Condensate-induced water hammer is an extremely dangerous phenomenon and operators should be trained to ensure they fully understand. Water hammer occurs when water in a pipe is brought to a stop or a change in direction that sends a shockwave through the system and produces a knocking or hammering noise. Water hammer can be both predicted and prevented, provided operators to understand its mechanisms and the one true way to prevent its occurrence.  Common misconceptions about the causes and effects of water hammer and how to alleviate it can lead to the worsening of the condition – to the point of a component or system failure, and even operator fatality.  Operators must understand that water hammer can occur with large or small volumes of condensate in the piping, and it may occur in pipes ranging from ½-inch pipes to 12-inch pipes.

Water Hammer Cause

Many operators and supervisors believe water hammer results from condensate heating and flashing to steam because they hear bubbles popping like popcorn, commonly during plant heat up.
However, the reverse is the case: steam admitted to the pipe is being suddenly condensed by the relatively cold condensate.

When steam contacts cold condensate, the steam condenses, drawing more steam to fill the resulting vacuum – but the condensate pool is also drawn toward that vacuum.  The Bernoulli Effect creates a wave in the condensate pool.  If that wave grows to seal the pipe, the water wave begins to accelerate toward the void more rapidly.  That vacuum created by the suddenly condensing steam accelerates the condensate toward the vacuum at up to 70 mph.  The Government of Western Australia, Department of Mines and Petroleum provides an excellent graphical representation in Mines Safety Bulletin No. 92.

If even one gallon of water (~8 lbs) is traveling 70 mph through a pipe and hits an obstruction (pipe bend, tee, or closed valve), damage to the system could be catastrophic.

Water Hammer Prevention

As with most undesirable events, condensate-induced water hammer is both predictable and preventable.  Based on what we know:

• Condensate will always form in a cold steam pipe
• Condensate will always flow to the low points in the line where steam traps should be located
• Installed steam traps have a definite maximum capacity
• Steam trap design and location consider condensate production for lagged piping only
• Lines must be completely free of condensate before steam is admitted to the line
• Steam traps are not meant to handle pools of condensate like those present during startup

There is no safe method to introduce steam into a line containing condensate.  Steam and water cannot be mixed safely in a piping system due to the unacceptable risk of condensate-induced water hammer.  If water hammer occurs, the only safe way to stop it is to completely isolate steam and continue to blow condensate from the line.  Never attempt to stop water hammer by blowing
down the line “more”.

Understanding the mechanisms by which condensate-induced water hammer happens combined with strict compliance with the procedure will prevent condensate-induced water hammer from occurring.

Learn more about providing detailed safety lessons to your plant.

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