WATER HAMMER: DANGERS AND TIPS TO PREVENT IT FROM HAPPENING
Recently, one personal care plant reached out to MIEPL for help after a recorded safety incident caused by water hammer. After a swing check valve was forced shut rapidly by product moving through the pipeline, the piping was jarred from its supports, and a piece even fell from overhead to the ground.
This falling pipe resulted in costly downtime and safety violations, not to mention the cost to engineer, reconfigure, and repair — all of this headache caused by an easily preventable problem.
This issue is also not exclusive to processing industries. All of us have heard the occasional pounding of the pipes in our homes when we turn off the faucet too abruptly. Well, this phenomenon is called “water hammer,” and it can occur in the piping systems of process industries as well.
In these situations, though, the consequences of this condition can be significant due to the volume and pressure of the fluids being moved through the pipes. We’ll discuss water hammer in more detail in the following paragraphs, and provide some tips on how it can be avoided.
Also called hydraulic shock, water hammer is a pressure surge that results when a fluid is forced to stop or change direction suddenly in a piping system.
The momentum of the fluid abruptly stopping creates a pressure wave that travels through the fluid in the pipeline, subjecting everything in the pipe system to significant forces.
Water hammer most commonly occurs when a valve is closed suddenly at the end of a pipeline. The moving fluid slams into the now-closed valve, creating a hydraulic shock wave that resonates throughout the pipeline.
Certain types of check valves—including swing check valves, tilting disc check valves, and double door check valves—are intrinsically prone to closing rapidly due to their design. Use of these types of valves in a piping system, then, can lead to problems with water hammer.
Water hammer may also be caused by pump failure. If a pump pushing fluid through a pipeline system fails suddenly, the velocity of the moving fluid also changes suddenly. The fluid downstream of the pump attempts to continue flowing, creating a vacuum in the line that can lead to water hammer.
IMPACTS OF WATER HAMMER
First of all, consider that fluids are not compressible. When in motion, and under some velocity, fluids can generate a considerable amount of force when their motion is suddenly arrested. For example, take the case of 100 gallons of water flowing in a 2” pipe at a velocity of 10 feet per second. When this flow is rapidly brought to a halt by a fast-closing valve, the force generated is equivalent to that of an 835-pound hammer slamming into a barrier.
Looking at it another way, if a fluid flow is stopped in less than one-half of a second (which might be the standard closing speed of a typical valve), then a pressure spike can be generated that is over 100 psi greater than the standard operating pressure in the piping system.
At a minimum, water hammer causes pipeline noise and vibration. However, far more severe outcomes are possible, including the following:
Leaks at pipe fittings and joints
Failure of other pipeline components such as flow meters, pressure gauges, etc.
Damage to piping support systems
Damage to the product being processed, especially in food & beverage processing and pharmaceutical manufacturing applications
TIPS TO AVOIDING WATER HAMMER
1. Proper System Design
Before fabrication even begins on your system, it's essential to work with a trusted partner that understands sanitary processing and can design a system to meet the specific needs of your process. This partner should understand the complexities of hygienic processing and the dangers of water hammer in order to develop a design that eliminates these risks.
For existing systems, it's crucial to consider the operating characteristics of your pipeline system. This can be done in a number of ways. The fluid velocity in the pipes, for example, may be lowered. Pipe sizing charts for some applications recommend no greater than 4.9 feet/second of process fluid flow. However, this can be a conflict when designing pipelines that need to be clean-in-place (CIP) cleaned, since CIP uses turbulent flow with velocities greater than 5 feet/second.
The following will also help to lower the velocity of the fluid in the pipe, and hence reduce the chances of hydraulic shock:
Use shorter branch pipe lengths
Use shorter lengths of straight pipe
Add elbows and expansion loops to the process piping system. Water hammer is related to the speed of sound in the fluid, and elbows reduce the influence of pressure waves
Arrange the primary pipes in loops that supply shorter, smaller run-out pipe branches. With looped piping, lower velocity flows for both sides of a loop can serve a branch
2. Proper System Programming
Changes in pressure, which can lead to water hammer, occurs every time a fluid is accelerated or slowed by pump condition changes or valve position changes. Usually, this pressure is so small, and the change is so gradual, water hammer is practically undetectable. However, in processing facilities that move product quickly down long piping runs, the pressure created from turning a pump on or off can cause significant water hammer.
You can eliminate these extreme pressure changes through proper system programming, such as programming pumps to ramp up or down gradually. This process can stretch the pressure change out over multiple seconds, or even longer than a minute. Central States Industrial Equipment (MIEPL) can evaluate your process system to help minimize or eliminate the potential for water hammer through proper system design or programming.
3. Proper System Training
Properly-trained processing plant personnel go a long way towards mitigating or eliminating water hammer. Adequate training teaches operators the importance of correctly opening and closing manual or actuated valves — minimizing the effects of water hammer.
Instituting good pipeline control practices, such as startup and shutdown procedures, also ensures your system operates correctly, efficiently, and safely. MIEPL provides startup support to ensure operators, managers, and safety personnel feel comfortable and confident in their abilities to operate and maintain their system safely.