I'd like to help you answer this question, if I may.
First of all if you are welding an oil line your design code should be B31.4. B31.8 is for gas transmission lines. API 1104 is only for procedures, welding, fabricaiton , NDE, etc. 1104 tells you how to weld the pipeline, but B31.4 gives you supplemental requirements for various facilites.
Your preheat and interpass temperatures can be found in ASME B31.4 paragraph 434.8.8 and is only required for steels having a carbon equivalent in excess of 0.32% (heat analysis) or a carbon equivalent (Carbon + 1/4 MN) in excess of 0.65% (heat analysis) unless other variables or conditions require preheat. In this case, if preheat is required it must be done so with a qualified procedure. B31.4 doesn't specify an actual interpass temperature (min or max). Only that it must be considered and used during procedure qualification.
Now if you are tying into a facility that falls under B31.3, that is a completely different code. There will be PWHT requirements on the plant side but not on the pipeline side.