ASME VIII High Strength Stainless

[engpes]

I am designing a low pressure / low temperature ASME VIII, Div I stainless steel tank (DP: 75 psig; DT: 100 F; SA240-304 SS Material).

I have a vessel clip/lug (not lifting) that my stresses are getting above the allowable limits for SA240-304 SS.

My question is this:

1.) Is there an ASME VIII, Div I allowable stainless grade material with a higher yield strength than that of SA240-304 SS (30 ksi)? I would need something in the neighborhood of 40 ksi yield.

Adding steel is not really an option, as space and functionality come into plate. Thank you.

 

[prex]

Not among the commonly available stainless steels of the series 304 and 316. 316N goes up to 35 ksi, but I don't know whether it is commonly available in small quantities.
Of course I assume you are using the higher allowable stresses for 304.
It appears odd to me that a single lug is causing your problems: there are plenty of design solutions to lower the stress around a lug: pad plate, wider lug, change shape or position if bending moments are involved...

prex

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[SnTMan]

engpes, duplex S31803 offers higher yields, however that won't help the shell stresses, if those area a problem.

Agree w/ prex, there should be other ways.

Regards,

Mike

 

[XELR8]

Here are a few suggestions:

1) Check your material certificates for your 304 plate and see what the actual tensile strength is. You can use this as your value.
2) Check the strain at your calculated stress and see if its less then 2%. If it is your probably ok.
3) What stress is high, primary, secondary? How did you calculate your stress value?

Can you send a drawing or your calculations?

Thanks!

 

[TGS4]

XELR8 - you do realize that your recommendations in 1) and 2) are directly not permitted by the ASME Section VIII, Division 1 Code?

There is an interpretation out there that says that you may NOT use actual values for calculating an allowable.

And how do you justify 2)? Where in the Code is this permitted?

I would, however, second your question in 3). To the OP, what is your issue - what stress is excessive, and how will having a material with a higher yield impact your result?

 

[XELR8]

Hi TGS4,

Thanks for your information and clarification.

I understand the ASME Code and your point. I was not trying to answer the ASME Sec VIII code but rather what would work if your outside of the code rules already?

Why was the clip under designed per ASME Code Sec VIII in first place?

Thanks!

 

[engpes]

The shell thickness is well oversized and the membrane stresses are fine. I also have a 1/2" repad as well. The length of the padeye is set and cannot be increased due to spacing issues. Also the width is limited by a clevis that attaches to the lug.

The only problems I am having is with the bending stresses in the lug itself.

I am currently considering the use of duplex as it offers the yield stress that works.

 

[TGS4]

Is the bending stress that is causing you an issue primary bending or secondary bending?

 

[XELR8]

Look at adding gussets perpendicular to the lug for reducing the stress on the "lug". If the hole size of the clevis pin is of concern add a pad plate to lug. Use a clevis through the clevis of the lug to reduce the moment on the weak axis of the lug. Can you describe how you calcualted the excessive bending stress in the lug? There are many solutions with limited information but more accurate information would help resolve this issue sooner.