Author Topic: #9 max steam pressure  (Read 1538 times)

ALAIN DELASSUS

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#9 max steam pressure
« on: February 17, 2018, 05:59:07 PM »
I've caught on a notice put up in the cab that the maximum steam pressure in the boiler is 140PSi. I'd like to know if it was the same pressure when it was built in 1891 or if it is the mandated pressure required by the authority that checks the boiler.

Jason M Lamontagne

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Re: #9 max steam pressure
« Reply #1 on: February 17, 2018, 11:13:35 PM »
The Portland Company’s original MAWP was 140 psi.  The replacement boiler, as a new ASME power boiler, could be designed to whatever pressure we chose.  We chose to use the original.

Some designers design to a higher MAWP than that to be used in operation, as a means of overdesign to account for deterioration.  We’ve always felt that is a fallacy; instead we design for the intended pressure, and calculate the minimum required thickness of each component; when that number is compared to as built thickness, one readily has as built corrosion allowance.  Likewise for anytime in the boilers life.

See ya
Jason

ALAIN DELASSUS

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Re: #9 max steam pressure
« Reply #2 on: February 18, 2018, 12:08:58 PM »
Hi Jason

Thank you so much for answering my question so fast  after your busy day cutting and burning trees. I'm glad that event was popular It was a great idea. Your explanations are very interesting.Out here the AMTP locomotive max steam pressure is 176 PSI/ 12 bars. I think that the water quality is the  main boiler  corrosion factor. In Pithiviers the water is rather chalky and we have to treat  it. The locomotives were fit with blow down valves 30 years back. Actually these are  the  boiler tubes that are often rust ridden and out here we 've got often leaks despite the water treatment.Some of the engineers think that the tubes are not thick enough.  What about the water in Alna  Do you treat it ?

Have a nice Sunday

Jason M Lamontagne

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Re: #9 max steam pressure
« Reply #3 on: February 23, 2018, 05:13:45 PM »
Hi Alain,

We do treat the water with oxygen scavenger; we are fortunate to have very soft water, with very low initial conductivity.  We also apply a "nitrogen cap" whenever we shut down, meaning the steam space of the boiler is connected to a nitrogen bottle, through two regulators.  Thus, as the boiler cools and would otherwise pull a vacuum and ultimately air with oxygen, instead nitrogen is pulled in.

Our boiler corrosion is mainly from oxygen, which used to be promoted with the boilers stored with cold water and air in the steam space in between fire up dates.  The scavenger and nitro cap are doing a good job of getting that under control.  We are also considering installing a heated standby system.

Chalky water doesn't sound good for a loco; sorry you have to deal with that...

Thanks,
Jason

ALAIN DELASSUS

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Re: #9 max steam pressure
« Reply #4 on: February 26, 2018, 06:07:03 PM »
Hi Alain,

We do treat the water with oxygen scavenger; we are fortunate to have very soft water, with very low initial conductivity.  We also apply a "nitrogen cap" whenever we shut down, meaning the steam space of the boiler is connected to a nitrogen bottle, through two regulators.  Thus, as the boiler cools and would otherwise pull a vacuum and ultimately air with oxygen, instead nitrogen is pulled in.

Our boiler corrosion is mainly from oxygen, which used to be promoted with the boilers stored with cold water and air in the steam space in between fire up dates.  The scavenger and nitro cap are doing a good job of getting that under control.  We are also considering installing a heated standby system.

Chalky water doesn't sound good for a loco; sorry you have to deal with that...

Thanks,
Jason

Hi Jason

 Thank you for your very interesting reply. I've never heard of  that very clever nitrogen system . I'll ask if anybody know it when I go to Pithiviers. On the AMTP just after dropping the  fire  the boiler is filled up  in one go and the pressure falls fast to 29.5 PSI or so. Of course we do it to avoid refilling the boiler before the next lightning and also to avoid melting the fuse for lack of water because  the fire box is  still very hot despite the fire dropping and some part of the water will be changed into steam . I think  the way we do is very harmful for the boiler  hence the leaks. It would be better if somebody could refill the boiler little by little by means of the low pressure injector to limit the thermic shock . But at the end of the day everybody is eager to get back home and we don't have a night hostler. How do you proceed ?

Best regards.


ALAIN DELASSUS

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Re: #9 max steam pressure
« Reply #5 on: February 27, 2018, 04:24:35 PM »
Hi Jason

 As the Pithiviers engine shed isn't heated the locomotives are wintered to avoid the frost and the corrosion. The boiler the water tanks and all the pipes are emptied the boiler is thoroughly rinse. The smoke box  the fire box and the ash pan are cleaned up and washed. Then a special grease is put inside the boiler tubes after they have been scraped and washed. Not that winter is very cold out here but every now and again it freezes enough to damage pipes and even a boiler. It's kind of rare but it was 16°F last night. The humidity rate is the main concern. It's often very  high inside the shed because not only it's not heated but its doors are only open  the week ends. Anyway given the size of the shed it'd cost an harm and a leg to insulate it and fit it with a heating system.  So we make do with the humidity and the ensuing corrosion. What is your heating system in the shop ?  And what is the heated stand by system you've mentionned  in your previous reply?

