What is water hammer? Which areas are prone to water hammer incidents? Why is that?

In thermal power plants, water hammer phenomena most often occur in steam pipes. The following situations are associated with a frequent occurrence of water hammer in steam pipes: (1) When a steam pipe is brought online from a cold standby state, insufficient warming of the pipe can occur due to the valves being opened too quickly or too widely； Or when the pipeline drain valve is not turned on and the drain pipe is blocked, water hammer is more likely to occur in the pipeline. (2) The load on the turbine or boiler increases too rapidly, or accidents such as overfilling of the boiler’s drum or foaming occur, causing steam to contain water and enter the pipes. (3) After the operating steam pipeline is shut down, the corresponding drain valves are not activated in a timely manner or are not opened sufficiently; as a result, steam that leaks into the shut-down pipeline gradually cools down into water and accumulates within the pipeline. After a certain period of time, water hammer occurs in the pipeline. 　　When the above-mentioned water hammer phenomena occur in steam pipes, the main sign is vibration in the pipe system; the pipe itself, its supports/hangers, and the areas where the pipes pass through walls all vibrate, with the intensity of the vibration increasing as the intensity of water hammer increases ； Secondly, a harsh noise is emitted from within the pipeline; however, the sound produced by water hammer varies depending on the situation. For example, in pipelines that are not properly warmed up or lack proper drainage, a \"thudding\" sound is heard intermittently during operation ； When steam carries water into the pipes, it produces continuous whistling sounds similar to air raid alarms ； After being taken out of service, steam pipes that experience water hammer as mentioned earlier often emit sharp noises similar to those of metal striking, in multiple stages. The third sign is that when steam carrying water enters the pipeline, vapor leakage tends to occur at the flange joints of the pipeline; in cases of severe water hammer, the flange gaskets are damaged, resulting in substantial vapor leakage.

