Creep strength data for ASME steels

[athomas236]

In my experience, it is becoming more and more the practise these days to undertake fatigue and creep life evaluations of boiler components both as part of the initial design and at stages through the operating life.

For British, German and European Norm materials creep strength data is published and readily available but this does not seem to be the case for ASME.

If I am wrong regarding ASME materials then I would appreciate it if some one could tell me of a source of elevated yield and creep data.

If I am right and this data is not easily available then how do US engineers undertake such creep life evaluations.

Best regards,

athomas236

 

[davefitz]

in general, before any material is included in the section II tables, it will first be a Code Case, allowing for temporary use. In the process of developing the Code Case, the relevant creep testing data ( and other data)is submitted.So one way to obtain the original data is from the code case for the material, usually in the 3 yrs period prior to the adoptance in the section II tables.

As time goes by , these data are revised based on newer findings, as seen by the relentless decrease in allowable stresses for the creep strength enhanced alloys.

 

[metengr]

In my experience, it is becoming more and more the practise these days to undertake fatigue and creep life evaluations of boiler components both as part of the initial design and at stages through the operating life.

For British, German and European Norm materials creep strength data is published and readily available but this does not seem to be the case for ASME.

If I am wrong regarding ASME materials then I would appreciate it if some one could tell me of a source of elevated yield and creep data.

Creep strength data is not directly published by ASME B&PV Code, because allowable stresses are used instead. ASME B&PV code for Section I boilers uses a design by rule approach, in lieu of a design by analysis. Allowable stresses are established by committee rules and this value becomes the controlling factor for design.

If you review any of the allowable stress tables in Section II, Part D you will notice that the allowable stress value above a certain temperature changes from bold font to Italic font. The Italic font change shows the time dependent effects that control allowable stress values (either stress rupture or creep deformation limits).

Now, regarding creep-fatigue effects. ASME Section I (Boilers) chose not to deal with creep fatigue in design. The thought was that there is enough generous design margin to accommodate both creep fatigue, and peak stresses in service. Basically, this approach has been demonstrated by past experience for most boiler components (I don't necessarily agree with it but it is hard to dispute it).

 

[jte]

athomas-

Though the material list is somewhat limited, you may find ASME III-NH useful:

http://catalog.asme.org/Codes/PrintBook/BPVCIII_NH_2007_BPVC_Section.cfm

jt

 

[ijzer]

Creep properties for ASTM materials can be found in SPT 151, STP 124 and ASTM Data series DS 5S2. These data were used to make the stress tables in ASME IID

 

[athomas236]

Gentlemen,

Thanks for all your answers, they are much appreciated.

I have seached the ASTM website for the publications mentioned by ijzer but without success. The website has a list of all STPs which does not include numbers 151 and 124. In addition, I cannot find any reference to data series DS 5S2.

Any further assistance in tracking down these documents would be appreciated.

Regards,

athomas236

 

[ijzer]

The following is mentioned in the publications I refered to:

DS 5 S2 : SBN 8031-2000-1 Libary of Congress Catalog Card Number 78-77331 Dated 1969. Supplement to DS5 , formerly STP 124. An evaluation of the Yield,Tensile, Creep and rupture strengths of wrought 304,316,321 and 347 stainless steels at elevated temperatures.

STP 151 dated 1953, 2nd print 1964 , the ASTM-ASME joint commitee on effect of temperature on the properties of metals.Report on the elevated-temperature proprties of Chromium-Molybdenum Steels.

 

[unclesyd]

The aforementioned documents concerning SS are presented in the booklet "High Temperature Characteristics of Stainless Steels" A Designers Handbook Series published by the Committee of Stainless Steel Products of the AISI. The publication number is SS 802-479-25M-CP, 1979.


For all the documents mentioned you might want to try the following website. They have found several documents for me at a very reasonable price.

http://www.lindahall.org/

 

[metengr]

Keep in mind that the creep data for Cr-Mo alloy steels is what it is and current allowable stresses used in ASME B&PV design code for time dependent effects have been revised downward over the last 30 years, especially for the 1.25 Cr-0.5Mo alloy steel.