Remember there is every likelihood that there will already be condensate in
the line downstream of the valve. People tend to forget that as a steam line
cools, the pressure can often go below "ambient" This means the drainage
steam traps wont work, and theres a nice little pond at the bottom of the
pipe. There are nearly always low points where condensate can accumulate.
The bend from a horizontal run to a vertical is a classic slug generation
point. Once sufficient condensate is stacked up at the bend to block the gas
path, its time to call the dry cleaners. The cold pipe and hot steam
condensing will add to the problem. The superheat effect is unlikely to have
much influence on things during the pipe warming phase as the majority of
heat carried in the steam is normally latent. If lines arent warmed
carefully you'll get hammer. Thats why operators warm them.
Your question appears to suppose that saturated steam and water cannot
coexist. They can and do in a boiler, for example.
The most common causes I have encountered in condensate hammer incidents are
boiler/evaporator priming, steam trap failure and inattention to line warmup
procedures.
Cheers
Steve
Cheers
Steve
>From: Christopher Wright <chrisw@skypoint.com>
>Reply-To: <a href="/group/PipingDesign/post?postID=0XKGNeoDt4cRAjQFwttdCvNuDYclH86PJYhtecUcd2ewbIYaHME_ebR9CpVVQcxIO5pjb0bMWnR_yPPyurhUoqRM">PipingDesign@yahoogroups.com</a>
>To: <a href="/group/PipingDesign/post?postID=0XKGNeoDt4cRAjQFwttdCvNuDYclH86PJYhtecUcd2ewbIYaHME_ebR9CpVVQcxIO5pjb0bMWnR_yPPyurhUoqRM">PipingDesign@yahoogroups.com</a>
>Subject: Re: [PipingDesign] NYC steam line rupture
>Date: Sun, 22 Jul 2007 23:05:44 -0500
>
>
>On Jul 21, 2007, at 5:27 PM, Steve McKenzie wrote:
>
> > Condensate hammer is often caused by opening valves which isolate
> > portions
> > of a circuit.
>Just so I understand--I've got two sections of pipe with a closed
>valve between. One section contains 200 psi superheated steam; the
>other is unpressurized and at some lower temperature. You open the
>valve and the incoming steam condenses as it enters and the
>condensate hurled around by entering steam before it condenses. Seems
>like a very fine line since you need to have superheated stem in
>direct contact with condensate. All this has to happen before the
>incoming steam condenses or the condensate heats up. Have I left
>something out?
>
>Christopher Wright P.E. |"They couldn't hit an elephant at
>chrisw@skypoint.com | this distance" (last words of Gen.
>.......................................| John Sedgwick, Spotsylvania
>1864)
><a href="http://www.skypoint.com/~chrisw/">http://www.skypoint.com/~chrisw/</a>
>
>
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