11 replies to this topic

[chandru]

Dear all,

Why ASME B31.3 specify the hydrotest pressure for process lines are 1.5 times of design pressure. Why not other fractions i.e., 1.6 or 1.4 times of design pressure. Is there any reason for specifing 1.5 times of Design pressure.

Thanks and Regards,
Chandru

[fallah]

Dear all,

Why ASME B31.3 specify the hydrotest pressure for process lines are 1.5 times of design pressure. Why not other fractions i.e., 1.6 or 1.4 times of design pressure. Is there any reason for specifing 1.5 times of Design pressure.

Thanks and Regards,
Chandru

Chandru,

It is in relation to allowable stress. Actually as per B31.3 allowable stress values at design temperature for piping materials shall not exceed two-thirds of corresponding yield strength.

It is obvious, as per above with 1.5 times of design pressure value for hydrotest there wouldn't be any possibility that the hydrotest pressure to be exceeded the yield strength.

Fallah

[ankur2061]

Chandru,

I had posted on Hydrotest pressure for vessels and piping sometime back on the forum along with attachments of relevant sections of ASME Section VIII Div. 1 for vessels and ASME B31.3 for piping. Below is the linK:

http://www.cheresour...__fromsearch__1

This should help in your understanding.

Regards,
Ankur.

[chandru]

Thank you very much for your reply Mr.Fallah and Mr.Ankur

Similarly is there any reason for selecting pneumatic test pressure as 110 % of design pressure.


Thanks & Regards,

chandru.

[ankur2061]

Chandru,

Check out the following link:

http://www.cheresour...__fromsearch__1

This should help.

Regards,
Ankur.

[chandru]

Dear Mr.Ankur,

Thanks for refering the topics, I read the topic and i could find details as

1. Severity of pneumatic test over hydrotest as the gases are compressible fliud.
2. Temperature correction factor, if operating temperature is different from test temperature.
3. practical experience of pneumatic test about pressure rise during testing.

Actually i am looking for the reason why 110% of design pressure rather than any other values like ...105% or 115% of design pressure.

In this topic Mr.Fallah has explained how 150% of design pressure is arrived for hydrotest. Like this any reason for arriving 110% of Design pressure for pneumatic test.

Thanks and Regards,
chandru

[ankur2061]

Chandru,

I would like to understand why do you want to know the logic for the penumatic test pressure for process piping as per ASME B31.3 to be 110% of the design pressure. Are you doing some kind of research on this subject. Because unless you are doing some kind of research on the subject, I don't see any reason for you to try to find out whether it can be 105% or 115%.

As I had mentioned in the post "Pneumatic Test Pressure", pneumatic test is generally done to find out samll leaks in completely installed piping systems using soapy water and where introduction of water inside the piping system cannot be permitted due to process reasons. A soapy water leak test can be done at lower pressures then the test pressure.

Hydrotest is generally a more reliable test for piping integrity testing compared to pneumatic test and the norms for hydrotest are very well defined in ASME and other international standards.

Regards,
Ankur.

[fallah]

Chandru,

Due to the hazard of released energy stored in compressed gas, i think ASME piping codes (e.g. B31.3) do consider the Penumatic Leak Test pressure not higher than the maximum allowable value would be set for overpressure protection during operation i.e. 10% above the piping design pressure. Hope, you would be satisfied by this explanation.

Fallah

[chandru]

Dear Ankur & Fallah,

Thank you for your prompt and quick reply for my question.

I am not doing research, raised the question to know the basic behind the hydrotest & pneumatic test values.
I am satisfied with your answers.

With Regards,
Chandru

[Shakil]

Sorry for little diversion!

 

If hydrotest is done at 150% of Design pressure (DP) or MAWP won't the tank will blow off as we are exceeding design pressure?

 

As hydrotest is done at 150% of DP but at room temp. and DP is at design temp. So obiously the Allowable material Stress value is high at R.T rather than design temp.? So what is the use of doing hydrotest at room temp?

 

Plz clarify!

[fallah]

Shakil,

 

For your first question refer to second post of this thread (by fallah)

 

About your second question you should be informed in all cases hydro test pressure would be calculated along with the correction due to allowable stress difference in room temperature and design temperature... 

[kkala]

I think <http://www.cheresour...iple-psv-sizing> is useful for the first question of Shaki, hydraulic test does not exceed the limit of  stress that would destruct the material.

As falllah explains, for e.g. design pressure=10 barg at 400 oC design temperature, hydraulic test pressure shall be higher than 15 barg, specified by applicable code. The hydraulic test is done at ambient temperature, it would not be practical/safe to do it at some high temperature. But, simply and imprecisely saying, strength increase due to lower temperature is added to test pressure.