Ferrite Number (WRC) on weld overlay 2

[teokal]

Dear all,
I am facing the following problem: We are constructing a vessel which is cladded and we perform weld overlay (clad restoring) in two different sections, one with 317L (we are using as per our client's recommendation ER 385 and E 385), and the other 316L (ER 316L and E 316L). The requirement for F Number is 3 to 8 (WRC). Measuring today, I found out that: Welds 316L made by electrode (SMAW) and those with 1,2 mm wire with flux (SAW), are OK. The 4mm diameter with flux (SAW) are 0,30 to 0,40 F N, which is far away from the requirement... Both 1,2mm and 4mm wires together with their flux, are of the same brand name! Also, all the welds made for 317L (with 385 filler metals) have again 0,30 to 0,50 F N, instead of 3 to 8. How can we raise the F N? Or I should start crying? I know that ASME code is dedicating two pages for the Ferrite number and in fact is not sure if we really need to measure the F N, or even if the known measuring processes are correct and reliable...
Thank you all guys...

 

[metengr]

The ferrite level is only important to assure minimum exposure to solidification cracking when depositing austenitic stainless steel weld metal. The lower ferrite number is better for corrosion resistance, while balancing higher ferrite content to avoid solidification cracking in the weld deposit. I would not worry about lower ferrite numbers for clad overlay welding, if no cracking is observed (Liquid PT verification).

Your comment

I know that ASME code is dedicating two pages for the Ferrite number and in fact is not sure if we really need to measure the F N, or even if the known measuring processes are correct and reliable...

Where did you hear this information??? This is news to me.

 

[teokal]

Dear Metengr,
Your response is a relief, although my supervisors are extremely typical, and I suppose that they wouldn't be reliefed by PT on weld overlay, which is already performed and everything is OK... They are paper maniacs and they want to see the correct paper by witnessing the test, they are not flexible nor can use their knowledge... But anyway this is a problem of mine... About your question, please check ASME II part C, SFA 5.4/SFA 5.4M, Annex A, section A6 "Ferrite in Weld Metals" (page 92 in the 2007 edition. Interesting point: A6.4 "In the opinion of the WRC subcommittee, it has been impossible, to date, to accurately determine the true absolute ferrite content of weld metals"... This section related to Ferite content can be found in all annexes of ASME II for SFA's of Stainless steel filler metals.
Thank you again, metengr