RE: [MW:6182] MW: 6118- Post Forming Heat Treatment of NACT plates

Dear Mr. Pradip Goswami

Thank you for the quick reply. we are mainly concerned when a plate supplied in NACT condition undergoes a normalizing+tempering treatment after forming. In this case how does it effect the properties of material, thou ASME supports this type of heat treatment, since NACT is specialized process adopted by steel mill which is carried out in a controlled atmosphere (in particular accelerated cooling) to achieve the results and same in our opinion can't be replicated by a fabrication shop.

Since steel mill is unable to achieve the desired properties by just N&T, and that is reason plates will be supplied in N+AC+T, later these plates are subjected to N&T post forming, how can it be possible to guarantee the same properties of plate in NACT condition?

---

From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of pgoswami
Sent: Thursday, July 29, 2010 8:34 AM
To: materials-welding@googlegroups.com
Subject: [MW:6174] MW: 6118- Post Forming Heat Treatment of NACT plates

Mr Bathula,

 

Please find a query  on the similar issue posted in www.eng-tips.com. I have that presentation from Arcelor but would not like to share in the forum, due to the fact that it was exclusively for API forum(2004 forum).

 

However the free download datasheet on Gr387 steel (CromElso-11), indicates that:- 

1. Such plates could be supplied with:- Normalizing and Tempering or Normalizing, accelerated cooling and tempering depending on thickness and required impact properties.  The second option would yield more consistent properties for thicker plates.
2. PWHT in the range 660-690° C / 1120°F ± 20°F at 2 minutes per mm or 1 hour per inch.  

 Recommended FORMING  - Cold forming (+ stress relief for high strains) or hot forming can be applied

1. Cold forming (< 500°C/930°F) : to be followed by PWHT  
2. Warm forming (500°C to tempering temperature)
3. Hot forming (940-1100°C/1725-2010°F) : to be followed by complete heat treatment.

ASME SA-387  requirements  for heat treatments:-Except for Grade 91, all plates shall be thermally treated either by annealing, normalizing- and -tempering, or, when permitted by the purchaser, accelerated cooling from the austenitizing temperature by air blasting or liquid quenching, followed by tempering. Minimum tempering temperatures for Gr12 shall be – 620⁰C.What ASME is  calling for through  accelerated cooling is to enhance mechanical strengths and to ensure through thickness effect on thicker plates.

 

If the DE is to be normalized the effects of NACT may be lost. Moreover assuming that D.E thickness is close to shell thickness or 90mm, whichever is close cold forming may cause harm to the material., hence warm forming may be beneficial.

 

If you ask the mill, I am sure they would be able to provide some data, especially on the cooling rates.  Reputed mills which manufactures TMCP (Thermo mechanically Control Process) steels should be able to get some data.

 

As this steel is specially heat treated may be sharing the fabrication conditions for DE with the mills would generate more information.

 

Thanks.

 

Pradip Goswami, P.Eng.

Welding & Metallurgical Engineer/Specialist

Ontario Power Generation Inc.

Email-pgoswami@sympatico.ca,

pgoswami@quickclic.net

 

 

---

---

 

---

From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Raghuram Bathula
Sent: Sunday, July 25, 2010 5:22 AM
To: materials-welding@googlegroups.com
Subject: [MW:6118] Post Forming Heat Treatment of NACT plates

Dear all

Can body share views on heat treatment carried above tempering temperature for NACT plates? one of the case i have come across is stated below.

 

MOC: SA387 Gr11, Thickness 90mm, Delivery condition: Normalised+accelerated cooled+tempered (NACT)

Contract requirement: Cold formed D''end shall be normalised.

Since plate delivery condition is NACT, Mill certifies plate with 2NACT+3PWHT cycles on simulated coupons.

Fabricator will perform 2nd NACT (Fabricator assures that they do rapid quenching with water and tempering)  after cold forming (since normalising is mandatory irrespective % strain)

 

I am of the view that so far no mill has disclosed how will they perform NACT (complete cycle and cooling rates), thou Simulation is done at mill, in my opinion it is impossible to replicate the same NACT process at fab shop, and can't represent the simulation done at mill.

 

Also it is not known how mill perform accelerated cooling (by direct water quenching or water sprinklers or forced draft....?) one of the process photograph i have got on the web attached here with shows sprinklers .