Turbine Outlet Design Pressure - Centrifugal Pumps 1

[Chance17]

Most Turbine documents have inlet Design Pressure and Outlet design pressure.
I don't understand the need for an Outlet Design rating.
Is this an actual mechanical casing rating?
Is this a pressure at which turbine fails to deliver power?
Is this a pressure for bearing loads.
Given 120-psig steam on the inlet, what are the consequences if the outlet is blocked??
Any information is helpful

 

[JJPellin]

In my experience, the only value for turbine outlet pressure on the datasheet is the one provided by the end user. The turbine manufacturer needs this number in order to rate the turbine power under given steam supply and exhaust temperatures and pressures. If the outlet pressure goes up, the turbine will deliver less power.

If you block in the outlet of a turbine, it will stop running and pressure up to full supply pressure. I would normally expect this to trigger the sentinel valve and relief valves to open, relieving the excess pressure.

Johnny Pellin

 

[Chance17]

I am looking at a turbine installed in the field.
The inlet flange is 250# ASA
The outlet flange is 125# ASA
It appears the inlet pressure rating is different than outlet.
I'm not clear how I should evaluate the turbine mechanical pressure limit

 

[JJPellin]

Only the turbine manufacturer can tell you the pressure limit for your turbine. In my experience they do this poorly or not at all. The turbine pressure limit may be based on the case split-line and not the inlet or outlet flanges. Contact the turbine manufacturer. When we have asked this questions, they have given us values just a few pounds above the pressure we told them we intended to run. This did not allow us any margin for setting our relief valves. There are a few things that are very likely. The turbine is not rated to take full steam supply pressure up to the outlet flange. I have never seen a turbine that was rated this high. Thus, you must have a full sized PSV to protect against over-pressure. At that point, it is just a question of the proper setting for the PSV.

Johnny Pellin

 

[georgeverghese]

If there is a pressure equalising line between the drive end and non drive end seal / bearing assemblies as in compressors and pumps, this may be an additional limitation on the permissible upper discharge pressure on the turbine exhaust.

 

[Aub_Engineer]

The outlet rating of the turbine is the pressure rating after the steam pressure has dropped across the turbine blades.
It is important if you are placing the turbine between a high pressure system and a low pressure system. You don't want the low pressure system have a higher operating pressure than this outlet rating.

Also, be careful with installations that have outlet ratings lower than the inlet ratings. I have seen operators try and start turbines in the same way they start centrifugal pumps - with the discharge line blocked in. Hopefully you see a safety valve on the discharge side to prevent this from happening. Some steam turbines come with a "Sentinel Valve" that will whistle if the casing begins to overpressure.