Once installed at the seabed, subsea rigid pipes in Carbon steel (CS), Low Alloys Steels (LAS) or in Corrosion Resistant Alloys (CRAs) can be wet stored for various durations. During this idle period, the lines can be filled with natural seawater generally treated with different types of chemicals, to mitigate localized corrosion initiation of stainless steel or the general corrosion of carbon steel. The chemicals are usually oxygen scavengers combined with or without biocides and corrosion inhibitor. Field experiences show that satisfying efficiency is obtained with some chemical’s combination. However, only few data are available in the literature to quantify separately the actual benefit of these chemicals and their combination. The needs to investigate sustainable alternative chemicals for these wet storage operations are also anticipated. In order to quantify the individual and synergistic effects of the selected chemicals, API 5L X65 carbon steel and UNS S31603 stainless steel were exposed for one year in seawater treated by different available combinations of oxygen scavenger, biocides, and corrosion inhibitors. Environmental-friendly chemicals have also been assessed as possible alternatives to conventional biocides. The corrosion rate of carbon steel coupons immersed in specific exposure cells, that simulate the confined exposure conditions during the wet storage, have then been determined by weight loss measurements after 3 weeks, 2, 6, and 12 months. The impact of the treatments on the corrosion rate and the bacterial activity have also been studied by Dissolved Oxygen Content (DOC) and Open Circuit Potential (OCP) monitoring, Electric Resistance (ER) measurements, and bacterial analysis. The current investigation shows that low DOC levels have been achieved which inhibited the so-called “biofilm ennoblement” of stainless steel. Thus, no corrosion occurred for UNS S31603. Such results are also applicable to most CRAs under similar exposure environment. The synergic effects of oxygen scavenger, biocides and corrosion inhibitor on the corrosion rate of carbon steel are also discussed.