The corrosion of oil and gas production system is dependent on several different fluid parameters for examples carbon dioxide bicarbonate organic acid amongst others. In addition the operating conditions can vary through the project life affecting the yearly estimated corrosion rate and need to be understood by the project team so that meaningful corrosion predictions with some degree of accuracy are provided by the dedicated corrosion engineer. This paper presents three corrosion studies on production flowline systems from three different offshore sample fields at the design stage. The effects of the key operating conditions (temperature and flowrates) and water chemistry (bicarbonate content organic acid content and H2S and CO2 partial pressure) on the predicted corrosion rates are discussed. Electronic Corrosion Engineer ECE 5 corrosion model has been used through all the corrosion studies. NORSOK M-506 model and FREECORP model have also been used to compare with some ECE 5 corrosion results. It has been found that the corrosion rates can be relatively high when both CO2 partial pressure (above 70 psi) and water production rate (above 40000 BPD) are at high levels for a multiphase flowline system. In such case carbon steel flowline solution is too risky even when applying a corrosion inhibition system thus CRA clad flowline is usually recommended. For a gas production flowline system containing organic acid (above 100 ppm) and CO2 (above 0.2 mol%) a potential solution is to inject pH buffer (e.g. bicarbonate) in addition to traditional film forming inhibitors.