TURBINE AUXILIARIES (CONTROL OIL SEAL STEAM ,DRAIN SYSTEM ) PIPING ABC OF THERMAL POWER PLANT

OTHER IMPORTANT MISC. INTEGRAL PIPING SYSTEM IN TURBINE ISLAND

A. Control Oil system.

In 500 MW Units, fire Resistant Fluid (FRF) used for the control systems and LP Bypass system mainly to 

avoid fire accident in case of leakage of working fluid over high temperature parts of turbine.

This system consists of following equipment.

a. A FRF tank with pumps mounted .

b. Oil vapour exhausters. 

c.  Filters  and FRF coolers.

The process pertains to FRF system is similar to TG lube oil system. 

However Piping size of control oil system is small bore piping with some 

exception.

The fluid circulated in the system is divided for different purposes. Such as control fluid,

secondary fluid, Trip fluid and start up fluid etc. Control oil transmits signal from

Governing Rack ,LP Bypass rack , Spray water racks etc to equipments like Control

valves ,IPCV , Extraction valaves , LP Bypass valves etc.

Precaution needed during erection stage for small bore piping.

A. Control oil piping is small bore piping that includes pipes , gasket , different size “ O –

ring” , fastners and other assorted fittings  for sealing purpose. Therefore it is requested to

make a check list of each line and supervisor should monitor the completion by using proper

material at proper place. This will reduce time during HT of the line and also save time and

money during flushing. Please remember FRF is very costly fluid.

B. Piping erected as ascending radient should have minimum 67 mm(1:15) slope.

C. Descending gradient should have minimum 175 mm slope.

E. Maintain gradient as far as possible if high point is unavoidable then provide venting

provision with orifice.

SEAL STEAM SYSTEM

Seal steam system comprises of following sub systems :

  

Seal Steam Lines, valve Stem Steam Leak-Off Lines and Seal Ring Steam Leak-Off Lines.

In laying these lines, provide sufficient compensation for thermal expansion. The service

temperature for all lines can be assumed to be approximately 450 degC. These pipes expand

by approximately 6 mm/m between the cold state (initial temperature 20 degC) and the hot

state.

Seal pipelines to be connected to the cylinder only after full assembly.

Seal and leak off steam pressure is very very low therefore impulse line for pressure

measurement should carefully laid to avoid pulsation of signal.

DRAIN SYSTEM

One of the important integral piping system contains small bore to large bore piping

including numerous motorised valves , manual valves and pipe fittings. Insulation of the

line is also an important criteria for  drain piping.

 All drain lines shall have as steep a gradient as possible, an all cases at least 20

mm/m.

 In erecting these lines, provide sufficient compensation for thermal expansion. The

service temperature in plant can be assumed to be approximately 450 deg C.

 These pipes expand by approximately 6mm/m between the cold state (initial

temperature 20 OC) and the hot state.

 On drain lines made from thick-wall piping, ensure straight pipe sections at least 500 mm

long between the drain sockets (on casings and pipes) and the first bend in the pipe.

A few PID diagrams of different system ( of BHEL make set) are attached .

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