An Interactive Guide to Industrial Valve Testing
Explore the critical differences between structural integrity and performance tests for industrial control valves.
Strength vs. Performance: The Core Distinction
Valve testing isn't one-size-fits-all. The two primary tests answer fundamentally different questions about a valve's fitness for service. This section provides a direct comparison of their purpose, procedure, and criteria.
Hydrostatic Shell Test
- 🎯Purpose: To verify the structural integrity and strength of the valve's pressure-containing shell (body/bonnet).
- 🔧Target: Valve body, bonnet, and external static seals.
- ↔️Valve Position: Partially open, to pressurize all internal cavities.
- 💨Test Pressure: High pressure: typically 1.5 times the valve's rated Cold Working Pressure (CWP).
- 💧Test Fluid: Almost always a liquid (water) for safety.
- ✅Acceptance: Zero visible leakage from the pressure boundary; no structural deformation.
- 📚Standards: ASME B16.34 & API 598.
Seat Leakage Test (Closure Test)
- 🎯Purpose: To quantify the shutoff performance of the valve's internal sealing mechanism (seat/plug).
- 🔧Target: Internal closure element (plug, ball, disc) and seat ring interface.
- ↔️Valve Position: Fully closed, with specified actuator thrust applied.
- 💨Test Pressure: Varies by class; can be low or high pressure.
- 💧Test Fluid: Can be a liquid (water) or a gas (air, nitrogen).
- ✅Acceptance: An allowable leakage rate defined by a specific classification.
- 📚Standards: ANSI/FCI 70-2, IEC 60534-4, API 598.
Deep Dive: The Hydrostatic Shell Test
This test is the first line of defense against catastrophic failure. It validates that the valve's body can withstand pressures far exceeding its normal operating conditions, ensuring it won't rupture in service. Explore the procedure and pressure requirements below.
Hydrostatic Test Procedure at a Glance
Preparation
Valve is cleaned, unpainted, and mounted. The closure element is set to partially open.
Execution
System is filled with water, vented of all air, and slowly pressurized to the target pressure.
Inspection
During a hold period, the valve is visually inspected for any leaks, weeping, or distortion.
Visualizing the Safety Factor
The test pressure isn't arbitrary. Standards like API 598 mandate testing at 1.5 times the valve's pressure rating at ambient temperature (CWP), as defined by ASME B16.34. This chart illustrates the significant safety margin being verified.
Deep Dive: The Seat Leakage Test
After confirming strength, the focus shifts to performance. This test quantifies how well a valve shuts off flow. Unlike a simple pass/fail, it classifies leakage into different levels, allowing engineers to match a valve's shutoff capability to the specific needs of the process.
Interactive Leakage Class Explorer
Note: Class I is an agreement between user and manufacturer with no required test and is not shown. Chart is for illustrative comparison of relative tightness.
Which Seat Leakage Standard Should You Use?
This is one of the most critical and misunderstood decisions in valve specification. The choice is not a preference—it's dictated by the valve's function. Use this tool to get a clear recommendation.