Leonardo,
Section IX is about welding procedure and performance qualification. Preheating is a variables as required by Section IX to be qualified by the manufacture himself.
In other word, Section IX doesn't give you preheat temperature for your specific application but rules of how to qualify.
Section IX is not a CONSTRUCTION section. Take a look at the construction section governing your product you can find mandatory or recommended preheat temperature.
E.g.,
Non-mandatory appendix A-100 of Section I;
Non-mandatory appendix R of Section VIII;
Para. 131 of B31.1;
Para. 2.5.1 of NBIC Part 3
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Note that all Code give minimum preheating requirement. From engineering judgement you may need to consider more than Code mimimum requirement.
As most Codes state:
"The need for and the temperature of preheat are dependent on a number of factors such as chemical analysis, degree of restraint of the items being joined, material thickness, and mechanical properties. The welding procedure specification for the material being welded shall specify the preheat temperature requirements."
That is to say, "you are on your own"~ LOL~
To establish a preheat temperature, in addition to meet MINIMUM Code requirement, you can refer to some pubilcation of material mill such as V&M for a specific material or handbook/guideline from a filler metal manufacturer such as Esab/Metrode for a specific filler metal. Also to some industry practice such as technical reports by EPRI......
degree of restraint is up to your product, so, again, you are on your own.
(Take a look at Annex I (Normative) Guideline on Alternative Methods for Determining Preheat of AWS D1.1-2010, you will know how much you need to consider to establish preheat temperature.)
Hope the above would be of help.
Jovi