Boiler blowdown

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46Tall
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Boiler blowdown

Postby 46Tall » Sat Nov 07, 2015 6:26 am

We have a low pressure boiler, approx. 3 bar, that we've been blowing down on a fairly regular basis and there is a bit of disagreement as to the valve order. One side believes the ships side valve should be opened first then the boiler valve and then close the boiler valve first followed by the ships side valve. The other group believes the boiler valve should be opened first followed by the ship side valve.

Any feedback on this issue along with encountered experiences would be much appreciated.

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Merlyn
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Re: Boiler blowdown

Postby Merlyn » Sun Nov 08, 2015 1:07 am

Back in my steam days of reciprocating and then turbines we always opened the ships side valve first and then the usually non return blowdown valve secondary as normal all valves to be fully open to extend valve seats life and reduce the happy hours spent grinding/lapping, ( especially those large upside down valves and throttle valves )
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JK
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Re: Boiler blowdown

Postby JK » Sun Nov 08, 2015 4:55 am

Blowdown: open ship side, isolation valve, then blowdown. Close in opposite order.

If you are blowing to empty, listen carefully for the change is sound and close the blowdown. It was worthy of derision on the steamers, if the doors were knocked in and the boiler had a bunch of water left in it.

I should add, I also worked on the steam recipes, my boilers were a bit larger then 3 bar.

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Merlyn
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Re: Boiler blowdown

Postby Merlyn » Mon Nov 09, 2015 1:41 am

Memories flooding back of resuperheat turbines on a Shell Tanker I worked on. You cannot see any steam leaks until it condenses back into water. Thousand degrees plus at pressures upto three thousand psi plus. Deadly stuff. Leaks we were told were to be found with a broom handle, if it cut the broom in two then that's where the leak was. The rumour was that any part of the body coming into contact with resuperheat steam would be reduced to a skeleton in front of your very eyes although I have to say throught my career I never heard of such happenings but was always very wary of resuperheated steam engine rooms.
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JK
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Re: Boiler blowdown

Postby JK » Mon Nov 09, 2015 2:27 am

LOL. I was told the exact same thing. I had the exact same reaction.


Going back to the blowdown, the reasoning in opening the lines in that order was to keep full boiler pressure from sitting in the line. By opening the boiler valve last, there is control of the situation if there is leakage. I was always wary about the blowing down as you were wedged behind the boiler.

Saying that, we once had a situation where the blowdown valve was overhauled and the bonnet bolted on with the valve in the closed position. The flange did not meet. That boiler was filled, hydro'd and flashed to working pressure. I'm sure the individual who discovered that must have just about had a heart failure. I didn't see the valve seat as I was working on something else, but our machinist 3rd worked a long time to get it repaired.

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Merlyn
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Re: Boiler blowdown

Postby Merlyn » Mon Nov 09, 2015 4:38 am

Seem to remember some of those old boilers had a scum valve fitted, up top by the waterline level for use before the main blowdown valve was brought into play as some of the blowdown valves were not at the lowest point of the boiler and apon strip down some floating scum was still present in the boiler. Bit like cleaning out a fuel tank. Always some scum below the lowest drain off. How I remember setting up large gun metal/ bronze/ brass castings in a four jaw non centralising chuck to take a valve seat cut, think they were thirty or forty five degree angles from memory. Being offset in the lathe the last thing in the world you wanted was for the job to take charge and leap out of the chuck, for sure the job would be scrap besides those throttle valves were a gantry job to load them in the chuck and could cause you serious injury. Scary stuff.
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JK
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Re: Boiler blowdown

Postby JK » Mon Nov 09, 2015 5:41 am

yes, the scum valve was just high enough over my head behind the boiler that I couldn't quite touch it.
The foolishness of youth,, I came out from behind the boiler more then once white with asbestos dust.

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JK
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Re: Boiler blowdown

Postby JK » Mon Nov 09, 2015 5:56 am

I just remembered about a job we did when the ship side cock scored and started leaking and needed replacing.
We had 3 boilers on line and the cock was on the port side, just aft of the fuel pressure pumps and heaters. There was about 2 feet from the boiler to the ship side and a 20" or so,deep longitudinal above the cock and a frame just forward, so it was tight quarters. We were all a little nervous.
The diver plugged the overboard, he was nervous because he could hear the pumps knocking and wasn't sure what was going on.
We cautiously backed off the bolts, we had a moment of glee when it was confirmed the right overboard was plugged, then realized the tapered cock was jammed. We were all standing there, sweating profusely, discussing the issue, when the brand new to ships fireman looked in at the job. He offered a solution, we all looked again and darn wasn't he right. Just proved everyone has something to contribute even if they have no idea what exactly we were doing.

