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Boiler hydrotest by water at normal temperature

Sunday, April 02, 2017   By: pradeep [1918] 2 Stars
Dear All
Why boiler hydrotest done with water with ambient temperature which is 30-35 deg celcius instead of hot water. Is there is any technical aspect apart from safety concerns


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Monday, April 03, 2017   By: cmolanes@itba.edu.ar [50] 4 Stars
Mr Pradeep:

The main reason to hydrotest a boiler with water, as is done with any other pressure vessel, is to avoid the risk of pressurizing with air, or a gas, or steam, since as they are compressible fluids, to rise the desired test pressure, a large amount must be compressed, so in case a failure should occur, a catastrophic explosion may result.

Using an incompressible fluid, such as water, cheap and available, only a little amount is needed, after having the vessel filled, to attain the test pressure, so in case a failure occurs, only a small amount of fluid will be dispersed, and safely. Using hot water, in principle adds nothing and is unnecessary, because even with hot water the metal temperature will be far lower than the working metal temperature when under steam.

If you are thinking in some test other than the common pressure test, of 50 percent more than the working pressure I am envisaging, then perhaps you would eventually need hot water.


Claudio Molanes

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Monday, April 03, 2017   By: Jim Watts [764] 5 Stars
There is a very important technical reason for temperature specification.
It is to avoid water that is too cold.
Water that is too cold will endanger the drum to fail in Brittle fracture mode which can occur below design pressure and is sudden and catastrophic.
A separate high temperature limit is imposed for the personal safety of the inspectors entering the confined space of the boiler.

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Tuesday, April 04, 2017   By: cmolanes@itba.edu.ar [50] 4 Stars
Hullo Jim!

Thanks for your additional comments. I had nor thought of it, since where I live and have worked, such low temperatures are not found, the lowest in winter say about 10 degrees, so brittleness was not of major concern as far as what I have experienced. The higher limit is very sensible, too.

I should have had a broader scope before answering, but as Mr. Pradeep spoke of ambient temperatures of 30-35 Celcius then I imagined that he lives, as I do, in a tropical area, or testing in summer time.

Claudio Molanes

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Wednesday, April 05, 2017   By: Jim Watts [764] 5 Stars
Hi Claudio,

It is understandable people in warm climates never think of cold water issues.
As a mater of interest I include a report which has a photo of one of the most famous brittle fractures in a boiler.
It occurred in a Boiler Drum at Cockenzie Power Station in England, the water was at 8 degrees C.
It is on page 16 of the PDF included.

Learning from ignorance v2_1369218320_2(1).pdf

Click on picture for full size view or to view PDF!

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Friday, April 07, 2017   By: cmolanes@itba.edu.ar [50] 4 Stars
Thanks Jim! A very interesting paper, with both technical and historical interest.

I did not know the term economizer nozzles but I guess they are the welded short pipes where the downcomers are welded to. I also found strange that the authors mentioned coal fired plants, omitting fuel oil and gas fired natural circulation boilers, but probably they are not common in Great Britain. The title, learning from ignorance, is very accurate as well, and now mine is somewhat less.

Claudio Molanes

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superheated steam ideal gas
By: cmolanes@itba.edu.ar [50]

Mr. Pradeep:

Steam behaves well as an ideal gas if not too close to the saturation line if you place yourself on a Mollier chart, when the temperature and enthalpy lines coincide and are straight, horizontal lines, then it behaves as ideal, and this you can easily see on the chart.

I would rely though most on the steam values given by the chart or steam tables, because they are confident independently of the region , e.g. they stand both for ideal and real gas, but the ideal gas equation ....   Read All
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