UCS 79 % extreme fibre elongation 5

[rsaeed]

Hi all
In UCS-79 the formula is
% extreme fibre elongation = 75t/Rf (1-Rf/Ro)

now i have an elliptical head 2:1 D=3500mm h=875mm K=1 and for corrosion case D=3506mm, h=878mm and K=.998

Now I cant figure out where do I get this Rf and Ro to find the percentage elongation which is comming out to be 9.255% when done by consultant using PVelite. I just want the same from the manual calcs.

Can anybody please explain this Rf and Ro?
Thanks in advance for this.

 

[gr2vessels]

If you are using plate for the blank of your dished end, then the ratio of Rf to infinity is 0, hence your formula is only dependent of Rf, which is the smallest radius of the outer surface of the dished end knuckle area.
Cheers,
gr2vessels

 

[rsaeed]

Thanks gr2vessels for your reply, After posting that search I progressed further and found another reference of UG-32(d) which reads as
"An acceptable approximation of a 2:1 ellipsoidal head
is one with a knuckle radius of 0.17D and a spherical
radius of 0.90D."
From here I took the radai and using formula found out for each and than add it because that is the only way to get 9.255% which is the result of PVElite. I am actually doing backworkingn to get these results as how they come, its just for learning. I am not getting this that do we really have to add these two calculated results for .17D and .9D?? or am i doing it wrong??
The calcs are aas follows.
Percent Elongation per UCS-79 (75*tnom/Rf)*(1-Rf/Ro)

for 0.17D for 0.9D
D 3500 mm 3500 mm
Rf 595 mm 3150 mm
Ro infinity infinity
t 61.5 mm 61.5 mm
Elongation
7.75210084 + 1.464285714 = 9.216 percent


Thanks in advance for your reply

 

[jamesl]

Rf is centerline radius. So Rf=595+61.5/2=625.75.

The extreme fiber elongation is around 7.37%. Something was wrong with PvElite result.

 

[rsaeed]

James1 mate can you please have a look on the attached file to see if we are doing it properly in the light of given parameters and conditions.

I still doubt in our interpretations because of the absence of references.
In the one I did is because for my calcs there is no reference showing that after taking Rf=0.17D adn Rf=0.9D we have to """"add""" them. I only added because I could only get 9.3% by adding it.

Secondly, where have you worked out this formula which in paramatric form is coming as Rf=.17D+t/2. I cant see this formula in the codes, Can you please give the reference so that I can also have a look on this. May be that will work!!!


What do you say ""gr2vessel"" for this?

 

[jamesl]

As I said, per UCS-79, Rf is the radius at centerline of the head wall, not at the I.D. So you need to add half of the thickness.

I verified the result with Compress from Codeware. I trust it more than PVelite (just my personal opinion).

 

[rsaeed]

Thanks james for your reply but mate!
Do you agree with taking 0.17D and 0.9D for Rf?
The calc you doing is from 0.17D will you not repeat this for 0.9D as well?
Will you add both the elongations later on?
Can anybody from PVElite take this as a challenge from a Compress user James? And verify that its wrong in PVElite. I have attahed the whole design data in the older post.

I want to see this concept on sketch which dimension exactly is Rf and why they are two? I assume that that ellipsoidal shape is comming with the combination of the two radai.

I am annoyed with the situation of not reaching the detailed explanation of this. Dont have book or some reference material!!

 

[starrproe]

rsaeed,
Your ellipsoidal head dimensions are -
ID = 3500mm
Min. Thickness = 61.5mm
Nominal thickness = 75mm

Procedure for calculating fibre elongation is -

Centreline diameter = 3500+2*(Min. Thickness/2)
= 3500+2*61.5/2
= 3561.5mm
Centreline radius of knuckle(Rf) = 0.17*(Centreline diameter)
= 0.1727*3561.5 = 605.4mm

% Fibre elongation per UCS- 79 = (75*Nominal thickness)/Rf
= 75*75/615.1 = 9.2%

PV-Elite output you have attached shows fibre elongation of 9.25%.

Please note - Fibre elongation for knuckle region always governs because maximum deformation during forming takes place in this region due to it's small radius(0.17D).

