Where exactly should the leak detection hole for the reinforcement ring be placed?
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API650 5.7.2.10 and GB50341 10.1.6 specify that the leak detection holes (also known as telltale holes) on the opening reinforcement rings in vertical cylindrical storage tanks should be located on the horizontal center line, as shown in the figure below; this is different from the requirement in JB/T4736 Article 5.6, which states that the screw holes should be placed at the lowest position of the shell. Why? Image: First of all, whether it is a storage tank or a pressure vessel, the small hole on the reinforcement ring serves three purposes: one is to introduce compressed air at a certain pressure in order to check the quality of the weld joints. II. It can serve to expel air during welding, removing the air from the gap between the reinforcement ring and the housing. III. During the operation of the equipment, if a leak occurs in the weld covered by the reinforcement ring, it can serve as a warning signal; therefore, the leak detection hole is also referred to as a signal hole. If the small hole needs to be connected to a compressed air nozzle, threading is required. As for small holes in things like support pads or pipe pre-welded parts, if they are used only for venting or leak detection, a simple hole is sufficient. Some argue that API650 or GB50341 place the leak detection holes on the horizontal center line rather than on the longitudinal axis, taking into account the fact that circumferential stress is greater than axial stress, thereby reducing the negative impact of the leak detection holes on the strength of the reinforcement ring. This view is debatable, as the leak detection holes are much smaller in size than the reinforcement rings ； Furthermore, the leak detection holes are usually located near the outer edge of the reinforcement ring, as the local stress generated by the openings has already diminished to a considerable extent by this point; therefore, the impact of these leak detection holes on the reinforcement effect is very limited. Japanese standards specify that leak detection holes should be placed at a 45-degree angle to the axis, which seems to balance both leak detection and minimizing the reduction in the strength of the reinforcement ring caused by the small holes.
If the manufacturing standards do not specify the location of the signal hole, it shall be placed at the lowest point of the mounting position in accordance with the reinforcement ring standards. If the manufacturing standards require something that differs from the standards for the reinforcement rings, then the requirements of the manufacturing standards shall apply.
First of all, whether it is a storage tank or a pressure vessel, the small hole on the reinforcement ring serves three purposes: one is to introduce compressed air at a certain pressure in order to check the quality of the weld joints. II. It can serve to expel air during welding, removing the air from the gap between the reinforcement ring and the housing. III. During the operation of the equipment, if a leak occurs in the weld covered by the reinforcement ring, it can serve as a warning signal; therefore, the leak detection hole is also referred to as a signal hole.
Personally, it should be placed at the lowest position so that leaks can be detected more quickly
For vertical cylinders, the leak detection holes in the reinforcement ring are located on the horizontal line at the center of the pipe connection. There are probably several reasons for this: 1. The stress experienced by the reinforcement ring of the pipe connection is the same as that experienced by the shell itself; the axial stress is half of the circumferential stress. Placing the holes horizontally results in less weakening of the reinforcement at those locations； 2. Most larger vertical tanks are placed horizontally for pressure testing; therefore, during the hydraulic test, the leak detection holes can be located at the lowest point, which makes it easier to check whether there are any leaks in the welds between the connections and the tank shell ； Regarding these two points, my view is that if there is a sufficient amount of extra reinforcement area, it is not necessary to arrange it in a horizontal position ； If the tank is smaller, the pressure test can be carried out with it standing upright, or it can also be placed at the lowest point along its axis ； Such detailed aspects actually have a relatively small impact on the overall design of the container, and designers need to take them into consideration as a whole. Standards cannot be applied mechanically.