HX Rerate

[picasa]

There is a shell&tube HX that needs to be rerated for new higher tube side pressure. Shell side pressures stays the same. The thing is that now the new tube side design pressure is higher than the shell side design pressure. Before the tubeside design pressure was lower than the shell side design pressure. The absolute value of difference between the new tubeside design pressure and the shell side design pressure is lower than what it was before.

For that rerate, is it necessary to repeat the design per ASME UHX (latest edition)?

What kind of load cases need to be considered? UHX-12 shows three different load cases: Pt and Ps=0, Ps and Pt=0, Pt and Ps. Do all these load cases need to be considered for the rerate?

How to decide whether the new calcs are done per TEMA or ASME UHX?

 

[TomEun]

To my thinking,
The re-rating, repair, and alteration should be followed up the code which was based on the original fabrication.
That is, if the H/EX was built per TEMA before January 1, 2004, the re-rating per ASME Section VIII, Div.1, UHX (mandatory from January 1, 2004) is not necessary.
* Please find API 510, para.7.1.
However, you may have to consider the worst operating condition for the differential pressure anytime.

Thomas Eun
thomaseun@shaw.ca

 

[metengr]

The re-rating of this heat exchanger is an alteration. Either API or NBIC requirements should be followed for an alteration, which normally refers engineering to be performed in accordance with the original code of construction.