Water hammer: A phenomenon in pressurized pipelines in which significant pressure fluctuations occur as a result of sudden changes in the flow velocity of the liquid. Sudden opening and closing of gates in pipeline systems, sudden shutdown of water pumps in water supply pipelines, operation of the guide vanes of turbines, and turning off faucets in indoor sanitary fixtures can all cause water hammer. 　　Water hammer can cause severe vibrations in pipeline systems; the calculation of indirect water hammer requires knowledge of how flow velocity changes over time, and it can lead to noise and cavitation. Understanding the variation patterns of water hammer pressure is of great practical significance for the design of water conveyance pipelines and for reducing the destructive effects of water hammer. The fundamental issue in water hammer is the calculation of the maximum pressure, which generally occurs at the wave propagation section (such as at a valve). 1. Classification of water hammer accidents in hot water boilers and heating systems: (1) Water hammer accidents caused by local vaporization in the boiler occur frequently in pipe rack-type hot water boilers, or in hot water boilers converted from steam tube boilers. (2) Water hammer accidents in the economizer. (3) Water hammer accidents caused by steam entering the hot water pipeline occur only in hot water boilers with a constant pressure in the steam drum. (4) Water hammer at the inlet of the circulation pump caused by a sudden power outage or other reasons that lead to the sudden stoppage of the circulation pump. 2. Phenomena and causes of water hammer accidents (1) Water hammer accidents caused by localized vaporization in the boiler; a knocking sound can be heard outside the boiler, and in severe cases, the boiler tubes affected by water hammer vibrate violently. (2) When water hammer occurs in the economizer, a knocking sound can be heard; in severe cases, the flanges of the iron economizer leak water or even crack. (3) When steam enters the water supply pipe and causes water hammer, a knocking sound of steam and water can be heard inside the hot water outlet pipe, and sometimes vibration occurs in the hot water outlet pipe. Steam intrusion into the water supply pipe usually occurs under the following two conditions: ① Improper design or placement of the hot water outlet pipe ； ②During boiler operation, the water level was not properly controlled, resulting in an excessively low water level. (4) In the event of a water hammer accident caused by a power outage or sudden pump shutdown, the pressure in the system’s return pipe rises significantly, while the pressure at the pump outlet drops sharply. 3. Handling of water hammer incidents (1) Water hammer incidents caused by localized vaporization in the boiler can be handled in accordance with the procedures for vaporization incidents. (2) In the event of a water hammer accident in the economizer, if there is a bypass flue, it should be opened, while the main flue should be opened or closed accordingly. As the flue gas temperature in the economizer decreases, the water hammer phenomenon slows down accordingly. At this point, the return water valve of the economizer should be opened wider to increase the flow rate of return water; once the water hammer phenomenon has subsided, the flue gas can then be directed through the economizer. For small and medium-sized hot water boilers without bypass flues, different approaches should be adopted depending on the connection type between the economizer and the boiler. (1) The economizer and the boiler are connected in parallel. First, the combustion should be reduced; once the water hammer phenomenon subsides, the inlet valve of the economizer should be opened to increase the amount of water flowing through it. Only after the water hammer phenomenon has been completely eliminated can normal combustion be resumed. And pay attention to monitoring the inlet and outlet temperatures of the economizer. (2) The economizer and the boiler are connected using bypass pipes. The combustion should be reduced, while monitoring the inlet and outlet water temperatures of the economizer. If the temperature rise of the water in the economizer is not significant, it indicates that the water hammer is caused by air pockets in the economizer. At this time, the safety valve at the top of the economizer should be opened to drain water and steam. Resume normal operation only after the water hammer phenomenon has completely disappeared. For the case where the economizer and boiler are connected in series, the above method can also be applied. (3) In the event of a water hammer accident in a dual-purpose boiler for steam and hot water caused by steam entering the hot water outlet pipe, the combustion should be reduced immediately, and the circulation pump should be stopped. At the same time, water is added slowly to increase the water level at the upper part of the hot water outlet pipe. During the above operations, the boiler pressure should be monitored at all times to keep it within the normal range. If the aforementioned water hammer phenomenon occurs frequently, the structure of the hot water outlet pipe and its installation should be checked to ensure they are proper. Special attention should be paid to the following two points regarding the structure and installation of the hot water outlet pipe: ① The distance between the hot water outlet pipe and the lowest water level in the boiler should be more than 50 mm ； ②The inlet and diameter of the hot water outlet pipe (also known as the water intake pipe) should be such that the flow velocity remains below 0.3 m/s, in order to prevent steam from being drawn in due to too high water flow speeds. (4) Water hammer accidents at the inlet of the heating system’s circulation pump occur at the moment the pump stops operating; operators do not have time to take action before the accident or damage occurs, and can only take preventive measures. Currently, there are two methods commonly used to prevent water hammer accidents caused by pump shutdown. ①A bypass pipe equipped with a check valve is installed between the inlet and outlet of the circulating water pump. Its working principle is that during normal operation, the pressure in the outlet pipe of the circulation pump is higher than that in the return pipe, causing the check valve to close. At the moment of sudden pump shutdown, the kinetic energy of the water is converted into pressure energy, causing the pressure at the pump inlet to increase while the pressure at the outlet pipe decreases. At this point, the check valve on the bypass pipe opens, allowing the return water to flow around the circulation pump and through the bypass pipe to the outlet pipe of the circulation pump, thereby eliminating water hammer. ②Install a safety valve on the inlet pipe section of the circulating water pump. When the pressure in the return pipe rises due to a sudden pump shutdown, the safety valve opens automatically to release water and reduce the pressure. The opening pressure of a regular safety valve is set at the operating pressure at that point (operating pressure refers to the higher of the pressures under the conditions of the circulation water pump being in operation and when it is stopped) plus 0.05 MPa; the static weight type is the preferred design for such safety valves.

The two people upstairs wrote really comprehensively. Top down! Also learn* a bit

