There was a failure in our plant in one of the high temperature line. We contacted the consultant who designed this line. They sent us old C-II model in version 4.5 stating that the results would be different if it is tried to open in the new version. They sent the C-II report as well showing that the sustained case stress were well within allowables. Now I opened the model in the new version and ran analysis. The sustained case showed the failure. So what is the reason for this? Is it that allowables have been revised by ASME Codes? Or something else?

In general, the results from one version to the next should be the same. There are exceptions: Piping Code changes (SIFs), material changes, software configuration changes.

What Piping Code was implemented in the analysis?

Richard,
Thanks for replying!
In their report:
1) The material used is ASTM A312 TP304H.
2) The ASME B31.3(2002) version is referred.
3) The temperature is around 1400 Degree F.
4) The hot allowable shown in their report is 20000 psi.

ASME B31.3 version 2008 gives hot allowable at this temperature to be 2.4 ksi. So my question :Did ASME code give 20 ksi as hot allowable in version 2002? If yes, how drastically the code revised the allowable for this material!!!!!

Hi,
I have checked with ASME 31.3 2004, the allowable hot stress for A312 TP304H at 1400 F is 2.3 ksi .I dont have a copy by 2002 but there cannot be such drastic change of allowables to 20 ksi.
The line must have running for several years and if it would have been sustained load only then it would have failed much earlier.May be within first year of operation itself.
There can be several causes of failure in line, vibration induced fatigue being on of them.
Try to check out these also

In ASME 31.3 2002, the allowable hot stress for A312 TP304H at 1400 F is 2.3 ksi

A steel with 20 ksi at 1400F most probably do not even exist.

Regards,