What are the steps involved in a boiler hydrostatic test?

A boiler hydrostatic test is a pressure testing method. Since industrial boilers operate continuously under high-temperature and high-pressure conditions, to ensure absolute operational safety, new boilers or those that have undergone major overhauls must undergo an overpressure test at 1.25 to 1.5 times the working pressure, while routine maintenance requires a working pressure test.

Boiler hydrostatic testing is primarily divided into four stages:

1. Preparation & Isolation

System Isolation: Disconnect or isolate pipelines, pressure switches, water columns, and precision instruments such as pressure gauges that cannot withstand high test pressures.

Installation of Pressure Gauges: Install at least two pressure gauges that have passed metrological calibration and have the same measurement range.

2. Filling and Venting

Control Water Temperature: Fill the system with clean, softened water at a temperature between 20°C and 70°C. Water temperatures that are too low or too high can adversely affect the boiler.

Venting: Open the vent valve on the boiler and slowly fill from the bottom until a steady stream of water flows continuously from the vent valve without bubbles, then close the valve.

3. Gradual Pressurization and Pressure Holding

Pressurize in stages: Start the test pump and control the pressurization rate at 0.2–0.3 MPa/min. Pause and inspect when the pressure reaches 10% of the working pressure; after confirming no abnormalities, continue pressurizing to the rated working pressure.

Overpressure Test (as applicable): For newly installed or overhauled boilers, continue increasing pressure to the test pressure (typically 1.25 or 1.5 times the working pressure). Shut off the test pump and maintain the pressure for 20 minutes. During this period, the pressure gauge needle must remain stationary.

4. Pressure Relief and Comprehensive Inspection (Inspection & Acceptance)

Slowly reduce the pressure back to the rated working pressure, after which inspectors may enter the site.

Acceptance Criteria: No water droplets or mist on the metal walls or welds of any pressure-bearing components; no water leakage from bell mouths or flanges; no residual deformation visible to the naked eye on pressure-bearing components.