Valve Standard Reference
MSS SP-55
ManufacturersQuality Standard for Steel Castings and Forgings for Valves, Flanges, Fittings and Other Piping Components
MSS SP-55 is the visual quality standard used to evaluate steel castings for valves, flanges, and fittings.
Overview — MSS SP-55
MSS SP-55 is the visual quality standard used to evaluate steel castings for valves, flanges, and fittings. It provides a photographic reference chart showing acceptable and unacceptable casting surface defects categorised by type (porosity, shrinkage, cracks, laps) and severity. MSS SP-55 is universally referenced in purchase orders for cast steel valve bodies and bonnets to define the permissible surface quality before painting or coating.
Scope
Applies to all steel castings used in valve bodies, bonnets, closures, and other pressure-containing components. Covers carbon steel (A216 WCB), alloy steel (A217 WC6, WC9), and stainless steel (A351 CF8M) castings. Defines 10 defect types with photographic reference standards.
Applicable Valve Types
All cast steel valve types
Applicable Pressure Classes
Key Requirements — MSS SP-55
10 defect type categories: porosity, shrinkage, cracks, cold shuts, laps, shifts, fins, swells, inclusions, rough surfaces
Each defect type rated on a 1–5 scale of severity (1 = best, 5 = worst)
Purchaser specifies maximum acceptable severity for each defect type
Typical acceptance criteria: Type I (linear) max grade 3; Type II (non-linear) max grade 2
Castings not meeting the agreed criteria must be repaired by welding per ASME or rejected
Inspection performed on as-cast or blast-cleaned surface — not painted
Testing Requirements — MSS SP-55
Visual inspection against MSS SP-55 photographic reference chart
100% visual inspection of all critical areas (flow path, seating surfaces)
Documentation Required for MSS SP-55 Compliance
Visual inspection record referencing MSS SP-55 acceptance criteria
Foundry inspection report
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