2007 DIV2 Limit Load, Tables 5.4 and 5.5
2007 DIV2 Limit Load, Tables 5.4 and 5.5
(OP)
Hi,
I have a simple but fundamental question about the Limit Load Analysis according to 2007 Div.2 part 5, and on the concepts of LFRD approach.
Let's suppose I have to design a vessel with the following data:
Design Pressure: 70psi
Operating Pressure 50psi
According to the assessment procedure (5.2.3.5e) convergence shall be achieved for the prescribed load combinations.
For example, the first global criteria is:
1.5*(P+Ps+D)
Here comes my question: according to the code the first term is the "max allowable working pressure".
Shall I assume the design value (70psi) or the operating one 50psi)?
If use the operating value, then the design pressure becomes "useless", on the other hand it seems weird to me to apply a further magnification factor to the design value, which already includes a safety coefficient.
I found out in 4.1.5.2 two separate definitions, one for Design Pressure, and the other for MAWP, so I'm assuming that the 50psi value shall be used, but I would rather like to have your opinion on the matter.
Thanks
I have a simple but fundamental question about the Limit Load Analysis according to 2007 Div.2 part 5, and on the concepts of LFRD approach.
Let's suppose I have to design a vessel with the following data:
Design Pressure: 70psi
Operating Pressure 50psi
According to the assessment procedure (5.2.3.5e) convergence shall be achieved for the prescribed load combinations.
For example, the first global criteria is:
1.5*(P+Ps+D)
Here comes my question: according to the code the first term is the "max allowable working pressure".
Shall I assume the design value (70psi) or the operating one 50psi)?
If use the operating value, then the design pressure becomes "useless", on the other hand it seems weird to me to apply a further magnification factor to the design value, which already includes a safety coefficient.
I found out in 4.1.5.2 two separate definitions, one for Design Pressure, and the other for MAWP, so I'm assuming that the 50psi value shall be used, but I would rather like to have your opinion on the matter.
Thanks





RE: 2007 DIV2 Limit Load, Tables 5.4 and 5.5
Design Pressure - maximum setting for safety pressure relief devices required by the ASME code. These devices are required to be 100% open at this setting, but may begin to open before the pressure vessel reaches design pressure. In the case where a burst disk is used as the safety device, it may burst before the design pressure.
MAWP - The design pressure is not suitable for routine use of the pressure vessel, especially where the vessel holds expensive and/or toxic materials. The MAWP is chosen suitably below the design pressure so safety devices can be selected that will not relieve during normal operation.
RE: 2007 DIV2 Limit Load, Tables 5.4 and 5.5
could be a typo or the newest code may be using MAWP now
RE: 2007 DIV2 Limit Load, Tables 5.4 and 5.5
I think that it would be appropriate to actually read ALL of the definitions in 4.1.5.2 BEFORE plowing in to Part 5. Remember, the various Parts of the Code are not stand-alone documents, they are all in the cohesive context of one Division of the ASME Code. It ALL goes together.
RE: 2007 DIV2 Limit Load, Tables 5.4 and 5.5
thanks for your reply. As I said in the opening post, I read all the 4.1.5.2 definitions, before posting. As you correctly pointed out, a good part "n-1" knowledge is requested before going to part "n".
Nevertheless, still was not sure about the correct answer. Please do not take my word as offending, simply I'm not english mothertongue, therefore I may be missing something that is obvious to you.
So I'm correct in assuming that, in my case, I shall assume the MAWP=PDES because in my case "calculations are not made to determine the value of the maximum allowable working pressure"?
So, in the formula
1.5*(P+Ps+D)
I shall assume P=70psi?
Thank you
Ishmael
RE: 2007 DIV2 Limit Load, Tables 5.4 and 5.5
Yes. Set P=70 psi.
Now, no offense, but please, please also read the Foreword to the code on page xix, in particular
I do not doubt that you are a competent engineer. What concerns me is that the question seems to indicate that you do not have previous experience in dealing with the design of ASME vessels nor do you have a mentor who is helping you understand the ASME philosophy. Although I recognize that some large, relatively low pressure vessels can find economic benefit from using Div. 2, it is not commonly used for a vessel at 70 psi. Another indicator of potential lack of experience with ASME pressure vessel design.
So again, no offense, but get help. Paid help, not the free kind like this forum where you get what you pay for, though sometimes more.
jt
RE: 2007 DIV2 Limit Load, Tables 5.4 and 5.5
I understand your concern. Just some explanations.
a) 70 and 50 psi are two sample values, used just for the sample, although I actually deal with vessel in that pressure range.
b) I cannot disclose further details, but the vessel has some shape discontinuities that cannot be handled by Div 1 rules.
c) In addition, the use of Div 2 is not up to my decision, is always in the Customer requisiton for this kind of applications.
d) I'm a Mechanical Engineer in structural mechanics, I have 9 yrs experience in FEM and vessel design, but I usually do not use limit load analysis. Typically I adopted the past Div.2 Appendix 4 stress categories, because with the 2004 and previous editions of the Code the use of non linear FEM in div 2 was much less direct.
I'm now practicing (late, I know) with the 2007 new part 5, because in the last two years I used different european codes, like the EN13445-3, which addressed much more clearly the use of FEA in the DBA route.
I'm not saying I'm the best expert in the world, but my calculations have been revised and approved by Customer engineering contractors, independent Notified Bodies (PED), third part consultant in Europe, USA, Canada,and Japan. I'm not a kid playing with engineering toys, I just had a (may be silly) doubt in a for me new application I wanted to share.
I think that there are no silly questions, just silly answers. I want to point out that this IS NOT THE CASE OF YOUR ANSWER, I'm sincerely grateful to your and TGS4 replies and warning. I do understand your concern. I asked several times my managers for a Div1/Div2 2007 training course, I hope I could attend it in a near future although no such courses are available in Europe, and an oversea course is kind of expensive.
e) I have seen much more concerning questions asked in the eng-tips forums
Sincerely,
Ishmael
RE: 2007 DIV2 Limit Load, Tables 5.4 and 5.5
Ok. Glad to see you have a background in vessels. In you previous FEA work, when someone came to you with a specific part (say for a Div. 1 vessel) which needed FEA approach (linear or nonlinear), did you use the DP or MAWP as you pressure load? The new Div. 2 defines MAWP pretty much the same way as Div. 1 does, so there should be no confusion. Operating pressure does not play a role here until you start looking at issues like fatigue.
jonezaz-
Sorry, can't let this one by since someone may read it and think its true:
First, I'll note that DP is not mentioned in the Manufactuer's Data Report - take a look at Div. 2 Table 2.D.3.
Secondly,
Note that MAWP shall not be less than the specified design pressure. So to state that the MAWP is chosen at some value below the DP is flat out wrong. The same holds for Div. 1. See UG-98 and also UG-99(b) footnote 34 which indicates that you don't actually have to determine the MAWP - you may use the DP as the MAWP. In other words, using the DP as the MAWP is conservative. In other words, MAWP is always higher than DP.
jt