My responses:
1) Cannot be quantified.
2)Process department has to mention this as a note in the Line Designation table( LDT) for the specific lines.It is "their job".As a thumbrule lines with slope and other partially filed lines,large diameter lines, blowdown lines are potential cases. Again, it is upto the process department .Also kindly ask the people who have told you that "process department does not provide the information" a question "which department does ?". I presume their reply may be "pipe stress".
3)If you don't get the data , assume some value. Mark an e-mail or an inter-department memorandum as to what you have considered and let others ( process/projects )agree /disgaree to that.I would recommend using "guide with hold downs" instead of conventional guides at the guide locations.Involve your bosses in getting the data.Your lone effort may not be enough.
Regards
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anindya