Temperature limiation for using external pressure charts

[ags1]

UG-20 (c) states ""design temperatures for vessels under external pressure shall not exceed the maximum temperatures given on the external pressure charts."

Sec IID,Appendix-3,Fig-3-500.1 shows the temperature limitation for each material for the actual r/t ratio. For my case I have material SA240 304H, at 770°C, r/t ratio is 23.5. If I refer this curve of ss304H in Fig-3-500.1, I found I can not use external pressure charts for more than ~475°C.

If we refer external pressure chart HA-1 for SS304H material, the maximum temperature curve available is up to 815°C.

Commercial s/w available for pressure vessel design do not limit temperature as per Fig-3-500.1 and directly refer the curve as provided in external pressure chart. And if curve is available they don't check the limitation for use as per Fig 3-500.1.

Please share the interpretation on this. What should be right approach and interpretation?

 

[JStephen]

See Section 3-500(d)(3). It looks like if you're below the curve in that Appendix 3, the limit is not affected by creep. Above that curve, you do further analysis for creep per the reference in 3-500(d)(2) but are still limited by the external pressure charts.

 

[TomBarsh]

A previous thread asked the same question:

http://www.eng-tips.com/viewthread.cfm?qid=123610

 

[ags1]

Thanks.. JStephen.