Section VIII, Div. 1 1974 Boiler Code

[Ken_C]

we are trying to model a vessel designed and built in 1974 so we can assess if a higher SG fluid can be used. Applying current Section VIII, Div. 1 code edition software a portion of the vessel shell fails (significantly) at the original design condition (before we bumped up the fluid SG). Before we hone in on operator error, has the methodology changed since 1974 used to determine shell thickness?

Also, the material used is SA-387-C (annealed), which based on my research is the current SA-387, Gr. 11, Cl. 1. The temperature is 1010F. Could the allowable stress have changed since 1974 to cause the software to show shell failure?

Note that without getting into lots of details that other smaller diameter portions of the shell (<=138" dia) are OK...it's the large diameter portion (144" dia.) that fails.

Thanks for your time!

 

[mk3223]

You should evaluate the existing vessel based on the material properties of the 1974 Code, instead of the present Code. As the changes of the material science and manufacturing through the years, old material might not be made any more, or be substituted with equivalent but new material. In this case, you can't evaluate the old vessel using the properties of the equivalent/new material.
Suggest to find a copy of the 1974 Code and redo the assessment.

 

[JStephen]

Some of the allowable stresses have gone up, I'm not sure if any have come down. Was it possibly not designed for the full-of-liquid condition?

You wouldn't necessarily re-rate using the current code, as noted above- you should be able to approach it as a change-of-service per national board rules.

 

[Ken_C]

Thank you for your comments...reinforces what i felt...we need the 1974 code. Any idea of places where we could find if we want to take this further?

 

[metengr]

The National Board of Boiler and Pressure Vessel Inspectors retains copies of ASME B&PV Code and provides for a fee copies of pages. You will need to be specific about what information you need, namely allowable stress values in Section II, part D for the material, because you will be paying for each page of copied material.

 

[Ken_C]

Thank you!

 

[Ken_C]

Found the answer:
current code allowable for A387 Gr. 11 is 5,880 PSI at 1010F, vs. 7,340 PSI for A387 Gr. C when the unit was built.

in this case, the allowable got smaller.

 

[mk3223]

Ken_C, Thanks for sharing the good finding of the 1974 Code. It seems these two materials are in the same A387 "family" but different "grade".