Anvil 312822802 3 in malleable iron union class 300 FNPT

Three-Inch Class 300 Malleable Iron Union

This three-inch union joins pipe sections with female NPT threads and is rated Class 300 for heavy-duty service. Malleable iron construction resists shock and vibration in steam, water, oil and gas lines. FM Approved and UL Listed, it meets ASME B 16.39 for code-compliant installations. Brass seat material provides a reliable seal across the full temperature range.

Sustained Load Behaviour

At 550 °F saturated steam the fitting holds 230 psi without creep, and at 150 °F it withstands 600 psi continuously. The malleable iron body distributes thermal stress evenly during long heating cycles, while the brass seat maintains tightness through repeated expansion and contraction. Hex size of 3 7/8 in allows firm make-up torque without rounding, preventing leak paths under cyclic pressure.

Upgrade Path and Fit

Replaces lower-class unions or threaded couplings that cannot meet Class 300 pressure requirements. The jump is worth it when system design calls for 600 psi at 150 °F or 230 psi steam at 550 °F and code demands FM and UL marks. Not suited for lines requiring socket-weld or flanged connections, or for diameters other than three-inch FNPT.