Cone design per 2017 Div 2, Section 4.3.11.4

[jtseng123]

Dear all,

I have a question for the code equations 4.3.46, 4.3.47 and 4.3.56.
If I am using 12 mm thk for small end, large and, and cone, it meets all equations and internal pressure.
However, our Licensor/Client asks us to use 36 mm thick based on their standard design for this specific equipment. By crunching 36 mm into equations, all of them fail.

Question: shall the tc, tL, and ts be the calculated thickness ? or the final thickness which can be thicker than required ? By reading step 1 and 2 of sections 4.3.11.4 and 4.3.11.5 and from Fig 4.3.9. it seems the calculated thickness shall be used for these equations.

Please help. Thanks.

 

[racookpe1978]

What is the length of the cone?
What is the dia of the large end and small end?

What is the minimum bend radius possible for rolling a 36 mm thick plate at the fab shop you are actually going to use? Tangent lengths at the end of end rolled section may be limiting as well.
What pressure is the assembly, and is this particular assembly at the "usual" pressure and temperature and chemical conditions (alloy) that the customer expects?

 

[jtseng123]

racookpe1978, fabricator can do whatever we ask.

My only question is the interpretation of the code equations: Whether calculated thickness, or the final thickness (which can be very thick for all kinds of reasons, such as reinforcing junctions, thickness availability, for weight, wind and seismic loads, etc.) shall be plugged into those cone design equations ?

 

[jtseng123]

Our fabricator wants to use Part 5 to do the cone section analysis.
Can Part 5 analysis be used for Div 2 Class 1 vessel ? That means it will be a mix of Part 4 and 5 for Class 1 vessel. Is it allowed ?

 

[TGS4]

See 4.1.1.5.1.

A mix of Part 4 and Part 5 is permitted, but Part 5 is not permitted in lieu of Part 4 rules for Class 1.

You need to provide some details before it can be judged whether there is an "issue" for the Part 4 rules.

 

[jtseng123]

TGS4, Yes there are issues for all three equations that I mentioned, by using 36 mm (12 mm is good per code calc)thick as requested by Licensor, the cone length falls short, not meeting 4.3.46, and the radius to thickness ratio for both ends are less than 20, not meeting 4.3.47, 4.3.56. That is the reason I started this post by asking: shall the tC, tL and tS be the calculated thickness in lieu of final selected thickness. But no one has the clue.
That forces fabricator to use Part 5 using FEA to check the stress on the cone, with Class 1 design. I am going to accept this final resort since there is no way out, plus code does not clearly saying thickess shall be the required thickness or the final thickness. Using the final thickness does not make sense to me from stress point of view, from an obvious simple example: the ratio can be just at the lowest end of 20, but vendor is selecting 1/8" thicker due to market availability, that the ratio drop below 20 and we call it not meeting Part 4 ? Not making sense at all.

 

[TGS4]

If you honestly think that there is a problem with the calculations, as an engineer you have an ethical obligation to inform the Code Committee of the problem.

Unfortunately for you, paragraph 4.1.1.5.1 is very clear and not really subject to further interpretation. It doesn't say that for a Class 1 vessel that you can use Part 5 in lieu of a rule in Part 4 if you don't like the answer from Part 4. It says

Class 1. Rules in Part 5 shall not be used in lieu of rules in Part 4.

So, go ahead and submit the inquiry to the Code Committee. When you receive the tracking number back (it will be in the form of BC2018-XXXX), please advise of the number and I will personally follow-up to ensure that it is being addressed. And in the meantime, you should probably plan to attend the ASME Code Committee meetings.

https://www.asme.org/events/boiler-pressure-vessel-code-week

 

[jtseng123]

TGS4, but in para 4.3.11.4 saying if all equations are not satisfied, Part 5 can be used. It does not say I have to switch to Class 2. My interpretation is, for Class 1, Part 4 must be followed but if it fails like my case for the cone using the final thick thickness, I can use Part 5 since the specific paragraph saying so and the vessel can still be under Class 1. Is it incorrect ? Fabricator's AI advised us it is acceptable. We are the purchaser and this is the first time we deal with new code, it gets confused how to implement/interpret the new code, he says they say.

 

[TGS4]

That's not what it says at all. Which of the criteria in Step 3 are not satisfied?

 

[jtseng123]

TGS4, please see attached sketch. This is a special process equipment that the geometry from licensor can not be changed.

 

[TGS4]

You are very confused regarding the difference between an applicability criteria and a rule.

4.3.11.4, Step 3 defines whether your geometry is applicable in the subsequent Steps 4 through 7 requirements/equations/calculations. Step 3 also clearly states that if you fall outside the limits of applicability, then you must use Part 5. That does not violate the requirements of 4.1.1.5.1 - there are no rules in Part 4 that are appropriate for your specific geometry.

 

[r6155]

jtseng123
Code “is clearly” saying thickness is the minimum required thickness, not the final thickness

See 4.3.13 NOMENCLATURE
t = minimum required thickness of a shell.
tC = thickness of the cone in a conical transition.
tL = thickness of the large end cylinder in a conical transition.
t S = thickness of the small end cylinder in a conical transition.

Your attached calculations are wrong.

Regards
r6155

 

[jtseng123]

r6155, if your interpretation is correct, both PV Elite and Compress are wrong. Our fabricator using Compress, telling me it fails on Part 4 so they want to use Part 5. I used PV Elite to back check, same thing as my attached calc. Both programs are using the final thickness, that is why I posted for help.

Code only says "thickness", but it does not say it is minimum required or final (nominal) thickness.

 

[TGS4]

Again jtseng123 - it doesn't fail on Part 4, the geometry is such that the Part 4 rules are not applicable. You need to be much more precise in your terminology.

 

[r6155]

jtseng123, you can consult with people of PV Elite and Compress. I only use my own program calculations

PD 5500 is like ASME: t= minimum thickness, not final thickness.

Regards
r6155

 

[racookpe1978]

All:
This is exactly why I first asked "What are the proposed dimensions of the PV cone: thickness, inside radius, outside radiuss at small end, inside and outside radius at large end, length of cone?"

I suspect that the equations are being misapplied to a geometry that violates first assumptions of the derivation: Or even a case where the (OD/2 - Thickness) is negative or a near-point.