Low ferrite % for A790UNS S31803 during qualification 3

[jazimed]

I'm about to prepare a PQR with a Pipe smls NACE BE 4'' S-40S A790UNS S31803 B36.19. Test coupon: two pup pieces of 150mm butt welded each one to another

The welding process used for qualifcation is as follow:

Root Pass:
- GTAW Process
- Filler metal: ER2209 2.4mm
- shield gas: Argon
- Current: 90A
- Voltage: 9 V
- Heat Input 9.7 Kj/cm

Hot Pass:
- SMAW Process
- Filler metal: ER2209-17 2.5mm
- Current: 50-66A
- Voltage: 21-27V
-Interpass temperature: 150°C
- Heat Input 14 Kj/cm

filling Pass:
- SMAW Process
- Filler metal: ER2209-17 2.5mm
- Current: 44-58A
- Voltage: 21-27V
-Interpass temperature: 150°C
- Heat Input 12 Kj/cm

The problem that I'am facing is having a ferrite percentage very low in the Base metal (37%), the HAZ (30%) and the weld joint (25-20%). the mean used for ferrite measurement is the ferritoscope. at the other hand the material certificate of the pipe is indicating 52% of ferrite according to ASTM E562. I don't know whether there is a problem with the base metal or there is something wrong with the welding process. Any help here?

 

[jazimed]

Just Received the metallography examination report and it's showing the ferrite% as follow: BM= 50%, HAZ= 44%, Weld(root)=34% Weld(cap)=29%. Now I'm 100% sure about the conformity of the base metal.

Obviously, the SMAW process is affecting the ferrite % in the weld. That's why I'm intending to use the GTAW for the hot and filling with the same settings as the root:

Hot and Filling Passes:
- GTAW Process
- Filler metal: ER2209 2.4mm
- shield gas: Argon
- Current: 90A
- Voltage: 9 V
- Heat Input 9.7 Kj/cm

 

[jazimed]

Also, shall I keep the interpass temperature 150°C or I have to go below that?