Weld repair of Super Duplex casting

[baski67]

We are facing problem in weld repair of Super duplex grade 5A Casting to radiographic quality. Can anyone suggest tips on what care need to be taken especially in gauging and excavating the casting and also subsequent solution annealing of castings

 

[EdStainless]

Clean, clean, clean
use matching filler (as close as possible)
keep interpass temp low
solution anneal per spec, rapid cooling is critical.
Have the castings already been annealed?

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Plymouth Tube

 

[JamesCKelly]

Agree w EdStainless in all points.
Do think it would be cool to know exactly which superduplex alloy is involved.
Whatever is "Grade 5" it does not refer to a specific alloy chemistry.

 

[metengr]

What is the problem or are you anticipating problems? Cleanliness is only one issue - you need proper technique and excavation preparation to ensure no lack of fusion defects. I would suggest you practice on a weld coupon and have it radiographed.

 

[baski67]

Material ASTM A 995 Grade 5A (25% Cr + 7% Ni ) and the electrode used is Selectarc Inox 2509MoWB.

The casting is already solution annealed as the spec and is taken for Radiography where in the defects revealed and we are working to salvage the casting.

We have used this electrode and done weld repair in the past and no issue but facing problem in this instance and the casting weight is 1600 kgs.

While gouging for removing the defects, multiple cracks propogate.

 

[metengr]

How are you removing defects? Don't use thermal methods for gouging defects. Also you may be chasing smaller cracks that were from the original defect but could not be seen by RT.
.

 

[EdStainless]

I hadn't even thought of that, but not arc gouging. You need to mechanically grind the material.
The heat from the arc may be causing enough embrittlement near the defects that you will only cause more cracking.

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Plymouth Tube

 

[Guest102023]

Agree with the last two posts; thermal gouging could damage what is now healthy material.

Be careful when quoting 'matching' filler metal for duplex SS, because the composition is typically overalloyed with nickel to produce the same ferrite/austenite ratio in the as-welded deposit. Follow the filler metal manufacturer's recommendations for that. Avesta will have lots of good info.

 

[Duwe6]

It you end up using GTAW -Tig - use a shield gas with 1-2% nitrogen. On stainless, especially duples, it is an alloying element and will improve the deposit strength w/o decreasing its ductility.

 

[Guest102023]

Duwe6,
I don't advise that unless it comes with a qualified welding procedure.

 

[JamesCKelly]

Wonder if it is possible to cool 1600kg fast enough, from whatever is that specified anneal temperature, to end up with any ductility? Have you checked the hardness of this casting?

 

[bruv]

A lot of good advice above - don't use thermal excavation techniques, practice on some similar material, carry out a PWHT with water quench. I would suggest you do a full ASME IX WPS/PQR, with bend and tensile tests, but it is worth doing radiography and LP testing first to check weld integrity. Talk to your welding suppliers about the most suitable filler to use.

It may be possible to cool 1600kg fast enough after PWHT - it all depends on section thickness, configuration of the piece being welded, and the size of the quench tank.

If your base material has been certified with impact testing, microstructure and ferrite volume, corrosion testing or is for NACE duty, take these into account before carrying out your weld PQR.

 

[Duwe6]

RE: Argon + N2 shield gas.

Per ASME Sect IX, any change in gas mixture makes a new PQR/WPS mandatory. I should have mentioned that.