The steam and water pipelines are the lifeline of thermal power plants, and their safe and stable operation is of great significance for the safe and economic operation of the plants. However, in the operation of thermal power plants, water hammer phenomena often occur in the steam and water pipelines. If not handled properly, such water hammer can increase the flow resistance in the pipelines; in severe cases, it can damage the pipelines and equipment, and even pose a threat to human safety. Therefore, taking preventive measures against water hammer in these pipelines is of great importance for ensuring the safe operation of thermal power plants. I. Water hammer phenomenon and its hazards When liquids such as water or steam flow through pressure pipes, sudden closure or opening of valves, or sudden shutdown or startup of pumps can cause sudden changes in the flow velocity of the liquid. Due to the inertia and compressibility of the fluid, this leads to repeated, rapid periodic changes in the pressure of the liquid flowing within the pipes. This phenomenon is known as water hammer. 　　When water hammer occurs, the pressure inside the pipe rises sharply, with values that can reach dozens or even hundreds of times the normal operating pressure. This puts significant stress on the pipe wall material as well as the equipment and fittings attached to the pipe. Along with the expansion and contraction of the pipe wall, this results in intense vibrations and noise, similar to the sound of a hammer hitting the pipe. Additionally, the high-frequency alternating pressures acting on the pipe wall, combined with the intense vibrations and impact of the fluid, cause many pitting marks to appear on the metal surface. If there are defects in the piping system at this time, it is possible to cause damage to the piping or equipment, leading to an accident. Therefore, water hammer not only increases the flow resistance of the fluid but also seriously endangers the safe operation of pipeline systems and related equipment. This is particularly severe in long pipes with high flow rates and large velocities, as well as in water pumps that transport water at high temperatures and with high flow rates. 　　The common pipe water hammer phenomena in thermal power plants occur in steam pipes, feedwater pipes, circulating water pipes, and other steam and water-related pipelines. However, the specific symptoms of water hammer in steam and feedwater pipes differ, and the corresponding preventive measures also vary. II. Water hammer in steam pipes and preventive measures 1. Common water hammer phenomena and signs in steam pipes In thermal power plants, water hammer most frequently occurs in steam pipes. The following situations are common examples of water hammer in steam pipes: (1) When a steam pipe is put into operation from a cold standby state, rapid or excessive opening of the steam inlet valve results in insufficient warming of the pipe ； Or when the pipeline drain valve is not turned on and the drain pipe is blocked, water hammer is more likely to occur in the pipeline. (2) The load on the turbine or boiler increases too rapidly, or accidents such as overfilling of the boiler’s drum or foaming occur, causing steam to contain water and enter the pipes. (3) After the operating steam pipeline is shut down, the corresponding drain valves are not activated in a timely manner or are not opened sufficiently; as a result, steam that leaks into the shut-down pipeline gradually cools down into water and accumulates within the pipeline. After a certain period of time, water hammer occurs in the pipeline. 　　When the above-mentioned water hammer phenomena occur in steam pipes, the main sign is vibration in the pipe system; the pipe itself, its supports/hangers, and the areas where the pipes pass through walls all vibrate, with the intensity of the vibration increasing as the intensity of water hammer increases ； Secondly, a harsh noise is emitted from within the pipeline; however, the sound produced by water hammer varies depending on the situation. For example, in pipelines that are not properly warmed up or lack proper drainage, a \"thudding\" sound is heard intermittently during operation ； When steam carries water into the pipes, it produces continuous whistling sounds similar to air raid alarms ； After being taken out of service, steam pipes that experience water hammer as mentioned earlier often emit sharp noises similar to those of metal striking, in multiple stages. The third sign is that when steam carrying water enters the pipeline, vapor leakage tends to occur at the flange joints of the pipeline; in cases of severe water hammer, the flange gaskets are damaged, resulting in substantial vapor leakage. 2. Prevention and treatment of water hammer in steam pipelines Pipelines that have experienced multiple instances of water hammer often suffer from problems such as loose supports and fittings as well as weld leaks. Therefore, the codes for the design of thermal pipelines stipulate that steam traps and drain pipes should be installed at the dead ends of pipelines that are not in frequent use, as well as at the lowest points along the pipeline sections. Although the design and installation of pipelines take into full account the need to prevent water hammer, in actual operation, various water hammer phenomena can still occur for various reasons. Therefore, appropriate countermeasures and preventive measures should be taken when such situations arise: (1) If water hammer occurs when the pipeline is put into use, the steam inlet valve can be reduced or closed to control the pipe warming rate appropriately, and the steam pipeline drain valve should be opened promptly. If the drain pipe is blocked and the exposed part does not feel hot to the touch, it should be tapped repeatedly; if necessary, it should be replaced. (2) It is necessary to avoid rapid and significant adjustments to the load of the turbine or boiler. In cases where the load changes frequently and significantly due to special circumstances, attention must be paid to