26-02-2016, 02:44 PM
All heat treatments are basically cycles of three elements, which are:
a) Heating
b) Holding or Soaking
c) Cooling
We use heat treatments to change properties of metal, or as a method of controlling formation of structures, or expansion/contractional forces during welding.In heat treating metals and alloys there are many elements for the welding inspector to check that may be of great importance, such as the rate of climb and any hold points in the heating cycle. The holding or soaking time is generally calculated at 1hour for every 25mm of thickness, but this can vary. Heat treatments that are briefly covered in this section are as follows:
1)Annealing
2)Hardening
3)Normalising
4)Stress relieving
5)Tempering
6)Pre-heating
The methods/sources that may be used to apply heat to a fabrication may include:
a)Flame burners/heaters (Propane etc.) Preheating
b)Electric resistance heating blankets. Pre-heating & PWHT
c)Furnaces. Annealing. Normalising. Hardening. Tempering
The tools that an inspector may use to measure the temperatures of furnaces and heated materials may include.
a)Temperature indicating crayons (Tempil sticks). Pre-heating
b)Thermo-couples. All heat treatments.
c)Pyrometers (Optical. Resistance. Radiation.). Furnace heat treatments
d)Segar cones. Furnace heat treatments
The welding inspector should observe that all heat treatments are carried out as specified and make records of all parameters. This is a critical part of the duties of a welding inspector who should also ensure that all documents are retained within the quality files.