APPLICATION & CONTROL OF PRE-HEAT
APPLICATION & CONTROL OF PRE-HEAT:
- CEV is used to determine pre heat.
- Check the pre heat [including tack weld]: before starting the first pass.
- Pre heat temp is normally expressed as minimum.
- Check the inter pass temp: next pass.
- Main purpose of pre heat is to slow down the cooling rate.
- Reduces the risk of hydrogen cracking.
- Improves fusion.
- Removes moisture.
- Point of measurement T<50mm. temp shall be measured on the surface of the work piece facing the welder, maximum distance of 50mm.
- Pont of measurement T>50mm. temp shall be measured on the face opposite to that being heated, allow 2mints per every 25mm of parent metal thickness for temp equalization.