Allowable stress intensity for WRC 107 1

[VIJAYANSA]

Hi All,

As per WRC 107, I calculated the Induced combined stress intensity in nozzle shell junction. Now, I need the Allowable stress intensity for comparison.

But in PV Elite calculation, the induced combined stress intensity is compared with allowable stress for Div 2 as per table 5A in Sec II part D (As per stress classification for nozzle necks part 5.6 in div 2).

I am little bit of confusing with the terms "allowable stress" and "allowable stress intensity"

I hope, there is a difference between allowable stress and allowable stress intensity (my opinion only). That is, "Allowable stress intensity" is as per the Maximum shear stress theory ( Tresca's theory), But "allowable stress" is as per the Normal stress theory ( Rankines theory).

So, in Pv elite calculation, the induced stresses are calculated as per Tresca's theory ( WRC 107) and comparing the results with Rankines theory.

Can anyone please explain this basic doubt.

Vijayan S A

 

[TGS4]

What is the Code of Construction for your vessel?

 

[VIJAYANSA]

Hi,

My code of construction is ASME SEC VIII Div 1 and I need to do the local stress analysis for the nozzle connected to vessel as per WRC 107.

 

[VIJAYANSA]

Hi TGS4,

And My material of construction is SA 350 LF2

Allowable stress at 95C is 1) as per Table 1A of sec viii Div 1, 137.89 Mpa
2) as per Table 5A of sec viii Div 2, 151.68 Mpa
doubt 1:

In Pv elite calculation, Induced stress intensity are calculated for nozzle local stress analysis as per WRC 107 (Trescas theory). And it was compared with 137.89 Mpa, which is an allowable stress of Div 1. But, my opinion, the induced stress intensity has to be compared with allowable stress intensity only. But in Sec II part D , there is no stress intensity values for vessel material as per div 1 and div 2....
This may be a basic doubt. Please give suggestion to understand.....

doubt 2:

In pv elite calculation, the following load cases are used for local stress analysis (WRC 107) as per div 2,
Pm < S
Pm + Pl < 1.5S
Pm + Pl + Q < 3S

Here S is the allowable stress as per DIV 2.
But in Pv elite calculation they are using Div 1 allowable stress. So, Is it adivisable for using the load cases from one code (div 2) and comparing the results with allowable from other code (Div 1) ???????

 

[TGS4]

In that case, your allowable stress basis will be per Table 1A or 1B of II-D, not Table 5A.

I will also note to you that your reference to (you said Part, but I think that you intended to say) Paragraph 5.6 is with respect to the nozzle neck. However, WRC 107 calculates the stresses in the vessel shell wall and does not have method to calculate the localized stresses in the nozzle.

With final regards to your confusion with stress vs stress intensity (and that should undoubtedly also include equivalent stress), currently there is no guidance in applying article U-2(g) to any part of stress analysis - be it something as simple as WRC 107 or something more sophisticated as a finite element analysis. I wrote a blog post in this specific topic - take a read through it and feel free to ask me questions here about that -

http://becht.com/blog/performing-an...sion-1-to-qualify-an-article-u-2-g-component.

Don't get too hung up on the invariant (Max Principal, Tresca, von Mises).

It's unfortunate that this guidance isn't in the Code yet, but something should be there for the 2015 Edition.