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Oil tank floor leak test method

2019/8/27

The tank floor must be leak tested after it has been built and repaired. Commonly used methods are: vacuum chamber leak test, magnetic flux leakage inspection, gas leak detection and water filling test.


Vacuum leak test


The thin plate is used to make a bottomless rectangular box. The top of the box is tightly embedded with a thick glass. The outer periphery of the box is covered with a non-breathable sponge rubber, so that the box is tightly fastened to the bottom plate. The box is painted with a reflective white paint. The box is equipped with a suction short pipe and an intake valve. When testing the weld, first apply soapy water on the weld, then buckle the vacuum box, and use a vacuum pump to draw the vacuum into the chamber at 55 kPa. Observe the presence or absence of bubbles in the box. If there are bubbles, mark it and weld it. Make up.


Often used to inspect welds, especially circumferential welds, not often used throughout the tank bottom.


2. Gas detection method


The helium leak detector is also used for leak detection of buried pipelines and tank bottoms. It does not need to clean the oil when detecting buried pipelines. The bottom of the tank is tested by first injecting helium into the tank bottom and then detecting the presence of helium inside the tank. This approach proved to be very effective at leak location. But it needs to drill holes in the bottom of the tank to inject gas. The most important issue is that the gas must be able to diffuse to all areas of the bottom of the tank, but this is not possible due to the impediment and impediment infiltration. Gas diffusion will encounter two problems:


The weight of the tank wall makes it difficult to diffuse the gas to the edge portion of the tank;


2 When a viscous product has leaked at the bottom of the tank, it will prevent the movement of the gas. The problem of gas diffusion can result in the inability to detect all leaks.


3. Ammonia leakage method


1 Clay the gap between the bottom plate and the foundation along the bottom of the tank, but leave 4 to 6 holes symmetrically to check the distribution of ammonia.


2 In the center and the periphery of the bottom plate, 3 to 5 holes with a diameter of 18 to 20 mm should be uniformly opened, and a steel pipe with a diameter of 20 to 25 mm should be welded and connected to the cylinder of the ammonia gas cylinder with a hose.


3 Apply a phenolphthalein-alcohol solution to the bottom plate weld. Its composition (mass ratio) is: phenolphthalein 4%, industrial alcohol 40%, water 56%. When the weather is cold, the alcohol concentration should be increased appropriately.


4 Pass the ammonia gas under the bottom plate, check with the test paper on the hole in the clay ring, verify that the ammonia gas has been distributed evenly under the bottom plate, and then start to inspect the surface of the weld. At this time, brush the phenolphthalein-alcohol solution on the weld. When it is red, it means that ammonia gas leaks out, and the leak is marked with lead oil.


When the bottom plate is connected to ammonia gas, it is strictly prohibited to move nearby. Before the welding of the bottom plate, the ammonia gas must be blown off with compressed air, and the welding can be repaired after passing the inspection.


4. Leak detection in hydraulic test


The hydrostatic test is a structural test that is only used when large repairs are made near the tank wall. Dyes can be used to help people locate leaks. But even if a dye is added to the water, it cannot be used as a leak detector. Most of the leakage at the bottom of the tank penetrates beyond the wall of the tank, but penetrates under the soil at the bottom of the tank and is not visible outside the tank. Mass measurement in the hydrostatic test makes it an effective leak detection method. It takes 2 to 3 days to determine if there is a leak in the tank. Only 6 to 10 feet of water can be used in the hydrostatic test.


5. Magnetic flux leakage scanning


The corrosion condition of the metal tank bottom plate can be used as a special detection instrument-magnetic eddy current scanner. The principle is magnetic flux leakage method. The instrument is equipped with a strong magnet. The magnet is equipped with a magnetic field strong sensor. When the bottom plate has defects, the magnetic field distribution It changes and the sensor detects this change in the magnetic field. The instrument accurately measures the depth, area and length of the crack.


Magnetic eddy current scanners can detect most of the bottom of the tank, but may miss areas near the tank wall and some obstacles. It is not as accurate as ultrasonic. It is impossible to detect the entire bottom of the tank without any omissions. The magnetic flux leakage and ultrasonic technology require that the bottom of the tank be kept dry, free from dust and corrosion products.


Tank bottom leak detection sequence: First, the entire tank bottom is detected by a magnetic flux leakage scanner, then the suspicious area is detected by ultrasonic waves, then the bottom plate weld is detected by a vacuum box, and the weld seam between the bottom plate and the tank wall is detected by magnetic powder or liquid penetrant.