Tilted Nozzle Reinforcement Area (ASME sec VIII)- How to compute? 1

[ggroppi]

Hi!
Has anyone experienced problems in verifying reinforcement area requirements in tilted nozzles?

I’ve some troubles with a 45° degrees downward oriented nozzle type 9.
In computing the limits of reinforcement I usually refer to Article D-5 of ASME VIII div.2.
So I find a limit in the normal to the vessel axis direction, then accordingly to ASME VIII- div 2 AD-540.2 I consider as reinforcement area the heavy barrel area comprised underneath the normal to the vessel wall limit H, that for a 45° tilted nozzle has the shape of a parallelogram.

My design software (Compress) in calculating this area is taking into account, in favour of safety, a smaller area than the one actually available. In fact, in cross sectional view, the software computes the area taking the normal to the vessel limit H times the heavy barrel thickness, tn - trn i.e. Area = H * (tn - trn), which is the area of a rectangle smaller than the parallelogram; while I’m used to compute the whole area of the parallelogram i.e. A = (H/sin beta) * (tn - trn), where beta is the inclination angle of the tilted nozzle (in my case 45°).

I cannot find in literature any other example of this kind of problem.
Does anyone know which is the “right” interpretation of the ASME code about this issue?
Does anyone have some experience with tilted nozzle in order to explain the reason of this two different ways of calculation?
How do you face the reinforcement problem?

I remark that this different way of computing the area leads to two different results: what, for me, is Adequate result in a “Not adequate” reinforcement for Compress, with the obvious consequences in the deficiencies report.

I posted a sketch of the problem at this URL

http://www.4shared.com/dir/904568/8806ba87/sharing.html

Please check it out.

Giangiacomo

http://www.atbrivacalzoni.com

 

[unclesyd]

Cross posting is discouraged.
You will get better results using just one Forum. This save members time and effort.

 

[deanc]

Have you looked in VIII Div1 Appendix L? L-7.7.1

If you have a number of these you may want to consider a "proof test" per UG-101.

 

[ggroppi]

Thanks deanc,
I checked the example L-7.7.1 and It's quite useful. The problem of interpretation still remains, because if the area of reinforcement must stay inside the limits stated by the Code, I cannot understand why we should neglect the surplus of area available in a tilted nozzle due to its inclination.

The Code doesn't clarify the problem, it seems strange to me that around the world nobody thought of it, but.... I think in the end I'll move to the Compress way of calculation...

In the meanwhile I'm looking forward to hear other ideas.

Giangiacomo

http://www.atbrivacalzoni.com

 

[LSThill]

ggroppi (Mechanical)

Check with Codeware Compress FE-Nozzle or Nozzle Pro.

 

[CodeRef]

I agree with lsthill,
Contact Codeware for answers to your questions because you are using their software and they are very capable of explaining this concept.

Now for my 2 cents...
The premise for performing these calculations is fairly simple. When an opening is cut in a vessel there is a stress intensification produced at the hole. The Code implements the equations of UG-37 based on an “area of replacement” concept. Near the opening, there should be “extra” metal provided equal to the area of the required metal missing due to the presence of the opening. This extra metal should be within one “decay length” in both the vertical and horizontal directions to be effective. The decay length is defined as that length along the shell in which the governing stress applied to an edge reduces to approximately zero. See UG-40 for limits (decay length)

As for your picture describing “rectangular” versus “parallelogram” limits of reinforcement; this is not in line with the Code defined decay length philosophy and the “area of replacement” concept.

See this interesting link I found using Google for a detailed explanation of hillside, inclined and radial nozzles utilizing Fig UG-37:

http://www.pdhonline.org/courses/m205/m205content.pdf

There are three kinds of people in this world; those who can count and those who can't.

 

[prex]

IMHO UG-40(c) should be considered mistaken, when it is stated that the limits of reinforcement are measured normal to the vessel wall: this is true for normal nozzles, but must be considered incorrect for hillside nozzles (and indeed the interpretation of example L-7.7.1 may be considered a corrective for this mistake).
In fact the limit should be taken along nozzle wall as the foundation of this kind of calculations, as correctly stated by CodeJackal, is the concept of decay length, that is meaningful only along vessel wall.
However, as the interpretation of code is not permitted to users (and App.L is non mandatory), personally I've always used the literal interpretation of UG-40(c), so that I agree with ggroppi.

prex

http://www.xcalcs.com

Online tools for structural design

 

[ggroppi]

Thanks all for your answer,

For CodeJackal: I understand and agree with your description of the limits as decay length. In order to be clearer I posted a new image on

http://www.4shared.com/dir/904568/8806ba87/sharing.html

where I've drawn the reinforcement limits in magenta color.

