Anant,

The design high pressure requiring Sch 120 wall thickness results in little flexibility for the size Nps-18 and Nps-10 piping straight lengths. Some more offsets with elbows would have more flexibility to reduce the loads.

If the layout is fixed and the geometry cannot be changed then the guide restraint gaps might be opened up from the 0.75 inch as designed to maybe 1.0 inch gaps. The thermal expansion is closing the gaps at the guides from the 200 deg F design temperature. Yes, the 200 deg F should be used applied for the Code stress compliance evaluation. Sometimes the operating temperature could be lower to justify using a lower than design temperature to evaluate the loads at supports and equipment.

If there are equipment loads to consider at the piping connections then the larger 1.0 inch gaps might result in excessive loads at the connections. Some added flexibilty in the piping routing is probably then needed. Please have mentor or piping designer work with you on re-design.