Allowable stress values changes in editions of ASME B31.3

[cespi82]

Hello everyone,

Have the allowable stress values in ASME B31.3 changed along with the release of the different editions of this code?
Can any of you route or guide me towards a historical reference or table where I can see the changes of the allowable stress values in time with the release of new versions?

This might be a silly question but I have also noted that these values in B31.3 differ from ASME Sec II-D. What is the reason for that? aren't they the same materials?

Regards!

 

[XL83NL]

Have the allowable stress values in ASME B31.3 changed along with the release of the different editions of this code?

Yes. I dont have a historical overview, but some values have 'improved' over the years.

What is the reason for that? aren't they the same materials?

Yes they are the same materials. II-D uses a different factor over yield and tensile compared to B31.3. See B31.3 302.3.2 and II-D Mandatory APpendix 1.
Also see

http://www.eng-tips.com/viewthread.cfm?qid=372382

 

[BenStewart]

With respect to differences in allowable stresses between the process piping code ASME B31.3 and those populated in ASME II-D (which is primarily intended for use with the B&PV codes) it is due to the factor applied to the ultimate tensile strength.

The allowable stresses in Annex A of ASME B31.3 are based on the minimum of yield/1.5 and UTS/3. If you're looking at Chapter IX then the allowable stresses in Annex K are yield/1.5.

There are a number of allowable stress tables in ASME II-D and which one you use depends on what your application is. Some of the Mandatory Appendices at the back explain how these are derived. As a cursory summary, for ASME VIII-1 vessels the allowable stress is the minimum of yield/1.5 and UTS/3.5, and for ASME VIII-2 vessels the allowable stress is the minimum of yield/1.5 and UTS/2.4.

In general I do not believe the factors have changed for process piping like they have done for the B&PV codes (i.e. ASME VIII-1 pre 99a which had a UTS factor of 4), although I seem to recall there was a change to some of the higher strength materials around the 2012 edition? If you're doing an assessment of older equipment, as a first pass, it's best to use the allowable stress from the code edition to which it was designed to.

 

[XL83NL]

As Ben mentioned, the factors for B31.3 havent changed, but some materials have been updated or upgraded, i.e. theyre yield and tensile properpties per the ASTM spec have changed, leading to a change in the allowable stress in table 1A of B31.3. However, such changes are very minor, and only for a few materials. I recall that it happened some years ago for either 304(L) or 316(L).

 

[cespi82]

Thank you XL83NL and BenStewart for your answers.

It seems that this will be a research job... find older versions of B31.3 and build a sort of table with the changes over time of the stress values.

If I ever manage to do that I will share it with you guys.

Regards!

Cesar