Dear Sir,

Lug Support Module of PVelite 2010 & Build March 2010 Both, does not takes into account Reinforcement pad parameters while performing WRC 107 Calculations, thereby giving wrong Stresses @ reinforcement pad edge.

Support required.

Hello Tahir

If you have lugs with reinforcement pads, PV Elites does the analysis at the edge of the lug, and at the edge of the attachment. So it does recognise the pad.

Dear Sir,

Yes the program does analysis at the edge of the lug and also at the attachment, but Iam not shure its upto mark.

Request to try one iteration in PVElite 2010.

1) Model A lug with Pad.

2) review the results

3) now change the Pad dimensions and thickness

4) Again review the results.

It performs result on the basis of Shell data & not on the RF pad data.
Hence you wont find difference in the analysis after revising pad data also.

But if you perform same in PVelite 2009 there's no problem associated with that version.

I hope you got my doubt.

Thanks.

Hi folks

If you set up the lug carefully you should be able to get the results for the pad:

Dear Ray,

Thank you very much Ray, there was a bit discrepancy in the model.
I fixed it & found that the Program is doing well & computing Vessel stress at reinforcement pad egde with consideration of Local Shell thickness as well as RF Pad element.

I have one more query to be discussed.

In case of vertical equipments which are mounted on Lug Supports, We have to check Local Loads at this particular junction during operating condition as well as Hydrotest condition.

Now, In the case of test conditions, while carrying out local load calculations, focusing upon (Pm) i.e Primary membrane Stress (Average primary stress across the cross section, excluding the discontinuities).

Wheteher these parameter i.e (Pm) stress shall be compared with Allowable stress @ design temperature of the material or The advantage of 90% of yield shall be taken into the consideration and then compared with the same.

Please advise.

Tahir,

You are correct the Pm (without discontinuities) should be compared t 0.95 * Yield for Div. 2 (or 0.9 * Yield for Div.1).

But, what is the allowable for Pm + Pl for the hydrotest case.

The Div. 2 code does provides allowables for Pm + Pb

But, what about Pm + Pl + Q category.

We need the allowables for all these 3 categories for stress comparison performed after the WRC 107 analysis.

We contacted some members of the ASME committee but could get an answer to this query.

If somebody knows a published reference please let us know.

In the mean time, I have modeled the hydrotest as an occasional event with design condition being the normal condition.

You get little higher allowable but not as high as 0.9 * yield, but at least you can check all 3 stress categories.

This would be available in the next build of PV Elite 2010. But, if you need it immediately send an email to support at coade . com and put it to my attention.

Hi folks

In ASME Section VIII, Division 2, the allowable stress intensity (in the case of carbon steel) is based upon the lesser of UTS/24 or Yield/1.5. Pm + Pb is based upon a plastic hinge, and thus the allowable stress for Pm + Pb is 1.5S. If the Allowable stress intensity is based upon Yield/1.5, then 1.5S brings us up the yield point. Both Pm and Pb are primary stresses. Under no circumstances should a primary stress go beyond yield. Only secondary stresses are allowed to wander into the plastic (beyond yield) region.

Any primary stresses generated at the hydrotest must never exceed 1.5S. That is my conclusion.

Hi there,

After a small self research I would like share my view.

Division -2 establishes different allowable stress limits for different stress categories.

S is allowable stress based on material of construction @ design Temp.

1) Pm <= S (General membrane)

2) PL <= 1.5S (Local Membrane)

3) PL + Pb <= 1.5S

4) Pl + Pb + Q <= Sps (Allowable limit on primary plus secondary range)

5 Pl + Pb + Q + F <= Sa (Sa can be computed from fatigue curves)

As Mr Ray said correctly 1.5S will bring the Primary stresses i.e General membrane, local membrane & bending closer to Yield point & if the Yield point is exceeded beyond the same it may cause gross distortion of the equipment.

Secondary stresses are restricted to 1.5S.

So according to my point of view we can take advantage of 90% yield stress for allowable stress, i.e @ test condition for Pm instead of going very close to 1.5S.

Any expert advise would be appreciated.

Once you wander into the plastic region (beyond yield) you will experience progressive collapse. This is known as ductile failure, and many folk have been killed as a result of this type of failure.