What is maximum limit for PWHT soaking temperature for P.No.1 Gr.1 & 2?

[Tariq Hussain]

Dear Friends,

 

minimum PWHT Soaking temperature is given in ASME Sec VIII Div. 1 UCS-56, My question is What is maximum temperature that we can use for PWHT with reference to some applicable standards or metallurgical point of view point?

 

OR

 

Can we do PWHT for P.No.1 Gr.1 & 2 (e.g SA 516 Gr. 60 & 70) maximum up to lower critical temperature i.e. 723 Degree Centigrade?

 

Thanks in Advance for your valuable share.

[Tariq Hussain]

[manpreet]

Hi,

ASME Sec Viii Div 1 UCS-56 only mandates min. PWHT temperature and even that can be reduced
further a bit by compensating more time per UCS-56.1

Max. PWHT temperature shall never exceed lower transformation temperature for below reason:-

Guessing that thickness of component would be more than 32mm or above so heat treatment
condition would be either Normalizing or Quenching and Tempering:-

For Normalizing:- component heat treated above Ac3 (upper critical temperature and cooled under
control to form Ferrite + Pearlite microstructure, PWHT is carried out to reduce residual
stresses produced during thermal changes but must be below Lower critical temperature not to
change the microstructure.

For Quenching and Tempering:- component heat treated above Ac3 and cooled in water/oil forming
martensite to gain better strength but with excessive hardness then tempering at below Ac1
(lower critical temp) to temper the martensite thus reduce hardness and increase ductility and
toughness.
PWHT temperature is generally kept below 30deg C below tempering not to alter properties
maintained however there would be slight decrease in strength and toughness, is the reason
often client require to simulate with test coupons of same heat treatment that PWHT does not
reduce mechanical properties below required.


Regards
Manpreet Singh



On Sat, 11 Feb 2012 09:13:17 +0530 wrote
>Dear Friends,minimum PWHT Soaking temperature is given in ASME Sec VIII Div. 1 UCS-56, My

question is What is maximum temperature that we can use for PWHT with reference to some

applicable standards or metallurgical point of view point?ORCan we do PWHT for P.No.1 Gr.1 & 2

(e.g SA 516 Gr. 60 & 70) maximum up to lower critical temperature i.e. 723 Degree Centigrade?
Thanks in Advance for your valuable share.

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[John Henning]

As you already know the construction codes (e.g. ASME I, ASME VIII) give a minimum PWHT temperature.  While these Codes do not specify an upper limit, ASME Section  IX, QW-407.1 tells you that a new PQR would be required if the PWHT temperature is above the lower critical temperature (T_PWHT > A1 temperature).  Thus any sub-critical PWHT qualifies a range from the Code minimum to the lower critical temperature.  Some common sense should apply.  The engineer must be aware of the change in properties that can occur as T_PWHT approaches the lower critical temperature.  Obviously, greater softening will occur but at the same time the tensile and yield strength will decrease and the ductile-to-brittle transition temperature (DBTT) will increase.  Upper shelf energy also tends to drop. 

 

Generally, this only becomes an issue when a transition joint between Cr-Mo and CS is required.  The Cr-Mo side of the joint will drive the necessity for PWHT and the temperature range for PWHT.   In my experience, the biggest challenge is selection of the proper filler metal especially if a complex assembly {with CS-CS welds as well as Cr-Mo} is PWHT’ed.  Then selection of the carbon steel filler metal or filler metal/flux is crucial to maintaining minimum required properties in the CS-CS welds. 

 

 

John A. Henning

Welding & Materials

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[TAHIR ALI KHAN Kaimkhani]

Sir what is the meaning of upper or lower transformation temperature

[Ankit Gandhi]

Dear as per ASME viii div.1 you have done simulation which is represent material property after pwht so you can rise temperature up to that simulation cycle.

Regards,

Ankit

[George Dilintas]

It is the lower transformation Temperature 725degC

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Dr. Georgios Dilintas,

Dipl. Ing. In Aeronautic and Space Engineering

Ph.D in Mechanics of Solids - Computational Mechanics

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Welding, Stress Analysis, Corrosion, QA/QC, Failure Analysis, Risk Analysis