back pitched high pressure steam lines

mark smith

i can't imagine some proposing to make HPS counterflow

i have sen a 14" blind flange blow off close up 'n personal

Arnold E. Clubine

Back pitched steam mains

A client is relocating a high pressure steam plant (100 psi) to the opposite side of the campus. The result will be that all of the existing steam mains will be back-pitched. The concern is water hammer and potential serious damage to the mains. Any thoughts or experiences here?

Tony Conner_2

The Biggest...

... issue with going from forward to reverse slope on existing steam lines is that the main isolation valves and drip traps will very likely not be arranged correctly. You can be left with situations where everything is fine - until a line valve is closed for some perfectly legitimate reason. You can have steam lines flooding with condensate, because now the drip trap is on the other side of the closed valve. If condensate is laying up against a closed valve, and there's steam on the other side of the gate, that's a recipe for disaster. There's an excellent chance opening the valve will trigger "condensation induced water hammer". A steam bubble forms in the relatively cold condensate, and instantly collapses. The inrush of water into the vacuum left by the collapsed steam bubble can result in absolutely unbelievable water hammer. There is no way a valve can be "cracked open" slowly enough to prevent this event.

I have first hand experience with condensation induced water hammer events, and I can state that they are absolutely terrifying. The nastiest one was on the low pressure part of a large steam distribution system - only 10 PSIG. Nobody was hurt, and there was no damage - but it made a HUGE impression on me.

Check out www.kirsner.org . Wayne Kirser is an engineer out of Atlanta that has done considerable investigation into water hammer in large steam distribution systems. He's got some excellent articles he's written posted there, along with pictures of some of the accidents he's investigated.

Tony Conner

It's...

... easy enough to run reverse slope safely. But whoever is designing it/laying it out needs to fully understand steam piping. I've never seen anything in any pressure piping code prohibiting reverse slope. Whoever is looking after this re-do needs to look at the line valves and drip trapping arrangements in the tunnels and/or manholes. I'd be very surprised if they can just make the flow safely go the other way without making changes.