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

You know, we have already discussed almost same issue before.

You can use advanced search function to find old posts. Please try.

about your query, refer to these two old posts.

http://65.57.255.42/ubbthreads/ubbthread...=true#Post45771

http://65.57.255.42/ubbthreads/ubbthread...=true#Post13195

Hello Caesar III.

Thanks for your valuable comments.

After reading the referred posts I understood that Caesar II gives the option to users to define weld joint strength reduction factors.
User has to define these weld joint strength reduction factors manually in material database or in input file since the value is not available in ASME B31.3(ASME B31.3 specifies value for longitudinal joints only).

However, I still have doubt that why B31.3 gives a option to use/ignore the weld joint strength reduction factors for circumferential joints since these will directly impact the allowable stress value of longitudinal stress(Primary stress) in the creep range.

B31.3 has very well addresses the fatigue issue(by using fatigue curve) in piping stress analysis but why the creep matter is ignored for welded joints?

Thanks

Hi Neeraj,

Regarding your query about the circumferential joint 'W' factor(AKA Wc factor), Mr.Dave, Durga gave me clear answer before.

'Bending stresses due to sustained loads is a concern around circumferential welds. But this (localized) bending stress can be spread and be carried nearby if there is creep. The pipe will not necessarily fail if creep occurs. This consideration is optional.'

You can find this reply on this posts below.

http://65.57.255.42/ubbthreads/ubbthread...=true#Post61380

Also, about the creep and how code affected by it, you may find this 'Mechanical Engineering News' interesting.

http://www.coade.com/Uploads/mechanical-engineering-news/may93.pdf

hope this helps you.

Hello Caesar III.

I really appreciate for your reference to the post where Dave has provide the rationale behind Code's intention to make WC(Weld joint strength reduction factor) option for girth welds.
Couldn't stop myself from quoting Dave's statement in this post,
===========================================
The term W signifies the reduced strength of weld material in the creep range. Longitudinal pipe welds and spiral pipe welds must be strong enough to contain the (membrane) hoop stress due to pressure. That's mandatory.
Bending stresses due to sustained loads is a concern around circumferential welds. But this (localized) bending stress can be spread and be carried nearby if there is creep. The pipe will not necessarily fail if creep occurs. This consideration is optional.
The Codes show a single W. CAESAR II breaks this single term into Wl & Wc to distinguish between longitudinal or spiral welds and circumferential welds.
====================================
Thanks