Allowable Material Stress for ASME VIII Div.1

[MikeG7]

2 related questions:
1) In a past thread,

http://www.eng-tips.com/viewthread.cfm?qid=345631,

it was stated by TGS4 that the code is explicit about not being able to take credit for the actual stress values when doing a vessel design, and only that the allowable stress values may be used. Can anyone point me to this section in the code I would like to know where to find it.
2) Past threads have discussed allowable stress values in detail. I have seen for myself that in ASME Section II, the allowable stresses are some factor of the Tensile and/or Yield stress (unless it is in the creep range), whichever is the lower. This factor is 1/1.5 to yield and 1/3.5 to ultimate tensile strength for most of the time. But I also notice it varies for bolting (factor is 5!). There are also other factors which don't add up to a number like 3.5 or 5 - I get some factors as 3.1 if I take UTS/Allowable strength at ambient.

I hate to call them "factors" but for the sake of this discussion don't know what else to call them. Is there any rules that was followed in order to determine these "factors", e.g. "5" for bolting, "3.5" for plate?

PS: I mostly refer to the factor on the UTS as in most cases (for my applications) it is not the Yield/1.5 that is the lowest value.

Appreciate your advice.

Mikeg7

 

[TGS4]

The allowable stress basis is described in ASME Section II, Part D, in the Appendices.

The prohibition on using minimum properties vs as-tested properties comes from an Interpretation. I will try to find that in the next day or two (unless someone else can chime in with that...).

I use the terminology "design margin" to describe the factors that make up the allowable stresses. The design margins on bolting are different - again see the Appendices in II-D.

 

[fegenbush]

Interpretation: VIII-1-01-106 from December 18, 2001 is the prohibition against using the tensile strength from the material test report.

 

[MikeG7]

Very helpful. Thanks all.