Dear all,

i have two questions.

First, when I try to run Fatigue Analysis for Nozzles, D/t ratio comes out to be greater than 100, but the Damage factor comes below 1 and all other results are within acceptable range. Vessel is to be U1 stamped.
Now what will be the implication of this, on U stamp as we cannot change thickness and diameter. I understand that stress intensity will increase in this case, as D/t goes greater than 100.



Second question is regarding inside diameter calculation for D/t ratio, inside diameter used by pv elite in the case of ellipsoidal head is 4501.59 mm while in the case of cylinder it is taken as 2500 mm, while user defined inside diameter for both is 2503.18 mm with a corrosion allowance of 1.59 mm.
Now why this diameter value is changed from 2500 mm to 4501.59 mm for head.


Best Regards....

Hello usmani

The application of the U1 stamp implies that you are registering a vessel manufactured in accordance with the rules of ASME Section VIII, Division 1. There is no reference to fatigue analysis in that code. You are obliged to to adhere to its rules. Fatigue concerns the theoretical life of the vessel, and that is not related to new construction. It is only in Division 2 where the fatigue analysis has to be performed. The Authorised Inspector cannot insist that a fatige analyis be carried out. If you include a fatigue analysis in the final report, it is only ancilliary to the Division 1 calculations. So, if the D/t ratio exceeds the prescribed value, the decision is up the engineer who signs the report.

I do not have enough information to answer your second question. That is a question for ASME.

Dear Usmani,

Reply to 2nd Question:

I assume your connection would be on spherical portion of dished end. So what PV Eltite has done is that first it has found out the crown radius of 2:1 Ellipsoidal head i.e. 90% of 2500 = 2250...so diameter would be 4500 mm and then corrosion allowance of 1.59 mm would have been added to arrive 4501.59 mm. However corroded ID should be 4500 + 2*1.59 = 4503.18 mm.

Hope above is clear.

Mukesh
www.theculminates.com
M:+91-9428500192