In a case like that the area along nozzle wall is inside the limits and it's obviously bigger than the one computed in the other way.
My concern it's not about the limits of reiforcement, those are pretty clear; but about what it's inside these limits and in this case the shape of the area available along the nozzle wall its a parallelogram (base: tn/sin(beta); Height: H ) not just a rectangle (base: tn; Height: H ).

As matter of fact this is a problem of Code interpretation, and apparently it's not trivial, because I've submitted it to Compress several weeks ago and they're still working on it.

If anyone has faced this issue in the past, please report

Giangiacomo

http://www.atbrivacalzoni.com

 

[prex]

No, ggroppi, if you take the limit along nozzle wall, then your H is also measured along nozzle wall and the available area is H(t[sub]n[/sub]-t[sub]rn[/sub]).
This interpretation is clearly enforced, as an example, in the italian code VSR.
Cela dit I agree with your literal interpretation of ASME code and always did my calculations as you are proposing. However if you intend to use Compress...

prex

http://www.xcalcs.com

Online tools for structural design

 

[LSThill]

Technical Note:

The CODEWARE COMPRESS VERIFICATION AND VALIDATION MANUAL HAS DETAIL SLOUTION. Please contact Codeware.com for the V&V Manual.

RE: On Assignment I had to do the Verification and Validation for DOE and was completed Jan. 2006. CODEWARE did Issued their VERIFICATION AND VALIDATION MANUAL HAS DETAIL SLOUTION in Feb. 2006.

 

[ggroppi]

Thanks lsthill, I'll ask for the Compress V&V Manual,

in the meanwhile
Some Udates:

I checked the Italian code VSR: It states to take reinforcement area limits along the nozzle wall direction and if we assume the same logic in ASME code the available area results the same as computed by compress (Area= H*tn in the image I linked previously), supposing take the same limit from UG-40(c) along the nozzle wall; but ASME code clearly states to take limits in the Normal to the vessel wall direction.

Reading some Codes I found something that is indubitably in my direction:
ASME B31.3 304.3.3(d) literally says:
"Reinforcement Zone: the reinforcement zone is a parallelogram whose length extends a distance of d2 on each side of the centerline of the branch pipe and whose width starts at the inside surface of the run pipe (in its correded condition) and extends beyond the outside surface of the run pipe a perpendicular distance L4"

The sketch, as usually, is posted at

http://www.4shared.com/dir/904568/8806ba87/sharing.html

What do you think of it? Please post

Giangiacomo

http://www.atbrivacalzoni.com

 

[CodeRef]

How about this!
The area of a parallelogram is the same as the area of a rectangle: Base x Height. The difference is that you have to be very careful about measuring the height, since it is not measured along the edge, but is perpendicular to the base.
Sooooooo a parallelogram and rectangle in this case are synonymous or (the same) correct?



There are three kinds of people in this world; those who can count and those who can't.

 

[Bobfromoh]

Your example is through one plane of the nozzle.
What happens when you look at the plane at 90 degrees.
The nozzle is no longer at an angle. Maybe it's done the way it is to keep the calculation from getting overly complicated?????

 

[CodeRef]

Upon further research,
ASME B31.1 and B31.3 allows for the angle in the Area required for reinforcement calclulation ie.. A = (H/sin beta) * (tn - trn), where beta is the inclination angle of the tilted nozzle. There is an additional/optional calculation for right angle connections that takes out the angle in the formula.
The piping codes (B31.1/B31.3) do not have a comparable Fig UG-37. Maybe this is because branch connection reinforcements will always be axial to the header where in vessels it is relative to the largest opening and Fig UG-37 is utilized.
When looking at ASME VIII Div 2, I find that it also follows the same line as Div 1 and accounts for reinforcement normal to the vessel wall.

I now understand and agree with your question as to why this is NOT considered in vessel design. Perhaps Bobfromoh has the answer....I don't know.


There are three kinds of people in this world; those who can count and those who can't.

