Dear sunil,
In general, the issue of ferrite content limitation is related to the preventive measures and i many cases, the conservative approach by the client based on some qualitative results during research. I would try to give some information so that your argument to dilute the client requirement may be fruitful.
In general, the ferrite content in weld metal depends on the chemical composition and the heat input during the welding. For 316 grade of material the ferrite control may be necessary for the following reason only:
a) High temperature (500 deg. C+)application: If the fluid conditions are such that the material is exposed to higher temperature for longer period, that may cause sigma-phase generated from ferrite.
b) Corrosive fluid with higher stress: The corrosive fluids (oxidizing acids/chlorides) + high pressure application that may cause stress corrosion cracking in austenitic ss. The oxidizing acids include the nitric acid/nitrates/sulphuric acid, etc.)
Under the above context, it is better to understand the process conditions and subsequently, the real reason for ferrite control. And ultimately, you may ask for a selective implementation of this requirement on limited area of the plant.
Reply to your query:
Query#1: Please advise whether it is possible/ practicable to meet the requirement stated in Point 1 above? If yes, How?
Reply: Generally, the welding consumable manufacturer control the ferrite content by chemical composition (there are some diagrams available like, schafler/Delong/WRC, etc.). But, the control of ferrite also depends on welding process (dia. of electrode/current, etc.). this is the reason that many-a-times, the manufacturers do not give guarantee of such a narrow range of ferrite (0-2%). I remember even avesta had denied guarantee of ferrite other than the Schaefler/WRC diagrams even though in actual weld metal the ferrite control was achievable. But, as mentioned by raghuram in the earlier mail, the availability seems to be there in the market. So, you can use/recommend them to your vendors. But, normally such consumable are 316LN or 316L-modified grades. I do not have the data about the welding consumable suggested by Raghuram, whether it is 316L or some other grade.
Also, please get the Client-confirmation about the method of the Ferrite no. control in weld metal. If it is chemical composition, then any manufacturer may be able to supply you such electrode batches.
Generally, manufacturers do provide 0F(Nil Ferrite) electrodes, the composition is adjusted such that, the weld metal solidification does not involve any ferrite. These fillers will meet your requirements, for sure, but the composition is modified with extra Ni and/or N.
Query#2: Also I understand that it is difficult to practically measure the ferrite content. If it is so, can you please elaborate it with detail and reason for the same?
Reply: You are right, it is very difficult to measure the %Ferrite in weld metal and it largely depends on the method you use to detect the same. The best and the most practical method (for surface Ferrite) is the magnetic probe method and it gives the ready results based on the average magnetic field it has detected on the surface. This, being the non-destructive and faster method, is quite popular. But it has got around +/-10-15% accuracy depending on the machine, operator and the environment. Thus, it gives you an approximation only.
Another method is microscopic method. This is more accurate and you can check the ferrite content even across the section as well. But the biggest problem is that you cannot extrapolate the results of one method to the other and vice versa.
In this view, the vendor will have to prove the ability of the process (WPS/PQR) to control the ferrite by both the above methods and he may follow the first one for the production welds.
I hope the above satisfy your requirement,
-----materials-welding@googlegroups.com wrote: -----
To: <materials-welding@googlegroups.com>
From: "Bathula Raghuram \(Mumbai - PIPING\)" <R.Bathula@ticb.com>
Sent by: materials-welding@googlegroups.com
Date: 18/01/2008 03:21PM
Subject: [MW:503] RE: 500] RE: 497] Ferrite content limitation for SS316L - URGENTMATTER!!
THERMANIT 19/15H (ThyssenGermany ), Rutox-F (D&H Secheron) are few brands which can give 0-2% Ferrite
Corporate Musings ?The Office Happening?:
From: materials-welding@googlegroups.com [mailto: materials-welding@googlegroups.com ] On Behalf Of Bathula Raghuram (Mumbai - PIPING)
Sent: Friday, January 18, 2008 2:02 PM
To: materials-welding@googlegroups.com
Subject: [MW:500] RE: 497] Ferrite content limitation for SS316L - URGENTMATTER!!
It is possible to get <2% ferrite consumables from Thyssen, Sandvik, or Avestapolarit etc. I will try to get the data sheets from these manufacturers, meanwhile request members to post if having these datasheets or specific brand names.
Measurement:
According to the Welding Research Council (WRC) it is not possible at present to determine the absolute ferrite content in austenitic-ferritic weld metal deposits. Variations resulting from differences in the welding and measuring conditions are to be anticipated even in specimens with pure weld metal deposit. The usual standardisation assumes a 2-sigma variation which means a variation of ±2.2 FN for 8 FN.
Welding Process control:
Greater variations are to be anticipated if the welding procedure permits higher absorption of nitrogen from the ambient air. High nitrogen absorption may lead to a weld metal with 8 FN falling to 0 FN in the ferrite content. Absorption of 0.10 % nitrogen typically reduces the ferrite content by 8 FN. In weld metal deposits dilution with the base metal leads to further ferrite reductions since base metals with the same composition usually have lower ferrite contents than the pure weld metal.
From: materials-welding@googlegroups.com [mailto: materials-welding@googlegroups.com ] On Behalf Of Agrawal Sunil (Mumbai -Stequ)
Sent: Thursday, January 17, 2008 7:05 PM
To: materials-welding@googlegroups.com
Subject: [MW:497] Ferrite content limitation for SS316L - URGENT MATTER!!
Subject: Request for advise about Ferrite content limitation for SS316L
Dear Members,
We are bidding for one of the Ammonia revamp project in India. In that regard I would like to have you advise/ opinion for the following matter:
1) Client has asked to restrict ferrite content to 2% for SS 316L. Client requirement is given below:
In case of equipment fabricated of SS316L, low ferrite filter material shall be so selected that ferrite content in two subsequent pass in contact with process fluid shall be max. 2%. The welding not in contact with process fluid may have ferrite content limited to 6%.
2) We requested client to give relaxation on above requirement with following argument:
Ferrite content shall be restricted to 3-10% (in weld zone material) in Specification, but practically ferrite will content reach up to 8-10%.
3) However, client still prefer to maintain the ferrite content restriction.
In my understanding, ferrite content limitation is mandatory to have specific corrosion control (mainly in Urea Plant) which is not the case in Ammonia Plant.
May I have your valuable feedback/ opinion that whether ferrite content limitation, as stated in point 1 above, is really necessary for Ammonia plant? If not, what is the maximum ferrite content that can be reached for Ammonia Plant. I would highly appreciate your feed back with technical back-up/ support/ past reference.
Query#1: Please advise whether it is possible/ practicable to meet the requirement stated in Point 1 above? If yes, How?
Query#2: Also I understand that it is difficult to practically measure the ferrite content. If it is so, can you please elaborate it with detail and reason for the same?
I need your feedback to convince the client to withdraw their requirement about ferrite content limitation.
I would highly appreciate your feedback by return mail as I need to have the data by this week end (at least before 22 nd Jan 08).
Thank you,
Sunil S. Agrawal
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