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 Post subject: Re: Hydro testing issues
PostPosted: Mon Dec 21, 2020 12:06 am 

Joined: Wed Aug 25, 2004 11:16 am
Posts: 735
Overmod wrote:
OK, I'll bite -- how in the SAM HILL did that happen???


Overmod

The photo is on pg 320 of the proceedings of the Eighteenth Annual Convention of the International Railway Fuel Association held at Chicago, Illinois May 11 to 14, 1926. It is part of the Report of the Committee on Front-Ends, Grates and Ashpans. Essentially you plug the nozzle and the tubes and then fill the smoke box with your favorite hose. This is to expose air leaks that increase the work load of the nozzle and stack to create a draft.

Robby Peartree


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 Post subject: Re: Hydro testing issues
PostPosted: Mon Dec 21, 2020 12:39 am 

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Kelly Anderson wrote:
Hydro testing smokeboxes to find air leaks was a thing. I recall seeing it mentioned in old standard practices.

Had to be a hell of a lot of sealing to do this. Flues, tubes, nozzle and stack. Lot of work.


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 Post subject: Re: Hydro testing issues
PostPosted: Mon Dec 21, 2020 12:48 am 

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JeffH wrote:
Overmod wrote:
Meanwhile, Robby Peartree raised some issues regarding Bourdon gauges used as pressure indication during a hydro test. He pointed out (nominally correctly) that these gauges are said to read most accurately at the middle of their mechanical range, and therefore if a hydro is to be pressurized, say, to 150psi, the gauge itself should read that in the middle of the range, not near one end of the indicated scale. He also raises a concern that sharp or excessive pressure excursions experienced near the outer scale limit of a 270-degree Bourdon movement might damage the gauge, either mechanically or by deforming the shape of the tube.


This depends on the accuracy class of the gauge. ASME B.2 is the standard governing this. For example, ASME class A gauges gives an accuracy of +/- 1 percent of the total span in the central 50% of the span, and 2% outside of this. But grade 1A and better have uniform accuracy from 0 to full scale.

Any Bourdon type gauge should be able to tolerate being pressurized to full scale without any fear of damage. Excursions beyond full scale may cause the bourdon tube to take a set if the metal in the tube is stressed beyond the elastic range. More commonly, the "movement" can be damaged if the extreme overtravel causes the sector gear to crash against another internal component.

Gauges can be damaged by violent rapid changes in pressure which mechanically shock them. The most frequent effect is that the pointer just gets knocked off zero and this is easy to correct. Long term operation under these conditions can cause premature wear-out of the mechanical parts. There is also a long-term tendency for the bourdon tube to work-harden when the pressure is oscillating in a narrow range. I don't think these details are important for hydrotesting, where the increase in pressure is controlled and gradual.



Hi

The book where I read this was written before ASME got into the boiler business. Some of these gauges out there are of that era of metallurgy. The basic principle that if you constantly push a mechanical instrument to an extreme end of its range of measurement you are stressing the mechanism to a point that an inaccuracy will develop. Since the Bourdon tube and the spring in the gauge work by deformation if you take it to an extreme of the travel it has more internal stress and more likely to permanently to deform the pieces. Once this occurs there will be an inaccuracy of reading given.

Robby Peartree


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 Post subject: Re: Hydro testing issues
PostPosted: Mon Dec 21, 2020 1:50 am 

Joined: Wed Aug 25, 2004 11:16 am
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Overmod wrote:
We haven't had the technical discussion of whether it is better to preheat the gas path on the fireside as opposed to preheat the waterside mass through pumped circulation. I theoretically have always favored the latter, but would surely entertain heating through the gas space or in some part of it in conjunction with circulation.


The 1926 proceedings of the International Railway Fuel Association discussion on the Arrangements on Oil firing Southern Pacific Section discusses that the SP was laying the fire brick up the side sheets to the fourth row of stay bolts . It states " The brick firepan lining is carried up on the side sheets to the fourth in order to prevent the flame from impinging directly against the lower portion of the side sheet. This practice diminishes the circulation in the lower part of the water leg and permits it to act as a settling chamber from which the mud which accumulates in this portion of the boiler may be blown out." Given that the entire boiler is subject to the hydro not heating this section could be disastrous.

