Welding of dissimilar materials

[arcpro]

Please share your experience on welding of dissimilar materials like carbon steel to stainless steel, chrome moly steels to stainless steels and carbon steels etc.
I want to know about the following:
1. Welding consumable normally used
2. Welding procedure (buttering / without buttering)
3. PWHT
4. In-service failures (if yes, some details please)

[ashfaqanwer]

The point of concern in dissimilar welding is the application of weld. Under which service and process conditions, you are going to operate the weld. Things remain OK for years where a dissimilar weld is under services like water, air, steam, nitrogen or even ammonia with not very harsh process conditions. Many a times for certain critical services especially hydrogen, dissimilar materials welding is not recommended. You can find many failures in process plants of dissimilar materials welding in service like hydrogen, synthesis gas.

CS to SS
1. ER/E309 when CS is under 19mm not requiring PWHT and Inconel 82/182 when PWHT is required
2. Buttering is preferred. Do it on CS side
3. PWHT after buttering with inconel is preferred and no PWHT after weld joint completion. Also note that PWHT is required if joint thickness is above 19mm and Inconel 82/182 is used
4. Much chances due to formation of martensite on CS side due to dilution which can eventually fail

CS to Cr-Mo Steels
1. Use consumables either suitable to CS or Cr-Mo side
2. Buttering not required
3. Yes, do as required by Cr-Mo side
4. If pre-heat, post heat, PWHT and inspection protocols followed correctly, lesser chances

Cr-Mo to SS
1. Inconel 82/182
2. Buttering is preferred. Do it on Cr-Mo side
3. PWHt after buttering with inconel on Cr-Mo side and no PWHT after weld completion
4. Dilution can occur in this dissimilar joint also

[sakib321]

em back
ashfaq bhai
can you please tell me the logic why E-309 is used for welding of CS with SS
that is why we not go for other wire i.e E-308 , E-347?

[ben]

During welding of CS and SS, dilution may occur as mentioned by Ashfaq. That's become the contributing factor in using E309 for CS to SS welding as it contains 24% Cr which then keeps the weld in austenitic range and avoids formation of martensite. Other SS electrodes you mentioned contains 18% Cr content.

One point I would like to add is that during welding CS to SS when SS contains Mo like 316 grade, use E309Mo instead of E309.

[ashfaqanwer]

Hi Sakib,
Welcome back.
Your query rightly answered by Ben. Hope you got the point.

[arcpro]

Thanks Ashfaq.
We have few dissimilar weld joints that have to be operated under hydrogen service. What extra precautions should we take?

[ashfaqanwer]

For hydrogen service, normally it is preferred to avoid any dissimilar welding of CS to SS but in case where it's a requirement I would advise to follow the buttering protocol religiously.
A buttering of about 12 mm must be done on the ferritic side just to avoid any formation of martensite and to avoid any failure which are likely to come up especially in hydrogen service.

[arcpro]

I will take care of that. Thanks.
If you have any experience of CS to SS joint failure in service, please share that.

[ben]

Google "failure of dissimilar weld joints" and you would be finding some useful links.