PREHEAT & PWHT

[ssklara]

HELLO ,


I want to know, for what basis PREHEAT & PWHT have to select for the weld joints????, ( i know based on the thickness of the base metal ) any other reason to select PREHHEAT & PWHT?

 

[kingnero]

most important factors for preheat are carbon content or carbon equivalent, combined thickness, hydrogen content of filler material and heat input of the selected process - this is for "normal" (low-alloyed) steels.
When dealing with high % Ni, martensitic, chromoly, ... steels, you should study each case to see what the metallurgical consequences are.
PWHT is also used to alter the inner structure of the steels, in case you could end up with a less desirable microstructure.

I suggest you ask either specific questions or read up (a lot) about this, as this is not something one can cover in an internet thread (it took me a certain % of two years at school, there's more to it than meets the eye - literally)...

 

[ssklara]

ok thanks for ur reply ,

if the carbon equalent is more than 0.55, do i need to do preheat?.

 

[kingnero]

Do you accept bainitic/martensitic end structure?

Either way, I'm inclined to say yes (you need preheat), but without the steel grade, the product you're welding, ... and such this is merely a wide guess. Nevermind how to determine how much preheat you need... What does your buyer ask from you? PQR/WPS? nothing?

 

[stanweld]

ssklara,
Re. 0.55 C.E., it depends on thickness of the material, the ambient temperature & welding process.

 

[Guest102023]

ssklara,

From this and other posts it appears you have been thrown into the deep end of the weld pool by your boss, who doesn't recognize the value of welding specialists. I'm not criticizing your efforts but these forums will be an inefficient and slow way of learning welding engineering fundamentals.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[wegm]

Please have a look at these links:

http://www.weldinguide.com/gdanastasiadis/viewtopic.php?f=15&t=378

http://www.weldinguide.com/gdanastasiadis/viewtopic.php?f=5&t=390

http://www.weldinguide.com/gdanastasiadis/viewtopic.php?f=2&t=381

http://www.weldinguide.com/gdanastasiadis/viewtopic.php?f=5&t=16