regulating the water level in the boiler’s drum. If necessary, the automatic control of the boiler’s water level should be disabled and manual control should be used instead. If the water level in the boiler drum is too high, the feed water supply should be reduced or the drain valve of the drum should be opened to lower the water level appropriately. At the same time, the steam pipeline drains should be activated promptly. Furthermore, when the steam load increases, combustion should be adjusted promptly by increasing the fuel and air supply, while paying attention to distinguishing between false water levels. The main cause of foaming in the steam space is an excessive salt content in the boiler water, which results in a large amount of foam forming on the surface of the water in the steam space. To improve the quality of the feedwater, it is appropriate to strengthen regular and continuous blowdown to prevent foaming. (4) When water hammer occurs in the steam pipeline after it is taken out of service, first check whether the relevant steam inlet valves are properly closed, and second check whether the drain valve of the pipeline that is no longer in use is open; if it is not open, it should be opened slowly and promptly. When a drain main system is in use, care must be taken to prevent the drain main from being under pressure, so as to avoid steam from other pipelines entering the disabled steam pipeline through the drain pipes, which could exacerbate the water hammer phenomenon in that pipeline. III. Water hammer in various types of water supply pipelines and measures for its prevention 1. Common phenomena and signs of water hammer in water pipelines In thermal power plants, water hammer in major water pipelines such as water supply pipelines and circulating water pipelines occurs relatively rarely and causes little damage. However, when it does occur, the pipelines and their supports can experience violent vibrations accompanied by sharp metallic noises, which can also cause varying degrees of damage to pipeline valves, welds, and supports. The main types of water hammer in water pipelines are as follows: (1) When there is steam or air inside the pipeline, and the outlet valve of the feed pump or circulation pump is not closed when starting these pumps, water hammer can occur due to the sudden change in the flow velocity of the fluid within the pipeline. (2) Abnormal operation of the water pump (such as cavitation, damaged impellers, etc.), or malfunction of the water pump’s outlet valve (such as damaged or detached valve cores, unstable operation of the outlet check valve), as well as unstable flow rates and large fluctuations in the fluid within the pipes, can all easily lead to fluctuations in the water supply pressure and inertial shocks within the pipes. (3) Water hammer is likely to occur when the water temperature inside the pipeline changes sharply. (4) When the valve on the water pipeline is closed (or opened) too quickly and abruptly, the flow velocity of the fluid within the pipeline is suddenly restricted or increased, causing the pressure inside the pipeline to change rapidly and repeatedly, which results in severe stress on the pipeline. 2. Prevention and treatment of water hammer in various types of feedwater pipelines In the design of various feedwater pipelines in thermal power plants, a considerable number of technical measures have been adopted, such as minimizing the length of the pipelines or ensuring a sufficient opening and closing time for the valves ； For example, increasing the pipe diameter reduces the flow velocity within the pipe, thereby decreasing the magnitude of velocity change when water hammer occurs, and accordingly reducing the value of the water hammer pressure ； Precautionary measures such as installing safety valves and special valves designed to resist water hammer on the pipes are in place; when the pressure in the pipes rises above the allowable level, the safety valves open to release pressure, thereby preventing the pressure from increasing too much. During operation, when water hammer occurs in the feed pipe, appropriate measures can be taken to control and prevent the occurrence and escalation of water hammer: (1) In the case of the first type of water hammer, the pump can be temporarily shut down to eliminate the source of energy for the water hammer in the pipe, and at the same time, the air valve on the pipe should be opened to release any air present. 　　Such water hammer generally occurs easily in circulating water pipeline systems, and the operating conditions most prone to water hammer are when the circulating water pump starts or stops, and when the outlet butterfly valve is opened or closed. Measures to avoid water hammer include adjusting the time curves for the opening and closing of the butterfly valve at the pump outlet to meet the design requirements; before starting the pump, it is necessary to fill the pipeline system with water and remove any air from it, and then remove any remaining air after the pump starts operating. (2) In the event of water hammer caused by abnormal operation of the water pump or the outlet check valve, it is necessary to switch to the backup pump immediately and inspect the water pump and the check valve. If it is caused by unstable or fluctuating flow rates, efforts should be made to adjust the relevant water pumps or valves to maintain a stable flow rate. (3) Attention should be paid to the regulation of high-temperature saturated water pipelines and related equipment to prevent sudden pressure drops and shocks caused by the vaporization of saturated water within the pipelines. (4) Adjust the opening and closing times of various electric valves according to the characteristics of the pipeline, and appropriately extend these times. By using the correct valve operation methods, during pipeline operations the sequence and speed at which valves are opened and closed must be strictly controlled.

It’s really comprehensive; I’ve learned a lot.

Learned it*:lol:lol

I like posts like this, with everyone having their say