steam pressure reduction when pipe increases in size

I have 95 psi steam in a 1” pipe and want to vent it to atmosphere for a short time. To make it safer I want to drop the pressure before it vents by increasing the pipe diameter. Is it possible to calculate the diameter I would have to increase the pipe to reduce the pressure to 10 psi.

Thank You

I never took fluid dynamics in college (stopped in the 2 or 3 hundred level of physics), but that sounds oddly like a homework question. Of course, I’ve never worked around steam pipes, so I really have no idea if something like this is a typical real world application (in which case…nevermind).

Steam ships vent for legitimate reasons, don’t they? Although, the pipes they use are rather long (from the boiler, or whatever, up to a high point in the ship, like the smoke stack). I imagine the length of the pipe will also have to be figured in, as well. The steam will lose some energy the further it goes down the pipe.

This is confusing me. In a contained system, the pressure of the steam will depend on its temperature. However to do work, it must flow from the source to the point of use. Thus it will be subject to the friction of the pipe. I am wondering if this might follow the simpler case of P1V1=P2V2. If you want P1 to be 9.5 times P2, then you make V2 9.5 more than V1. 3’’ pipe would come close. Good luck finding 3 1/2’’ inch pipe. I am not sure how long of a pipe you need, but 4’’ might not be much more expensive.

As the steam expands, it will cool further dropping the temperature. P1V1/T1=P2V2/T2. 2’’ pipe is a lot easier and cheaper then 3’’ or 4’’ I bet what you would have at the end of a 10’ or 20’ length would be fairly cool and lower pressure. Run it straight up, and nobody should get scalded.

You might find the answer by looking up Boyle’s law. Pressure and volume of a gas are inversely proportional if kept at a constant temperature.

Why would a steam ship vent steam, other than lighting off a boiler?

Why are you venting?

If you are wanting to vent to atmosphere you are dropping it from 95 psig to 0 psig. It is going to be a funnction of the lenght of pipe, amount of steam vented and the velocity. To go from approx 110 psia to 15 psia the volume is going to increase by 110/15 or about 7 times. If you use a long unsulated pipe the steam can cool before reaching the opening.

They don’t, not even lighting off a boiler. A cold boiler has no steam and you want to conserve pressure in a boiler that lost its fires.

The steam in a steam plant gets recycled. It goes from water to steam and condensed back to water and the cycle starts again. Otherwise you are wasting water. Especially important on a steam ship where fresh water has to be distilled from seawater.

No you do vent a boiler when lighting it off. The vent on the steam drum is opened and the vent at the superheater is opened. Done this every time I have lite off a cold boiler.

A cold boiler has air in it before steam is made. The steam drum vent is opened before lighting off the fire. It is kept open until nothing but steam is coming out of it. Leaving the air which contains o2 in the boiler could be harmful. The vent is closed about 10 psi.

The superheater vent is left open until until steam is being used from the boiler, normally until the desuperheater main steam valve is opened. If the vent is not left open then there will be no flow of steam through the superheater and it could fail because of over heating.

And you do not use fresh water in a ships boiler, but only distilled water.

In an industrial boiler, it is common practice to use tap water for make up. Various additives are added to control corrosion and scale. Some of the feed water is drained to control mineral build up.

When I managed a factory, we never vented steam or air. If we weren’t running 3 shifts or on Monday morning start up, we just turned on the breaker for the electrical controls and let it heat up.

I don’t know, I’m not an engineer. But I have worked on a conventionally powered CV, and I saw them blow steam (it was loud whoosh, but not a whistle). I couldn’t tell you which sub-system in engineering the steam was coming from.

Here is a picture of what I had in mind when I said steam ships vent: (hope link works)

I could have explained that better. Cold boilers are purged/vented with the forced draft fans. You also want to make sure there are no fumes from spilled bunker oil in the fire box.

Yes, the water is distilled. That is what I meant to say when I said you must distill seawater. The feed water is obviously distilled. If you are wasting feed water it will reflect in your fuel costs as you will be running the evaporator for longer periods of time.

I hope you added extra sulfite in the morning.