Hope it makes some sense....

Starrproe

 

[rsaeed]

Thanks Starrproe,
hmnn! good try mate but still one confusion please confirm this.
You result is comming exactly to be 9.291%

But if I do the following I am getting exactly 9.255% which is the exact answer. The difference is only in the formula """Centreline diameter = Dia+2*(Min. Thickness/2)"""" If you replace Min thickness by nominal thickness the result is getting its exactly value matching with PVElite. So please confirm where did you get this formula. I am writing it the way I THINK (not sure!)


Centreline diameter = 3500+2*(NOM. Thickness/2)
= 3500+2*75/2
= 3575mm
Centreline radius of knuckle(Rf) = 0.17*(Centreline diameter)
= 0.17*3575 = 607.75mm

% Fibre elongation per UCS- 79 = (75*Nominal thickness)/Rf
= 75*75/607.75 = 9.255%(exact Value)

Please confirm it!!!
Can you also check page 21 of the result file and in the last of page 21 there is a table showing three rows of nodal values. I am not getting from where did the Allowable stress came as 179260.0kPa. If you can tell this it will be great.

 

[jamesl]

rsaeed,

You should be clear from the beginning that the plate has a nominal thickness of 75mm, not 61.5mm.

The way you calculated knuckle centerline radius was wrong. The code recognizes Rf=0.17D based on the ID only. At centerline, there is no such relationship. You should use the 0.17D+t/2.
So the fiber elongation is still less than 9%.

 

[starrproe]

rsaeed,

By default, PV-Elite assumes 1.3 times allowable stress at ambient temperarue as the allowable stress during hydrotest.
This is the case with youur calculation as well.(Press F1 on your keyboard after selecting "Hydrotest is 90% yield." in Design Constraints header to see it yourself.)

Allowable stress for SA 516-70 @ ambient = 137598 KPa
Hydrotest allowable = 1.3*137859 = 179263 KPa

However, if you wish to limit your hydrotest allowable to 0.9Sy instead of 1.3Sa, you can do so by checking the box against "Hydrotest is 90% yield." in design constraints header of PVElite.

Hope it helps.

Starrproe

 

[Mandeep1]

I will try to clarify the issue,

Elliptical head inside diameter,

ID = 3500mm

Head nominal thickness,
tnom = 75mm

Centerline radius, Rf = 0.17 * ID + 75 * tnom

= 0.17 * 3500 + 75 / 2
= 632.5 mm

Percentage elongation = 75t/Rf (1-Rf/Ro)

= 75 * tnom / Rf * ( 1 - Rf / Infinity)
= 75 * tnom / Rf
= 75 * 75 / 632.5
= 8.893 %

this is what I get in PV Elite 2010

The issue was that in 2009 PV Elite was applying 0.17 * centerline radius. But, as "jamesl" correctly pointed out and also per interpretation VIII-1-01-57, Rf=0.17D is only based on ID.

So, in latter part of 2009 this was corrected in PV Elite. So, you can either use 2010 version.

If you have to use the 2009 version, find the PV Elite 2010 disc that was sent to your company, then browse on the disc and open a folder called "Older Versions" and go to the 2009 version and run the setup program.

If you cannot find your PV Elite 2010 disc, contact COADE technical support.

I hope that answers your question. I will try to add more clarification to the output.


best regards,
Mandeep Singh

 

[rsaeed]

Thanks James and Mandeep I got the problem almost solve now.
Mandeep in your post you have mentioned

Centerline radius, Rf = 0.17 * ID + 75 * tnom

whereas your working is showing it to be as follows:

Centerline radius, Rf = 0.17 * ID + tnom / 2

Just confirm the correct one please !

Also please note that I dont have PVElite software. I only have the result of PVElite for one of our vessels and I want to exeute that through manual calculations

 

[rsaeed]

starrproe and gr2vessel
Thanks for your reply mate!
I have got that Hydrotest allowable stress= 1.3*137859 = 179263 KPa
Where is this 1.3 times came from? Why PVElite is using that I mean is there any code reference for taking it 1.3times?

Another thing I am confused with is that if allwoable stress is 137892kPa for SA516Gr.70 than why are we exceeding that allowable by the stress of 1.3times which is 179260kPa. What is the practical interpretation of this?

