Pressure vessel hydrostatic test requirements and implications on design

For hydro test as per ASME code manufacturer of the equipment must follow ASME Boiler and Pressure Vessel Code Section VIII DIV.1 (Rules for Construction of Pressure Vessels), UG-99. We will discuss hydro test requirement in this discussion. Requirements as per ASME Boiler and Pressure Vessel Code Section VIII DIV.1 (Rules for Construction of Pressure Vessels), UG-99 –
  • Before hydro test all operations must be completed as no one can alter equipment thicknesses once hydro test is done.
  • All examinations (eg. all NDT tests) have to be performed, except those required after the hydro-test.
  • Hydrostatic test pressure at every point in the vessel is at least equal to 1.3 times the maximum allowable working pressure multiplied by the lowest stress ratio (LSR) for the materials of which the vessel is constructed.
Hydro test Pressure = 1.3 x Design Pressure x LSR. LSR=  (material stress at  its operating temperature)/(material stress at  its design temperature)
  • If end client or the equipment owner does not specify the MAWP (Maximum Allowable Working Pressure) as the design criteria then we may select the UG-99 (b) (36) – endnote (36) i.e. The MAWP (Maximum Allowable Working Pressure) may be assumed to be the same as the design pressure when calculation are not made to determine the MAWP (Maximum Allowable Working Pressure).
  • The hydrostatic test pressure reading shall be adjusted to account for any static head conditions depending on the difference in elevation between the chambers being tested and the pressure gauge.
  • Above equation represent the minimum standard hydrostatic test pressure as per ASME section VIII Div.1.
  • This Division does not specify an upper limit for hydrostatic test pressure. However, if the hydrostatic test pressure is allowed to exceed, either intentionally or accidentally, the value determined as prescribed in ASME Boiler and Pressure Vessel Code Section VIII DIV.1 (Rules for Construction of Pressure Vessels), UG-99 – (c) above to the degree that the vessel is subjected to visible permanent distortion, the Inspector shall reserve the right to reject the vessel.
Now we will see how to enter the hydro static requirement while designing of the vessel in PV Elite software Hydro test Type selection in PV Elite Software ( wisely choose endnote (36)) – Figure 1 : Hydro Test Input for Pressure Vessel Design in PV Elite Software. After selection check PV Elite software output to confirm the selection as below – Figure 2 – Design Data Hydro Test Type / Equipment Position During Test. Final output report with Hydro test pressure values as per above selection in PV Elite Software Figure 3: Hydro Test Pressure Result.

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