RE: NYC steam line rupture

From: <Altech_m2>
Date: Mon Jul 23 2007 - 11:37:00 EDT

One mechanism which has occurred many times before

• the steam valve is cracked open. Usually these are gate so the steam comes into the bottom of the subcooled condensate sitting on the other side backed up against the closed gate.
• As steam bubbles through the very cool condensate the steam collapses and the volume shrinks (steam tables show >100x). This creates many vacuum pockets which suck in more steam (The driver is the biggest pressure differential which is the collapsing steam in the condensate pool). This also lowers the pressure on the condensate side.
• The condensate will heat up but not as fast as the steam collapses and there is an inrush of more steam to fill the void (>100mph)
• The condensate will heat up but the rate of transfer of heat (from the incoming steam to the cold pool of condensate) is much slower than the rate of change of volume. This is the shock wave that carries the damaging driving force. Any condensate slug anywhere else will get picked up by this pressure wave and pressure differential

I wonder how much less the effect would be with a ball valve which would not introduce the entire stem intake under the pool of condensate but more vertically integrated. The same volume change would occur in steam collapse at fluid contact but it seems the steam might be more vertically integrated and so the pressure more evenly distributed.

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From: PipingDesign@yahoogroups.com [mailto:PipingDesign@yahoogroups.com] On Behalf Of Christopher Wright
Sent: July 22, 2007 10:06 PM
To: PipingDesign@yahoogroups.com
Subject: Re: [PipingDesign] NYC steam line rupture

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. <mailto:chrisw%40skypoint.com> com | this distance" (last words of Gen.

.......................................| John Sedgwick, Spotsylvania

1864)
http://www.skypoint <http://www.skypoint.com/~chrisw/> .com/~chrisw/

[Non-text portions of this message have been removed] Received on Mon Jul 23 11:37:00 2007