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Re: [MW:30165] Fwd: Nozzle crack propagation

By Materials & Welding
Dear Mr Chiranjeevi,

1. Seems that stainless Is not so stainless,
2. Crack follows a stress riser and seems fragile.
Then options are:
Fatigue, that depends on stress (under Sy because non yelding evidence) and cicles.
Corrosión fatigue
Not so probable but embritlement also .

More info check API 571


Saludos
César Alexis Viteri Pérez
From: materials-welding@googlegroups.com <materials-welding@googlegroups.com> on behalf of Chiranjeevi A <chiranjeevipuvvula@gmail.com>
Sent: Wednesday, October 16, 2019 3:32:17 PM
To: materials-welding@googlegroups.com <materials-welding@googlegroups.com>
Subject: [MW:30153] Fwd: Nozzle crack propagation
 

Dear All,
   Please find the attached snap, we found a crack circumferentially. The nozzle size is 6" and the material is SS.

  The following plant is under construction and the vessel erected around 1yr back. There is an argument that because of pipe loads that are not supported yet, it created tension and lead to crack.  Even I surprised that how a steel material started cracked like brittle for just for a few external loads. (This not the correct reason)

I clearly explained that any steel material that we design to be below the yield value. When the load beyond the ultimate limit it leads to fatigue and finally crack. This situation we can expect in operation if there is cyclic loading and the connected piping not supported properly. (which is an impossible situation).

 Finally, I suspect that 
 - the material of the nozzle is not SS. (Maybe zinc coated)
- (or) Because of  corrosion
- 

(or) during welding, it created a weaker section and started crack initiation for the external loads.

Experts kindly share your opinion and suggestions.

Thanks & Regards

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