Fatigue Analysis for Cyclic Service Div.1 1

[chaulklate]

Hi all. This is my first post, so go easy on me if I violate any forum protocols. I have a simple Section VIII Div.1 pressure vessel that will operate in cyclic service. I would like to perform a Fatigue Analysis as per the rules of Div.2, AD-160 Fatigue Evaluation, Appendix 4 Stress Analysis, and Appendix 5 Fatigue Analysis. I have refered to Appendix G Examples of Formulas and Rules and feel somewhat comfortable analyizing the shell. However, I am drawing a complete blank with finding proper formulas and methods to analyze the heads, nozzles, and thermal conditions. Can anyone offer perhaps a set of "sample" calculations that I could mimic, or offer some guidance as to where to find the proper forumlas? Any and all input will be greatly appreciated, I look forward to your responses.

 

[codeeng]

Article 4-3, 4-4, 4-5 and 4-6 cover analysis of hemi heads, toris/ellip heads, flat heads and nozzles respectively. This is a very detailed and time consuming exercise and I find that most designers choose to thicken-up and go for the exemptions. This may be a better choice in your case since you are dealing with Div 1 and assuming relatively thin sections.

 

[esce]

I have been looking for the same thing. I need a good example to follow. Have you had any success as yet?

I did find this. I have been thinking about buying it:

******************************************
Description
Order #: H00967
ISBN #: 0791813355
Published: 1995
Product Type: Print-Book
No. of pages: 596

ASME/JSME Pressure Vessels and Piping Conference, July 23-27, 1995, Honolulu, Hawaii. Compilation of papers illustrate application of fatigue and fracture mechanics techniques to assess the structural integrity of a wide variety of pressure vessel and piping components. Focus is on fatigue and fracture in vessels, piping, and material property evaluations; constraint effects in fracture mechanics; probabilistic fracture mechanics anaylses; user's experience with failure assesment diagrams. @By: H.S. Mehta, et al





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[chaulklate]

No, I didn't get any further than this. I checked out our company library and found some old papers on fracture mechanics, but it mostly dealt with why things failed, not how to prevent them from failing, nothing that suited my application. This seems to be a rare art, I haven't found anyone who is very experienced at it. I'm leary about buying a publication without looking at it first, you can never be sure if it will suit your needs and still be out a lot of money. I was hoping for some guidance from my vendors, but they have come back with completely different proposals so now I really need to figure it out so I can make the right choice to have it built. I could hire someone to do it for me, but what will I learn from that?? I will post here when/if I get something more.

 

[LSThill]

TEAM MEMBERS:

TECHNICAL REFERENCE API 579 Fatigue Analysis for Cyclic Service.

 

[davefitz]

You may want to consider the use of the european union pressure vessel design codes (PED- pressure equipment directive)when conducting a fatigue analysis, since they include fracture mechanics failure mode for pre-existing cracks in weldments and also the constituitive equations they use can be directly implemented with commerically available finite element codes.

The ASME sect VIII div 2 method was derived from methods based on manual calculations and simple bodies , as commonly done in the 1950's. It is difficult to finagle the results of a nonlinear finite element analysis into the format used by ASME sect VIII. I think ASME now allows the alternative use of the PED, and this may be part of a reciprical agreement with the EU to encourage the EU to accept the ASME code in other cases. Privately, I suspect the ASME may directly adopt the EU PED fatigue methods soon.

 

[jte]

esce-

I really doubt that the Pressure Vessels and Piping conference volume will provide the guidance you're looking for. There's a Fatigue and Fracture track at each PVP conference so buying a 10 year old volume may not make the most sense. You can check out the papers from last year's F&F track at

http://store.asme.org/category.asp?...name=Fatigue+and+Fracture_PVP2005TCK-3&Page=1

and buy the papers individually if you find one which works for you.

In general, I'd agree that there is little written material on how to apply the code rules for fatigue in design of new equipment. I was taught the old fashioned way, by a couple of guys with a combined 50+ years experience mentoring me for several years. I guess my generalized guidance would be to not worry about the shell and heads, worry about the details like the nozzle to shell intersections and ladder and platform clips etc. Minimize attachments and avoid fillet welds (full pen with fillet is ok). Use integrally reinforced nozzles or insert plates (locally thicker shell sections). Etc. etc. If the details work, the major components will also tend to work.

jt

 

[PVGuy]

The UHX rules in SC VII, Div. 1 are very similar to the stress analysis in article 4. This might be a good example to help you see the application of the rules. The derivation is included in the Journal of Pressure Vessel Technology Vol 128 (the most recent volume). My only other comment is that I performed Article 4 calculations 1 time for a Div. 1 vessel when the customer was determined to use a dished only head with a crown radius twice the diameter of the shell. It took me about 8 hours and it turned out that the stresses at the head-shell junction were so high that they were forced to change to a F&D head. Anyway, the ordeal results in flu like symptoms of headache, nausea, and exhaustion.