The standard, titled "Quality Standard for Steel Castings for Valves, Flanges, Fittings, and Other Piping Components—Visual Method for Evaluation of Surface Irregularities," is a critical industry guideline published by the Manufacturers Standardization Society (MSS)0;91;. It provides a standardized visual methodology for assessing the surface quality of steel castings used in piping systems. 0;92;0;a1; 0;baf;0;d1; 1. Scope and Purpose
As of this writing (2025), the active revision is MSS SP-55 – 2022 (formerly 2017, 2011). Always check MSS.org for updates. mss sp-55 standard pdf