The CO2 corrosion of carbon steel is one of the most prevalent internal damage mechanisms for oil & gas production tubing flowlines and pipelines. The corrosion rate typically increases with temperature up to a certain point and then decreases at higher temperatures due to the formation of protective scales of corrosion product on the steel surface. In oil & gas production it is common for a collection of organic additives (such as corrosion inhibitors scale inhibitors and hydrate inhibitors) to be injected into the process stream. All of these could clearly have an impact on the formation of protective scales on the steel surface beneficial or otherwise. We have used in-situ synchrotron diffraction technique to experimentally investigate the effect of common scale inhibitors amino trimethylene phosphonic acid (ATMPA) and poly(ethyleneimine) (PEI) and have found that they can cause a significant change in the scale formation process. Experiments were performed in sodium and magnesium chloride brines at ~ 1 bar CO2 80 °C and pH 6.3 such that protective scales would readily form in the absence of any organic scale inhibitors. To enable completion of synchrotron experiments within a feasible timeframe the corrosion process was accelerated through anodic polarisation under potentiostatic or galvanostatic control and these short-term results are also compared against longer-term open circuit data.