Flame Straightening Duplex 2205 1

[pipewelder1999]

Are there any manufacturers recomendations for flame straightenening 2205orsimilar material. I am interested in maximum temp and optimum cooling rate.

I have seen this being performed at a shop I am doing some other work in and I am looking for some information to give them to develop a procedure with. At this point the process has not been questioned by the end user but I think it will soon come as I don't t hink this is a practice that can be performed without tight controls.

Thanks and have a nice day



Gerald Austin
Iuka, Mississippi

http://www.weldinginspectionsvcs.com

 

[sayee1]

Flame straightening for Duplex. That is a NO-No situation as per my experience. Would be interested to know if others have performed flame straightening for duplex as well!

Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
email: sayee_prasad@yahoo.com
If it moves, train it...if it doesn't move, calibrate it...if it isn't written down, it never happened!

 

[pipewelder1999]

What tests could be done to see if damage has been done ?

GA


Gerald Austin
Iuka, Mississippi

http://www.weldinginspectionsvcs.com

 

[metengr]

I would have serious reservations about attempting to flame straighten a duplex ss component. What exactly is the scope of work - is this a casing or shaft?

Several items to consider;

1. The duplex stainless steel can form intermetallic phases within minutes at temperatures above 850 deg C.

2. Prolonged heating in the range of 350 to 550 deg C can result in significant loss of toughness (475 deg C embrittlement).

If you need to heat straighten it may be worthwhile to heat the entire component using a solution heat treatment temperature and rapidly cool to avoid the formation of sigma phase. Local heating by flame or contact heaters to straighten is not recommended for the reasons mentioned above.

 

[EdStainless]

You need to make sure that the temp never exceeds 600F. And you will need to re-pickle the surface (grinding won't do it) in order to restore the local corrosion resistance.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[GRoberts]

I would never try to flame straighten duplex sst myself due to all the toughness and corrosion problems that exist. If there is no way around it, the best route would be to solution anneal afterwards which would erase most or all of the deleterious affects caused by the flame straightening. However, solution annealing is often not an option. At the very minimum after a flame straightening attempt, CVN, corrosion, and micro examination should be done per ASTM A923.

 

[metengr]

As a follow-up, have you considered weld repair/re-machining of the duplex ss versus heat straightening?

 

[pipewelder1999]

Thanks to all for the responses. The fabricator stopped the practice the following morning after this posting.

The straightening was being performed on flat panels of 1/4" material . The distortion resulted from welding of stiffeners on the opposite side. The practice was only performed on a small amount of panels.

From what I saw, the heated area (Dull Red) was nearly identical to what was occuring during welding of the opposite side.

They have now used mechanical means to correct the distortion and bracing during welding to reduce this effects from welding.

Would the previous heating affect the ferrite number ?


Thanks
Gerald Austin

Gerald Austin
Iuka, Mississippi

http://www.weldinginspectionsvcs.com

 

[metengr]

If what you have observed is a dull red in the locations of direct flame exposure during heat straightening, this would correspond to a surface temperature at or below 1400 deg F. I believe the ferrite number will not change.

 

[sayee1]

Metengr
How does the FN change with temperature in Duplex ss, please elaborate and give the temperatures above which changes expected.
Thanx

Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
email: sayee_prasad@yahoo.com
If it moves, train it...if it doesn't move, calibrate it...if it isn't written down, it never happened!

 

[metengr]

Sayeeprasdr;

The ferrite content or volume fraction in duplex stainless steels is fixed by alloy content and cooling rate during solidification. During fabrication, the alloy is typically solution treated at 1950 deg F and rapidly cooled to develop a near 50-50 mixture of ferrite and austenite.

During exposure to temperatures below 1900 deg F, brittle intermetallic phases like sigma can form. I have included an interesting technical paper that indicates ferrite is reduced in content at the expense of sigma phase formation with exposure to temperatures above 1600 deg F after 1 hour. The ferrite is reduced at the expense of sigma and also forms a low carbon austenite phase.

As I had stated previously, I do not believe that the plate would have any measurable change in ferrite number because of the temperature (less than 1400 deg F) and short time duration, that was mentioned earlier. I believe that the area that was heated had probably converted a minor amount of ferrite into sigma and would show reduced corrosion resistance.

http://www.nit.ufscar.br/matres/volume2/num4/0038.pdf