Welding of SS-316L Control ferrite

Date 07-31-2008 16:01

I would shoot for an interpass temperature of 300 - 350 ' F (( 148 - 176 " C )) depending on your base metal composition -

A whole bunch of your ferrite # is dependent on your base metal ferrite conversion -

By js55

Date 07-31-2008 18:45

Thats pretty fricken narrow by anybodies estimation. If you need ferrite control I would assume you are purchsing filler materials with actual chemistries. Does the cert have an ferrite number on it?

By darren

Date 07-31-2008 19:15

if your trying to control your ferrite # that closely your pqr/wps is going to have to be designed by a very experienced engineer/welding control agent. we just went through some very controlled stainless welding and the parameters have to be strictly controlled and followed once you post more info and get some responses from the VERY seasoned experts here it will become very evident that the question that you are asking does not have an off the shelf answer.
what other chemical and structure restrictions are there?
darren

By ravi theCobra (**)

Date 07-31-2008 23:40

Back in '73 we were producing weldments in the range of 5 to 15 delta ferrite for the Nuclear Industry -

It is not out of the question - It's 2008 !

By Stephan (***)

Date 08-01-2008 17:02

Jeff,

I don't know what the present status of this discussion is right now, but allow me to make a little step forward from "behind the curtain" of devotional observation, by asking the following.

As raghubir singh writes they want to "control" the (?) Ferrite Number (FN) of a particular weld metal deposited upon a particular base metal (composition unknown) having a particular thickness by using a particular welding process (unknown).

Besides what has been reasonably said by you and the other appreciated colleagues (darren and ravi the cobra) in terms of that there is certainly a plenty of information necessary to make a - reasonable - statement on that, I have a question in general relating to the "control" of ferrite with SS welding.

This question is based upon the predication of ravi and perhaps it might be better to ask him directly but perhaps he can answer as well although I am asking you, as you are my personal "Alpha and Omega" in SS welding. :-)

As by all what I have read and tried to learn about "predicting" ferrite in stainless steel weldments I mean to remember a very impressive statement coming from Dr. Kotecky who has said in the course of a writte discussion about the "FN by DeLong vs WRC-92": "... predicting ferrite in weld metal has a lot in common with predicting weather(...) We all admit to a degree of uncertainty in both activities".

I have enjoyed his excellent descriptions showing how difficult it appears to make real predictions based upon what's given by the theories. There's a bunch of variables (as usual) which can play important roles on the final results.

So my question is: "Is it possible to "generalize" a particular FN only based upon the filler- and base metal composition + interpass temperature without considering the entire amount of different welding processes, dilution conditions,...?"

Or in other words...

AS ravi the cobra said they have produced in the 1970's FN between 5... 15 (likely based upon DeLong). I guess they have used a particular welding process when welding particular joint designs and wall thicknesses. These FN were achieved by using a particular interpass temperature of - fairly accurate - 148... 176°C.

So: "Is it then really possible that raghubir singh achieves similar FN (of course again according to DeLong) quite independent of what kind of welding process he uses?" Or "includes" the "scattering" between FN 5... 15 even all the - presumable - different conditions caused by different welding processes?

Hmmm, I hope I could make clear what drives me by asking this...

If not, please drop me a short note and I would like to try to express it in another way. :-)

However, first of all thanks in advance and my best regards,
Stephan

By js55

Date 08-01-2008 19:22

Stephen,
I had a long ole discussion on ferrite and diagrams and such, and then I lost it. So I ain't doing it again. But I'll say this. To put it succinctly, no. Depending upon the meaning of generalize. Too many variables.
Dilution is a major concern. Not only that, but FN will vary throughout a weld (you'll see more than a 5 FN variance from the root to the cap), so will dilution (you may get >50% with a GTAW root and <10% in the middle bead of a multi bead cap-especially with SMAW). This is a substantial variance. And then there's reproducing your qual results in production. So my question is, when you limit FN that much does it really mean anything? Do you cool it down on the root and crank it up on the cap to try and homogenize your FN?
Not only is this weather, its a bit of a game.

By ravi theCobra (**)

Date 08-01-2008 21:08

I am a very humble man so as not to offend you (all) -

My first question is what is the welding process ?   it has not been stated -

My second question is what is the expected ferrite transformation for the base metals themselves / all alone ?

Next comes the welding consumable ( s )   and the percent dillution -

untill the above are known this is just a discourse in HOT AIR   !

By Stephan (***)

Date 08-02-2008 14:40

ravi,

"... until the above are known this is just a discourse in HOT AIR !..."

Well said... :-)

Would be interesting to see, if there'll be provided some more information.

Best regards,
Stephan

By Raghubir Singh Date 08-03-2008 05:41

Thank u sir

for your kind help sir process we r using is SMAW and thickness is 50 mm and joint design is T joint fillet Weld

SIr pls tell me how u calculate Interpass temperature

with regards

Raghubir singh

By Stephan (***)

Date 08-03-2008 15:41 Edited 08-03-2008 15:53

Raghubir,

no need to say "thanks" I did nothing but our appreciated colleagues (js55, darren, ravi) did!

