cylindrical shell for external pressure at high temperature

The design data is:

as per ASME section VIII div. 1
design external pressure: 50 psig @ 1325F
material of construction specified by client: SA-240 321

According to ASME IID, Fig. HA-2 (ss 321) stops at temp. as high as 1200F. The only material that can support that external design temp. is N06625 but is corrosive to the application. Weld overlay is expensive and time consumming.
Therefore, to bypass the problem, my collegue suggested me treat the cylindrical shell as stayed/braced flat plate with ss 321 as material of construction.
Please comment.

Thank you all in advance,
qlananh

 

[butelja]

If this is a code vessel and the material is not listed above 1200 F, you CAN NOT USE THE MATERIAL ABOVE 1200 F.

 

[twjag]

butelja may be incorrect in his response. It is often the case that max temperatures in ASME Section II-D External Pressure Charts are lower than those in Allowable Tensile Stress Tables. Appendix 3 of ASME Section II-D provides the basis for the External Pressure Charts. As noted in 3-100, "use of the charts eliminates the need for complex calculations". You can perform the "complex calculation" for higher temperatures, if you have adequate material property data to satisfy the criteria in 3-600. If not, you are limited to the max temperatures in the External Pressure charts in II-D.