Re: [MW:4023] Linear Indications After Pickling and passivation and PWHT

Dear Raghvendra,

There may be following possibility :

During pickling and passivation acid might me collected at the toe of the weld for longer period  the material woud have desolved in acidic medium (0.5 X 0.5 mm what you mentioned). And upon washing only surface cavity would be visible.

410S does not contain enough Cr% required for Corrosion resistance and ofcourse does not have Ni hence it falls under martensitic SS instead of Austenitic SS which are good in corrosion resistence.
 
Check with you material / Metalurgy people to confirm the same and if the probable cause mentioned above is the actual root cause you need to change the method of pickling and passivation to avoid the same.

Regards.
CK

  

2010/1/12 PEMMARAJU RAGHAVENDRA <rpe@hzw.ltindia.com>

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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