317L to 5Cr Dissimmilar Weld 1

[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). 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?

 

[metengr]

BlackwellS;
I don't like this option because you still need to weld the flush patch plate to the existing 5Cr tower base metal that is 5Cr. This needs to be a full penetration weld with access to the ID surface to assure adequate tie in at the weld root with the existing weld overlay. You have fit-up and distortion concerns with flush patch plates, it could be a mess.

What about replacing the nozzles individually by simply buttering the weld prep surfaces on the tower base material (5 Cr) using Inco 82/182? Once the buttering is completed, perform a local PWHT.

Install the new 317L stainless steel nozzles using E317 or Inco weld metal. No preheat or PWHT is required for welding the nozzle into a buttered weld prep on the tower.

 

[BlackwellS]

Metengr,
Thanks for your response! 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 pipe.
BlackwellS

 

[metengr]

BlackwellS;
If you want to go the route of flush patch plates of 5 Cr, here are my suggested responses to your questions;

1. An idea on the appropriate rod for the root & subsequent passes (Inco 625, 309, etc.?).

I would recommend using Inco 82/182 for buttering the nozzle weld prep on the flush patch plate. Also, I would butter the entire ID surface of the flush patch, as well, with Inco weld metal. This way after PWHT of the flush patch plate, you can apply the E317 weld overlay for CR.

2. Preheat and PWHT temps.

For welding to the 5Cr base material you need a 400 deg F preheat. The PWHT will be 1300-1350 deg F for 1 hour at temperature after buttering.

I would butter, PWHT, and install the 317L stainless steel nozzle into the flush patch plate using E317 weld metal. Since you buttered the weld prep surface and ID surface, you don't need to PWHT the nozzle weld.

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?

Yes, because the corrosion resistance of the 317L stainless nozzle will be adversely affected by exposure to PWHT when you install the flush patch plate. You need to make the flush patch large enough to avoid heating the nozzle base material up to 800-1300 deg F.

This is why I would carefully think about the first option I suggested - remove the existing nozzles, clean, butter with Inco weld metal, locally PWHT, and install the new 317L nozzle into the buttered weld prep.

 

[BlackwellS]

I really appreciate your recommendations. Thanks!