TWO-PHASE FLUID FLOW
Steam hammer is similar to water hammer except it is for a steam system. Steam hammer is a
gaseous shock wave resulting from the sudden starting or stopping of flow. Steam hammer is
not as severe as water hammer for three reasons:
The compressibility of the steam dampens the shock wave
The speed of sound in steam is approximately one third the speed of sound in
The density of steam is approximately 1600 times less than that of water.
The items of concern that deal with steam piping are thermal shock and water slugs (i.e.,
condensation in the steam system) as a result of improper warm up.
Water and steam hammer are not uncommon occurrences in industrial plants. Flow changes in
piping systems should be done slowly as part of good operator practice. To prevent water and
steam hammer, operators should ensure liquid systems are properly vented and ensure gaseous
or steam systems are properly drained during start-up. When possible, initiate pump starts
against a closed discharge valve, and open the discharge valve slowly to initiate system flow.
If possible, start-up smaller capacity pumps before larger capacity pumps. Use warm-up valves
around main stream stop valves whenever possible. If possible, close pump discharge valves
before stopping pumps. Periodically verify proper function of moisture traps and air traps during