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Steam Hammer Prevention

Steam Hammer Prevention

Steam Hammer Prevention

I assume the slope of piping on submarines changes as the vessel navigates.  Where steam piping is installed, how is the piping designed to prevent steam hammer when the steam and condensate flow can vary from co-current to counter-current two-phase flow?  Is there a specific velocity that is not exceeded for sucessful designs?  Is there a maximum condensate depth, below which slug flow (steam hammer) will not be initiated?

RE: Steam Hammer Prevention

I am not sure the terminology is correct.

If the mixed flow is steady state, then you might generate slug-plug flow , but steam hammer and waterhammer are usually reserved for other phenomena.

For steam hammer , you initailly have a long pipe containing high pressure steam at a high velocity. At time T=0, a stop valve closes quickly ( such as a turbine stop valve in 0.2 sec), causing all steam in the pipe to lose momentum in 0.2 sec. Tha tchange in momentum leads to a sudden pressure spike and sever piping reactions.

For one form of water hammer , as similar phenomena occurs, but is usually caused by the closure action of a check valve. Another method of causing water hammer is to casue a steam bubble to form , then have the bubble collapse at the speed of sound , causing a severe pressure pulse.

RE: Steam Hammer Prevention

I am interested in the condition that steam piping contains condensate, the improper drainage of which can lead to slugs of condensate being formed and carried by the steam flow.  If steam is flowing up slope and condensate is flowing down slope there is counter-current steam/condensate flow.  If the ship rolls or pitches such that the flow of condensate is reversed, there is a different set of conditions.  How is this changing slope factored into the design?  Is there a specific maximum velocity which will prevent the pick-up of steam no matter which way the condensate is flowing?

RE: Steam Hammer Prevention

Yes, there is a velocity which will endure reentrainment of liquid regardless of slope. There are 2-phase flow diagrams , normally used in the oil industry but occasionally used on the boiler industry ( so called Baker plots)to predict the flow regime. There are newer correlation as well.

The avoidance of slug-plug flow is a function of pressure, liquid by weight, mass flow, tube diameter, and slope. One would back in too the most reliable design by first determing the max velocity permitted based on limitations of pressure drop and erosion-corrosion issues, and confirm a single pipe will not experience slug plug flow. If it does, then one can either install internal spiral turbulators to ensure stable annular flow , or one can use multiple paralle smaller diameter pipes .

RE: Steam Hammer Prevention

I understand further development of Baker's work by Mukherjee & Brill is often used in the petroleum industry for design of two-phase flow wet steam injection piping.  My recollection their work is primarily with respect to horizontal flow without any inclination of the pipe.

I see such tools as useful theoretical guides.  I anticipate that piping designers on ships/subs do not go to the Baker chart each time a pipe is sized.  I further anticipate that there are simplified charts or table already developed for such conditions.

Your suggestions to use tubulators or multiple pipes is interesting.  I know of the use of turbulators at low velocities, but would be concerned about erosion/corrosion at steam velocites 100 fps +/-.  I can see multiple pipes could offer some advantages...but need to think about that some more.

RE: Steam Hammer Prevention

If you can ensure stable annular flow, there will be significant slip between the liquid and gas phases, so the erosion corrsoion should be reduced over the case of mist flow or slug plug flow. For velocities as higheas 100 ft/sec with more than 15% liquid by weight, the use of incolnel or stainless steel wold be adviseable.

There are correlations for inclined tubes as well as horizontal and pure vertical tubes. See papers by Kiefer, Kohler and Hein ( from KWU Siemens ) in Int J of 2 phase flow for their referenced correlations.

RE: Steam Hammer Prevention

I have not reviewed work by Kiefer, Kohler, or Hein.  Thank you for those references.

RE: Steam Hammer Prevention

See the following papers by Y Taitel on inclined slug flow:

"two phase flow in inclined parallel pipes" Int J multiphase flow 25(6-7) pp1491-1503 sept 99

"prediction of slug liquid holdup : horizontal to upward vertical flow" Int J Multiphase flow 26(3)517-521 Mar 2000

"A consistent approach for calculation of pressure drop in inclined slug flow" ChemEng Sci 45(5) pp1199-1206 1990

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