vessel re-rate

[Sebra]

I want to re-rate a vessel which is designed for 1.5 MPag @ 190degC. This vessel has another design criteria which is 50kPag @200degC which has been ignored during the design. to re-rate it, Should I only check the design for 50kPag@ 200degC or I need to rerate the vessel for 1.5MPag @ 190degC.
basically should I consider the highest pressure @highest temperature for vessel re-rating or only checking the vessel design for missing operating condition will suffice?

Thanks.

 

[metengr]

The best approach is to evaluate highest design pressure at maximum design temperature.

 

[LittleInch]

I find it difficult to believe that 10C difference at 190C will make much of a difference unless someone really got it too tight or that most processes can be controlled that accurately.

If it passes 1.5 @ 200C, then 50kpa @ 200C should be OK.

You really need to understand where this data comes from and how much spare has been added from max operating to design temps.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Sebra]

Thanks for your responses. If it was in design phase I would have design it to 1.5MPag @ 200degC in the first place but it is too late now. I personally think 1.5MPag @200degC is the best practice however wanted to know that checking the design for 50kPag@ 200deg would be sufficient as well or not. in other word is it a code requirement to design it to highest pressure at highest temperature? from you answers I undestarnd that it is enough to check the design for 50kPag @ 200degC.

 

[loilfan]

Those are strange values for different design conditions. Is the 50kPa external pressure?

I have had to re-rate piping with a sliding scale of pressure based on monitoring UT thicknesses, but that wasn't at original design.

Perhaps it came from the PSV sizing? What service is this vessel in?