2 replies to this topic

[Luigi]

A plant expansion has been designed considering 150# steam, and the setting of the steam safety valves in the expansion is at 150#.

Steam for this expansion will be supplied from the existing steam system, that operates normally at 200 psi but has a design pressure of 250 psi.

I am planning to install a pressure reducing valve on the supply line to the expansion, and a safety valve downstream this valve, with a capacity that matches the flow through the pressure reducing valve 100% open (valve failure case) and at maximum upstream pressure. Is this an adequate arrangement and design criteria?

I also have some specific questions:

1. Should I take into account the relieving pressure of the boiler safety valve (250 +10%) to determine the capacity required for the new safety valve? I don't think so because it would be a case of double jeopardy, but will like to hear opinions.

2. Any suggestion of a specific kind of control valves to use in this application?


Any additional input would be appreciated.

Thank you

[JoeWong]

A plant expansion has been designed considering 150# steam, and the setting of the steam safety valves in the expansion is at 150#.

Steam for this expansion will be supplied from the existing steam system, that operates normally at 200 psi but has a design pressure of 250 psi.

I am planning to install a pressure reducing valve on the supply line to the expansion, and a safety valve downstream this valve, with a capacity that matches the flow through the pressure reducing valve 100% open (valve failure case) and at maximum upstream pressure. Is this an adequate arrangement and design criteria?

I would think your arrangement is OK.

Note : Your 150# rating test pressure (125%) may be higher than the CV maximum upstream pressure. If your downstream equipment (design to ASME) are protected from CV failure case, you may have a chance not to provide PSV on the piping...please check the piping code if short term pressure excursion upto test pressure is allowed...

I also have some specific questions:

1. Should I take into account the relieving pressure of the boiler safety valve (250 +10%) to determine the capacity required for the new safety valve? I don't think so because it would be a case of double jeopardy, but will like to hear opinions.

I would think it is double jeopardy as normally boiler has it Hi-Hi pressure and temperature trip.

2. Any suggestion of a specific kind of control valves to use in this application?

With such low pressure drop CV, normal control valve good for high temperature service (valve seat & extended stem) is good. Noise level should be lower than 85 dBa as low dP...Just have to conform with CV vendor.

Good steam engineerig tutorial link... http://www.spiraxsar...g-tutorials.asp

JoeWong

[Luigi]

Thank you for your comments.