ASME Section II Part D Stress Values

• May 18, 2009

• #2

rumandcola

Mechanical

Apr 6, 2009

47

The ASME allowable stresses are well below tensile and yield stresses. This value has a safety factor worked into it.

 

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• May 18, 2009

• #3

gr2vessels

Mechanical

Sep 29, 2004

1,971

The ASME VIII incorporates a safety factor of approx 3.5 in limiting the allowable design stresses, hence 60,000psi / 3.5 = 17100 psi. 60,000 psi is the listed minimum tensile strength and the 17100 psi is the allowable design stress for this material.
Cheers,
gr2vessels

 

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• May 18, 2009

• #4

jte

Mechanical

Apr 8, 2002

2,357

Just to be clear, ASME VIII Div. 1 sets its base allowable Tensile stress S as the lowest of ultimate at temp divided by 3.5, two thirds yield at temp, or time dependent (i.e. creep) limited values.

Be sure to apply this allowable stress appropriately, and don't confuse it with allowable compressive stress.

jt

 

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• May 19, 2009

• Thread starter
• #5

Charan5

Mechanical

Mar 7, 2007

24

Thamk you very much for the feedback, and it is clear in Appendix 1. Appendix 10 is something different.

 

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• May 19, 2009

• Thread starter
• #6

Charan5

Mechanical

Mar 7, 2007

24

Hello,

One more thing, I am wondering, is it okay to arrive allowable stress based on tensile stress values, even if the yields are much less than code minimum and 2/3 of yields is higher than tensile based stress values. For eg.60/3.5=17100 psi and 2/3*27Fy=18000 psi. Is this detrimental as long as the material is not stressed to yields for permanent deformation.

 

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• May 19, 2009

• #7

jte

Mechanical

Apr 8, 2002

2,357

Charan-

What exactly are you playing with? Do you have competent oversight / mentoring?

jt

 

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• May 19, 2009

• Thread starter
• #8

Charan5

Mechanical

Mar 7, 2007

24

Hello Jte,

I am not sure about your question. I am fully aware of the ASME Section I and VIII, and this is a situtation where we have tubes are chromized and in the process the stress values are reduced. Trying to justify the tubes for pressure containment using the allowables within code limits.

 

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• May 20, 2009

• #9

jte

Mechanical

Apr 8, 2002

2,357

So you have a material which is modified and thus no longer listed in II-D which you are using for a Section I or Section VIII component?

jt

 

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• May 20, 2009

• Thread starter
• #10

Charan5

Mechanical

Mar 7, 2007

24

That's correct. You might know, codes does not require the materials to meet every Section II propeties after fabrication, like bending, heat treatment etc. So, once you alter the material properties, it is up to the designer how to interpret and apply these values within certain boundary. Unfortunately code is not clear in defining the limits for every case.

 

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• May 20, 2009

• #11

TGS4

Mechanical

Nov 8, 2004

3,915

That's an interesting interpretation you have, Charan5. Do you have an official ASME Interpretation to back up that claim? Perhaps a reference to a particular Code paragraph that I am not familiar with could also enlighten me.

Where is this "vessel" going to be installed? What is your jurisdiction's thoughts on this?

 

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• May 20, 2009

• Thread starter
• #12

Charan5

Mechanical

Mar 7, 2007

24

Hello TGS4,

Some interpretations I-83-01 & I-95-03 which talks about similar cases. We have not checked with Jursidiction and it's in US.

 

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• May 20, 2009

• #13

metengr

Materials

Oct 2, 2003

15,478

I am not sure about your question. I am fully aware of the ASME Section I and VIII, and this is a situtation where we have tubes are chromized and in the process the stress values are reduced. Trying to justify the tubes for pressure containment using the allowables within code limits.

Click to expand...

Typically boiler tubes (Section I) may be chromized for corrosion resistance only, and the diffusion distance for chromizing is such that the argument could be made that bulk properties are unaffected. This is a post fabrication issue that the Code does not address. How and why would one decide on altering the allowable stress values?

The bulk properties are normally unaffected by this process unless you operate in the creep regime and there have been isolated cases where local creep damage has occurred immediately under the chromized layer (where chrome has combined with carbon to produce a lower creep strength ferrite zone). In this case, the orientation of the lower creep strength zone is not oriented in the direction of primary membrane stresses.

 

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• May 20, 2009

• #14

jte

Mechanical

Apr 8, 2002

2,357

Definitely an interesting thread. In addition to the interpretations Charan has provided, I'd also suggest that VIII-1-83-299 and VIII-1-07-04 deal with similar issues.

-83-299 said:

Question: In a brazed construction, does the fabricator have to demonstrate that the material properties after brazing are not below the minimum specified values?

Reply: No, provided the requirements of Section IX are met.

Click to expand...

-07-04 said:

Question: Must a stainless steel component which receives a significant amount of cold forming during fabrication, and is not subjected to a final solution anneal, satisfy the mechanical properties of Code approved Section II, specification in its final formed shape?

Reply: No.

Click to expand...

jt

 

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• Jul 11, 2009

• #15

twistobar

Mechanical

Oct 2, 2000

9

JTE, I agree those are interesting interpretations, bit I submit that they are not calling for modified allowable stresses to be used in the design and Section II allowable stresses should still be valid with the Interpretations.
Regards,

... a man's got to do what a man's got to do...

 

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• Jul 13, 2009

• #16

jte

Mechanical

Apr 8, 2002

2,357

twistobar-

Agreed.

jt

 

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• Jul 14, 2009

• Thread starter
• #17

Charan5

Mechanical

Mar 7, 2007

24

Thanks for all feedback.

 

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• Jul 20, 2009

• #18

GenB

Mechanical

Oct 24, 2003

1,362

gentlemen, where will I find the ASME stress related x 3.5,
why is 3.5 and not 4?
please advise.

 

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• Jul 21, 2009

• #19

jte

Mechanical

Apr 8, 2002

2,357

GenB-

Because the code committee, for various reasons, changed the factor against ultimate from 4 to 3.5 starting with the 1999 Addenda. Factors against yield, time dependent, and compressive did not change.

I'm sure you'll find much more on this if you search the forum. If you have a specific question, I'd suggest starting your own thread.

jt

 

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