PRE HEAT INTERPASS TEMP. REQUIREMENTS FOR FILLER METALS
The preheat and inter pass temperature must be sufficient to prevent the cracking.Previous Experience has shown that the minimum temperatures specified in are adequate to prevent cracking in many cases. However the increased preheat temperatures may be necessary in situations involving higher restraint higher hydrogen, & lower welding heat input or steel composition at the top end of the specifications. In converse, lower preheat temperatures may be adequate to prevent cracking depending on restraint, hydrogen level, & actual steel composition or higher welding heat input. Optionally, minimum preheat and interpass temperature may be established on the basis of steel composition, using recognised methods of prediction or guidelines. However should the use of these guidelines result in preheat temperatures lower than those of procedure qualification shall be required. Preheat shall be applied such that the surfaces of the parts are at or alone the preheat temperature for a distance equal to the thickness of the part being welded but not less than 75 mm in all directions. In joints involving combinations of base metals preheat shall be specified for the higher strength steel being welded.