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darren,
thanks for your precious reply!
So, now it comes...
"... the whole idea in controlling the ferrite is to create a specific corrosion/abrasion resistant weldment that as it wears provides a rate consistent with the parent metal, the pmi tests only indicate the top or last as welded pass ..."
This is what I meant to know since finally the ferrite content should - in most numerous applications - be seen as an indicator for e.g. the corrosion resistance quality of the weld.
But now please know that I have presently the tremendous honor to be allowed to read a document - coming from one of the most outstanding Stainless Steel-Welding experts I know - dealing with Duplex a/o Super Duplex Stainless Steels, their properties and their workability - of course with the emphasis on welding. There, I can see, the ferrite has, besides of what I have known in regard to corrosion properties, much more influence e.g. in terms of mechanical properties etc.
So one of my questions is: "What does Raghubir Singh want to control?" The Ferrite Number (FN) been calculated by a particular method (e.g. WRC-1992, DeLong) or the Ferrite Content in per cent measurable by various methods (Ferritescope,...)?
Whereas I guess the latter is even used for predicting the "corrosion resistance" (e.g. in weld overlay applications), the first named could - at least in my humble opinion - be an average indicator for the entire volume of the deposited weld metal, or as you have stated this so fine "... indicate what the entire weldment has as a ferrite constituent as a whole...", used e.g. for making a prediction on the mechanical properties of the entire weld volume being influenced even by its ferrite-content. And due to I guess it is even hard to perform to measure the "true" ferrite-content of e.g. the weld beads lying e.g. in the "interior center" of the fillet weld and having been welded over by the subsequent layers - since it is a "Multipass Weld" - I mean it is more reasonable to calculate the FN of the weld metal both for the areas the weld metal is directly diluted by the base metal and the areas the weld metal is rather not influenced by the reaction with the base metal (even the center of the fillet). This should be feasible since the base material thickness is 50 mm and thus the throat of the fillet weld should be (at least according to German codes) 35 mm which should mean again that a "higher" number of passes should be performed before the required size of the fillet weld has been achieved.
So...
When Raghubir Singh says: "... we facing problem in welding SS-316L Control Ferrite the thk. of plates is 50 mm and type of joint is T joint and fillet weld... " then it would be interesting to know what kind of "problem" they are "facing". Is it a mechanical - if even possible (hopefully Jeff will step in here) - problem induced by too high or too low ferrite within the presumable large weld metal volume or is it a "corrosion" relating problem. If however, at least in my humble understanding, the second named is the "problem" then it should be solvable by considering facts as e.g reducing the amount of dilution at the transition zones between base- and filler metal and approving the success of those measures by using e.g. a specific surface ferrite measurement to control the (surface adjacent) ferrite content (in per cent).
However, even though I do honestly not know, how the FN of a particular filler metal is being measured and standardized (see the predication of Raghubir Singh: "... we r using the E-316L with control ferrite (F.no 3 to F.no 8)...") I could imagine, that these numbers are - if not even calculated for the pure filler metal composition - being taken from the pure filler weld metal deposit. If this were the case, then I could imagine - although not knowing how many beads the fillet weld of Raghubir would contain - the filler weld metal deposit might have the composition as been stated by him - namely 3... 8 FN. This due to the fact, that the influence of dilution - at least for the final passes - might be low compared with the very first passes (root,...).
This again should drive him to take care of primarily low dilution with the beads adjacent to the base material and only secondly to worry about the interpass temperature with a base and filler material "normally" having a sound weldability.
But as I said. This is just my very personal and humble consideration thus I would like to step aside to handing over the baton to you and the other appreciated fellows - first of all - of course - js55! :-)
Best to you and thanks again,
Stephan
P.S. "... then again as i tell the apprentices welding is often not how well you can weld but how well you can lie... " :-)
This reminds me truly on a "philosophical" discussion we had just a few days ago here in the forum or in other words it's reminding me on either "Obama" or "Git R Done"! ;-)