## 1 Introduction  
One of the most widespread kinds of steel is low-carbon or mild steel, not only for structural purposes but also for several applications in industry. Therefore, its usage and operation range from machinery parts, building materials, and domestic appliances to cutting tools, conveying tubes, cables, and magnets. Due to its low concentration in carbon (up to 0.29 wt %), mild steel exhibits extreme durability, great affordability, and significant mechanical, thermal, and magnetic properties [1; 2; 3]. Due to mild steel's increasing utilization, there has been great concern for the susceptibility of such steels caused by environmental corrosive factors, such as the humidity, acidity, or salinity of the atmosphere [4; 5; 6]. Thus, lots of studies have been focusing on low-alloy (weathering) steel corrosion and how to encounter it in a functional way [7; 8; 9]. In general, metallic corrosion is associated with any chemical alteration of the metal that stems from interaction with its environment [10]. Although intense research studies have taken place over all these decades in order to face corrosion, it still remains in the foreground since it is a continuous and inevitable process [11]. The main classification of corrosion types emphasized in the literature is between uniform and localized corrosion [12]. Pitting corrosion is a type of localized corrosion in which the metal is corroded in depth via the formation of indistinguishable pits. In the case of water and usually oil-conveying pipes, the corrosion effect often triggers uniform surface degradation internally, in parallel with localized corrosion underneath and oxide film formation [13; 14]. Taking into account that pitting may cause the initiation of stress corrosion cracking [15], it is considered as the most detrimental corrosion effect. While uniform corrosion occurs during the subject of mild steel in various environmental conditions [8; 16], localized corrosion, such as pitting and scaling, takes place in the presence of heavy metal ions [17; 18] or in locally high pH values [19]. Localized corrosion phenomena may thin locally the inner wall in a pipe, resulting in the creation of areas susceptible to cracking [20]. The protection of metallic materials from the corrosion effect could be achieved by intervening either in the alloy structure or in the alloy environment. The intervention in the alloy structure can be performed by changing the alloying ratio, by creating/applying metallic or organic coatings/films on the surface, by decreasing mechanical operation tensions, by the use of anodic or cathodic protection, and by adding corrosion inhibitors in the corroding solution [21]. In the literature, several studies indicate corrosion inhibition as an effective protection method [22; 23]. A conventional classification of corrosion inhibitors is according to their inhibiting action. Therefore, there are adsorption inhibitors that undergo chemisorption in the metallic surface, film-forming inhibitors, which are divided into passivation inhibitors (oxidizing or non-oxidizing) and precipitation inhibitors (deposition of three-dimensional film). However, the most common discrimination is between anodic, cathodic, and mixed-type inhibitors, considering which half-reaction they suppress during corrosion phenomena. Most organic inhibitors are of mixed-type and act as chemisorptive inhibitors. Phosphates act as cathodic inhibitors, whereas benzoates and azelates represent non-oxidizing film-forming inhibitors [24]. Concerning inorganic inhibitors, ideally the central atom of the inhibitor tends to form a complex entering the metallic lattice, without the need of additional energy and with the necessary stability [25]. [PERSON] et al. compared the inhibition ability of phosphate, chromate, molybdate, and nitrite as potential inhibitors for mild steel, in 0.1 M NaCl near neutral solutions. They concluded that phosphate demonstrated higher inhibition efficiency compared to the other inhibitors.