MSS SP-25

Covers — the marking of new valves, fittings, flanges, and unions in threaded, soldered, brazed, flanged, or welded piping connections. Markings identify the manufacturer, rating/class, materials of construction, size, and special service limitations.

Does NOT cover (exclusions) — the following are governed elsewhere:

• Traceability records and material certification content → EN 10204 / ASME material specs.
• Pipe/tube marking → the applicable ASTM/API product specification.
• Positive material identification programs → API RP 578.

SP-25 standardizes what and how to mark; it does not itself grant any rating.

SP-25 sets minimum requirements for component marking:

• Content — manufacturer's name/trademark, pressure-temperature class, material designation, and nominal size.
• Method — cast, forged, stamped, or applied markings that remain legible for the service life.
• Consistency — a uniform scheme so buyers and inspectors read the same fields across manufacturers.

MSS SP-25 gives the industry one consistent language for marking valves, fittings, flanges, and unions. By fixing which fields must appear — manufacturer, class, material, size, and service limits — and how they are applied, it lets receiving inspectors and installers verify a component without the manufacturer's catalog.

Product design standards reference SP-25 instead of repeating marking rules, so a valve "marked per MSS SP-25 and rated to B16.34" is fully identified from the part alone.

Engineering Note: On receiving inspection, missing or unreadable SP-25 markings are grounds for rejection — verify markings against the purchase order and material certificates.