Pipe Class and Wall Thickness

How do we calculate?

According to IACS UR P2: for steam and thermal oil p > 16 bar or t > 300 °C is Class I; p ≤ 7 bar and t ≤ 170 °C is Class III. For fuel and oils p > 16 bar or t > 150 °C is Class I; p ≤ 7 bar and t ≤ 60 °C is Class III. For other fluids p > 40 bar or t > 300 °C is Class I; p ≤ 16 bar and t ≤ 200 °C is Class III. Anything in between is Class II; toxic fluids are always Class I.