Modeling a system with Alloy 800HT

[khuehls]

Has anyone modeled a system using 800HT? I'm working on a project where that is the owner's preferred piping material. However, it's not in the pull-down menu in Caesar. I've looked up the physical properties for the alloy and found that there are numbers all over the place. For example: on-line product data from Special Metals lists the yield strength at about 36 ksi in one place and 21 ksi in another. I called them to ask about the difference between the two and was told to just use 28 ksi!

So, if you've successfully modeled a system using this material, I'd be interested in how you set up the material in Caesar.

The application: 4" compressed air at 800 psig and 1500F using 800HT XXS pipe.

 

[XL83NL]

For example: on-line product data from Special Metals lists the yield strength at about 36 ksi in one place and 21 ksi in another. I called them to ask about the difference between the two and was told to just use 28 ksi!

If you use B31.3 as your design Code (most probably), you must use the stress allowables by that Code.
B31.3 listst stress allowables for UNS N08811 in ASTM B407, B409, B564, B366 and B408 in table A-1. Use those if your design is to B31.3.

On a side note: Im working on a 1350F 800 psig job with 800H (where I had to manually add the material to AutoPIPE - CII is not my field).
I can tell ya XXS will be on the edge of B31.3 req.'d wall thickness.

 

[khuehls]

XL83NL:
Thanks for response. Yes, we are using B31.3 for this one. Yes, as you predicted, the XXS pipe wall is not thick enough (.695 calculated vs. .674 for XXS). Also, I manually entered the material using the allowable stress from B31.3. I also entered elastic modulus, yield stresses, and expansion coefficients. Will Caesar II even use the yield stresses if I've entered allowable stresses?

Based on the wall thickness issues and the low allowable stresses at temperature, it does not look like 800HT will meet code requirements in this application.
Any material recommendations for this application? Again, 4" pipe, 1500F @ 800 psig.

 

[XL83NL]

I can not answer any question related to CII, but here's my 2 cents;
- review this thread for a reply I did regarding the use of WJSRF
- review ASME II-D and see what materials has the highest allowable @ temp. You can work out stress allowables for B31.3 usage from II-d fairly easy.
- the rules of the B31.3 base code dont apply actually to these limits as your way beyond Cl 2500 flanges. The standard lame equation (limited by max circ stress) needs to be replaced by the equations of chapter IX of B31.3. However, youre in the creep range, and chapter IX is not applicable
- eventually, you may find you're on the edge of conventional piping metals and may need to step up to the more advanced grades (centrifugally cast pipes used for steam reformers) or cement-lined pipe.

this is a tough one