Austenitic stainless steels, sensitized during welding
Austenitic stainless steels, sensitized during welding
(OP)
genteleman i have a question, i am building numerouse reators I will use one as an example, we are using SA387 GR.11 CL2 (P4) with a SS304 clad overlay (1/8th). I have concerns about sensitizing ss304 at PWHT temperature. should i be concerned or Austenitic stainless steels which tend to sensitized during welding and not PWHT?
I have heard that Sensitization can be reversed and material restored to full corrosion resistance by a full solution treatment after fabrication. Also, since sensitization problem is time/temperature dependent, thin materials, which are welded quickly, are not usually a problem.
I have heard that Sensitization can be reversed and material restored to full corrosion resistance by a full solution treatment after fabrication. Also, since sensitization problem is time/temperature dependent, thin materials, which are welded quickly, are not usually a problem.





RE: Austenitic stainless steels, sensitized during welding
304 is fairly high in Chromium, so you'd need to introduce a fair amount of carbon before you start seeing the effects of Chromium carbide precipitation.
Use of welding filler metals with the L suffix are required to maintain the low carbon content in the weld and HAZ.
If welding is done with GMAW process, it's important to avoid shielding gas mixtures which contain more than 2.5% CO2. The CO2 can contribute Carbon to the weld pool, and if the concentration in the shielding gas is high enough, you can overcome the ability of the alloy scavengers to absorb the carbon introduced into the weld. Shielding gasses composed of 93%Ar/5%He/2%O2 are recommended, if my memory serves me correctly.
My experience with this is in dealing with welding thin 409 stainless steels; where the protential for problems is large, because the Chromium content is very low.
In response to your last question, yes, sensitization is reversible with a full solution annealing. I don't know if this is practical in your application, given the effects such an annealing process might have on the underlying A387 material. Someone with more experience dealing with A387 will have to speak up here...
RE: Austenitic stainless steels, sensitized during welding
RE: Austenitic stainless steels, sensitized during welding
I hope that your overlay was done with a first pass of 309 or a similar grade, and that the top pass is low carbon 304.
I'll look for one in a format that I can attach here.
Local sensitization from local PWHT will cause a serious decrease in corrosion resistance (and chloride stress corrosion cracking resistance) of the 304.
It is not practical to re-anneal after fabrication since this would change the properties of the carbon steel and cause serious dimensional issues.
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Plymouth Tube
RE: Austenitic stainless steels, sensitized during welding
we do not plan on local PWHT, we will be using furnace application
RE: Austenitic stainless steels, sensitized during welding
Here is the situation with 304 stainless steel corrosion resistant weld overlay on a low alloy Grade 11 steel substrate - you need to butter the low alloy substrate first using 309L stainless steel. After this first pass, PWHT should be performed (only if required by Code based on weld deposit thickness). If a PWHT is required, the 309 is formulated for exposure to PWHT for low alloy steel.
After PWHT, the weld corrosion overlay can be deposited with no final PWHT because austenitic stainless steel filler metal requires no PWHT.
Now, if you had performed all of the welding and subjected the corrosion resistant weld overlay (304) to PWHT, you have indeed sensitized the 304 material. There is no reversing what has been done if you performed this fabrication step. The best you can do is to run corrosion testing and determine if this meets service requirements.
RE: Austenitic stainless steels, sensitized during welding
once again ENG-TIPS is the greatest resourse for our industry on the internet
RE: Austenitic stainless steels, sensitized during welding
"weld corrosion overlay can be deposited with no final PWHT because austenitic stainless steel filler metal requires no PWHT"
PWHT, depending on code and base thickness, could be required for the P11 base metal, but not for austenitic weld metal. One layer of 309 would not be enough to avoid producing an HAZ in the P11. Temperbead welding, to produce an acceptable HAZ, always requires at least two layers. Try using 304L on your final layer.
I've seen many vessels and other components that have been clad and subsequently PWHT with no ill affects on the clad in service. Stainless clad roll bonded plate has served the industry well for many years. 304 will pit in chloride solution even when not sensitized. Depends on what the vessel will hold and at what temperature. The clad typically does not see much stress in service to produce stress corrosion cracking, if that is your concern.
RE: Austenitic stainless steels, sensitized during welding
The term buttering should have been stated, in lieu of a layer of 309L. Buttering is used and discussed in ASME Section IX to allow for PWHT of base material, prior to welding subsequent passes to either complete a weld overlay or to finish a groove weld joint.
RE: Austenitic stainless steels, sensitized during welding
At the same time there are many with full furnace PWHT after cladding. While these may work fine for many years you can't say that there is no ill effect. The 304 clad in these units does not come close to the corrosion resistance of standard 304. If you can live with this then fine.
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Plymouth Tube
RE: Austenitic stainless steels, sensitized during welding
Steve Jones
Materials & Corrosion Engineer
http://www.linkedin.com/pub/8/83b/b04
RE: Austenitic stainless steels, sensitized during welding
RE: Austenitic stainless steels, sensitized during welding
Steve Jones
Materials & Corrosion Engineer
http://www.linkedin.com/pub/8/83b/b04
RE: Austenitic stainless steels, sensitized during welding