Corrosion and scale deposition on pipelines are two of the major flow assurance issues which have been recognized in the oilfield. Corrosion control of carbon steel pipelines requires understanding of the simultaneous occurrence of both processes. To date there have been few studies demonstrating the interactions between surface scale deposition and corrosion processes. Combined scale/corrosion inhibitors (mixture of scale and corrosion inhibitors) are gaining in popularity in the oil and gas industry as one of many methods to mitigate both those processes. A newly developed methodology of combined bulk jar scaling/bubble cell technique (corrosion) was used to assess the corrosion rate, CaCO3 deposition on the material surface and bulk precipitation in a CO2 environment. In this study the effects of single components of scale and corrosion inhibitors on the corrosion processes (general and localized corrosion) and scale deposition (bulk and surface deposition) have been investigated. Surface analysis techniques (SEM, EDX and Light Interferometry) and bulk analysis (Turbidity meter and ICP-MS) enable the corrosion/scale mechanisms to be studied in detail for X65 pipeline material. An experimental design method has been used to evaluate single and/or synergistic effect of single components of combined scale/corrosion inhibitor on the corrosion and scale processes. The methodology used in this study a newly-developed combined bulk jar scaling/bubble cell prove that is very effective tool in assessment of corrosion and scale interactions when they occurs simultaneously. Assessment of calcium carbonate precipitation on the sample showed that scale plays an important role of accelerating pitting corrosion by providing a suitable environment. XRD analysis showed that the calcium carbonate crystals which formed on the metal sample in the tests with 2-mercapthoethanol were calcite crystals only. The simple linear regression model was developed to predict corrosion and scale when these process occur simultaneously. The model also enables the interactions between the corrosion and scale inhibitor components to be quantified.