With the advancing capabilities for fabricating metal components using Additive Manufacturing (AM) (3D-Printing), designers are looking for ways to utilize the AM capabilities in new applications. A potential application for AM is the fabrication of pressure-retaining components or fittings with complex geometries that are difficult to fabricate using traditional methods (e.g., machining and welding). Using AM parts for pressure-retaining components presents new challenges to ensure the material will perform reliably and predictably to meet the specifications of the design. This paper summarizes work performed on 316L stainless steel vessels fabricated by AM. The AM vessels were evaluated before and after Hot Isostatic Pressing (HIP) post-processing, including destructive examination to evaluate the grain structure and strength. Tensile tests on baseline samples and samples subjected to HIP were compared to a test sample machined from conventional stainless material and leak tests were performed on an AM vessel using helium as a tracer gas. The role of the HIP post-processing is to reduce the metal porosity and other defects inherent in the 3D-metal printing process. HIP post-processing allows the finished product to achieve the strength, reliability and leak tightness requirements of national consensus standards, such as the American Society of Mechanical Engineers Boiler and Pressure Vessel Code.