317L to 5Cr Dissimilar Weld with overlay

[BlackwellS]

Thanks for taking the time to read this post. Does anyone out there have a suggested weld-procedure to weld a 317L nozzle into a 5Cr flush patch? I'm considering the option as a temporary replacement for a number of thermowells and vent connections on a 5Cr vacuum tower transfer line. I'd have 12x12x0.375 thk. flush patch, 1-1/2" sch160 nozzle, and 0.125" 317L overlay on the I.D. of the patch. The nozzle-to-patch weld would be a full-penetration weld. The service is two-phased reduced crude under vacuum ~720degF and I have a problem with napthenic acid attack at the discontinuities. The intent of the overlay is to protect the nozzle-to-patch weld from seeing the process (I need the higher Mo content in the 317L). The reason I'm leaning towards the patches is because we've had several thru-wall failures in the HAZ of the nozzles in addition to local thinning of the nozzle. FYI, we're also installing a reinforced 20" manway into the line to facilitate fit-up and grinding from the I.D. of the larger O.D. pipe. I'm looking for assistance with the following:

1. An idea on the appropriate rod for the root & subsequent passes (Inco 625, 309, etc.?).
2. Preheat and PWHT temps.
3. Should I be concerned with the required temp to PWHT the 5Cr material with the 317L nozzle attached? Does this need to be a local vs. baking the entire assembly?

Thanks in advance

 

[metengr]

Please do not cross post,
thread725-175154

 

[BlackwellS]

I didn't know that this was against any established protocol. My intent was to solicit feedback from other users who may not be members in the Structural Engineers forum. Thanks.