FN testing after solution annealing ?

[prem nautiyal]

Dear Friends

 

A vessel is being fabricated as per ASME Sec III NB.

 

MOC: SA 240 TP 304L.

 

Dish end nominal thickness: 28mm (having one Long seam) and has to be solution annealed after forming.

welding process: SAW.

 

Client specs call for Ferrite number to be tested on equipment and should be between 5-10FN.

 

Now dish end blank L/S joint has been welded by SAW with the consumable having 8FN (as welded).

Dishend blank L/S was inspected for Ferrite test and readings between 5.5 - 7 FN were observed in as "welded condition".

Now the dish end has to be released for solution annealing after forming.

 

My query is whether ferrite testing will have to be done again after solution annealing on the dishend Long seam ?

 

The fabricator is fearing that the FN values will drop below 5FN after solution annealing which is practically true and lot of experience and studies support it.

 

Also client is not sure whether Ferrite number has to be tested after solution annealing or not.

 

Expert advise required in this regard whether to check the ferrite number on weld after solution annealing (heat treatment) or in as welded condition when nothing is specified.

 

Regards

 

Prem Nautiyal

Sr.Surveyor

cell: 9769316004

[Raghuram Bathula]

Ferrite control required before heat treatment.

pl. refer the previous discussion on this topic @
https://groups.google.com/forum/#!topic materials-welding/tOJJKvvtzDY,
titled [MW:0] Ferrite content variation with PWHT time

[pgoswami]

Mr. Nautiyal,

 

Solution annealing followed by rapid quenching will reduce ferrite in the weld. Ferrite in austenitic s.s (delta ferrite) is a high temperature phase which  does not undergo much of  diffusion oriented transformation  once  formed. High temperature exposure dissolves ferrite fully or partly. If solution anneal is restricted @ 900-950 Deg C the changes in the ferrite no may not be appreciable, although there'll be some reduction.

 

PWHT following forming is performed to remove residual forming stresses. Hence high temperature solution anneal may not be necessary. 

 

Irrespective of the solution annealing temperature adopted, a PQR coupon needs to be welded, with ferrite no readings ( to be taken after forming) and IGC  Practice E (as agreed).

 

Please see below the extract from, a very well known text on welding of stainless steel. In case of any major discrepancy you may refer this document for guidance:-IIW-IX-1695-92-(IIW-1166-92,-IX-H-233-90)-Guidance-on-specifications-of-ferrite-in-stainless-steel-weld-metal.

 

Hope this clarifies your query.

 

 

Pradip Goswami, P.Eng,IWE

Welding & Metallurgical Specialist

Ontario, Canada

pgos...@quickclic.net

pgos...@sympatico.ca

 

Heat treatment in the range 950 to 1100°C (1740 to 2010°F) will completely  relieve residual stress and also result in modification of the as-welded microstructure without forming carbides or sigma phase. Heating above 950°C (17 40°F) followed by rapid quenching will remove any carbides in the original microstructure. Heating to temperatures approaching 1100°C (2010°F) will dissolve some or all of the ferrite, depending on the hold time at temperature, composition of the weld metals, and the as-welded ferrite content. If this extreme heat treatment is used, rapid cooling to room temperature by water quenching is generally required since carbide precipitation may occur during slow cooling.

---

From: material...@googlegroups.com [mailto:material...@googlegroups.com] On Behalf Of prem nautiyal
Sent: Friday, November 08, 2013 11:08 AM
To: material...@googlegroups.com
Subject: [MW:19215] FN testing after solution annealing ?

Dear Friends

 

A vessel is being fabricated as per ASME Sec III NB.

 

MOC: SA 240 TP 304L.

 

Dish end nominal thickness: 28mm (having one Long seam) and has to be solution annealed after forming.

welding process: SAW.

 

Client specs call for Ferrite number to be tested on equipment and should be between 5-10FN.  (This is required in as welded condition). 

 

Now dish end blank L/S joint has been welded by SAW with the consumable having 8FN (as welded).

Dishend blank L/S was inspected for Ferrite test and readings between 5.5 - 7 FN were observed in as "welded condition".

Now the dish end has to be released for solution annealing after forming.

 

My query is whether ferrite testing will have to be done again after solution annealing on the dishend Long seam ?

 

The fabricator is fearing that the FN values will drop below 5FN after solution annealing which is practically true and lot of experience and studies support it.

 

Also client is not sure whether Ferrite number has to be tested after solution annealing or not.

 

Expert advise required in this regard whether to check the ferrite number on weld after solution annealing (heat treatment) or in as welded condition when nothing is specified.

 

Regards

 

Prem Nautiyal

Sr.Surveyor

cell: 9769316004

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