relevance of ferrite number test for duplex SS weld used in structures

[pankaj...@in.transport.bombardier.com]

Hi,

Duplex SS is mostly used in pressure vessels and ferrite testing is one the important quality test for its welding because mostly it has to perform in corrosive environment with high thermal stresses.
We are using Duplex SS in rolling stock underframe where the environment is not highly corrosive and stresses are present due to static/ dynamic loading only.

Can anybody suggest what is the relevance of ferrite tests done on Duplex SS welds for application in structures.

Regards,

Pankaj Johri,   GradIEAust,
 
 
Please consider the environment before you print / Merci de penser à l'environnement avant d'imprimer

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[pgos...@sympatico.ca]

 
Hi Pankaj,
 
Since duplex stainless steels were originally developed for oil and gas industries, the issue of Ferrite/Austenite ratio or the balance were very important to get the desired mechanical strength, corrosion resistance (intergranular, pitting or stress corrosion resistance) and other properties as desired.
 
In your case as duplex s.s are used for rolling stocks, where there would be a lot of dynamic stresses. Hence you should require the mechanical properties of weld joints which are almost close to the same properties of base metals, such as UTS, % El and Impact if required (since the rolling stocks in Canada, could get exposed to minus 40 C, in the winter. Ferrite in Duplex welds alters mechanical strength, higher(>70%) means more UTS, less % EL. Usually Ferrite to Austenite (
 
It's my opinion that your spec should include the following tests:-
 

• ASME, Sec-IX Mechanical Tests, in conjuction with original base metal specs,
• Hardness Test- values should be set forth as close to that of base metals
• Ferrite Measurement:  proper and balanced microstructure are ensured.
• At least one form of Pitting corrosion test , either CPT or CCT, since the accumulation of salts or de-icers could cause pitting when stocks are idle, especially when the temperature is on the rise during spring/ summer.

 
Your query does not specify the grade of duplex S.S , to be used
 
You may plese refer the following document for further reference.
http://www.imoa.info/_files/stainless_steel/Duplex_Stainless_Steel_2d_Edition.pdf.
 
If you in Canada, call me @ the Tel No mentioned below for any discussion.
 
Thanks
 
Pradip Goswami, P.Eng,
Welding/ Metallurgical Engineering Specialist.
Ontario Power Generation Inc
Tel-1-519-5872201,Ext-3107 
Mobile (India-Till 17 March)-9830976290)

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To: material...@googlegroups.com
Subject: [MW:4545] relevance of ferrite number test for duplex SS weld used in structures
From: pankaj...@in.transport.bombardier.com
Date: Fri, 12 Mar 2010 16:22:37 +0530

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