Hello Friends.
I have one query related to weld joint strength reduction factor as specified in 302.3.5 (e) of ASME B31.3/2014 edition(For full requirement, please refer to B31.3):-
1. For wall thickness calculations:-"W" should be considered in the wall thickness calculations by multiplying "SE" with "W".
This requirement is well understood. Hoop stress will be affected by a weaker longitudinal joint at higher temperature and hence we should more thickness to offset this weakness.
2. "W" should not be considered for Occasional loads such as wind.
This requirement is well understood too since the duration of occasional loads is short and hence we can ignore the weakness introduced by weld.
3. "W" should be ignored while evaluating allowable stress range for displacement stresses, SA.
I get confused here. Why we should ignore "W"? I understand that girth welded joint is the basis for establishing SIF and fatigue curves are developed based on welded joint only.
However, " W" is related to creep and not fatigue". So, why we are ignoring the effect of circumferential weld joint strength reduction factor? What is the reason?
If we have a fatigue curve which is dependent on temperature such that "f" value is conservative for piping components operating in creep range then I could have understood this rationale.
4. No statement about consideration of "W" for longitudinal stress(Primary stress)".
Although code doesn't talks about it explicitly but I believe that code has no intention to apply circumferential weld joint strength reduction factor to girth welds since no value is provided in the code. Table 302.3.5 Weld Joint Strength Reduction Factor, W is applicable only to longitudinal joints.
This confuses me again. Why we ignore the effect of creep on circumferential welds?
Thanks
_________________________
NEERAJ BATRA
"The harder I work, The luckier I become"