Back in 2004 when Jack Anderson and I were discussing the conditions which NN 93 was being heated and that you had a hot fire on the grate but the areas of the boiler below the grates were still much colder than those areas above the grates. While you could not touch the areas above the grates the area below the grates were cold. The water circulation in the boiler just did not seem to affect the areas of the boiler below the grate area. For those of you unfamiliar with water circulation in a boiler consider the following article " Effect of Circulation on Locomotive Boiler Efficiency" here https://babel.hathitrust.org/cgi/pt?id= ... up&seq=258

No matter how you heat the water in the boiler it is important that all of the metal is brought up to temperature and you do not create a temperature differential. As some metals go thru a ductile brittle transition between freezing and room temp it is important to watch the temp of the steel when you hydro it. in the early 1990's they hydroed a gas line across Northern Arizona in December. After blowing out 180 feet of pipe they decided not to do that twice. For the record, temperatures in parts of Northern Arizona can drop to values well below the temp of freezing water. Another example is the hydro done on 4-8-4 that blew out a side sheet in the 1970s because it was done with cold water.

Robby Peartree


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 Post subject: Re: Hydro testing issues
PostPosted: Mon Dec 21, 2020 3:24 am 
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Robby Peartree wrote:
Another example is the hydro done on 4-8-4 that blew out a side sheet in the 1970s because it was done with cold water.


Which engine did that happen to?

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 Post subject: Re: Hydro testing issues
PostPosted: Mon Dec 21, 2020 8:46 am 

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Location: Strasburg, PA
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 Post subject: Re: Hydro testing issues
PostPosted: Mon Dec 21, 2020 9:34 am 

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[quote="Robby Peartree"] This is to expose air leaks that increase the work load of the nozzle and stack to create a draft.

Well, not really..... they will produce the same amount of draft whether or not there are leaks in the smokebox. They don't have the ability to decide to work harder or not, that's a factor of design and execution. The difference is what comes in from the smokebox doesn't come through the grates or firepan and therefore doesn't help the fire. It's more like the work it is doing is wasted.

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 Post subject: Re: Hydro testing issues
PostPosted: Mon Dec 21, 2020 10:09 am 

Joined: Thu May 24, 2012 1:37 pm
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Quote:
"Hydro testing smokeboxes to find air leaks was a thing. I recall seeing it mentioned in old standard practices."

That would make sense ... if done just to the point it produced seepage where the leaks were. This is fountains and fountains, as though supplied through at least a firehose at full firehose pressure! Is that just pressure head from filling to stack height?

Perhaps that would be appropriate to find 'every' leak even when there were already many bigger ones in evidence... but still! I'd think it would find every little area of incipient Swiss Cheese corrosion and blow it out definitively -- perhaps that too was part of the intent?

Hydro testing to "125% of nominal" in a smokebox would be what, considering that ambient in a working box would be subatmospheric... ? ;-}

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 Post subject: Re: Hydro testing issues
PostPosted: Mon Dec 21, 2020 10:32 am 

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One thing Robby has done is to absolutely confirm me in my belief that heating for a hydro should be done by heating the circulating water (preferable to feeding any particularly hot water to a cold boiler, imho; it might be interesting to consider how hot the initial fill should be) perhaps with multiple feed points to ensure that every part is heating at an appropriate rate and no spots are 'starved'.

That leaves only a kind of theoretical concern: are there any surfaces related to the pressure space that are heated by combustion gas more than conduction, that might require air heated to 'water test temperature' to be circulated through the gas spaces? My default opinion would be that there really are not.

