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Re: [MW:8066] RE: 8051] effects of scales on corrosion rate

By Materials & Welding
Dear Mr. Hegde
 
Goodmorning.
 
Can you please provide any code/client specification  for your suggestion  "genrally Hydrotest is not carried with scale".
 
Generally before hydrotest internal cleaning of the vessel is carried out to remove loose scales, foreign particles, dirt, any debris.
 
hard scales will not be removed.
 
Please Suggest.
 
Thanks and Regards
 
Asad Azmi
 
On Thu, Nov 4, 2010 at 8:59 AM, asad azmi <azmiasadayub@gmail.com> wrote:
Dear All,
 
Thanks very much for your Suggestions.
 
Fabricator has removed LOOSE SCALES by sweep blasting. hard scales are still on the surface. there is no specfic requirement for internal cleaning of the Vessel as per Client Specification.there is no Painting requirement on internal surface of the Vessel.
 
Hard scales can be removed only by Grit Blasing AS per surface preparation requirement SA 2 1/2  OR   SA 3.
 
As per Client Specification only loose scales, debris, dust  and other foreign particles has to be removed during internal cleaning of the Vessel.
 
I can not force Fabrictor to remove Hard Scales.
 
Regards
 
 
 
On Wed, Nov 3, 2010 at 5:05 PM, BHARAT GOLE <bharatgole@hotmail.com> wrote:
Hi,

Mill scale are formed during rolling operation is above steel in  galvanic list. hence it is cathodic to steel & if remain on steel will cause for electrochemical corrosion. Whenever electrolyte is available , corrosion will start  by completing corrosion triangle i.e Mill scale act as cathode  & Steel as Anode ( corrode sacrificially)

Once it removed by any surface preparation method , it will not reoccur

Please find attached document for more information.

Regards


Bharat B. Gole

 

 





From: pgoswami@quickclic.net
Subject: [MW:8052] RE: 8051] effects of scales on corrosion rate
Date: Wed, 3 Nov 2010 09:08:34 -0400


Hello Asad,
 
These scales would be harmful.There may not be issues during fabrication, but definitely during service,such as:-
  • Loose/soft scales may may get removed and clog the piping/valves and strainers downstream
  • Hard scales would stick to the vessel surface.If the operating media is corrosive, which any process fluid is always to certain degree, then it would ideal sites for crevice/pitting corrosion.
If required it would be advisable to get your client involved and influence the fabricator to get the scales removed completely.
 
Thanks
 
Pradip Goswami,P.Eng.
Welding & Metallurgical Specialist & Consultant
Email-pgoswami@sympatico.ca,
 

From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of asad azmi
Sent: Wednesday, November 03, 2010 6:34 AM
To: materials-welding@googlegroups.com
Subject: [MW:8051] effects of scales on corrosion rate

Dear All,
 
Greetings.
 
During inspection  of the internal surface of the CS vessel before despatch, heavy scales some loose and some hard  (adhered to surface) were observed  on the 33mm thick dished head. The Vessel  is PWHTed. Dished head is HOT FORMED.
 
 
pls refer attachment for your reference.
 
Contarctor is not willing to remove the scales completely. whether the scales which are adhered to surface are also need to be removed.
 
Pls suggest whether the vessel can be accepted with scales. what is the effect of scales on the metal surface. is it going to affect service requirement.
 
Thanks and Regards
 
Asad Azmi

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