Design Temperature over that specified in ASME Section IID

[jjlago]

First of all, Happy New Year!!!

We are making an special and odd design where some support of the vessel are exposed to high temperature, far above the 1000 ºF specified in the tables of ASME Section IID for the majority of the characteristics of the materials, apart for maximum allowable strength (that, depending on the material, can be obtained until even 1500 ºF).
Until konw we have been using this maximum allowable stregth as the unique value to make this calculations, but it makes the impression that these elements result to be overdimensioned.
¿Do you know any other way of getting values for these materials above 1000 ºF? The values I am referring to are, above all, yield stregth, tensile strength and moduli of elasticity.

Thank you very much for your attention.

 

[metengr]

Your post is rather confusing. Using materials above their specified maximum service temperature in ASME Section II, Part D, can lead to premature failure and harm to people and equipment. Other than a loss in strength, other time dependent damage mechanisms come into play at elevated service temperatures.

What exactly are you trying to accomplish by using material that is not suitable for elevated temperature service? Simply increasing thickness to enhance load carrying capacity is not enough.

 

[jjlago]

What I meant is that we want to use ASME materials, but the room temperature is above 1000 ºF, and for that temperatures the only data available in ASME Section IID is the maximum allowable stress, and it is rather confusing, because some materiales are said to be suitable for higher temperaturas than 1000 ºF (in the ASME Code itself) but no yield strengh values are provided for these temperatures.

Maybe it seems to be a little bit odd, but this is the first time that we have to face a situation like this.

 

[metengr]

jjlago;
Ok, let me try this approach. The mechanical properties of certain materials changes to a time dependent mode above a specific service temperature. The time dependent damage mode is typically creep deformation.

The allowable stress values listed in Table 1A of Section II, Part D, reflect both independent and time dependent effects.

Mechanical property data like UTS and YS are published for a group of materials in ASME Section II, Part D, like Tables U and Y-1 in particular. Again I need to stress the point that if you are using material at service temperatures in excess of those published in Part II, you need to proceed with extreme caution and solicit input from qualified individuals.

 

[jte]

jjlago-

It would help a lot if you would just state which materials you are dealing with. it doesn't help to be secretive when you are asking for free advice. Like metengr stated, you need to know what you are doing when playing with high temperature design. What is your failure mode? For example, if you are looking at catalyst bed support beams and you design based on some allowable tensile stress you pulled from II-D the design may fail early since you didn't consider the stability of the compression flange after some creep has occurred.

Again, you'll get the best answers with a well stated, clear, and detailed question. Not just generalities.

jt

 

[bvi]

Use the allowable stress values up to the maximum permitted temperature. The fact that the tables for tensile strength and yield strength do not go up to as high a temperature is not an issue.

 

[GenB]

If for support of the vessel, you can use structural design in serching for hi-temp materials. ASME SeII-D can sometimes be limited to temp vs pressure or viceversa.

 

[jjlago]

First of all, thank you for all your comments.

I will try to simplify the problem.
Suposing that due to design considerations that cannot be modified, the support lugs of a vessel are exposed to 1200 ºF.
The materials that we want to use are SA387Gr91Cl2 and Sa387Gr22Cl2 due to supply.

The only source for stress values for these materials are the stress tables in Part IID of the ASME Code, althogh the lugs are non-pressure parts.

Because of the special geometry of the lugs and the lack of reliable stress data we are making some FEM simulations, but we need a stress value to compare to, in order to verify if the lugs can resist or not.

My question is: Would you proceed in the same way? We do not know any other way to design it (It is the first time we have to face this situation).
We are concerned od the creep problem, but the temperature itself cannot be modified.

Thank you very much for your attention.

 

[metengr]

I would presume that the support lugs are located external to the vessel correct? What is the vessel material for use at 1200 deg F?

If the vessel metal temperature is 1200 deg F, and these are external attachments, the actual metal temperature of the attachment in air would be less provided they are left un-insulated. You did not mention the size of the support.

Why not use stainless steel supports versus a ferritic material? If this pressure vessel is operating at 1200 deg F, you would have a dissimilar material concern using the advanced ferritic (9 Cr). I would not use the Grade 22 material for the lug.