Water Hammer in Steam Systems Quiz
Kirsner Consulting Engineering

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Updated 9/10/2008

1. To have a water hammer event in a steam system, you must have a large volume flow of fast-moving steam. (True or False)

2. Condensate lying dormant in a steam system that is suddenly exposed to steam can flash causing a type of “waterhammer” over pressurization. (True or False )

3. Fast flowing steam picking up a slug of condensate and flinging it against an elbow is not, technically, water hammer. (True or False). Can a collision of this type actually rupture a pipe? (Yes or No )

4. When steam becomes totally enveloped in cool condensate so that it rapidly condenses, it's pressure drastically increases or decreases?

5. Is water hammer more , less, or equally likely in an uninsulated steam line? Why?

6. You have two valves to choose from in the shop --a Class 150 valve or a Class 250 Valve (both of which are labeled on the valve body casting); which is more resistant to failure in the event of a water hammer? (Class 150 or Class 250)

7. Saturated steam flowing over pooled condensate will eventually evaporate it, if given enough time. (True or False )

Waterhammer that shattered a Class 250 Cast Iron Valve killing an operator.

8. You're replacing a 3/4" bucket trap with another from the same manufacturer. The cast iron bodies are identical and marked with raised letters on the castings indicating 250 psi. The older trap worked just fine in your 225 psi steam system until it failed. There’s no reason the new trap shouldn't’ work just fine too. (True or False).

9. You're about to activate the cold steam line below by opening the closed gate valve to admit steam into it from the Main. You should--

  1. Just "crack open" the isolation valve to admit steam slowly and let the downstream trap come into play. (True? )
  2. Open the drain to see if there's condensate present and, if so, bleed it. (True ?)
  3. Keep full steam pressure on the Main to help bleed condensate thru the trap or drain. (True ?)
  4. Check the temperature of the bare pipe just upstream of the valve to determine if it's below the saturation temperature of the steam? (True ?).

10`. Suppose you determine that THERE IS pooled condensate upstream of the valve residing in the pressurized line. What’s the most important thing to do before opening the Valve to avoid a water hammer?

      • a. get the condensate out of the pipe. (True?)
      • b. Cut the steam pressure off in the Main (True?)

11. What's wrong with the design of the steam piping in the diagram above?

12. Suppose you elect to use an infrared gun to measure pipe temperature. What two factors MUST you be aware of to get an accurate temperature measurement using an infrared gun? a. color of the object (True ?), b. emissivity of the object (True ?), c. field of vision of the gun (True ?), d. temperature of the surrounding ambient air (True ?).

13. When a section of steam line is isolated and allowed to cool to room temperature, the most important reason to open a drain valve and leave it open is--

a. to let air fill and passivate the pipe. (True?)

b. to drain condensate formed from residual steam left inside the line. (True?)

c. to prevent a vacuum from forming in the line (True ?)

d. so drains will be open upon start-up (True?).

14. During warm-up/start-up of a 350' long 10" cold steam main from 62oF to the saturated steam temperature of 142 psig steam (362oF), about 450 #'s of condensate will form in less than 5 minutes in the steam line. If air is vented but no drain is opened and only a trap at the low point in the line is to be relied upon to drain the condensate to the condensate return system, roughly what percentage of the warm-up condensate load will accumulate in the line before the trap begins to discharge any condensate?
) 0%, b) 10%, c) 25% d) 50%, e) more than 50%.
15. The steam trap at right has failed closed. Noting the position of the valves, how high can the level of condensate be expected to build over time in the vertical rise? A., B., C., or D.?

16. What’s the most likely reason for the trap failure?,

17. If the steam in the Main were superheated, would condensate still build-up in the lines shown if the trap failed? No, Yes.

18. Checking for a condensate back-up at a drip leg, you discharge what you expect to be slightly subcooled 100 psi condensate thru a drain. If you’re right, what do you see exiting the drain: a, b, c, or d.?
    • a. a vapor-cloud jetting out the drain more voluminous than if live steam were blowing out.
    • b. condensate flowing out the drain with a small portion turning to vapor that wafts up from the condensate.
    • c. About ½ condensate and ½ steam
    • d. Blowing steam with a small dribble of condensate, but not as much steam as if the drain were blowing live steam with no condensate.

19. The water surrounding a steam main in a flooded manhole is boiling. What's likely going on inside the steam main? (Pipe is expanding due to rapid boiling, or Steam is leaking from pipe, or Pipe is beginning to corrode, or Condensate is filling pipe). Is this dangerous? Why?

This next two questions deal with Column-Closure Waterhammer

20. Pumped condensate from a receiver rises on its way to the Plant Condensate Receiver.

When condensate in the receiver is relatively cool during low steam loads, there’s no problem. But at high steaming loads, condensate tank temperature exceeds 200oF (so that vapor pressure of the condensate exceeds 11.4 psia). In this condition, every time the condensate pump starts, there’s a big “bang” which violently shakes the pipe riser and downcomer.

What’s happening when the pump cycles off?

Would adding a "soft start" variable speed drive to the pump motor hurt or help ?

Would a vacuum breaker added at the top of the system help? No, Yes

The key to understanding Column-Closure waterhammer is understanding "Vapor Pressure". Specifically, that if the pressure on condensate falls below the "vapor pressure" of the condensate, the water column will separate. False, True.

If you got a lot of questions WRONG on this Quiz, that's what was supposed to happen. In many instances, the Quiz is designed to bring to light misconceptions about waterhammer in steam systems which have been repeated so many times, they've become "Conventional Wisdom".

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