Fatigue analysis of Rectangular Autoclave 1140 x 2100 x 7040 mm

[mkdjssteel]

Dear all,

We are trying to figure out whether we need to do a fatigue life analysis for this autoclave to be designed to following condition. Vessel to be designed and manufactured as per ASME sec VIII div 1.

Size: 1140 mm (W) x 2100 mm (H) x 7040 mm (L)
Design temperature: 2.5 barg
Design Temperature: 130 Deg C
Maximum working pressure: 1.6 barg
Maximum working temperature: 121 deg C
Materials of construction: 316/L SS
The autoclave cycle varies but a typical cycle will be 2Hrs where it is heated up to 121 deg C and Pressurised to 1.6Bar and then cooled down to ambient temperature. This makes a maximum of 12 Cycles a day. Our expected life expectancy of this vessel is 20 years. Total estimate maximum number of cycles: 87600.

Went through ASME sec VIII div 1 and found both clause UG-22 and Appendix 46 do not really not proper guideline in deciding whether this vessel required fatigue life analysis. Also Div 2 section 5 looks like the way to go, but looks very complex.

Our local code AS1210 in Australia does not cover non circular vessels. Therefore we have to use ASME Sec VIII for this design.

In AS1210 there is clear guidance to decide whether Fatigue life analysis is required for specific vessel. Please see below excerpt (item no 3.5). Just wondering whether there is any clear guideline like below in ASME sec VIII div 1?

Any advise is highly appreciated.

 

[IdanPV]

Maybe ASME VIII-2, 5.5.2.2 will be suitable for your case.
Make sure to evaluate the possible harmful effect of the design feature listed in (a) throguh (f).

 

[mkdjssteel]

Thank you very much for your suggestion @IdanPV.

Looks like that clause may be the most useful in this case as the customer has 4 off similar autoclaves already running for years. Out of the harmful effects item a) "non integral" is applicable as current drawing shows the nozzle weld detail as fig UW-16.1 (k) below and ANSI 150# S.O flanges. Nozzle size range from 8" -1" NPS. So we may have to do FEA on these nozzles or change the nozzle design to a integral design?

 

[IdanPV]

Note that the Code wording is:
"The possible harmful effects of the following design feature shall be evaluated."
My understanding is that you shall evaluate the possible effect of the feature that you mentioned, and check how it's effect the design life of the equipment.
Keep in mind that when it comes to fatigue, it is better to use full penetreation welds.