meteor exploding above the earth and the leaving a huge crater in the ground. The crater is the result of the explosion and not the meteor's contact with the ground because it blows into billions of pieces. Don't hold me to this but if my memory is correct sonic velocity of the slug is reached almost instantly. I haven't been involved in steam system design in several years so that statement could be incorrect. Steam expelled thru a blowdown valve is totally different and the slow opening valve is part of the reason and partly because the lack of drain system back pressure. Blow down tanks are also vented for quenching to the allowable temperature for draining.

  3. #16
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    Can't blame the boiler company that repaired it, the repaired section stayed behind and the rest of it launched.
    Federal Reserve, stealing your kids futures since 1913

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  4. #17
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    To be clear this has nothing to do with this thread. One of my early jobs was at a steel company. The certified welders there were not just good they were great. What they in their words "stuck together" stayed together. They liked to say they could weld cigarettes together. In hot weather on non-certified welds they would start a bead then lift their helmet and lay a perfect bead without looking. One of the things they taught me was that if not properly prepared a perfectly good weld would show up as a crack when xrayed. That was reinforced when I was exposed to mating metric steam pipe to American. In my opinion boiler welders are among the best or they don't get the job.

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  6. #18
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    oh man, i agree with you 2,300%.

    IDK what the term is, but the pipe fitters working on critical pipe fittings that are getting ultrasonic or x ray inspections are magicians. they make welding look like ... operating a hot glue gun.

    whats even more impressive is they can make these welds on their backs... crouched over, or contorted in all sorts of tight spaces. its one thing to make a beautiful bench weld( still very hard), but its something else to make a simillar quality weld out in the field where its 105f, and you barely have enough room to breath.

    lol i worked on a rehab project for a potato chip plant... some plant piping had to be relocated and this guy was blasting tig filler like nothing at all just feeding it through his fingers without ever reproping or stopping(until he needed a new rod) . no foot pedal, or torch wheel... just a scratch start on a dynasty 3000.

    i welded for 2 years in high school... dude made me fell like complete ****.

  7. #19
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    Welding is one of those things like flying. To be any good, you have to do it al lot.

    When I was first welding, my stuff was all birdsh**. After a couple of years, I was as good as the best guy in the shop. It would take me several months to get back to that level again. But, I would miss my passion: diagnostics.
    [Avatar photo from a Florida training accident. Everyone walked away.]
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  8. #20
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    I did some fitting which only required tack welding and did get past the mud dobber stage but didn't work at it long enough to get really good. Another thing neat to watch was bending the rod to get into a tight space and using a mirror to see what they were doing. Where I worked the welder were also pretty mischievous. They loved to con a new guy into welding galvanized steel. Sometimes the victim ended up vomiting into his helmet. Nobody really understood that was dangerous.

  9. #21
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    Quote Originally Posted by timebuilder View Post
    Welding is one of those things like flying. To be any good, you have to do it al lot.

    When I was first welding, my stuff was all birdsh**. After a couple of years, I was as good as the best guy in the shop. It would take me several months to get back to that level again. But, I would miss my passion: diagnostics.
    yea man i know what you mean.

    i weld probably like 6 hours a YEAR. mostly fixing junk ive broken. i have a junk tig machine too. its fine for random steel brackets though. ac is garbage.

    its like driving a car. you think you are half decent at it untill you see a real race car driver.

    its just amazing to watch a real welder.

  10. #22
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    Quote Originally Posted by WAYNE3298 View Post
    The reaction is primarily due to the expansion of the water in a confined space. Steam piping design starts with pipe wall thickness calculation. The allowable hoop stress in my experience has always been greater than the allowable stress in bending which explains why the slug travels down the pipe instead of rupturing it in the straight run. The force of impacting with a change in direction is similar in my opinion to the results of a large meteor exploding above the earth and the leaving a huge crater in the ground. The crater is the result of the explosion and not the meteor's contact with the ground because it blows into billions of pieces. Don't hold me to this but if my memory is correct sonic velocity of the slug is reached almost instantly. I haven't been involved in steam system design in several years so that statement could be incorrect. Steam expelled thru a blowdown valve is totally different and the slow opening valve is part of the reason and partly because the lack of drain system back pressure. Blow down tanks are also vented for quenching to the allowable temperature for draining.
    i dont follow your logic tbh.

    a meteor is going like 60,000 mph. they explode because hitting the air that fast causes insane heating, and when something is not like a solid lump of iron,and is entering at a steep angle, it will just explode like a molten bullet hitting a pool of water.

    when they explode close to the ground the blast keeps going and hits the ground like an atomic bomb.

    i dont think you can compare that to steam tbh.

    i fully understand how a slug of water followed by a slug of steam could cause severe whipping and damage to pipes, but water weighs a crap load so i dont see how a slug of water can accelerate very fast without an insane amount of steam and pressure chasing it down the pipes.

    water weighs a hell of alot so it will accelerate slowly unless there is LOTS of steam behind it.
    this is why i brought up the slow opening valves?
    i mean if the valve were SLAMMED open i could see this happening, but isnt steam all geared towards slow opening slow closing? how could you open a valve fast enough to accelerate the plug of water like that?

  11. #23
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    The comparison to a meteor exploding was an attempt to demonstrate the reason for the force behind the water. Sounded like a good analogy at the time but maybe not. There are several things involved such as quenching and expansion. We can only speak in terms here of how slugging in general damages piping systems because we don't know the specifics in this situation. Wayne Kirshner has an article on line that explains this much better than I can. You should even find pictures of piping that was destroyed due to slugging. Water in the pipe attempts to cool the steam and condense it but the steam starts to drive the water down the pipe. At some point the water seals the pipe which dramatically increases it's velocity. Warm up procedures admit steam slowly in case there is water in the system and if properly done steam created slugging hammer does not happen.

  12. #24
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    queequeg,
    Rather than trying to further explain this since you are an engineer if you send me an email I will send you some info on water hammer that I'm not going to put on here. Are you familiar with standard steam pipe design velocities?

  13. #25
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    Thread Starter
    https://www.youtube.com/watch?v=l3i_ZGPtm68&sns=em

    water to steam expands 1700 times @atmosphere there is no relief valve that can Handel that expansion rate. look at this video about a 50 gallon water heater

  14. #26
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    Quote Originally Posted by WAYNE3298 View Post
    queequeg,
    Rather than trying to further explain this since you are an engineer if you send me an email I will send you some info on water hammer that I'm not going to put on here. Are you familiar with standard steam pipe design velocities?
    as i said earlier, i know less than nothing about boilers/steam generators lol. but id love to see the link... ill PM you in a minute.

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