How is steam hammer prevented in submarine piping, or maybe, is it prevented?

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?

Technically, "steam hammer" is caused by the change in momentum of a large mass of high pressure steam that is suddenly stopped by a fast closing stop valve. Steam hammer is a problem on some very large central station  power plants  during a steam turbine trip event or closure of a bypass valve(Safety Valves), but in those cases the steam pressure is over 2400 psig and the pipe length is over 200 ft long. The operating pressure and pipe length in subs is less than these problematic values.

For the case of 2 phase flow, I would assume the subs would use a centrifugal steam-water seperator that ensures the mixture is accelarate over 5 G's so that the sub inclination is nor too much of a factor.

steam flow driven waterhammer is a large problem on modern combined cycle power plnats, specifically in the hot reheat dump/bypass line to the condenser. This is typically a 14" dia pipe , slighlty sloped to the downstream direction. The spray attemporator typically oversprays at low steam flows , due to incorrect control logic. The steam veloctiy is on the order of 200-250 fps in this line.

At very low steam flows, and with excessive spray water flow, the excess water accumulates on the bottom of the 150 ft long pipe. The water level can build up to several inches high due to the slight slope. If the steam control valve then opens wide in response to a high reheater pressure event, then the water is accelerated to 250 fps and forms large slugs . When these slugs hit the elows at 250 fps they cause severe piping damage.

The oil and gas industry has a lot of experience with 2 phase flow in pipelines, as so they have  "Baker plots" and other correlations that will predict what 2 phase flow regime will occur in the pipe. For example, in  offshore Gulf of Mexico drill rigs, the output of oil and gas is comingled and transported together in the same underwater pipeline to the onshore seperation plant.  Europeans have other correlations.

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