Hi all
i have one query regarding the selection criteria of different material while the design and operating parameters
of the Steam is same .
In detail , HP steam main line ( from HRSG to Turbine ) having size DN 300 , Design Temp. 572 ,Design Pressure 153 the material chosen is alloy steel (A335 P91) .
Also the drains of the main line having size DN 25 , Design Temp. 572 ,Design Pressure 153 the material chosen is alloy steel (A335 P91) .
But the sampling ( continuous) lines taken from this main line having size DN 10 , Design Temp. 572 ,Design Pressure 153 the material chosen is stainless steel (A312 TP316 H) .

What could be the reason for selecting different material for sampling line as compare to material of main line and its drain ???
Regards
SG