I think Robby did know that leaks in the smokebox don't mean primarily that there is additional 'pumping work' to eject the additional air that seeps in, but that the effective "vacuum" induced by the draft is partially destroyed, and its flow patterns perhaps badly changed, by the effect of the leaks. While the former effect might demonstrate a nominal back-pressure increase, I would think it would be slight, and otherwise additional mass flow might actually enhance the effect of entrainment or ejection of the combustion gas. The latter effect on the other hand can be critical.

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 Post subject: Re: Hydro testing issues
PostPosted: Tue Dec 22, 2020 11:04 am 

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SD70dude wrote:
Robby Peartree wrote:
Another example is the hydro done on 4-8-4 that blew out a side sheet in the 1970s because it was done with cold water.


Which engine did that happen to?

UP 8444

Robby Peartree


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 Post subject: Re: Hydro testing issues
PostPosted: Tue Dec 22, 2020 11:41 am 

Joined: Wed Jan 28, 2009 4:30 pm
Posts: 191
Also happened to the D&R #8 in the late 1970's. Zippered the stay bolts down one side so fast you couldn't discern the breakage of individual bolts. Broke almost a dozen before the pressure dropped off. Good times.


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 Post subject: Re: Hydro testing issues
PostPosted: Tue Dec 22, 2020 11:57 am 

Joined: Tue Sep 14, 2004 7:52 am
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Location: Strasburg, PA
I remember reading an ICC report about a PRR engine that did that under steam. As I recall, it had a patch across the bottom of the backhead, including the mud ring and the bottom row of bolts, then butt welded to the balance of the backhead. Turns out that several bolts in that first row were broken. The extra load broke the weld, which broke the remaining staybolts in the patch, which broke the balance of the weld, peeling the patch open as if the top of the mudring was a hinge and emptying the boiler directly into the cab. Needless to say, that was it for the crew.

You don't need low water or crew incompetence to have a catastrophic failure if you aren't keeping up on your inspections and maintenance.

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 Post subject: Re: Hydro testing issues
PostPosted: Tue Dec 22, 2020 12:47 pm 

Joined: Fri Nov 07, 2008 11:21 am
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Quote:
Another example is the hydro done on 4-8-4 that blew out a side sheet in the 1970s because it was done with cold water.

Quote:
Also happened to the D&R #8 in the late 1970's.
Quote:

I have a hard time believing that a locomotive boiler failed BECAUSE of a cold water test.
Sure, someone reported that it happened because of cold water, but I don't believe it.
Yes, I know all about the ASME and National Board temperature specifications.
Yes, I know about riveted boiler joints leaking when cold, etc.

Bottom line is that locomotive boilers are made of various grades of mild steel. Nothing exotic, nothing horribly thick. Normal plain old steel. If a boiler failed due to a test, it was because there was something amiss, not from using cold water.

I have witnessed many cold water tests. Cold water was used simply because hot or warm water was not available nor possible. Testing piping and vessels in the field in the winter, with snow blowing.....

If mild steel is so prone to brittle fracture, then every steel bridge in the world needs to be closed when covered with ice or snow.

My two cents.


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 Post subject: Re: Hydro testing issues
PostPosted: Tue Dec 22, 2020 5:23 pm 

Joined: Thu Dec 12, 2013 1:26 pm
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I've heard of an incident in which a hydro was done with cold water and then the boiler was left overnight with the water bottled up in the boiler and unfortunately it was tight enough that the pressure did not bleed off. And the water temperature rose enough to increase the hydrostatic pressure high enough to do some damage.


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 Post subject: Re: Hydro testing issues
PostPosted: Wed Dec 23, 2020 1:19 am 

Joined: Wed Jan 28, 2009 4:30 pm
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I did not mean to imply that the D&R boiler failure was a cold water cause. It was the result of wasting of stays and when one failed the surrounding stays let go.

The analogy to iron bridges in the frigid winter is a great example of iron is OK in the cold. But the brittle/ductile transition is real and demonstrable in the lab.

I would also like to share a hydro of a 1905 boiler that was so tight that it held MAWP for several days and as the day warmed the pressure rose and at night it would fall. Eventually we bled of the pressure. One of the better hydros I have been affiliated with.


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