ASME and API codes does not mentioned about the requirements of ferrite No. But API RP 577 and AWS welding handbook Vol.4 chapter 2 have the details.
AWS have the deatail as follows.
It is difficult to determine how much ferrite is present in weld metal.The ferrite content should be measured as a ferrite no which is not consider an abosolute ferrite percentage. There is excellent agreement between laboratories when measuring ferrite
using standard technique and ferrite no.
Delta ferrite level of atleast 3FN will eliminate fissuring in weldmetal deposited from
austenic filler metals E 308, 31. Higher level ferrite is required 4 FN for E309. 5 FN in 318 and 6 FN in E347 weldmetal to assure free from fissuring.
Mr Louis provided a nice answer to the problem. Further clarifications to this problem are as follows:-
· The ferrite in question for austenitic stainless steel is delta ferrite, not alpha-ferrite (the main metallurgical phase in all ferritic steels)
· Delta Ferrite, to the extent of 3-8.FN (depending on the grade of austenitic S.S e.g 304/316/321/347…. ) is required in the weld metal, to prevent hot cracking. This is allowed by any boiler and pressure vessel code, such as ASME, API etc.
· Delta Ferrite is a high temperature phase. It typically precipitates and solidifies along the grain boundary of austenite grains in the weld metal. Welds being a cast structure would definitely have some delta ferrite in 300 series of alloys (e.g. 304,316,321, 347 …. etc). Delta Ferrite in the above amount is mandatory for austenitic S.S weld metal
· The amount of ferrite in the weld could be measured due to residual ferromagnetism in the weld. This occurs due to presence of ferrite, which is magnetic. Usually Ferrite is measured by Ferrite Scope.
Base metal or weld fillers would not have residual magnetism, because they do not contain delta ferrite in the processed and finished structure. Ferrite may be formed during original casting of plates, however through subsequent thermal processing (hot rolling… etc) it almost gets converted to austenite.
Note this residual magnetism does not have any or significant effect to the intended services of austenitic stainless steels.
Thanks.
Pradip Goswami, P.Eng. IWE.
Senior Engineer/Specialist(Welding-Metallurgy)
Engineering & Training Services Division
ONTARIO POWER GENERATION Inc.
PO Box-2000, RR-55(South)
Nanticoke, Ontario,N0A1L0
Tel:-(519) 587-2201, Ext 3107--in Nanticoke
(416) 231-4111, Ext 5925--in Kipling,Toronto
Fax: (519) 587-6814
Email-pradip.goswami@opg.com.
-----Original Message-----
From: pgoswami [mailto:pgoswami@quickclic.net]
Sent: Friday, March 19, 2010 6:23 AM
To: GOSWAMI Pradip -THERMAL
Subject: FW: Re: [MW:4087] Magnetism in SS 304 & 321 after welding
Pradip Goswami
88,Garth Trails Crescent
Hamilton,Ontario, L9B2X1,Canada
Email-pgoswami@sympatico.ca
Email-pgoswami@quickclic.net
Tel-905-679-9677
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of A D
Sent: Tuesday, January 19, 2010 5:19 AM
To: materials-welding@googlegroups.com
Subject: [Norton AntiSpam] Re: [MW:4087] Magnetism in SS 304 & 321 after welding
In Austenitic stainless steel welding one of the susceptibility problems is hot cracking. So avoid this problem, need some delta ferrite in welding ( which is magnetism) .So consumable manufacturing is carried out based on this ferrite requirement. In my previous projects 3 to 8 FN requirement is given by client specification, For clear detail please refer AWS handbook - Volume 1.
--- On Fri, 15/1/10, suneel gore <novatekcorp@yahoo.co.in> wrote:
From: suneel gore <novatekcorp@yahoo.co.in>
Subject: Re: [MW:4050] Magnetism in SS 304 & 321 after welding
To: materials-welding@googlegroups.com
Date: Friday, 15 January, 2010, 10:17 AM
One of my customer also have faced similar problem , in case of welding SS 304 & 316 Plates , Tacking By E 316-16 Electrodes & welding by ER 316L FIller wires The welded are attracts magnet , but same on filler , or plates or on stub ends it does not If is it the case of residual magnetism due to DC Welding ? Suneel Gore
--- On Thu, 14/1/10, Singh Rishi (TIPO - QA/QC) <R.Singh@Panipat.ticb.com> wrote:
From: Singh Rishi (TIPO - QA/QC) <R.Singh@Panipat.ticb.com>
Subject: [MW:4045] Magnetism in SS 304 & 321 after welding
To: materials-welding@googlegroups.com
Date: Thursday, 14 January, 2010, 6:25 PM
One of my friend is facing a problem, which I'm putting to the group as I'm not sure about the solution.. SS joints after welding has becoming magnetic ( Ferrite number is not a criteria for these joints) and hence attracted by magnet ( including Socket Joints )- mostly pipe to fitting joints , but his Client is doubting that they are becoming magnetic because it's root has been welded by CS filler wire- rest passes by SS filler wire. This , he insists is done by welder to do the job faster and save purging- as per his past experience in some Gulf project. There are some thousand of SS joints ( 304, 321 ) in his plant, which is ready. What can be done, apart from PMI & Ferrite ( on which he doesn't have much faith as they show the reading of the Final pass ) , to convince him about the integrity of the joint without cutting/ drilling / damaging the joint. Please share any literature which relates Magnetism to the Welding/ Ferrite percentage. Welding Processes involved are GTAW (mandatory for all root welding ) and SMAW ( for above 8mm thk ) |
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