Hydrotest at night vs at noon 4

[tika5828]

Is there any difference if we do hydrotest at night vs at noon? As we know, at night ambient temp is colder and water is colder. Does it cause different hydotest pressure? I heard from QC Engineer, they did hydrotest at night and hydrotest pressure is lower than it should be. Is it because water temperature effect or because of leaking?
As I know, water is incompressible fluid, and temperature of water should not have significant effect on water pressure. Please correct me if I'm wrong.

Thanks so much!

 

[BigInch]

Water IS compressible (a function of both temperature and pressure). Lower temperatures contract both pipe and water, water more than pipe, so pressure reduces when the temperature drop.

The things that we know for sure can get you into big trouble.


Independent events are seldomly independent.

 

[LittleInch]

Are you referring to piping or buried pipelines? Piping will suffer from a wider change in temperature than buried pipeline, but short buried sections can also be affected by above ground sections.

BI is totally correct - water may normally be referred to a "virtually" incompresisble, but then so is steel and you know that expands and contracts due to chage of temeprature. Water has a greater thermal expansion co-efficitn and so althought the pipe circumference expands and contracts with temperature, it does not equal the water expansion. Many hydro tests need calcualtions to dmonstrate that the temperature fall or rise is due to temperature effects and not a leak. It needs to be calcualted taking into acocunt the strength of the pipe, but change in pressure can be 3 to 4 bar per Deg C.

See

http://www.eng-tips.com/faqs.cfm?fid=1339

for more info or search more effectively for water expansion effect in hydrotest.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[JR97]

Regardless of the time of day, sufficient time must ba allowed for the temperature of the fluid (water) and pipe to equalize. If a large amount of water must be added, additional thermal stabilization periods may be needed during pressurization. That said, if you are monitoring the pressure with adequate gaging and tak the necessary steps to add or remove water due to temperature changes during the test; it doesn't matter what time of day it is during the test.

 

[racookpe1978]

If there is ANY way possible, do NOT do it on night shift UNLESS your nightshift is already (1) on shift and has been night-accommodated AND (2) that same nightshift is ALREADY doing all of the other pressure tests and flushes and valve lineups.

The valve lineups and unusual system manipulations for a major hydrostatic test cannot be reliably nor easily done by a sleep-starved crew working without dayshift planning, scheduling, cooperation, tooling, assistance and control.

HOWEVER, if the nightshift crew is already in a running mode and IS comfortable with what is needed and is expected to be done operationally and mechanically and physically, THEN it IS easier to do the work on nightshift BECAUSE there are fewer bodies running around interfering with the "testing" that has now become a routine event.

Make sense? makeshift and temporary nightshift crews working overtime from their original daylight hours with daylight "assistance" of the "daylight" test engineers and controllers and management were what fouled up Chernobyl.

 

[chicopee]

For pressure vessels, water temperature has to be maintained within a range. Is there a similar restriction for piping?

 

[BigInch]

No temperature range must be maintained, but widely varying temperatures are not extremely conducive to a successful test in any case.

racook, *Good Point*. Excelent way to multiply the risk by doing the test at night!

Independent events are seldomly independent.

 

[racookpe1978]

I heard from QC Engineer, they did hydrotest at night and hydrotest pressure is lower than it should be. Is it because water temperature effect or because of leaking?
As I know, water is incompressible fluid, and temperature of water should not have significant effect on water pressure.

When we ran nuclear primary systems "solid" with no pressurizer and no air anywhere in the entire system (a volume MUCH larger than a simple isolated pipeline!) we could see the pressure change hour-by-hour in the pipe and vessel systems inside the containment based only on sunlight levels changing outside the walls.

Absolutely YES, a temperature change WILL change system pressure during ANY solid operation such as a pressure test.

 

[tika5828]

Thank you all for the valuable answers!