Welding terminology: Who can explain the watertightness of flaw detection?

[Crack detection] detects cracks or defects in metal materials or parts. Commonly used flaw detection methods include: X-ray flaw detection, ultrasonic flaw detection, magnetic particle flaw detection, penetrant flaw detection (color flaw detection), eddy current flaw detection, gamma ray flaw detection, fluorescent penetrant inspection and so on. Physical flaw detection is nondestructive flaw detection without chemical changes. The ship structure of dense cabin was invented in the Tang Dynasty, and was widely used in seagoing ships and some inland ships after the Song Dynasty. The so-called watertight cabin is to divide the cabin into unconnected cabins with bulkhead plates. The number of carriages is 13, and there are also eight. This ship structure is a great invention of shipbuilding in China, and it has many advantages. The ancient ship unearthed in Quanzhou, Fujian Province has 13 cabins. First of all, because the cabins are closely spaced, even if one or two cabins are damaged and water enters, the water will not flow to other cabins. As a whole, the ship still maintains considerable buoyancy and will not sink. If there is too much water, the ship will not be able to support it. As long as the cargo is abandoned and the load is reduced, it will not sink to the bottom of the sea soon. If the ship is not seriously damaged and there is not much water inflow, as long as the goods in the water inflow area are removed, the damaged place can be repaired without affecting the ship's continued navigation. If the water is serious, you can also drive to the nearest port or land for emergency repair. Therefore, the watertight compartment not only improves the anti-sinking performance of the ship, but also increases the safety performance of navigation. Secondly, the ship is divided into compartments, so it is more convenient to load, unload and manage goods. Different shippers can load and unload chemicals in a single cabin at the same time, which improves the loading and unloading efficiency and is convenient for management. In addition, because the bulkhead is closely connected with the hull plate, it plays a role in strengthening the hull, which not only increases the overall transverse strength of the ship, but also replaces the process of rib reinforcement and simplifies the shipbuilding process. Because of these advantages, watertight cabin structure is widely welcomed. 1974 Southern Song Dynasty ships unearthed in Houzhu, Quanzhou Bay, 1976 Yuan Dynasty ships discovered in Xin 'an, South Korea, and 1982 Southern Song Dynasty ships discovered in Fashi, Quanzhou all adopt watertight compartments. Xin 'an seagoing ship has 8 cabins, and the French seagoing ship also has about 8 cabins. The watertight compartment structure adopted by Chinese ships has long been appreciated by foreign countries. In Yuan Dynasty, the Italian executor Kyle Poirot described China's ships in detail in his travel notes. British Bentham once inspected the ship structure in China, improved the shipbuilding technology in Europe, and introduced the watertight cabin structure into China. In A.D. 1795, he was commissioned by the British Royal Navy to design and manufacture six new ships. In his paper, he said that the ship he built "has bulkheads to increase strength, which can protect the ship from flooding and sinking, just as China people do now." Later, Mrs. Bentham pointed out in her biography for her husband: "This is not the invention of General Bentham. He himself has publicly said,' This is what China people do today, just like what ancient China people did.' " Since then, China's advanced watertight cabin structure has been gradually absorbed by shipbuilding technology in Europe and even the world, and it is still an important structural form in ship design.