Please find my response on darrens post below.

I just wanted to agree with him and his questions as he stated them in his reply to you.

It is too little information you have provided by now.

Please know, you will find some of the most outstanding welders and/or welding, metallurgical,..., experts here in the AWS forum and I personally do not know somewhat comparable in the world, since everyone of them is willing to share his/her expertise freely with you and me. This is truly unique...

But finally to speak with darren again who hit - as ususal - the nail by saying : "... you have to be able to provide the answers to some important questions on these topics or it is all for not."

Best regards,
Stephan

By Stephan (***)

Date 08-02-2008 09:59

Jeff,

thank you for this meaningful response, Sir!

"... So my question is, when you limit FN that much does it really mean anything? Do you cool it down on the root and crank it up on the cap to try and homogenize your FN?
Not only is this weather, its a bit of a game."

Luckily I see that I don't have to find other words for what I have meant.

Thanks again!
Stephan

By darren

Date 08-03-2008 06:06

hey stephan,
agreed, 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 the cannot indicate what the entire weldment has as a ferrite constituent as a whole so it really is a crap shoot/magic show/game

then again as i tell the apprentices welding is often not how well you can weld but how well you can lie.
welding is not like being a doctor, we are not shooting to become the best we can be, just good enough to pass this fine line is where profit is made.
darren

By Stephan (***)

Date 08-03-2008 15:25

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"! ;-)

By Raghubir Singh Date 08-03-2008 05:44

sir thanks

for giving me some good information

sir we r using Smaw as welding process and thk of base metal is 50 mm

with regards

raghubir Singh

By darren

Date 08-03-2008 06:22

diameter of rod?
amps?
pre heat?
post heat?
brand name of rod?
can you publish the mtr? of the rods and parent metal?
there are more but these have to be answered right away, before you can get a real answer.
if you want to know how the magician pulls the rabbit out of a hat you must first prove that there is some value to the magician in letting you know.
only being sarcastic but really as ive learned through this very learned forum you have to be able to provide the answers to some important questions on these topics or it is all for not.
darren

By ravi theCobra (**)

Date 08-04-2008 16:04

Q.E.D.

By Stephan (***)

Date 08-04-2008 16:28

ravi,

I beg your pardon...

What does Q.E.D. stand for?

May it find a place within the row of "BS" terms or may this be rather found relating to "Quantum Electro Dynamics" issues? :-)

Thanks a lot in advance for pointing me in the right direction!

Best regards,
Stephan

By ravi theCobra (**)

Date 08-04-2008 17:09

Quod erat demonstratum -

By Stephan (***)

Date 08-04-2008 17:55

Ahaaa!

I see!

Thanks ravi!

By 803056

Date 08-04-2008 16:33 Edited 08-04-2008 16:35

You are welding an AISI type alloy 316L austenitic stainless steel base metal using and E316L SMAW electrode. That would be the combination I would expect. As for the maximum interpass temperature, I would stick with the industry standard, 350 degrees F. If the interpass temperature exceeds 350 degrees, allow the base metal to cool before resuming welding. Use a cooling fan to hasten cooling between weld passes.

If this welding is to be performed in any position other than flat, I would specify an AWS A5.4 E316L-15 (same as ASME SFA5.4 covered electrode). Root passes in grooves or fillets should be E316L-15, rather than -16 or -17 covered electrodes. No preheat is required provided the surfaces to be welded are dry. The electrodes should be treated and stored like any low hydrogen electrode, i.e., stored at 250 degrees F in an electric electrode holding oven and limit their exposure time (time out of the oven).

Grind out weld starts if best results are required. Make sure all welding slag is removed between passes. Most welders believe they will "burn" out the slag on the next pass, but that is rarely the case as evidenced by radiographic test results.

A good reference book is: Welding Metallurgy and Weldability of Stainless Steel
J. Lippold and D. Kotecki, Wiley Interscience 2005

You can also refer to AWs D1.6 Structural Welding Code for additional information, but my first reference is the better of the two in my opinion.

Ferrite content is measured using the magnetic properties of the weld, i.e., a gage with a magnet is used to measure how strongly the magnet is attracted to the ferrite in the weld. Few people use the metallographic approach any longer due to the widely varying results that method produced.

Weld a sample using the welding procedure you expect to use in production to verify the correct ferrite content is produced.

Good luck - Al

By MBSims

Date 08-04-2008 20:44

If I understand the question correctly, you are welding fillet welds on 50 mm (2 in.) thick 316L stainless steel with E316L electrodes, and the electrodes have ferrite numbers ranging from 3 FN to 8 FN. You have not stated what ferrite number you wish to achieve in the final weld deposit.

