The standard is one of the most important quality benchmarks in the valve and piping industry. First adopted in 1961, this document provides a uniform, visual method for evaluating surface irregularities in castings used for valves, flanges, fittings, and other piping components. With the recent release of the ANSI/MSS SP-55-2025 edition, the standard has been updated and expanded, making it more relevant than ever for manufacturers, inspectors, and engineers worldwide.
– Linear fractures caused by internal or external stresses. Type II: Shrinkage – Voids left during metal solidification. Type III: Sand Inclusions – Sand trapped within the molten metal. Type IV: Gas Porosity – Voids caused by entrapped gas. Type VII: Overlaps & Folds – Incomplete fusing of molten metal surfaces. For each type, the standard provides examples of both acceptable unacceptable mss sp-55 standard pdf
Surface defects aren't just about looks. A small crack or "hot tear" can become a point of failure under pressure. MSS SP-55 ensures that every inspector, manufacturer, and end-user is literally on the same page by using a set of . The standard is one of the most important