Hydrotesting Procedure
Hydrotesting, or hydrostatic testing, is a procedure used to verify the integrity and strength of piping systems, pressure vessels, or components by filling them with a liquid (typically water) and pressurizing to a specified target value for a defined amount of time.
Below is an outline of what a hydrotesting procedure may contain when it is aligned with standards like ASME B31.3 for process piping:
Example Hydrotesting Procedure Contents
Planning and Preparation:
Review Requirements: Confirm the test pressure, typically 1.5 times the design pressure for ASME B31.3 systems, adjusted for temperature and material properties (per ASME B31.3, Section 345.4). Most often this will be found on the piping line list provided in the contract.
Develop Test Boundaries: Document the scope, test boundaries, pressure, duration, fluid, safety measures, and inspection requirements. Include a test diagram showing isolation points.
Select Test Fluid: Water is the standard, and may require water quality testing before using. For sensitive systems, use clean, potable water or specific fluids per code or client specs.
Walkdown System: Visually check welds, joints, and supports for compliance. Ensure all welds, work scope, nondestructive testing examinations are complete before testing (e.g., NDE per B31.3).
Isolate System: Install blinds, plugs, or valves to isolate the test section. Remove or isolate components not rated for test pressure (e.g., instruments, relief valves, etc.).
Setup:
Install Test Equipment: Connect pumps, pressure gauge(s) (calibrated, with range 1.5–4 times test pressure), and relief valves to protect against overpressure.
Vent and Fill: Remove air by filling the system with test fluid from the lowest point, ensuring all high points have vents to eliminate air pockets.
Check for Leaks: Perform a low-pressure pre-check (e.g., 25% of test pressure) to identify gross leaks before full pressurization.
Pressurization:
Gradual Increase: Raise pressure slowly in increments (e.g., 10% of test pressure per minute) to monitor system response and avoid shock.
Reach Test Pressure: Achieve the specified test pressure (e.g., 1.5 × design pressure per B31.3, adjusted for temperature). Hold for a minimum duration, typically 10 minutes for B31.3, or as specified.
Monitor: Continuously observe pressure gauges and system for leaks, deformation, or pressure drops.
Inspection:
Visual Examination: Check all welds, joints, and connections for leaks or signs of failure during the hold period.
Record Data: Document test pressure, hold time, ambient conditions, and any observations. Note any leaks or issues for repair and retest.
Depressurization and Draining:
Release Pressure: Slowly reduce pressure to avoid damage, using controlled venting or draining.
Drain Fluid: Remove test fluid, ensuring proper disposal, especially if additives were used.
Dry System: If required, dry the system with air or nitrogen to prevent corrosion.
Post-Test Actions:
Remove Test Equipment: Take out blinds, plugs, and temporary fittings.
Restore System: Reinstall components removed for testing (e.g., instruments).
Document: Complete test reports, including signed records of pressure, duration, and inspector approval. Retain per code or client requirements.
Repairs and Retest: If leaks or failures occur, repair (e.g., reweld, replace gaskets) and repeat the test.
Key Considerations
Safety: Hydrotesting involves high pressures, posing risks of rupture or injury. Ensure personnel are trained, barricade test areas, and follow safety protocols (e.g., PPE, emergency plans).
Code Compliance: Adhere to ASME B31.3 (or other relevant standards like B31.1, API 570) for pressure, duration, and inspection. For closure welds not hydrotested (e.g., golden welds), alternative NDE (radiography, ultrasonic) is required.
Environmental: Manage test fluid disposal to avoid contamination, especially with chemical additives.
Exceptions: For systems where hydrotesting is impractical (e.g., due to contamination risks), pneumatic testing or alternative methods may be used with stricter safety controls (per B31.3, Section 345.5).
Example for ASME B31.3
Test Pressure: PT = 1.5 × PD × (ST/SD), where PT = test pressure, PD = design pressure, ST = allowable stress at test temperature, SD = allowable stress at design temperature.
Duration: B31.3 states a minimum of 10 minutes at test pressure, followed by inspection at reduced pressure if needed.
Closure Welds: If a closure weld cannot be hydrotested, it must undergo 100% NDE (e.g., RT/UT) and meet stringent quality requirements.