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Merlyn
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Re: Boiler blowdown

Postby Merlyn » Tue Nov 10, 2015 12:53 am

But what was the solution to free off the taper problem? A knocking stick?
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Merlyn
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Re: Boiler blowdown

Postby Merlyn » Tue Nov 10, 2015 1:24 am

Talking back to the asbestos subject as I said before we knew no better back in the sixties and apon an engineroom shutdown the first job was to attack miles of asbestos clad piping, sometimes a foot thick or more with today's equivelant of a chainsaw. Bulkhead stop and onwards, miles of it. The whole eight hour shift would be spent peering through a thick fog of it, whatever job you were assigned to would be covered in it, deeply too. All over every turbine, it was everywhere and we breathed it in daily not knowing any better, everyone else had done it for years so why should we be any different? Ignorance indeed. However I remember we were never directly involved with replacing it for when all joints/dismantled repaired items and turbine covers etc were reassembled for a specialist plastering crew were always brought in, interesting to watch them, a labourer mixed it all up and off they went at a terrific speed, swirling the trowels round the bends and curves, clever stuff indeed. This breathing disease developed from asbestos that anyone was unfortunate to catch was not to show for some forty year plus period and was a killer indeed. Heard of people locally getting it but so far so good here. I see massive claims have successfully been brought ref this subject but in all cases it brought no respite from the disease to the unfortunate sufferer. Asbestosis I believe, horrible disease indeed.
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JK
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Re: Boiler blowdown

Postby JK » Tue Nov 10, 2015 1:43 am

Merlyn wrote:But what was the solution to free off the taper problem? A knocking stick?

I honestly can't remember, I think I sweat my brain out that day. It was easily 130F in that spot.

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JollyJack
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Re: Boiler blowdown

Postby JollyJack » Tue Nov 10, 2015 8:39 pm

HMS Niade, Leander Class frigate, a high pitched whistle along the steam line to the main turbines. A stoker ran his hand along the pipe to find the leak and was amazed when 3 fingers of his right hand dropped off, he never felt a thing!
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Merlyn
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Re: Boiler blowdown

Postby Merlyn » Wed Nov 11, 2015 12:51 am

Crikey so it was all true then, I never knew whether to believe it or not but didn't want to be a first on our firm to find out, this title I certainly did not want. The turbine ships were in abundance when I started out in the sixties down our way but the price of fueloil drove the suck bang blow merchants to the forefront rapidly. Haven't worked on an up and downer or a rounder for donkeys years but a lot of it all still remains photographed forever in the back of the brain, good days indeed.
Remembering The Good Old days, when Chiefs stood watches and all Torque settings were F.T.

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JK
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Re: Boiler blowdown

Postby JK » Wed Nov 11, 2015 10:34 am

yes. 30 years on , I could probably flash a scotch marine boiler, up and down plant from cold using compressed air. I might be able to muddle my way through a couple of diesel ships, if I had been on them for any length of time. Funny how that goes.

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Merlyn
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Re: Boiler blowdow

Postby Merlyn » Mon Nov 16, 2015 3:41 am

Scotch marine boilers eh, tube stopper job? Remember? Shut down leaky furnace, steam on two until alongside or on the hook, shut down the other two fires, allow to cool, out with the ice buckets with spanners in it, open the furnace door, blast of heat, strip, ice cold overhauls and in you go. No mention of claustrophobia here or hide it to show you are not a woosy. Haul yourself across all those corrugations, miles and miles of it til you reach the other end of the boiler tube stack face. Stand upright, carbide light in hand, locate leaky tube/s, out with the plugs, taper hammer in or taper expansion screwed expander type, really got a sweat on now twofold, air temp and whether some wag is going to shut the furnace door on you, seen it done several times. Allways shouts of, oh look, someone's left the furnace door open, better close it. At least if you had a lead light in use they could not close and lock off the door on you. Back out,flash up and test. No more than ten per cent of the total tubes to be done but many ships had nearer twenty per cent stopped up. Plugging the other end was nowhere near so scary. I also remember the boiler blow off relief valve settings, part of the refit would be entail stripping the valve to expose both seat faces. If bad, let go all pipe work and crane valve assembly off the ship and back to the workshops, into a lathe, set it up concentrically and carefully cut the seat in the housing. Recut the the actual valve itself in a three jaw self centring chuck, then coarse, medium, fine grinding and reassemble and back to the ship. Now with a full head of steam the relief pressure blow off had to be reset, another scary job. Someone in the boiler room watching the psi gauge shouting to others in the chain, ( no r/t here ) " on the blood " when the gauge reached the red sector of the gauge and the charge hand would wind the big spring loaded adjuster up or down as the case may be. Loads of steam here. Reckon you could still do the firebox furnace run? Probably be more scary now than then.
Remembering The Good Old days, when Chiefs stood watches and all Torque settings were F.T.


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