Valve Body Casting Inspection and Quality Assurance

Valve body castings must meet strict quality standards to ensure pressure integrity and long service life. Inspection methods detect internal defects that could lead to premature failure.

Common Casting Defects

Casting defects in valve bodies include porosity, shrinkage, cold shuts, inclusions, and hot tears. These defects reduce wall thickness and can initiate cracks under pressure cycling.

• Porosity: Gas bubbles trapped during solidification

• Shrinkage: Voids formed as metal contracts during cooling

• Cold shut: Incomplete fusion between two streams of molten metal

• Inclusions: Slag or sand particles entrapped in the casting

• Hot tear: Crack formed during solidification due to thermal stress

Non-Destructive Examination Methods

NDE methods detect defects without damaging the casting. Radiography and ultrasonic testing are most common for valve body inspection.

• Radiographic testing (RT): X-ray or gamma ray reveals internal voids and inclusions

• Ultrasonic testing (UT): Detects subsurface flaws and measures wall thickness

• Magnetic particle testing (MT): Surface and near-surface defects in ferromagnetic materials

• Liquid penetrant testing (PT): Surface-breaking defects in any material

• Visual examination (VT): Preliminary check for obvious surface defects

Acceptance Criteria and Standards

ASME B16.34 references ASTM standards for casting quality. MSS SP-55 provides a photographic guide to surface quality levels for valve castings.

• ASTM E446: Reference radiographs for steel castings up to 2 inches thick

• MSS SP-55: Visual quality standards for steel castings

• ASTM A703: Supplementary requirements for pressure-containing castings

• Severity levels: Level 1-5 in ASTM radiograph standards; specify maximum acceptable level

Casting Repair and Weld Overlay

Minor casting defects can be repaired by approved welding procedures. Weld repairs must be post-weld heat treated if required by material specification and re-examined.

• Extent of repair: Define maximum repaired area as percentage of wall cross-section

• PWHT requirement: Depends on material and thickness; check ASME code

• Re-examination: Full NDE on repaired area after heat treatment

• Documentation: Repair records must be maintained with casting traceability