Determination of Pressure Stress Intensification Factor (SIF) for WRC-107/537 calculations

[PVDEngg]

Most of the available literature refers to VIII-2 Part 4.5 for SIF determination. But, I could not locate the exact information or relevant equation in Part 4.5, using which I could calculate SIF manually. Second reference is PVP-399. Which eventually boils down to VIII-1 Appex 1-10 till 2017 edition and VIII-2 Part 4.5 via Code Case 2398. However, neither Appx 1-10 did nor VIII-2 Part 4.5 nor CC 2398 talk about determination of SIF.

How (Reference or method in place) SIF is determined?

And secondly, it seems that some design software use option to use Stress Indices from VIII-2 Part 5 Annex 5-D, which is ruled out by other software(s). Not considering overly conservative stress indices meant for fatigue analysis makes sense.

But, any suggestions on how to take up with accepting WRC-107/537 calculations without no SIF considered in calcs? Considering stress indices, I think, would be conservative approach. And so does not considering any SIF could be very non-conservative.

Thank you very much for the knowledge sharing.

 

[DriveMeNuts]

What SIF are you try to find and what for?
Peak Stress? For Part 5 fatigue?
Nozzle local membrane stress relative to general hoop stress?

I find that VIII-2 Part 4.5 provides a good local membrane SIF for the geometries it covers. Membrane stress SIF = PL/PM where PL is equation Div 2 4.5.55.

My understanding is that Div 2 4.5 is the latest mathematical refinement of the PVP-399 method. The PVP-399 test data and philosophy remains unchanged.

 

[Trestala]

If you are talking about SIF for WRC 107/537 calculation in Compress, you can refer to TomBarsh's reply here.

You can also refer to Sec. 11.2 of "Structural Analysis and Design of Process Equipment" by Jawad and Farr.

 

[PVDEngg]

@DriveMeNuts: Yes, I was referring to Nozzle local membrane stress relative to general hoop stress, that you explained later in your reply. Thank you.
@RaymondN: Thank you. I did check both the references before posting my queries. But still could not decipher it to get my answer, any before these replies.
Replies from both of you did answer part of my question.

Meanwhile i read Appendix B in WRC-107 (1979 revision). It does have some equations and a graph to determine SIF for stresses due to external loads. But in paragraph 2 it also mentions that stress 'concentration' factors (SCF) SHOULD be considered if material is brittle or fatigue evaluation is undertaken. I guess, SIF we are discussing is not different than this SCF.

I need to understand this, with what DriveMeNuts has explained (Membrane stress SIF = PL/Pm where PL is equation Div 2 4.5.55:

Pm = General Primary Membrane stresses due to internal pressure = PRn/t (lets call it as pressure stress for ease)
PL = Local Primary Membrane stresses including stresses due to discontinuity due to internal pressure)
PL+Pb+Q= Local Primary Membrane stresses including stresses due to discontinuity due to internal pressure + Combined longitudinal stress resulting from axial load ("P") + Stresses due to combined bending moment (resultant of Mx and My)

So while carrying out calculations for local stresses at nozzle due to external loads with internal pressure: what we can readily calculate is Pressure stress "Pm".
and then "PL" is determined from "Pm" by multiplying it with SIF (if I am not mistaking). And then calculation of combined stress due to axial load and bending moment.
So, if we don't have SIF, how can we calculate "PL" itself?
And how does it go with Section VIII-1 application, where nozzle reinforcement calculations are not stress analysis based like VIII-2? We don't work out "PL" there. How SIF plays role there?

or in nutshell, for VIII-1 applications, if fatigue is not applicable, we can simply overlook SIF, i.e. =1. And for VIII-2 applications, following 4.5 calculations takes care of SIF?
So, for VIII-1 applications with fatigue service requirements, we can use WRC-107 Appendix B guidelines.

Thank you.

 

[DriveMeNuts]

There are some methods which rely on charts or graphs and involve you taking an SIF off of the graph and then multiplying it by the hoop stress. (PD 5500 Appendix G.2.6 is a good example)

For Div 2 4.5 and WRC 107 you don't calculate an SIF as the maths is too complex. You find variables and then calculate a stress and then make sure that stress is less than the allowable. If you really wanted to, you could use that final stress to calculate a membrane SIF, however that is rarely useful.

Your aim is to find a stress. There are different methods of getting there. SIF lookup method, mathematical method and FEM are just a few.

 

[Trestala]

Defining SIF against SCF should be made.

Stress Intensity Factor (SIF) is the multiplier to the stress due to pressure at the location near the opening. It is for consideration of the "stress intensification" because of the presence of the opening under pressure loading. In Compress, SIF is used to multiply Pm either at nozzle edge or pad edge.

Stress Concentration Factor (SCF) as defined in WRC 107 is the factor for considering the stress concentration at junctions due to external loads. Sharp corners will have higher SCF compared to smooth welds.

 

[PVDEngg]

Hello gentlemen,

Thank you, DriveMeNuts for the reference PD 5500 Appendix G.2.65. It helps with SIF for spheres at-least.
Thank you, RaymondN.