Super Duplex PQR

[RauMech]

Hello Forum,

One of my collegue explained an issue that he is having with Super duplex PQR develpoment, as we will also have this material,

Weld Coupon is performed on a 10" NPS X 10S (0.165" wall) A790 S32750 Type 2507 EFW pipe welded with ER2594 GTAW root, Fill and Cap, in the 3GR (rotated to maintain 3G) position.

Max O2 level required was between 50ppm to 1000ppm, so half of the coupon welded with closer to 50ppm and half been welded around 900ppm.

One of test that required to do was Ferric Chloride corrosion test as per ASTM A923 method C and acceptabile corrosion rate was 10mmd.
All mechanical test are within the limit excpet the corrosion test where the portion been welded with less than 100ppm section (50mmd)..where the section been welded closer to 1000ppm it is less than 10mmd.
So the query - any reason for this change? is this acheivable? or acceptable?

Appreciate any kind advise on this -Rau

 

[EdStainless]

How did you change the oxygen?
Sounds like you may have 'boiled off' a lot of the nitrogen in the weld.
Or the heat input changed.

You did a real A923 right? samples were machined and all surfaces were freshly ground first?
This is not a test for corrosion resistance. It is a test for the presence of detrimental intermetallic phases.
You should be able to see them in the micros.

Did you try any impact testing?
It would be a good confirmation.

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Plymouth Tube

 

[metengr]

The maximum oxygen level required was incorrect. For the superduplex GTAW, the gas mix for shielding should have been either Ar+2%N₂ +
10-30% He or welding grade Ar. The backing gas should be the same or use of 90% N₂ + 10% H₂

 

[RauMech]

Sheidling used was welding Argon and backing was 95%Ar+5%N

Re Ed's query - the testing was done in 'as weld' condition, no machining or polishing been done, we suspect that could be one of the reason, but in 18.6 or so it says should meet the fabrication condition as well?
They havent done a micros on this section, only on the other part where the result is good they done.

Yes done impact at -40C, transverse : Weld metal 62-68J and HAZ 76-80J

 

[EdStainless]

A923C requires the use of samples with all surfaces freshly ground. You are trying to expose any intermallics so that you can detect them by corrosion.
Doing a critical pitting temperature test is an different procedure.
You can't do the two at the same time.

If the micros look clean and you passed impacts then you are OK.
You need to fix your procedure for Practice C.

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Plymouth Tube

 

[RauMech]

Yes, we did clean the coupon to 120 grit and the results shows zero corrosion...
Thanks very much for the apt advise.