Hi Folk,

I was checking PL line 10" with 6" bypass,checked stress range did the following load cases:
1.all hot (T1)
2.main line hot bypass cold (amb) (T2)
3.main line cold (amb) bypass hot (T3)
4.all cold (T4)

got stress range as T1-T4;T2-T4;T3-T4 to cover stress range as per 319.3.1(a) ASME B31.3 "max design minus (alg) min design"

But was told to do sum abs stresses from cases 2&3 i.e. due to moment reversal on bypass line (please see Appendix S (S303 "moment reversal stresses") in ASME B31.3 2006 edition) as additional check that was not done before and was not in ASME B31.3 before 2006 and line failed so this approach is new newer done this way.

So this is addition to 319.3.1(a) ASME B31.3?

Any comments folk?

Thanks

Regards

Eldar

Torpag ugrunda olen varsa Vatandir

We are, and always have been, working with stress ranges as well as absolute stresses. See, for example, paragraph 319.2.3(a) from B31.3 (2004).

"When the system is later returned to its original condition (or a condition of opposite displacement), a reversal and redistribution of stresses occurs..."

Also see paragraph 319.2.3(b) from the same Code.

"...the algebraic difference between strains in the extreme displacement condition and the original (as-installed) condition (or any anticipated condition with a greater differential effect)..."

You have been doing it wrong all these years, apparently.

I think you have not understood me.

I agrree with you that is how to compute the full stress range but I am talking about the thermal stress range I am saying that in on/off cases particulay in baypass or similar systems there are stresses caused by reversal moments not reversal of disp strain please see appendix S in ASME B31.3 i.e.paragraph S303 page 283 this means that the stresses caused by reversal moment should be considered as exseption.

Regards

Eldar

CAESAR II "recommends" the three expansion cases you mention (I will not quibble about that T4, instead I will think of that as the "installed" position - usually something like W+P1) but that may not be all you need to follow the intent of the Code. The Appendix S example on stress reversal shows that additional strain ranges might produce a greater stress range; namely T1-T2, T1-T3, and T2-T3.
But the Code does not state that these stresses sould be formed as "absolute stress summations" (that's a CAESAR II term, not a Code term). They are range calculations like any other.
As Craig points out this has been the Code approach for quite a while now (50 years?) - to evaluate the maximum stress/strain range. Things got more complicated over the last 20 years or so with the inclusion of nonlinear conditions included in the analysis.
And then there is the problem of accummulating damage from the several expansion stress ranges. Your job is not complete in just examining the largest stress range. You must alter your cycle count for this largest range by converting the other, lower, stress ranges into equivalent cycles at the maximum range. See (1d) in B31.3 para. 302.3.5(d).

Do not assume that CAESAR II "recommends" all that is required. It only recommends the most obvious cases to collect expansion stress range(s) and sustained stress(es).

Dave,

But if you look at s303 table S303.7.3 the disp stress range is summed as absolute

I see negative signs in Table S303.7.3 so it is not absolute summation. The numbers in Tables S303.7.1 and S303.7.2 are all equal and opposite so a range calculation (S303.7.1 - S303.7.2) may appear like an absolute summation.
Paragraph S303.8 states that Table S303.7.3 "considers the algebraic strain difference between the two operating cases".