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In the pulse pressure life test of an electric water heater inner tank, the equipment frequently alarms "pressure holding failure," but no water leakage is visible on the naked eye. How to troubleshoot?
1. Analysis of the Cause of the Problem
The inner tank of the electric water heater is the most important pressure-bearing component of the entire machine. It endures long-term tap water pressure and alternating temperature differences between hot and cold, making it prone to leakage, deformation, cracking, and other issues. The situation you encounter—"equipment alarm but no visible leak to the naked eye"—usually does not mean "no leak," but rather a very low leak rate (micro-leak), or the leak occurs in an area difficult to reach with regular visual inspection. Common causes include:
Microcracks in welds: The longitudinal welds or circumferential welds of the inner tank develop hair-thin microcracks under pulse cycling stress, with a very low leakage rate (several milliliters to tens of milliliters per hour). After leakage, water may be absorbed by the outer insulation layer of the inner tank and will not flow directly to the surface to form visible water stains.
Microcracks in the enamel coating cause electrochemical corrosion: The inner enamel coating shows tiny damage during pressing, and the exposed metal substrate undergoes electrochemical corrosion in water containing electrolytes, resulting in pitting. Corrosion products may temporarily block micropores to stop leaks, only to be flushed again in the next cycle, resulting in intermittent leakage.
Deformation or improper installation of sealing rings: The sealing ring at the inlet/outlet of the inner tank permanently deforms during long-term cyclic pressure, producing extremely fine micro-leakage channels. Because water may seep into the gaps of the flange threads and be locked by capillary action, it will not drip immediately.
Thread leakage at pipeline joints: Extremely small thread leakage at the connection between the inner tank and the inlet/outlet pipe requires specific detection methods to locate the area.
Leakage in the testing equipment itself: The pressure testing equipment (including pipelines, joints, control valves, and pressure sensor interfaces) may have leak points inherently, causing the system to fail to hold pressure and be mistakenly identified as inner tank leakage.
2. Detailed Inspection and Operational Methods
Step 1: Verify whether the inner liner leaks or equipment leaks (most important)
Operating method: Completely isolate the inner tank from the pressure test pipeline (remove the inlet and outlet connecting hoses), and use a dedicated threaded sealing plug to seal all the inner tank interfaces. Then, connect the inner tank separately to the compressed air source, introduce 0.4~0.6MPa compressed air, and immerse the entire inner tank in the water tank (note: the inside of the tank must be filled with water and exhausted before pressurizing; otherwise, changes in compressed gas volume will affect the judgment). Observe whether continuous bubbles emerge from the sink. If the inner tank itself is not leaking, it proves the problem lies in the equipment piping or interface—this method is the most straightforward "decisive judgment."
Step 2: Locate the leak point in the equipment pipelines (if the first step confirms the equipment is leaking)
Common leakage points in pressure testing equipment include:
Pressure sensor connector: Check whether the sensor interface thread is wrapped with enough raw material tape or sealant
Solenoid valve/check valve seat: After repeated on-circuit testing, particles may get stuck between the valve core and seat and cause poor sealing
High-pressure tube connections: The crimping between hose ends and metal joints is prone to micro-leakage due to aging fatigue
Quick coupling sealing ring: Frequent insertion and removal of the inner tank can cause wear on the O-ring of the quick coupling
Method to locate: Under no-load conditions (no inner tank connected), seal the end of the equipment pipeline, apply pressure to the set value according to the test procedure, hold pressure for 5 minutes, and observe the pressure attenuation curve. If the pressure drops significantly, check each of these areas one by one. Spray soapy water (or leak detect) at each joint with a spray bottle and observe for continuous bubble formation.
Step 3: Locate the inner pot's micro-leakage (if the first step confirms a leak).
If the bubble immersion method confirms leakage in the inner pot but the exact location is not visible to the naked eye, the following methods can be used:
Dry Pressure Holding Method: Wipe the inside of the inner tank clean and keep it dry, introduce compressed air at 0.8~1.0 MPa, and hold pressure for 30 minutes. Apply specialized gas leak detection sprays (bubble leak detection fluid) to suspicious areas (welds, pipe openings) to observe for bubble formation.
Differential pressure detection method (high precision): Equipped with a high-precision differential pressure sensor (resolution 0.1Pa) on the pressure testing equipment, the inner tank under test is connected in parallel with a known leak-proof standard reference chamber. After applying the same test pressure, isolation is maintained, continuously monitoring differential pressure changes between the two chambers. If the differential pressure exceeds 10Pa within 10 minutes, a micro-leakage is identified. This method can detect trace leaks that traditional holding methods cannot detect.
Stained Penetrant Testing (for welds): Spray red or fluorescent colored penetrant at the weld seams on the inner wall of the inner liner, let it stand for 10 minutes, then clean and spray a developing agent. Where there are cracks, red streaks will clearly appear. This method is very suitable for detecting microcracks that are difficult to observe with the naked eye.
Step 4: Address each leakage cause separately
| Causes of leakage | Handling methods |
|---|---|
| Microcracks in the weld seam | If the quantity is small, professional welders can grind the cracks and perform argon arc welding for repairs, followed by X-ray inspection and pressure verification after welding; If there are many cracks or sensitive locations, the inner pot should be scrapped immediately |
| The enamel coating is slightly damaged | If the enamel layer on the inner tank surface is damaged and cannot be repaired on site, it must be returned to the enamel manufacturer for re-enameling |
| The sealing ring is aging and deforming | Replace with the same model EPDM sealing ring (note temperature resistance rating≥ 120°C), and apply a small amount of silicone grease during installation to ensure sealing |
| Thread leakage at the interface | After disassembly, remove the old sealing material, rewrap the raw material tape (no less than 5 turns), and evenly apply pipe thread sealant |
| Equipment joint leakage | Replace worn O-rings or quick coupling assemblies; tapered threaded joints need to be rewound with raw material tape and sealant |
Step 5: Establish a regular preventive maintenance plan
Before each test, check the integrity of all quick coupling O-rings, and replace them immediately if hardened or deformed are found.
Perform an empty pressure self-check on the pressure testing equipment once a month to confirm that there are no leaks in the equipment itself.
Every six months, the sealing plug test verifies the overall airtightness of the equipment pipelines.
Establish equipment operation logs to record holding pressure attenuation data for each test for trend analysis and early warning of potential issues.