As per calcs of UG-99(b) Note 34 we are taking the test pressure of 5850Kpa + hydro head =5884.31kPa so its stress is comming out to be 168028kPa which is also above allowable stress of 137892kPa

What is the yeilding stress value for this material? can you please write that here with the reference of source? I will be grateful.

 

[Mandeep1]

I had a typo in one of the formulae, here is the correct one,

Centerline radius, Rf = 0.17 * ID + tnom / 2
= 0.17 * 3500 + 75 / 2
= 632.5 mm

You can ask your client to use the updated PV Elite version.

On your query of hydrotest allowable,

ASME Div. 1 code does not provide a hydrotest allowable. By default PV Eltie takes Minimum of 1.3 * S, 0.9 * Yield for the hydrotest allowable.

But, as Starrproe pointed out you can instruct to use 0.9 * Yield for Div. 1 hydrotest allowable.

The 1.3 factor is also used to get the hydrotest design pressure.

I did not see any failure in your output for hydrotest.


best regards,
Mandeep Singh

 

[gr2vessels]

ASME VIII-1, Clause UG-99(b) states:
"Except as otherwise permitted in (a) above and 27-4, vessels designed for internal pressure shall be subjected to a hydrostatic test pressure which at every point in the
vessel is at least equal to 1.3 times the maximum allowable
working pressure34 to be marked on the vessel multiplied
by the lowest ratio (for the materials of which the vessel
is constructed) of the stress value S for the test temperature on the vessel to the stress value S for the design temperature (see UG-21). All loadings that may exist during this test shall be given consideration". The same applies in fact for all Clause UG-99, with some exceptions as detailed in the Clause.
Read also the definition of MAWP, Clause UG-98.
Cheers,
gr2vessels

 

[rsaeed]

Good Morning All,
Thanks for all of your contributions and I got few answers but one thing I think I couldnt clearified in the question. I am trying it again as under:::

The word """Allowable Stress""" is the one which is confusing me. From this word I understand that the material should not be stressed more than this at a given temperature. For example from ASME section II part D table 1A the allowable stress for SA516Gr.70 is 20,000 psi (137892 kPa) for (-20F to 100F)(-28.8C to 537.7C)

Why are we going beyond this stress value by applying hydrotest pressure? (we can see after calculations that the stress comming out to be 161954 kPa corresponding to our calculated hydrotest pressure (5884.31kPa) which is more than 137892kPa and that means we have exceeded the allowable here.) Refer Pg21 of the cals attached previously.


I know the yeilding will start at 38000psi (262000kPa) but still the """Allowable Stress""" should be respected. This is where I stuck and not getting. The calculations are clear, the one which gr2vessel mentioned I can see them happening in the PVElite calcs as well but that is for pressure where as PVElite is taking 1.3times of Allowable Stress (not only pressure) to get another value of allowable stress for keeping the stress due to hydrotest pressure inside that new stress limit.

I hope the above will clarify the query.

Thanks and best regards.

 

[SnTMan]

rsaeed, the allowables tabluated in Sec II, Part D are for DESIGN. As noted by Mandeep1 Code does not address or limit stresses applied during hydro.

Once solved for a given thickness, it is obvious that when applying the same formula at a higher pressure (hydro) with the thickness fixed the allowable must be allowed to increase.

Regards,

Mike

 

[gr2vessels]

I think I know where the mistery is;- the allowable stress for the design of pressure equipment is calculated by ASME (and all the other pressure vessel codes and standards in the world) and the basis of calculating those values are detailed in Appendix 1 of ASME Section II, Part D. Read carefuly the Appendix 1 and come back with question if needed.
Just remember, the vessel should operate always safely, hence a safety factor is used to calculate the allowable for any listed materil. However, the hydrotest pressure, to prove the safety of the finished equipment, has to go a bit higher than the design pressure (for example the code says 1.3 x the design pressure or the MAWP). If the test is completed without damages to the equipment, then it is proven the vessel will operate safely at the design pressure or the MAWP.
Cheers,
gr2vessels

 

[rsaeed]

Thanks very much.