 

[ggroppi]

CodeJackal,
I'm happy to read that you saw the difference that I was trying to underline.
In the last sketch I posted is evident that the reinforcement area in the nozzle wall is a parallelogram inclined of the angle beta with the area that you wrote down A = (H/sin beta) * (tn - trn).
I don't think that in ASME VIII div 1 and div 2 this is not considered.
ASME VIII says that the reinforcement has to stay inside 2 limits, one normal to the vessel wall and the other parallel to the vessel wall.

In My opinion all the area of heavy barrel ( thickness: tn -trn) in the nozzle wall inside those limits has to be considered available for reinforcement, when it's not explicitly excluded, and, if the nozzle is tilted the area will be bigger than a perpendicular nozzle of the same thickness.
But this is not explicit in ASME VIII, and my main problem remains because design softwares compute a smaller area...

If anyone has an opinion that could be useful please post

Bobfromoh,
if I've understood correctly your observation, I think that in the plane at 90 degrees the chord of the opening is smaller because the nozzle is not inclined (the shape of the opening should be oval)... Is it what you asked?

Giangiacomo

http://www.atbrivacalzoni.com

 

[CodeRef]

So, in effect, the ASME Vessel Codes are unwittingly or wittingly imposing the use of repads or similar designs of attachment such that normal to the vessel reinforcement calculation is required.
Why waste heavy wall pipe for inclined nozzles when there is obviously no benefit (unless external loadings apply)

Interesting...


There are three kinds of people in this world; those who can count and those who can't.

 

[LSThill]

Technical Note:

• "A Proposed Method for Finding Stress and Allowable Pressure in Cylinders with Radial Nozzles," PVP Vol. 399. This paper is the technical basis for ASME Code Case 2398.

Bildy, Les M., 2000, "A Proposed Method for Finding Stress and Allowable Pressure in Cylinders with Radial Nozzles," PVP Vol. 399, ASME, New York, NY, pp. 77-82.

Permission has been granted by ASME to post this paper. Should you be interested in ordering the complete publication in which this paper was originally published, you can contact the ASME Information Central.

PHONE
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Mexico: 95-800-843-2763
Outside North America: 201-882-1167
FAX: 201-882-1717 or 201-882-5155
EMAIL: infocentral@asme.org
URL:

http://www.asme.org/catalog

 

[Bobfromoh]

to ggroppi:
The original question is only looking at one plane through the nozzle/shell intersection. As you go around the circumference of the nozzle, the shape of he "parallelogram" is constantly changing. What calculation should be done to account for the changing geometry? It seems to me the Code is using a worst case area calculation?

 

[ggroppi]

Bobfromoh,
I agree with you that the area available in the nozzle neck is varying around the circumference of the nozzle; the shape of the opening in the shell varies as well, in fact in design software you can find 2 calculations one for the long chord cross section and one for the short chord. The configuration I posted is intended as the worst one, ignoring a part of the area available in the nozzle wall the Code is taking a very conservative approach (maybe too much conservative????). Why?

Giangiacomo

http://www.atbrivacalzoni.com

 

[CodeRef]

ggroppi,
The link lsthill tried to show, but was not successful is here:

http://www.codeware.com/papers.html

This paper explains the approach that Section VIII-1 takes toward opening reinforcement rules. The proposed method considered is based upon the approach given in App. 1-7(b)of VIII-1 Ironically App 1-7(b) applies to larger radial nozzles, but, a review of the results given in Table 1 of the paper, reveals that this method agrees well with both FEA and burst test data.

Some conclusions I have gathered from this paper are that pad reinforced nozzles calculated using ASME VIII-1 rules should result in more accurate results than for integrally reinforced nozzles the larger the nozzle becomes. Rules given in UG-36(c)(3)(a) for smaller integrally reinforced nozzles are substantiated in principle through this paper and are found to be very conservative.

Though this paper does not specifically address other than radial nozzles (in general),I think the paper supports the ASME's "normal to the vessel" philosphical approach when calculating nozzle reinforcement.

So, in summary, you can be confident that the current rules are adequately conservative and not overly conservative and that the proposed method in the referenced paper indicates as much.

I especially like the graphed comparisons shown in Appendix A between VIII-1,VIII-2, FEA, burst data and the proposed method.


There are three kinds of people in this world; those who can count and those who can't.