×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Steam Hammer?

Steam Hammer?

Steam Hammer?

(OP)
Can a sudden change Steam flow cause a pressure change like water hammer does?

I have a long (2km) large dia (1050mm) steam main. (Flow is 110 kg/s @ 4.5 bar.g.) We have a vent to control pressure at the upstream vent. If the flow is stopped at the downstream end and directed to the vent does the change in momentum cause a pressure change at the downstream end?

Does anyone have refernce that covers this?

Thanks

RE: Steam Hammer?

Yes , steam hammer can cause similar pipe transients as a waterhammer event.

In large fossil steam boilers, the HP  main steam line is at 1000F at 2500 psig, approximately 16" inside daimeter made of P91 or P22 material, about 200 ft long from boiler to turbine inlet. When the turbine strips, the stop valves close in 0.2 seconds, causing the all of the stored mass in the steam line to change veleocity  from  400 fps to 0 fps in 0.2 seconds. If you compute the forces caused by this deceleration, they are significant and there is also a resulting pressure pulse generated.

In general, for the valves which are permitted to close at a slower rate ( ie , bypass valves), the rate of closure in the valve positon range 20-0% open  is restricted to limit the magnitude of the transient.

RE: Steam Hammer?

The Max pressure rise can be calculated by multiplying the density of the fluid by speed of sound of fluid by velocity of fluid. You can then estimate the forces by pressure X area
This value will only be achieved if the valve closure times are less than the time it takes for a sound wave to travel from the valve(which is closing) back up to the reservoir and return - in your case a distance of 4km.
The speed of sound can be reduced by the elasicity of the pipe wall, thus reducing the pressure rise.
Max load on any single straight length of pipe can be calculated by factoring the max pressure rise by the a value of leg length divided by the wavelength of the transient (valve closure time x speed of sound). This assumes linear closure and bends of 90 degrees at both ends.

Alternativly you could buy a fluid transient program and input results into pipe stress analysis program and then perform a time history analysis. Wavenet was one from the 80 & 90,s
 

RE: Steam Hammer?


I would add that normally the main reason to have such header pressure elevation is the time between the instant when valve closure happens and pressure control action. You could model the problem by as a resistive capacitive system (dividing your entire system in sub-volums and connecting then with pressure loss coefficients).
Then you begin to close the valve and detect the pressure elevation in the pressure element point. Given a PI control function and a maximum velocity for valve actuation you can have the RC response. Then add the max value calculated as ZEVEN has showed.
This will be a good answer for the pressure evolution along time.
Hope it works for your case
regards

fvincent

RE: Steam Hammer?

(OP)
I my case the calculation is going to be even harder because the steam is saturated and when the pressure rises the steam will condense!

Cheers
Kevin

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources