Dear Mr. MonerZ,
Thank you for your reply....
It is not a hydrotest, it is pneumatic test pressure. Process fluid is Gas, so that i taken as 1.1 X design pressure.
In ASTM B31.3 (2008) for B 167 inconel material, for this max temperature is 1200 Deg Fahrenheit (648.88 Deg c), allowable stress is 2 ksi.
But i got data's from our material supplier. Allowable stress at temperature 1100 deg c i.e. 5100 KPa
kindly crosscheck this allowable stress is ok.
Regards
Elias