It is referenced extensively in valve and piping specifications (such as API 600 and ASME B16.34) to define what a "commercially smooth" casting looks like.
Always obtain the official MSS SP55 standard PDF from authorized resellers like IHS Markit, Techstreet, or directly from MSS. Avoid scanned, watermarked, or outdated free versions, as they often lack the critical photographic plates in sufficient resolution. mss sp55 standard pdf work
Acceptable only if they do not weaken the section or cause leakage. The PDF’s photographs show maximum allowable density and size. It is referenced extensively in valve and piping