## 5 Corrosion Concerns of Additively Manufactured 316L Material Grade  
Big oil and gas companies such as General Electric (GE), Equinor, and Shell have previously shown early progress in using AM technology for the manufacturing of specific heat exchangers and gas turbine nozzles. However, before they can be able to widely use this technology for the production of other parts in offshore applications, they need to evaluate the incoming economic, health, safety, and environmental risks associated with using additively manufactured parts [35]. Additively manufactured parts previously had proven to have satisfactory mechanical performance for high-pressure applications [36]. Therefore, the mechanical strength of the additively manufactured parts, except for fatigue-related problems, is not a very challenging issue in the oil and gas industry. Instead, the main challenge is the risks incurred by corrosion mechanisms, as the corrosion performance of the additively processed materials is under question. According to [PERSON] et al. [37], in wrought stainless steel, most of the localized corrosion happens in MnS locations. In the additive manufacturing process, the manganese and sulfur elements lose the chance to produce inclusions in the form of MnS, because of the high cooling rate and the rapid solidification during the process. Therefore, due to the low MnS type inclusion content of the additively manufactured samples, these samples show a higher resistance to localized corrosion than the wrought counterparts. The passive film at the surface of stainless-steel parts plays vital role in the corrosion resistance of the material. This passive film includes oxides and hydroxides of chromium and iron. Based on the electrochemical impedance spectroscopy study, the researchers showed that the passive film in AM 316L is richer in iron and chromium and is much denser, thicker, and has fewer defects than that of the wrought counterparts [37]--increasing the general corrosion resistance of the AM 316L steels. It is well known that hydroxides prevent the penetration of anions such as Cl\({}^{-}\) in chlorine-containing environments; AM 316L samples are also more prone to pitting corrosion. This finding is supported by other experiments [36; 38] that report that the pitting corrosion increases in AM 316L samples due to the Cr/Mo segregation in the microstructure. However, several other investigations have reported different results about the pitting resistance of AM 316L material grade. According to this research, the reduction of MnS content in the microstructure of the AM samples enhances the passive film formation and reduces the pitting promotions [37; 39; 40]. \begin{table}
\begin{tabular}{c c} \hline \hline
**Qualification Step** & **Parameters to Be Controlled** \\ \hline Non-destructive Testing & Visual inspection, X-ray, CT scan, ultrasonic, dimensional checks, hardness test. \\ Destructive testing & Grain size test, inclusion level, mechanical testing such as tensile, bend test, Charpy test, fatigue, weldability, corrosion tests. \\ Quality controls of the process & Statistical quality controls and sample tests, Comparison of data obtained from different quality control samples. \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The Main concerns in the qualification of final product. Intergranular corrosion is the main problem in high-temperature applications, especially in the temperature range between 500-850 \({}^{\circ}\)C. In this mechanism, the secondary precipitates are formed at the grain boundaries, which leads to the production of chromium-free regions at the microstructure, and eventually causes intergranular corrosion. Chromium carbide deposition at the grain boundary is one of the key factors in assessing the rate of intergranular corrosion. SEM analysis by [PERSON] et al. [41] showed that the amount of chromium carbide deposits in the grain boundaries of AM 316L is substantially lower than that of the wrought stainless steels.