The pressure vessels build as per ASME Sec.VIII Div.I year1999 editions or earlier follows the hydrotest pressure of 1.5 times the MAWP.
Any vessels construction following after the 1999 editions follows the hydrotest pressure of 1.3 times the MAWP (maximum allowable working pressure).
The reason for using or changing the factor 1.5 to 1.3 is quite logical.
Suppose you are fabricating a pressure vessel of Carbon steel plate confirming to SA 516 Gr. 60 (I.e. specified minimum ultimate tensile strength of material 60,000 psi) then by applying factor of safety of 3.5 which is based on vessel constructed earlier than 1999 code you have design stresses of 60000/3.5=17,142 psi.
Now you are fabricating the vessel by following later editions I.e after1999, where the factor of safety has changed to 3.0, then in this case you have a stress value of 60000/3.0=20000 psi.
Now if your vessel design temp is 300℉ ( The Allowable stress for SA 516 Gr. 60 at 300℉=18,900 psi) now you are hydrotesting the vessel built by both the editions of the code the you have
For 1999 edition or earlier:
Hydrotest pressure =1.5*MAWP* stress at test temperature / stress at design temperature.
=1.5*MAWP* 17142 / 18900
=1.36 MAWP.
For later editions:
Hydrotest pressure =1.3*MAWP* stress at test temperature / stress at design temperature.
=1.3*MAWP* 20000 / 18900
=1.37 MAWP.
Which are almost the same.
Thus by following any edition of this pressure vessel construction code the hydrotest pressure remains the same.
I hope I have satisfied your queries / doubt.
Regards,
PARAG PANSARE.
Sent from my HTC
----- Reply message -----
From: "nishant nair" <nishant852003@yahoo.com>
To: "materials-welding@googlegroups.com" <materials-welding@googlegroups.com>
Subject: [MW:17573] Hydrotest pressure criteria
Date: Sat, Apr 27, 2013 19:02
From: "nishant nair" <nishant852003@yahoo.com>
To: "materials-welding@googlegroups.com" <materials-welding@googlegroups.com>
Subject: [MW:17573] Hydrotest pressure criteria
Date: Sat, Apr 27, 2013 19:02
Why hydrotest pressure is taken 1.3 times of design pressure? What is the criteria that fixes the term 1.5 times or 1.25 times, etc.??? Thanks in advance, |
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