Over the years, we’ve entered countless boiler rooms where water hammer was dismissed as normal. We hear people say, “It always sounds like that at startup.” This is scary because water hammer is not normal and is extremely dangerous. If it isn’t dealt with, it can wreck your system, lead to costly repairs, and put everyone’s safety at risk.
4” strainer that was completely blown apart due to water hammer
What is Water Hammer?
Water hammer occurs when there is a sudden and forceful change in the velocity of water or steam within piping. Problems commonly present themselves as a loud banging on startup in the plant boiler room. Some other symptoms that you may also see are broken traps, air vents, valves, pipe supports, pipes and flanges.
In steam systems, water hammer is particularly dangerous because it involves liquid condensate and steam moving at extreme speeds. To prevent these issues, understanding the different types of water hammer and their causes is critical.
Common Causes
At a high level, some common causes of water hammer are:
- Header Full of Condensate
- Undersized Traps
- Broken or No Trap
- Improper Startup (Too Fast or Unsupervised)
- Boiler Carry-Over
3 Types of Water Hammer in Steam Systems
There are three main types of water hammer: differential shock , thermal shock , and hydraulic shock. Each type originates from different causes and has unique characteristics.
1. Differential Shock
Differential shock is the most dangerous and destructive form of water hammer in steam systems. It occurs when condensate accumulates in the steam lines, forming a pool of water that interacts with high-velocity steam. As steam flows over the surface of the condensate, it creates waves—similar to wind blowing across the surface of a lake.
Eventually, if these waves grow large enough they will block the circumference of the pipe. The steam will then pick up a slug of condensate and propel it downstream at 100 feet per second (or faster!). When this high-speed water slug slams into an elbow, valve, or pipe wall, it can cause severe mechanical damage. In high-pressure steam systems, the impact can be even more devastating due to the increased velocity of the steam.
How to Prevent Differential Shock :
- Maintain proper drainage of condensate by installing adequately sized steam traps and drip legs.
- Ensure that piping slopes to allow for continuous condensate removal.
- Perform regular trap maintenance and maintain good water chemistry (to prevent carry over).
- Follow proper system warm-up procedures and make sure to drain legs on supervised start-ups (every leg!).
- Consider a night setback switches to prevent cold start-ups while also saving energy.
2. Thermal Shock
Thermal shock is another cause of water hammer in steam systems. It happens when live steam enters a cooler, flooded condensate return line, causing rapid condensation of the steam bubbles in the liquid.
Consider this scenario: a steam trap fails, allowing live steam to blow through the system and mix with cooler condensate in the return line. As the steam encounters the cooler liquid, the steam bubbles enter the liquid. These bubbles then collapse reducing their volume instantaneously . This produces a loud, percussive sound that can resemble popcorn popping.
Thermal shock often causes repetitive banging noises. If ignored, it can lead to significant stress on the piping and steam traps, potentially resulting in system-wide damage.
How to Prevent Thermal Shock :
- Ensure proper steam trap maintenance and testing.
- Never combined high pressure and low pressure condensate returns.
3. Hydraulic Shock
Hydraulic shock occurs when a column of liquid experiences a sudden change in velocity. This is typically due to the rapid closing or opening of a valve. Though it is more common in water systems, hydraulic shock can also occur in steam systems, especially within flooded condensate lines.
For example, when a solenoid valve in a water line opens or closes abruptly, it creates a “thunk” sound. This is hydraulic shock in action. An everyday example of this is when your washer kicks on and begins filling and then the solenoid valve shuts the water off. When a valve shuts quickly, the trapped liquid can slam into the valve seat, generating a shockwave that reverberates through the system.
How to Prevent Hydraulic Shock :
- Regularly check for flooded lines and ensure proper condensate drainage.
System Startups
2” tee that was completely blown out as a result of water hammer
Water hammer is often more pronounced during system startups, especially after a period of inactivity. When you bring a steam system offline, condensate will collect in low points of the piping and at steam traps. This creates prime conditions for differential or thermal shock.
During startup, steam rushes into the system, interacting with the trapped condensate, and can trigger violent water hammer. Proper startup procedures are essential to minimizing the risk of water hammer. These include slowly introducing steam and following system warm up procedures. Also, being sure to open and drain legs on supervised startups and allowing time for condensate to drain from the system before full operation. Taking the time to slowly warm up the system will significantly reduce the risk of damage during startup.
The Consequences of Ignoring Water Hammer
Water hammer is not just a noisy inconvenience—it poses a real threat to steam systems. Over time, the constant pounding from hydraulic, thermal, or differential shock can cause fatigue in piping and components. This leads to leaks, cracks, or piping failure.
Key equipment such as steam traps, elbows and pumps can be severely damaged, leading to unplanned downtime and expensive repairs. In the worst-case scenario, a major rupture could result in injury to personnel or significant damage to your facility.
Best Practices for Preventing Water Hammer in Steam Systems
To minimize the risk of water hammer, consider implementing the following best practices:
- Regular Maintenance: Conduct routine inspections and maintenance of steam traps and valves to ensure they are functioning.
- Proper Piping Design: Ensure to size piping correctly and slope it to allow for effective condensate drainage.
- Condensate Removal: Use well-maintained steam traps to remove condensate from the system before it accumulates.
- System Monitoring: Utilize pressure and temperature sensors to detect abnormal conditions that could lead to water hammer.
Conclusion
Water hammer is a serious threat to steam systems that, if ignored, can lead to equipment failure, costly repairs, and dangerous safety risks. It occurs due to sudden changes in steam or condensate velocity, often from improper system design, poor maintenance, or incorrect startup procedures. The destructive effects of water hammer, including differential, thermal, and hydraulic shock, can wreak havoc on pipes, valves, and traps.
Preventing water hammer requires careful attention to piping design, ensuring proper slopes for condensate drainage, and installing adequately sized steam traps. Regular maintenance of steam traps and valves, along with monitoring for pressure and temperature fluctuations, is essential for early detection. Additionally, water hammer arrestors can be a valuable tool for absorbing shock waves and protecting your system.