A suitable interpass temperature for 316L stainless steel is 350 F maximum. This will minimize sensitization of the base material, which will make it more resistant to stress corrosion cracking. Ferrite formation in austenitic stainless steels is affected by electrode chemistry, base metal chemistry, weld dilution rate, weld metal cooling rate, and other factors. Interpass temperature is related to weld metal cooling rate. Lower interpass temperature increases the cooling rate and (usually) increases ferrite number of the weld deposit.

The choice of E316L electrodes is appropriate if the weld deposits need to match the base metal. 316L has molybdenum added to increase resistance to pitting. If pitting corrosion is not a concern, then E308L could be used. If there is no ferrite number range in the job specifications or applicable code, then a range of 3 to 8 FN should be sufficient to prevent hot cracking. A minimum of 5 FN is required by some codes and suggested by most electrode manufacturers to minimize the potential for hot cracking.

If this does not address your question, please provide more information on what you are trying to achieve.

Here is a link to a welding guide for stainless steels that may be helpful:
http://content.lincolnelectric.com/pdfs/products/literature/c64000.pdf

By Stephan (***)

Date 08-05-2008 15:11

Marty,

most excellent responses both Al's and yours - if I am allowed to say that!

You know, as I have read the value 350°F for several times now, please let me ask.

This is - as you wrote - a maximum value.

Is there, so my question, likewise a minimum value? For instance the 300°F as stated by ravi the Cobra?

Or in other words. Would this material grade being preheated necessarily prior to welding? Even up to the - if so - "minimum interpass temperature" to achieve an FN between 3... 8 FN?

Independently of what we have discussed in regard to dilution etc.?

As I know myself a bit I am surely complicating everything again - as usual - therefore I beg your forgiveness!

But this is a very interesting thread, since it would - at least in my humble understanding - clarify the question if "standard" alloys as AISI 316L grade must be preheated or not, or if eventually the wall-thickness would affect the decision to "preheat" or "not preheat" the material.

Thanks a lot for a short feedback in advance and my best regards,
Stephan

P.S. Excellent link!

By MBSims

Date 08-05-2008 16:09

I have not seen any data to suggest that maintaining a "minimum" interpass temperature has a benefit toward increasing the ferrite content of a weld deposit. A 60 F minimum preheat is typical for austenitic stainless steels, regardless of base metal thickness. We have applied weld overlays on large diameter (NPS 12 to NPS 28), heavy wall pipe with water inside the pipe. The minimum interpass temperature would typically be around 100 F on the first layer and around 250-300 F on the final layer, depending on pipe size and wall thickness. The weld materials were purchased with a minimum of 8 FN based on chemical analysis. The final layer would typically have a lower ferrite number than the first layer, even though the final layers had a very low dilution rate and were more representative of an "all weld metal" specimen. This suggests that increasing the minimum interpass temperature decreases the ferrite number. This makes sense because increasing the minimum interpass temperature reduces the weld metal cooling rate.

I do see a benefit of controlling heat input, since weld metal cooling rate is also a function of welding heat input. A weld made with 35 kJ/in heat input would be expected to have higher ferrite content than one with 70 kJ/in heat input.

By Stephan (***)

Date 08-05-2008 18:18

Marty,

thanks a lot for your valuable response!

I see...

It's very interesting what you have described to the weld overlay.

As I understand it, 316L solidifys as ferrite and if the conditions are -at least a little (what I however do honestly not know :-)) - comparable with the conditions to be found with the solidification behavior of Duplex Stainless Steels*, then a higher cooling rate may increase the ferrite content.

Hmmm, you see. And that was the reason for me to very first asking if the different conditions with different processes are all conceived when talking about "FN-Calculation".

Even this is the reason...

Using a "High-Performance" Process, generating a high "heat input" may generate - under similar "low" temperatures prior to welding, e.g. non preheated, a lower ferrite content than even using a "Low-Performance" Process. Just as you stated so excellently.

Thanks again and best regards,
Stephan

* Thanks to the expert who has explained this to me so outstandingly! I am sure he who'll read this, will certainly know who is meant... :-)

By 803056

Date 08-05-2008 16:20

Hello Stephan;

It is my understanding that preheating is not required for austenitic stainless steel as long as the surfaces are dry.

As Marty stated, the maximum interpass temperature is often listed as 350 degrees F to minimize the time the weld and HAZ are exposed to the temperatures where sensitization occurs.

Most of what I have read about controlling the FN is that the chemistry of the filler metal and base metal have the most influence in determining the presence of ferrite. The FN of the filler metal (if properly selected) is usually high enough to avoid cracking in the weld bead due to the presence of LMPC. The problem areas are typically in the HAZ where the filler metal can not influence the presence of ferrite.

Best regards - Al

By Stephan (***)

Date 08-05-2008 18:22

Dear Al,

most excellent!

Thanks a lot for taking your precious time to reply so brilliantly!

I have learned a lot again!

I bow my knees before all of you! :-)

Best regards,
Stephan

By cudaxtreme (*)

Date 08-05-2008 15:02

Are you by any chance working on the Shell ECC project?