Allowable design stress in ASME II Table 1-100

[Ajay Mehta]

In ASME Section II MANDATORY APPENDIX 1 BASIS FOR ESTABLISHING STRESS VALUES IN TABLES 1A, Para 1-100 (a), if the 90% of Yield strength is allowed as Allowable stress in Austenitic Material and if it exceeds St / 3.5 (Ultimate strength / 3.5), is it still allowed? Para 1-100 (a) says:
.
(4) Two sets of allowable stress values are provided in Tables 1A and 1B for austenitic materials and specific
nonferrous alloys. The higher alternative allowable stresses are identified by a footnote to the tables. These stresses
exceed two-thirds but do not exceed 90% of the minimum yield strength at temperature. The higher stress values
should be used only where slightly higher deformation is not in itself objectionable

The Foot Note of Table 1-100 suggests for Austenitic Material, the allowable stress can be between 0.66 Sy and 0.9 Sy.
NOTE:
(1) Two sets of allowable stress values may be provided in Table 1A for austenitic materials and in Table 1B for specific nonferrous alloys. The lower values are not specifically identified by a
footnote. These lower values do not exceed two-thirds of the minimum yield strength at temperature. The higher alternative allowable stresses are identified by a footnote. These higher stresses
may exceed two-thirds but do not exceed 90% of the minimum yield strength at temperature. The higher values should be used only where slightly higher deformation is not in itself
objectionable. These higher stresses are not recommended for the design of flanges or for other strain sensitive applications.

 

[SnTMan]

Ajay Mehta, not sure if you have a question or not. But, when two sets of allowables, a higher and a lower, are listed in Table 1A, either may be used. However, as stated in Apx 1 and notes to Table 1A, the lower values are generally used for design of flanges, that is, gasketed, bolted joints, and other features where a small amount of distortion my be detrimental to the design.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Ajay Mehta]

Hi Mike,
Thanks for your prompt response.
My interpretation from my above references is that in the cases of Austenitic materials it is allowed to choose Allowable strength between 0.66*Ys (Yield strength) and 0.9*Ys in certain applications as suggested even if that exceeds value of Tensile strength/3.5. I need to confirm this.

 

[SnTMan]

Well, not exactly although those are among the basis for the allowables given in the various tables in Sec II Part D. If you are doing Code work, your allowables will come from the appropriate table in Sec II, Part D. For example Table 1A or 1B for Sections I, III, VIII Div 1 & XII, Tables 2 or 4 for Sec VIII, Div 2, Table 3 for bolting, etc. Note these values are tabulated for the range of permitted temperatures for a given material. You would normally use the appropriate value for the given design temperature

Having said that, where a higher and a lower set of values is present the designer is generally allowed to use either set. Generally the lower values are used for flanges, etc as discussed earlier, but at least Sec VIII, Div. 1 does not mandate it. Some client specs do, some even prohibit the use of the higher allowables at all.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Ajay Mehta]

Hi Mike,
Thanks again! I am using SS 304 material with Ys being above standard suggested in ASME II part D. So I am using the table 1-100 formula where Allowable is required to be the Lower of the two values derived namely 1) Ts/3.5 and 2) Ys/1.5.
However there is a sub-paragraph and a Note below the Table 1-100 which says for Austenitic materials allowable can be as close to Ys and 0.9*Ys (0.6Ys < Allowable Strength < 0.9Ys). If I go 0.7Ys and if it exceeds Ts/3.5, is that OK?
That is what I understand and interpret from the code. I need to confirm that.
Thanks and kind regards,

 

[SnTMan]

Ajay, which Code (if any) are you working to? It is generally not permitted to take advantage of tensiles / yields above the minimums tabulated in Sec II, Part D. See, for example, Sec VIII, Div 1, UG-4.

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Ajay Mehta]

Hi Mike,
I am referring to ASME Section II MANDATORY APPENDIX 1 "BASIS FOR ESTABLISHING STRESS VALUES IN TABLES 1A AND 1B".
In the appendix, in clause 1-100 "DERIVATION OF ALLOWABLE STRESS VALUES" there is a paragraph "Two sets of allowable stress values are provided in Tables 1A and 1B for austenitic materials and specific nonferrous alloys. The higher alternative allowable stresses are identified by a footnote to the tables. These stresses exceed two-thirds but do not exceed 90% of the minimum yield strength at temperature. The higher stress values should be used only where slightly higher deformation is
not in itself objectionable. These higher stresses are not recommended for the design of flanges or other strain sensitive applications."
There is also Table 1-100 where the footnote reiterates the same guidelines
"NOTE:
(1) Two sets of allowable stress values may be provided in Table 1A for austenitic materials and in Table 1B for specific nonferrous alloys. The lower values are not specifically identified by a footnote. These lower values do not exceed two-thirds of the minimum yield strength at temperature. The higher alternative allowable stresses are identified by a footnote. These higher stresses may exceed two-thirds but do not exceed 90% of the minimum yield strength at temperature. The higher values should be used only where slightly higher deformation is not in itself objectionable. These higher stresses are not recommended for the design of flanges or for other strain sensitive applications."

 

[Geoff13]

You are being too selective in extracting words from clause 1-100. Both the words in the (a)(1) thru (a)(4) formulas, as well as the nomenclature, state things like "... the minimum specified tensile strength ..." and "... the minimm specified yield strength ...". Properly applied these formulas and definitions will lead to the values found in Tables 1A and 1B.

Nowhere does the Code allow the use of the actual yield or tensile found on a material test report. As noted by SnTMan, Division 1 clause UG-4 only allows you to select allowables from Tables 1A and 1B. The very first words of Appendix 1 state that the "... values in Table 1A and 1B are established by the Committee only", further making it clear that you are not allowed to pick your own allowables and still call it a Code vessel.

 

[TGS4]

You are permitted to use the allowable stresses in Table 1A for their intended purpose, obeying the limitations in the applicable notes. Appendix 1 provides the explanation for the values in the Table, but it is not your job to question the values. The Code Committee has determined that the values in Table 1A meet the requirements for the Codes that use them. Period.

Quit over-thinking it.

 

[Ajay Mehta]

Hello Gents,
I have reproduced the clause UG-4 below;
"UG-4 GENERAL
(a) Material subject to stress due to pressure shall conform to one of the specifications given in Section II, Part D,Subpart 1, Tables 1A, 1B, and 3[/highlight], including all applicable notes in the tables, and shall be limited to those that are permitted in the applicable Part of Subsection C, except as otherwise permitted in UG-9, UG-10, UG-11, UG-15, Part UCS, Part UIG, and the Mandatory Appendices. Material may be identified as meeting more than one material specification and/or grade, provided the material meets all requirements of the identified material specification(s) and/or grade(s) [see UG-23(a)]."
Above statement allows use of Mandatory Appendix 1 above the Tables of strength values.
Table 1-100 is provided to calculate allowable strength for the materials which may have different mechanical properties (e.g. Ultimate or Yield strengths). They also provide guidelines for better use of Austenitic materials where elongations are higher for certain applications.
UG-10 can be applied for allowable strengths.

 

[SnTMan]

Nothing more to say.

The problem with sloppy work is that the supply FAR EXCEEDS the demand