QW406.1&3 Preheating temperature

[Mohd Siraj]

Dear all,

Why ASME-IX is mentioned exact 55ºC increase(IP) or decrease preheating is essential variable?

Is there any specific reason?

reagards,

[Lalu Rajendran]

Hi,

As per Sec IX, 55ºC (100ºF) increase(IP) is a supplementary essential variable and decrease in preheat in the same proportion is an essential variable.

There are four primary reasons to utilize preheat: 

(1) It lowers the cooling rate in the weld metal and base metal, producing a more ductile metallurgical structure with greater resistant to cracking 

(2) the slower cooling rate provides an opportunity for any hydrogen that may be present to diffuse out harmlessly without causing cracking 

(3) It reduces the shrinkage stresses in the weld and adjacent base metal, which is especially important in highly restrained joints 

(4) It raises some steels above the temperature at which brittle fracture would occur in fabrication. Additionally, preheat can be used to help ensure specific mechanical properties, such as notch toughness.

regards,

LALU

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[Maulik Thakkar]

Dear sir,

The logic is well described in EN standard
T8/5 cooling rate.

Regards,
Maulik H. Thakkar
L&T, Welding Engg.

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[Hareesh K V]

Dear Sir,

Which EN standard is to be referred?

Regards,

Hareesh K V
+91-8547859202

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[wilfred kojo]

Hi,

In addition to Lalu's comments,  preheat reduce weld cooling rate with those benefits as stated Lalu. Notwithstanding excessively slow cooling rate leads to grain growth which adversely affect the toughness the weld, hence the upper limit (supplementary essential variable). 55ºC decrease or increase is the window within which the properties of weld can be guaranteed without much change. 

Regards, 

Wilfred Kojo ( AWS CWEng )

Sent from Yahoo Mail on Android

On Thu, 10 Mar, 2016 at 11:53 am, Lalu Rajendran

<lal...@gmail.com> wrote:

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