: Provides formulas to size relief valves for liquid-filled vessels where temperature changes could cause thermal rupture. Depressurizing Systems

If you have API 521 (6th Ed), you effectively have ISO 23251. However, most international projects and European regulators require the ISO version specifically.

The standard outlines detailed mathematical formulas for calculating the required relief area. These calculations vary depending on whether the fluid is a vapor, a liquid, or a two-phase (multi-phase) mixture. 3. Disposal Systems

Useful for European engineers seeking national adoptions (e.g., BS EN ISO 23251).