24 Hours Hydrostatic Test

Dear Mr. cckla,

For a given Working Pressure, the Design Pressure and Hydraulic Testing Pressure is derived based on the material. As long as the Hoop Stress for the system is NOT crossed and maintained below the Hoop Stress technically you can keep the Test Pressure for 24 Hours.

But it is not required to keep the Hydraulic Test Pressure for 24 Hours. It is sufficient you keep the Pressure for Half-an Hour for incompressible fluids and for 1 hour for compressible fluids. Measure the drop in pressure in relation to time and if the drop in pressure is 0.25% or less than 0.25%, the system is OK.

Further the duty condition of fluid flow - whether it is hot fluid or cold fluid the temperature plays a role in material strength. Depending on the temp. to maintain the maximum permissible limit of hoop stress, the Working/Testing Pressure will vary.

DHAYANANDHAN.S

Drop in pressure to time mean 0.25%/(how many minutes or hour) ? Is this guideline suitable for test in any duration ?

Dear Mr.cckla,

Pl. read 2nd Para (in my Reply, posting No.1, next to your posting) and a sentence reads as "for Half-an Hour for incompressible fluids and for 1 hour for compressible fluids."

So the pressure drop to be observed for incompressible fluid is 30 minutes and for compressible fluid it will be 60 Minutes.

Let us see what further comments are receieved.

DHAYANANDHAN.S

I ever heard pneumatic test with 110% of design pressure. But in short duration

Well, there is the story about an underground pipeline, perhaps 48in diameter and a couple of miles long, that was subjected to a <...pneumatic test...>.

The end of the test came when the coupler at the end of the pipe blew off, demolished a scaffold, sent scaffold poles flying in all directions including upwards, whereupon one of the poles dropped through the roof of a building and impaled and killed someone who was asleep.

That is why hydraulic and hydrostatic testing is the right way to do it. All that happens is that innocent bystanders get wet.

I think you may be confusing the 24 hour static test with a timed pressurized test. When we installed waste drain piping in residential homes we would cap off the drain end and then fill the piping and vent stacks with water to see if there were any leaks. We did not apply any extra pressure, only static head pressure!

This is done on the waste drain which is usually made from ABS plastic.

You don't want to pressurize ABS. It has a tendency to explode!

This definitely not waste drain piping. This happen in cold water, fire protection and chilled water

24 hours with pressure is a normal practice for underground (burried) piping systems instalation inside the batery limit of the plant. You have to record the pressure and also the temperature. As I said is normal and according to many project spec. and is an API/ ASME recommendation .

Normally, 24 hours hydrostatic test conducted during time of installation before it is buried and expose to weather. What would be the guideline of acceptance when pressure rise under hot sun and drop at night time ? What is the test pressure ? Is it still at 150% of design pressure ?

Not before, after buried:

1.- coated pipe

2.- weld pipes (Or thread)

3.- Coat welds after NDT

4.- Holliday Detector

5.- Buried (Soil compactation i.e Kholer machine)

5- 24 hours Hydro test (ie Barton pressure Temperature)

What if leaking found after buried ? The rectification work would not be difficult ?

Yes cckla, is very difficult

But you do not want your fire system fails when you need it.

To detect a possible leakage point patience is required. (A lot)

Therefore, you should make a thorough inspection before burying the pipe.

But the hydrostatic test should be done with the full system ready before operation.

Believe me

A "casual" 2-hour test before burying might address some of cckla's concerns about post-burial rectification difficulties.

Thanks 88y

Yes, should be a good practice. But is not usual. Cost & time are mandatory

Wp

24hr test won't be practical as temperature can vary widely.

Because, that is what was done in world war II