【2026 Steam Pipelines】The fundamental causes of water hammer in steam pipelines and methods for dealing with it

I. Formation and hazards of water hammer in steam pipelines: Whether it is pipelines transporting superheated steam or saturated steam, if drainage is insufficient during system startup or operation, condensate will be present in the steam. If the valve is suddenly opened at this time, the steam carrying condensed water will start to flow, forming waves; when there is a large amount of condensed water, it can cause water blockages. The water plug is pushed forward by high-speed steam currents; due to the inertia and incompressibility of water, it strikes pipe walls, elbows, valves, and other pipe fittings, causing repeated and severe periodic changes in the pressure of the fluid flowing within the pipes. This phenomenon is known as water hammer. Once the water shock reaches a bend in the pipe or a valve, flow stops instantly, releasing kinetic energy that causes a pressure change and generates shock waves which impact the pipe and valves, resulting in direct water hammer. To prevent excessive thermal stress and water hammer in the steam pipes during operation, which could cause permanent deformation or cracks in the pipes, it is necessary to pre-warm the steam pipes with steam before putting them into use. The principle for warming pipes with steam is to start with the main pipes before moving on to the branch pipes, and to warm each section sequentially according to the flow direction of the medium ； When heating the pipeline, increase the temperature first and then the pressure; raise the pressure only after the pipeline is overheated.

Example: During the commissioning of the low-pressure superheated steam pipeline in a company’s low-temperature methanol washing unit, a water hammer incident occurred. The reboiler of the methanol-water separation tower in this unit uses low-pressure superheated steam as the heating medium, with a pressure of 1.5 MPa and a temperature of 240°C. Low-pressure superheated steam is led from the steam main to the low-temperature methanol washing zone; the branch pipe is relatively long, about 100 m in length, and contains 2 sections of Ω-shaped expansion joints (the expansion joints are 1.5 m high). During operation, when the drain valve at the end of the steam pipeline was opened, a steam pipe water hammer accident occurred. The pipe experienced severe longitudinal vibration accompanied by loud noises (sharp sounds similar to metal striking), which caused the pipe supports to fall off and the pipe to shift.

Cause of the incident: After this section of steam pipeline was taken out of service, the opening degree of the corresponding drain valves was insufficient. With the low-pressure superheated steam inlet valve not being closed properly, steam leaked into the pipeline, gradually cooled down to water, and accumulated there. During operation, poor drainage led to a water hammer accident in the steam pipeline.

When a water hammer accident occurs in steam pipes, the main phenomena are as follows: first, the pipe system experiences intense vibration; both the pipe itself and its supports (hangers) vibrate, and the more severe the water hammer, the greater the vibration； Secondly, a harsh noise is emitted from within the pipeline; however, the sound produced by water hammer varies depending on the circumstances. For example, pipelines that are not properly warmed up or lack sufficient drainage tend to emit a ‘thumping’ sound in stages during operation ； When steam carries water into the pipes, it produces continuous whistling sounds similar to alarms ； When water hammer occurs in steam pipes after they are shut down, sharp sounds similar to metal knocking are produced in multiple stages.

II. Reasons for water hammer in steam pipes 1. The steam pipes were not warmed up or drained of water before steam was supplied to them. 2. Improper operation: the steam inlet valve is opened too quickly or to an excessive degree when the steam pipeline is put into use, or the pipe warming is insufficient. 3. Condensate is introduced into the front-end system; for example, water may be present at the steam outlet of the front-end boiler, or condensate from the front-end delivery system may enter the steam pipeline network.

4. The steam pipeline design is unreasonable; a drain system is not installed at the end of the pipeline or at the lowest points. 5. The hydroscoper selected is too small, or the diameter of the drain pipeline is too narrow, preventing the condensed water from being removed in a timely manner and thus causing water hammer. 6. After the steam pipeline was taken out of service, the corresponding drain valves were not activated in a timely manner or were opened to a insufficient degree; as a result, drainage was impaired during restart, leading to water hammer. 7. During the heating of the steam pipes, the rate of temperature and pressure increase was too fast; the principles for heating steam pipes were not properly followed.

III. Measures to address water hammer in steam pipes 1. During the pipe warming process, if water hammer occurs and causes the pipes to vibrate, it is necessary to promptly reduce or close the steam inlet valve in order to control the warming speed appropriately, and also to open the drain valve on the steam pipe to discharge any accumulated water.

2. If severe liquid slugging occurs during the steam pipe warming process, the main steam isolation valve must be closed immediately, and the drain valves should be opened slowly one by one in accordance with the flow direction of the medium to remove water and relieve pressure. At the same time, the steam pipeline network is depressurized over a short period of time to prevent more serious accidents from occurring.

3. When water hammer occurs in the steam pipes after they are taken out of service, check the corresponding steam inlet valves to ensure they are tightly closed. At the same time, inspect the drain valves and traps in those steam pipes to confirm that they are in the open position.