Visual Inspection
Welds and Connections
Carefully examine the welds on the tank body and all connection points with pipes, valves, manholes, etc. Welds should be continuous and uniform, free of defects such as porosity, slag inclusions, or cracks. Sealing gaskets at connection points must be intact without signs of aging, deformation, or damage.
Tank Surface
Inspect the tank surface for leakage traces, such as liquid seepage, crystallization (if the tank previously stored substances prone to crystallization), or rust stains (if the leak involves water or corrosive liquids).
Even minor leaks may leave visible marks on the tank surface over time. For chemical storage tanks, these marks may appear as discoloration or signs of chemical corrosion.
Pressure Testing
Positive Pressure Test
Charge the tank with pressurized gas (typically air or nitrogen), then close the inlet valve. For tanks with lower design pressures (e.g., atmospheric to low-pressure tanks), the test pressure is generally 1.2 to 1.5 times the working pressure. For medium- or high-pressure tanks, determine the test pressure according to relevant standards and design requirements.
Monitor pressure changes inside the tank using a high-precision pressure gauge. Within the specified test duration (generally determined by tank size and application, ranging from 1 to 24 hours), if the pressure drop remains within permissible limits (e.g., not exceeding a certain value per hour, such as 0.05 MPa, with specific values based on the tank's design standards), this indicates satisfactory tank sealing performance.
The soap bubble method may also be used for supplementary inspection. Apply soap solution to potential leakage points such as welds, joints, and valves. The formation of bubbles indicates a leak at that location.
Negative Pressure Test (Applicable to certain tanks requiring negative pressure resistance)
Evacuate air from the tank to create a negative pressure environment, reaching the specified test pressure (typically 1.2–1.5 times the design negative pressure). Monitor pressure changes with a pressure gauge, observing pressure recovery during the test period.
If pressure recovery exceeds permissible limits, it indicates tank leakage and poor sealing performance.
Liquid Level Test (Applicable to Liquid Storage Tanks)
Static Liquid Level Observation
Fill the tank to the specified liquid level (e.g., full capacity or a marked level), then allow it to stand undisturbed for a period (e.g., 24–48 hours). Observe whether the liquid level decreases. If the level drops significantly beyond normal evaporation rates (evaporation must be considered for open tanks; for sealed tanks, normal evaporation is negligible), this indicates tank leakage and poor sealing performance.
Dynamic Liquid Level Observation (Applicable to Tanks with Filling/Discharging Operations)
During normal filling and discharging operations, verify whether liquid level changes correspond to the volume of material being added or removed. If the liquid level rises slower than expected during filling, or falls faster than expected during discharging, this may indicate leakage causing abnormal fluid loss.
Gas Detection (Applicable to Tanks Storing Special Gases or Requiring Strict Leak Prevention)
Sniffing Method (Applicable to Odorous Gases)
For tanks storing odorous gases (e.g., ammonia, hydrogen sulfide), conduct visual inspections around the tank perimeter to detect potential gas leaks. Operators can use their sense of smell for preliminary leak detection, though this method lacks precision and poses safety risks when dealing with toxic gases.
Gas Detection Instrument Method
Employ specialized gas detection instruments, such as combustible gas detectors or toxic gas detectors. Move the detector probe over potential leakage points on the tank, including weld seams, connection points, and valves.
If the detector sounds an alarm, it indicates a gas leak at that location and poor tank sealing performance. This method can accurately detect extremely low concentrations of leaked gas, making it a relatively reliable approach for assessing seal integrity.
