주식회사 금가
Heat Treatment
-
General Description
Pre-heating
Post-heating
Post Welding Heat
   Treatment
Measurement of
   Temperature
-

Electric Resistance Heat Treatment
-

The Gas Combution type Heat Treatment
-
Hardness Measurement
-
Services
Vessel
Plant


Inspection & Supervision
-
Inspection
-
Supervision

NDT
HOME > Business > Heat Treatment > General Description > Pre-heating

Pre-Heating is, as a subsidiary process of welding work, before and during welding, the operation of heating the part of the base metal on which welding metal is melted and attached. The fundamental purpose of putting in operation of Pre-Heating is to prevent from cracking at Welding zone and the Heat affected zone

The effects of Pre-Heating when welding are as below

1) Make heat loss decrease so that the hardness level of the material can decrease by slowing the cooling velocity of welding       part.
2) Repress one-side sitting of impurities can make cracking.
3) Make thermal transforming volume by welding derease.
4) Make easy to emission of hydrogen and repress the happening of the crack by hydrogen..
5) By eliminating water on the base metal on which welding metal is melted and attached, make welding metal prevent from        incoming hydrogen in the welding metal.
6) Make easy for welding metal to melt and attach.


There is Interpass Temperature related to Pre-Heating.

The welding part completed through Multi-Pass is affected by the remaining heat of the last pass.
Interpass Temperature is the temperature of base metal at welding part heated by the welding heat of the last Pass, just before the Multi-Pass welding raises Arc.
If Interpass Temperature is beyond 200℃, hardness and impact value may drop, and for stainless steel it happen to raise Weld Decay. So Interpass Temperature should be below the appropriate temperature.
So, Interpass Temperature is presented as maximum temperature, however, always minimum Pre-Heating temperature should be kept as well, and this should be applied when temporary welding of assemply cast, maintenance welding and Gouging as same as the conditions of main welding.