[MW:4019] Linear Indications After Pickling and passivation and PWHT

Dear All,

I have a typical problem with my vendor who is manufacturing Coke drums for us.
The stage of NDT including RT is such that we need to take RT before PWHT and before overlay.

One of the section ( shell to Shell) under went the above process and cleared. After that it was overlayed by AWS class Inconel E NiCrFe3 electrodes on base plates ( SA387 Gr.11 ClassII) with 410S cladding on either side. Later the same was subjected to Pickling and passivation and went for PWHT.

Now durng APWHT stage, when we are performing PT and RT, surprisingly we are getting two wagon track linear indications on either sides of weld toes from inside ( on cladding side) which are exactly the border junction of ENiCrFe3 inconel and 410S cladding of the shell plates.
It is having a depth of around 0.5mm and width also same.

Could any one explain the cause of formation of this indication at the above juncture. As per our estimation, it could have happend due to pickling and passivation. Since another shell with above processes ( except pickling and passivation ) has not got any such indications.

Thanks for your time and efforts.

Regards,
Raghavendra

Larsen & Toubro Limited
www.larsentoubro.com

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