Alloy625 CA

to assign a corrosion allowance, you need to have developed corrosion rates (experience) or from pilot studies and/or reference materials.

if this is piping covered under B31, then part of the problem is addresses in the method used to set the allowable stress for the materials.

Or did you want actual estimated rates of corrosion? If so, we need the flow rates, temp. and chemicals involved.

yes, estimates at this stage would be sufficient.
The flow rate of the gas stream comprising 69% Cl2, 19% N2, 5% O2 & other is 27537 kg/hr.
The temperature is 190°C and pressure is 280 kPa
thanks for your help with this.