Ferrite Testing 1

[dbsmith]

Can anyone offer guidelines for the appropriate use of ferrite testing of pipe welds in austenitic stainless steel? Is testing to determine the ferrite number of a completed weld anymore useful than examining the material certifications of the base metal and the filler metal?

 

[Metalguy]

Yes, it's quite usefull. Wrought SS pipe (say 304/304L/316/316L)should be 0 FN. While you can estimate the FN of the weld metal from the comp., nothing beats an accurate measurement. In case you aren't aware, a FN of around 5-15 greatly helps prevent weld metal cracking.

 

[dbsmith]

Thanks for the response. The customer has specified FN from 4-14, right in the range you recommended.

 

[Metalguy]

Good. Once in a while I get one right!<g>

 

[PAN]

Ferrite percent and Ferrite Number ??
thread725-34135

 

[TomEun]

FN = Ferrite Number
Ferrite percent = vol% ferrite
(Fe) = wt% of Fe

FN = (vol% ferrite) x [-0.025813 (Fe)2 + 5.408679 (Fe) - 102.3902]/100

References
1. Welding Journal, 76(1): 24-s to 37-s, 1997
2. Welding Journal, 61(11): 352-s to 361-s, 1982

TomEun

 

[CalvinKelly]

A convenient instrument for measuring ferrite is the: Feritscope MP30, from Fischer Technology Inc., 750 Marshall Phelps Road, Windsor, CT 06095-2199 tel 860-683-0781

http://www,fischer-technology.com

Ferrite in welds is reported as &quot;ferrite number&quot; rather than an actual volume percent ferrite. This is because it is rather difficult to get two labs to agree on ferrite % by metallography. The welding guys got together some years ago & decided to use the term &quot;ferrite number&quot; instead of an actual %
If the weld isn't cracked I'd say you have enough ferrite.