Why preheat is done?
FIRST UNDERSTAND WHAT IS PREHEAT:-
Preheat is the application of heat to a joint immediately prior to welding and
is usually applied by either a gas torch or induction system.
NOW:-
one of the main
reasons is to assist in removing hydrogen from the weld.
HOW PREHEAT TEMPERATURES ARE CALCULATED
Preheat temperatures for steel structures and pipe work are calculated by
taking into account the carbon equivalent (CEV) and thickness of the
material and the arc energy or heat input (kJ/mm) of the welding process.
REFER STANDARDS BS EN 1011 FOR PREHEAT TEMPERATURES.
***In general, thicker materials require higher preheat temperatures.
