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Ferrite Testing

Ferrite Testing

Ferrite Testing

(OP)
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?

RE: Ferrite Testing

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.

RE: Ferrite Testing

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

RE: Ferrite Testing

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

RE: Ferrite Testing

Ferrite percent and Ferrite Number ??
Thread725-34135

RE: Ferrite Testing

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

RE: Ferrite Testing

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
www,fischer-technology.com
Ferrite in welds is reported as "ferrite number" 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 "ferrite number" instead of an actual %
If the weld isn't cracked I'd say you have enough ferrite.

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