Effect of corrosion allowance in Hydro test pressure 1

[KPMISTRY]

Hello,
I have observed one point during hydro test pressure calculation. In my vessel, there is 1.5 mm corrosion allowance & I consider my design pressure as a MAWP bcz there is no other loading which mentioned in UG-22. So during hydro test calculation should I go with reverse calculation of thickness with allowance to find new MAWP & than find hydro test as per ug-99 by consider new MAWP...?

Kejul

 

[moltenmetal]

No.

You test at a multiple of the MAWP. You do not attempt to subtract out the corrosion allowance by adjusting the MAWP higher.

 

[jte]

No, it depends.

The response provided by moltenmetal is the "UG-99(b)" approach. Perfectly legal with VIII Div. 1.

But, some owners require the "UG-99(c)" approach which bases the hydrotest on the MAP (N&C) which is Max. Allowable Pressure, New and Cold. This MAP is, as the "N & C" part makes clear, taken in the new condition. Meaning that any CA is included as contributing to the strength of the steel when the maximum pressure is calculated. The "C" part of that points out that the allowable stress of the steel at ambient temperature is used in calculating the allowable pressure.

So KPMISTRY, the answer to your question depends on what your client spec's call for.

 

[moltenmetal]

A star to jte for pointing out the distinction.

Your resulting test pressure may or may not change- it depends on which component limits the MAWP. And it is a certainty that you will not be testing every component at a pressure which effectively subtracts is corrosion allowance.