✅ Purchase the official PDF from MSS (or an authorized reseller like Techstreet or IHS) – those contain properly screened defect images. Free scans from unknown sources are unreliable.

To ensure uniformity and safety across manufacturing processes, the Manufacturers Standardization Society (MSS) of the Valve and Fittings Industry developed the .

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The core of MSS SP-55 is its collection of reference photographs (or electronic images). The standard categorizes surface irregularities into distinct types. For each type, the standard provides four levels of severity:

While MSS SP-55 is the cornerstone of visual casting inspection, it is frequently paired with other international standards to form a complete Quality Control Plan (QCP):

If you need assistance aligning this with like ASME B16.34 or ASTM?

Acceptable only if they do not weaken the section or cause leakage. The PDF’s photographs show maximum allowable density and size.

Translate the PDF into a simple checklist:

It defines what constitutes acceptable and unacceptable surface imperfections, allowing for visual comparison.