Valve Body Casting Defects and Quality Control

Cast valve bodies are subject to a range of internal and surface defects that can compromise pressure integrity, reduce fatigue life, and cause premature failure. Understanding casting defects, their causes, and appropriate inspection methods is fundamental to valve procurement and quality assurance programs.

Common Casting Defects

• Porosity: gas bubbles trapped during solidification create voids ranging from microporosity to macroscopic holes; detected by radiographic testing (RT) or computed tomography (CT)

• Shrinkage: internal cavities formed as metal contracts during cooling; most severe in thick sections and near the thermal center of the casting

• Hot tears: cracks formed during solidification when thermal stress exceeds the strength of semi-solid metal; typically found at section changes and near gates

• Cold shuts: surface defects caused by two streams of metal meeting without proper fusion; visible as seams or laps

• Misruns: incomplete filling of the mold cavity due to insufficient metal temperature or flow velocity

Non-Destructive Testing Methods

Radiographic testing (RT) per ASME B16.34 Appendix D provides a volumetric examination that detects internal porosity, shrinkage, and cracks. Acceptance criteria are defined in ASME E446 for steel castings by severity level. Ultrasonic testing (UT) per ASTM A609 is preferred for thick sections (above 50 mm) where X-ray penetration is limited. Magnetic particle testing (MT) and liquid penetrant testing (PT) detect surface and near-surface defects in accessible areas.

Radiographic Acceptance Criteria

• Class 1 (highest quality): only category A-1 linear indications and B-1 rounded indications allowed

• Class 2: typical for ASME Class 600 and above valves, tighter limits on shrinkage and porosity

• Class 3: acceptable for Class 300 and below general service valves

• Weld repair areas require same RT quality level as adjacent base metal

Weld Repair of Casting Defects

Weld repair is permitted by ASME B16.34 subject to pre-approved weld repair procedures, qualified welders, post-weld heat treatment equivalent to the original casting heat treatment, and re-examination of the repaired area to the same acceptance criteria. Major repairs (more than 20 percent of wall thickness) require engineering review and customer notification.

Procurement Controls

Specify casting quality requirements in the purchase order, referencing ASME MSS SP-55 for visual inspection, applicable RT class per ASME B16.34, and any additional NDE requirements. Require material test reports (MTRs) per EN 10204 3.1 or 3.2 for all pressure-containing castings. Third-party inspection at the foundry is recommended for critical or large-diameter valves.