Welding AL6XN - is annealing needed if done with a filler metal?

[wk390107]

Hello everyone,

We are currently experiencing chlorine corrosion issues on a lid to a piece of equipment in our plant. The lid is currently made out of 316L and the decision was made to make the lid out of AL6XN, but I have a few concerns about welding it.

I know that welding AL6XN can reduce its corrosion resistance and due to size of the lid (5' x 4.5' x 1/4") it is fairly impractical to have the lid annealed. Would using a c276 filler metal and not annealing the lid be enough to return the AL6XN to its pre-welded corrosion resistance? I have read a few papers on welding AL6XN, but am still unsure if AL6XN needs to be annealed after welding even if a high molybdenum filler metal is used.

Thanks a ton!

 

[metengr]

Welding AL6XN does not absolutely require a post weld solution treatment step. I would recommend using a 9% Mo filler wire (like 625). Using welding guidelines similar to austenitic stainless steel is recommended; no preheat is applied and you limit the interpass temperature to 300 deg F would suffice.

 

[Metaljon]

We normally use Alloy C-22 (13% Mo)for welding AL6XN. You can also use 9% Mo as Metengr suggests but Alloy C-22 is better. Although AL-6XN alloy is a single-phase alloy, when welded it will transform to austenite, chi phase and delta ferrite. The formation Chi phase and delta ferrite decreases the corrosion resistance which is why an overalloy weld alloy is required. You have to be careful to minimize the heat tint to no darker than a light straw color. Any darker weld heat tints should be removed otherwise it will effect the corrosion resistance of the material.

 

[EdStainless]

I second Jon's comments.
Use 22 filler, and pickle to remove all heat tint, grinding isn't enough.

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Plymouth Tube

 

[Guest102023]

Before spending money on silver bullets, has the precise mechanism and cause of the corrosion been established? Other than 'chlorine', although I suspect you mean 'chloride'. There may be other factors making welded 316 unsuitable in this particular situation. Such as insufficient removal of heat tint, to which AL-6XN is also vulnerable.

If you go that way though, Metajon's advice is sound and complete.