Pressure Ratings of Valves – Shell Strength & Seat Tightness (ASME B16.34).

Pressure Ratings of Valves – Shell Strength & Seat Tightness (ASME B16.34).

In piping systems, the pressure rating of a valve defines the maximum internal pressure it can safely handle at a given temperature.

ASME B16.34 is the key standard that governs these ratings for steel valves.

A. Shell Strength

1. The ability of the valve body and bonnet to withstand internal pressure without failure.

2. Verified through hydrostatic shell tests (typically 1.5 × rated pressure as per ASME B16.34).

3. Ensures the valve maintains structural integrity under maximum pressure conditions.

B. Seat Tightness

1. The capability of a valve to prevent leakage when fully closed.

2. Tested using low-pressure air/gas or high-pressure hydro tests.

3. Tightness classes are specified in API 598 or ISO 5208.

C.  Pressure Rating Classes (ASME B16.34)

1. Common classes: 150, 300, 600, 900, 1500, 2500.

2. Allowable pressure decreases as temperature increases.

3. Material selection directly affects the allowable pressure.

D.  Engineering Tip:

1. Always refer to the ASME B16.34 pressure–temperature tables and ensure both shell strength and seat tightness meet or exceed your system’s operating requirements.