Richard-San & Dave-San,

I am referring a presentation by INTERGRAPH on "Recent changes in ASME B31.3 and their Implementation in CAESAR-II"

In that Reg, Weld Strength Reduction factor. I confused with this two statements

1. Mandatory consideration in membrane stress
2. optional in bending stress.

It means for Longitudinal welds "WL" is manditory and for Circumferential welds "WC" is optional. Is My understading is correct or not.

Please find the attachment for the ppt.

any comments?

Any comments??

Any one who knows answer for this question, please share your valuable information..

IMO, sustained stress is mainly affected by Longitudinal stress(Membrane stress), but for expansion stress bending stress is governing reason of failure.

The W factor is siginicant in the category of Sustained stress, not the expansion stress according to Peng's pipe stress engineering.

I guess that's why the w factor is mendatory consideration in membrain stress.

CAESARIII,


"WC" is only applied to Sustained case only. Now As we know that, Wc is become optional for reduction of sustained stress allowables.

Then what it means,,

1. Mandatory consideration in membrane stress
2. optional in bending stress.

Durga,

In Roark's Formulas for stress and strain Longitudinal and circumferential stresses are called membrane stress.

We know that Wl is affected by hoop stress, and Wc by longitudinal stress.
That's why w factor is mendatory consideration in membrane stress.

About the Wc and Wl,
Acc to Peng's book, wc is oconsidered as everywhere because it is used to connect each pipe, there are too many points to identify. So we assume Wc exists eveywhere in the pipe system, we just adjust stress intensity and allowable values for this.

CAESARIII,

WL is manditory Till date for calculation of thickness to control the longitudinal weld failures.

Now WC is optional for reduction of sus stress allowables.

Now Membrane stress are either tensile or compression so lONGITUDINAL OR CIRCUMFERENTIAL MEANS WL -- manditory

But what abt bending ??

MK,

Do u have Roarks formulas for stress and strain fifth edition. I have seventh,, Do u have fifth edition by any chance??

Durga,

Bending stress in sustained stress usually come from weight and pressure. Might it be the reason weld strength reduction is optional for bending stress?

However, in my opinion, it doesn't mean Wc is optional and Wl is mandatory.

No, I only have 7th edition.

MK,

As per Code "For a longitudinal or sprial welded piping components, the product of weld quality factor SE shall be multiplies by the weld joint strength reduction factor W when determining the required wall thk for internal pressure" --- This W is WL - Longitudinal weld joint strength reduction factor -- it is manditory used in cal of thk..

AS per Code " The designer is responsible for the application of weld joint strength reduction factor to welds other than longitudinal and sprial i,e Circumferential."--- This W is WC, whether apply or not it is user choice.

I think it is clearly explained,, Any opinions on this...

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.

Yes, Thanks For your Explanation.

Thank you for clear answer, Dave.