321 SS to 9cr
321 SS to 9cr
(OP)
I have a client asking me to research a 321ss to 9cr repair procedure. After doing my own research, I will also consult with a metalurgist as well as a selected weld engineer and compare notes.
A crack was found in a fairly heavy 1.5" thk. x 12"-16" long 321 stainless lug welded to a 9cr pad welded to a 9cr pipe. Existing filler material or weld procedure unkonwn. Cracks are small but can be seen with the naked eye. My guess is this lug is in an approximate 1200f environment or possibly higher continuously. I do not know how often it cycles.
The 321ss Lug to the 9cr pad weld is a full penetration weld. Not sure why they chose this combination (I would have attached a 9cr lug/s directly to the header with a hole in it for pinning the stainless support hanger)
Initial research has me leaning towards grinding out the existing weld cracks to penetrant test acceptable, Apply 400 f preheat with ER preheating (if possible) GTAW process using,ERNiCr 3 filler, slow cool to ambient prior to heat treatment followed by normal 9cr heat treatment (1350-1425f, couple hour soak, slow cool under insulation).... No wet type NDE until after heat treatment. The rub with this is perhaps the 321 cant handle the heat treatment.
I see some have recommended a butter weld (presumably a 1/4" thk layer of enco 82 butter weld to the 9cr pad and heat treat) in new construction. Would this then eliminate the need for heat treatment of the lug to the butter weld?
This is not possible without complete removal (which whether they realize it or not is going to happen sooner or later). Their intent for now is to buy some time for a permanent fix later.





RE: 321 SS to 9cr
1. Have a small sample of the full penetration weld removed and pad weld removed on the 9Cr base material for chemical analysis by a met lab to confirm filler metal compositions.
2. Once the filler metal compositions are known, you can decide on a specific repair option and filler metal selection regarding the 321 ss lug to the 9Cr pad.
3. If the cracks penetrate into the 9Cr pad, you need to know the filler metal of the pad, as deposited.
4. I can see several options once the filler metals are identified.
Note: In lieu of lab chemical analysis a portable alloy analyzer may work.
RE: 321 SS to 9cr
Ti - 6.47
FE - 8.81
Mn - 6.89
Ni - 61.75
Cr - 14.85
Zn - 0.106
RE: 321 SS to 9cr
Regarding weld repair, I would remove the crack(s), ensure removal by LPT. Use Inco 82 to weld a butter layer over the 9Cr pad. PWHT. Complete the remainder of the weld using Inco 82. Perform a LPT after completion.
RE: 321 SS to 9cr
RE: 321 SS to 9cr
You may get lucky and only need to repair the crack excavation within the full pen weld using Inco 82 and not touch the 9Cr pad material. Thus is why you have options.
RE: 321 SS to 9cr
Doomed to fail immediately and perhaps create a worse condition than exists today? Just asking your opinion. Keep in mind the cracks are small and all on the 9cr side of the weld at the toe. Perhaps due to nothing more than the final cover weld was just a little bit bigger than the butter weld (which I suspect is what happend here.)
RE: 321 SS to 9cr
See my last sentence below from my last post to you...
You may get lucky and only need to repair the crack excavation within the full pen weld using Inco 82 and not touch the 9Cr pad material.
The above would be your best scenario, preheat and weld repair without touching the 9Cr pad material.
IF the crack enters the 9Cr pad material, you should PWHT because of the material composition. This is an air hardening grade of alloy steel. Perhaps you can use a temper bead technique with the Inco 82 to attempt to temper the 9Cr heat affected zone. This is marginal at best and would require a WPS qualified.
IF no PWHT is considered, you would most likely crack again and possibly into the 9Cr base metal, which would not be good.
RE: 321 SS to 9cr
This seems a similar situation. 1200 F is right up there...
Nathan Brink
RE: 321 SS to 9cr
RE: 321 SS to 9cr
I don't see it as hugely different if the extent of the weld repair isn't too significant...
Nathan Brink
RE: 321 SS to 9cr
RE: 321 SS to 9cr
One possible change is to weld the 321 lug to a 321 sleeve , and the sleeve held in place( mechanically) by small 9Cr lugs.
"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick