welding T22 to Stainless

[muld0020]

I have a new T22 tube weld to an old ER308L weld overlay (20yr). I need to develop this procedure, and was wondering if there was any good advice out there for filler selection, preheat, and PWHT?

Weld process will be GTAW. My first thought is to use ER309L filler wire. My second thought would be an Inconel 625.

 

[metengr]

For service temperatures at or above 800 deg F, I would use Inconel for the filler metal to reduce the effects of carbon migration along the weld fusion zone on the T22 side of the weld joint. This would lead to dissimilar metal weld failure if 309L filler metal is used.

Preheat should be 400 deg F. Depending on the wall thickness of this weld joint, PWHT may not be required. If PWHT is required, I would butter the T22 side of the weld joint, PWHT and finish with Inconel to avoid exposing the stainless steel to PWHT temperatures.

 

[muld0020]

Thanks!

 

[davefitz]

as further support to meteng , the incolnel has a coeficient of thermal expansion more simialr to T22 than does the 304 SS. This is important if the DMW is in a heated zone and will experience temperature cycling from ambient- shutdown to ( 1150 F) operating.

If a DMW experiences such large temperature swings plus has a large difference in thermal expansion coeficient, then a very large shear stress would be developed across the plane of the weld interface. Shear strss has the peculiarity of being a maximum at the mid-wall , so the creep fatigue cracks that eventually cause tube failure originate at the mid wall location in these cases.

One other practical detail when welding incolnel to T22 or other ferritics is that a manual welder will not use suffient amps to esnure good penetration due to apparent splatter, so these welds shjould be made with an automated welder to ensure good penetration.

 

[davefitz]

a propos to the original question, I just reviewed an abstract on a new DMW filler metal developed by EPRI ( and being used at the new AEP Turk supercritical plant) called epri P87- does anyone have any direct experience with this new weld filler as applied to a ferritic to austenitic DMW?