Allowable stress at hydrotest temperature

My apologies if this query has been answered before.

I have a heat exhanger with tubesheets and floating head components in duplex 2205 which are failing in shellside hydrotest (acc. PVElite). [We are using test stresses a bit more than ASME]. But it turns out that the stresses that PVElite allows in hydrotest are only 1.3 times the allowable design stress at ambient. In actual fact, I would allow 90% yield for those components. To quote figures in Megapascals, we are talking about 403 MPa (90% Sy) instead of 230 MPa (1.3* Sa) (that is 75% difference!).

I am aware that I can set my own allowables within the program, but I would like to know why PVElite is so conservative by default when it causes so many problems with high yield materials like duplex? Will it be changed in future?

Regards,

RonJ

Hi Ron,

By default PV Elite uses the minimum of 1.5 * S, 0.9 * Yield. But, you can indicate the program to just use the 0.9 * yield from the Design Constraints tab.