Thanks for replying.
First to Yallapragada1022, that link doesn't work for me.
Second to EdStainless, let me further explain my problem. I am using a thermal hydraulics program that requires surface roughness for piping materials, or any metal surfaces over which fluid my flow. We are using French mechanical drawings that specify stainless steel component roughnesses with a default surface roughness of 6.3 micros Ra. I am used to working with american drawings where surface roughness is specified in average roughness. I know that the code asks for absolute roughness which is equivalent to 2 times the AA or 1.8 times the RMS. I am not sure how to convert Ra into absolute roughness, but from what I have read, think that Ra is similar to AA in regards to piping materials.
Does this help?
Eventually the roughness is used in a fit of a Moody diagram to calculate friction loss (pressure loss) in the fluid system.