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Jeff Schumaker

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Re: #9 max steam pressure
« Reply #6 on: February 28, 2018, 01:29:22 PM »
Hi Alain,

We do treat the water with oxygen scavenger; we are fortunate to have very soft water, with very low initial conductivity. 

Thanks,
Jason

Jason,

Out of curiosity, what is being used as an oxygen scavenger?

Jeff S.
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Jason M Lamontagne

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Re: #9 max steam pressure
« Reply #7 on: March 01, 2018, 02:29:35 AM »
Hi guys,

Alain, yes, topping boilers off with water until the injector quits as a shut down procedure is pretty harsh on a boiler- we train our crews to work the water up to about 3/4 glass for the put-away, getting to that level gradually over the last 30 minutes of operation or so.  Also- most of that water should go in while there’s still a fire in the belly.

We also train to keep a fire hot until dumped.  There used to be a tendency to save coal, and “fire down” on the last trip, to the point where on fire dumping, it was all dead, we were down on pressure, the water wasn’t boiling, and injecting up to that 3/4 glass would be really shocking.  Now- last trip is fired no different than the others, and the boiler kept on the ready until the end.  The extra coal consumption might amount to a few dollars.

A quick btu loss calc on no 9 shows it to be less than a typical household water heater can handle.  The initial thought is to add a zone to the existing bay 4 heating system (oil fired hot water), and use a standard household hot water heat exchanger.  A circulator pump and quick disconnects to the blowdown and feed inlets.  In the winter the heat loss would be into a room were heating anyway.   The system isn’t yet implemented but we’d like to this spring.

Jeff: our ox scavenger is sodium sulfite.  This grabs O2 and becomes sodium sulfate.  We test effectiveness by measuring residual sodium sulfite.

See ya
Jason

ALAIN DELASSUS

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Re: #9 max steam pressure
« Reply #8 on: March 01, 2018, 02:47:36 PM »
Hi  Jason
Thank you for your  interesting reply . Sure the shut down procedure we use on the AMTP isn't the right one for the boilers . But what is a btu loss calc  ulation ?

Jason M Lamontagne

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Re: #9 max steam pressure
« Reply #9 on: March 01, 2018, 02:58:28 PM »
BTU loss rate was calculated by simply measuring boiler water temperature during a cool-down at two times (24 hours apart), and knowing how many gallons of water are in the boiler.  We want to do it again but looking around 20000-30000 BTU/Hr on No 9.

Thanks,
Jason

Jeff Schumaker

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Re: #9 max steam pressure
« Reply #10 on: March 01, 2018, 03:31:23 PM »
How much sodium sulfate is produced in a weekend? How does it get removed from the system?

Jeff S.
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Bill Baskerville

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Re: #9 max steam pressure
« Reply #11 on: March 01, 2018, 03:51:24 PM »
Jeff,

I may be jumping out of my comfort zone, but each return trip south we blow out the mud ring with two blasts.  This, of course helps keep the mud ring clean, but it also reduces the water level in the boiler, which allows fresh water to be injected from the tender.  This reduces the sodium sulfate levels in the water.

The same principles are used in cooling towers to reduce the solids and chemical buildups in the tower water.  In cooling towers a monitor measures the concentrations and when they build up to a specified level a drain valve is opened and contaminated water is drained out to be replaced by fresh water.
Wascally Wabbit

Jeff Schumaker

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Re: #9 max steam pressure
« Reply #12 on: March 02, 2018, 03:13:52 PM »
Makes sense to me, Bill.

Jeff S.
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Dag Bonnedal

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Re: #9 max steam pressure
« Reply #13 on: March 05, 2018, 09:26:43 PM »
Hi,
I am responsible for the steam locos on the 600 mm gauge ÖSlJ, Mariefred, Sweden and have been working with our locos for 45 years.
https://en.wikipedia.org/wiki/%C3%96stra_S%C3%B6dermanlands_J%C3%A4rnv%C3%A4g
https://rotonen.se/tag/mariefred/
I have been following your absolutely amazing work over the internet for several years, but this is my first contribution on the forum.
In the 1970-ties we had problems with our boilers, but around 1980 we were lucky enough to have an active member working professionally with industrial boilers. He introduced water treatment for our boilers. This consists of a water softening filter, adding phosphate and sodium hydroxide (pH adjustment) plus blow down valves on the locos.
This made a dramatic difference. In 2016 we had to put our loco #4 aside for retubing and other boiler work (consequences of the mistreatment in the 70-ties). The tubes were installed in 1979 and the loco has run 1400 days with the same set of tubes (2.3 mm thick). Our loco #8 had new tubes in 1978 and is still running with the same set.
We also have a dehumidifier installed in the loco shed for drying out the boilers and water tanks as well as dry storage during the winter (cold).
I have also thought about the idea mentioned by Jason with nitrogen attached to the boiler. But I have been unsure about the safety issue. Do you have any warning system for the possibility of large amount of nitrogen leaking and giving a lethal low oxygen level in the premises?

Regards
Dag

« Last Edit: March 05, 2018, 09:49:06 PM by Dag Bonnedal »

Robert Hale

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Re: #9 max steam pressure
« Reply #14 on: March 06, 2018, 07:16:20 PM »
This whole topic begs the question of what plating for the steel used in the boilers could be used to mitigate any corrosion? Zink oxide? Titanium nitrating? Nickel?

Rob