## 6 Risk-Based Qualification of AM Process  
Additive technology is in its growing stage, and variability in AM machines and equipment can lead to inconsistency in the microstructure, the existence of defects, and uncertainties in the mechanical and corrosion performance of the finished parts. While additively manufactured components may have different applications, the criticality of active damage mechanisms in different operating conditions can be different. For example, porosity type defects are critical for sour service applications and in conditions where the fatigue mechanism is active, such as in low-diameter piping branches under vibrations. Therefore, it is a worthy and economical method to set the scope of the qualification activities based on the severity of the actual operating condition. A risk-based qualification process helps to reduce the qualification costs by concentrating on the most critical damage types and less on low-risk conditions [43]. Qualification activities aim to reduce the risk of the presence of defects in the material and ensure that the components are produced based on the customer's requirements. A risk-based qualification process defines the scope of the inspection, types of real-time monitoring, control techniques, and also the material inspection methods used based on the risk of the active damage mechanisms. In this process, risk is defined as the product of the probability of an error (POE) and the consequence of an error (COE). \begin{table}
\begin{tabular}{c c} \hline \hline
**Corrosion Mechanism** & **Susceptibility of AM 316L in Comparison to Wrought 316L** \\ \hline General corrosion & Improved \\ Pittsing & Contradictory reports \\ CLSCC & Not reported \\ Localized corrosion & Improved \\ Intergranular corrosion & Improved \\ Hydrogen-induced cracking (HIC)/Sulfide stress cracking (SSC) & Not reported \\ CO\({}_{2}\) corrosion & Not reported \\ Fatigue resistance & Decreased \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Comparison of the corrosion susceptibility of additively manufactured 316L and wrought 316L material grade. Figure 3 shows different steps in the risk-based qualification process. As is clear, the main steps include damage mechanism identification and the development of an inspection and test plan (ITP). The risk level of the active damage mechanism plays a vital role in the definition of the inspection and test plan for the component. In this process for high-risk categories, ITPs are developed using advanced test methods and considering the extended scope of inspections. However, less expensive inspection and test methods are considered for low-risk damage categories. For this reason, the inspection and test methods can be categorized into three levels, such as the example provided in Table 6. In this example, category A relates to inspection and test methods with the capability to identify 80% of possible errors and defects, while category B methods include inspection and test methods capable of identifying errors and defects with certainty between 60 and 80%, and finally, category C include the methods which are able to identify errors and defects with certainty between 40 and 60%. The purpose of the risk-based qualification process is to reduce the risk of the presence of unacceptable defects in a component. According to Figure 3, at the end of the qualification process, the appraiser would assess if the risks are in a tolerable range or not. If the answer is no, it is necessary to review all steps and make corrections where required until the component achieves an acceptable performance. In this procedure, all steps except the execution of the qualification plan can be performed offline and are based on available technical data. The goal of the qualification plan is to keep the scope and number of tests as minimal as possible. While the scope and number of tests affect the cost of the qualification job, it is the type and method of the inspection that dictates the number of inspection stands in the execution stage.