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PROJECT RE-ENGINEERING

ALL UTILITIES

HP BYPASS WARM UP LINES ARE RE-ENGINEERED TO AVOID ACCUMULATION OF CONDENSATE ESPECIALLY DURING START UP.

HISTORY:

HP bypass valves, after few months of operation were found passing in some sites. On inspection of

internals of the valves, it was observed that there was erosion in valve stem. On close monitoring

and study it was identified that condensate attack on valve stem, during cold and warm start up may

be the probable cause for the damage. Since original warm up system is found to be not

effective, during cold/warm up start up.

RE-ENGINEERING ADOPTED:

To avoid accumulation of condensate in the upstream of valve during cold start up and to ensure

proper warming up, the following design modifications in the warm up line system have been

adopted after thorough discussion held between design engineers from BHEUTIRUCHY,

PIPING CENTRE-MADRAS, PEM-DELHI, TECHNICAL SERVICES- DELHI,

TECHNICAL SERVICES-PSSR on 20/21.2.98.

The warm up line tapping shall be from the bottom of the upstream line of the valve. The stub size

may be of dia 60.3 mm. The tapping also shall be as close as to the valve may be around 200 mm

from valve inlet weld end.

The warm up line shall be connected either to down stream of MS strainer or to the HPBP

downstream line. In case of warm up line connection to HPBP downstream, it shall be after the

temperature measurement point at a distance of not less than 5 mtr.

Two temperature measurement provisions are to be given in the HP bypass fine, one at the upstream

of the valve and the other at the warm up line.

The warm up line also shall be connected to flash tank through drain piping with two valves, one

manual and the other of motor operated.

The revised engineering scheme is given in the sketches.

PERFORMANCE OBSERVATIONS:

In Kothagudam TPS Unit-10, the warm up line tapping was shifted to bottom and the warm up line

was connected to flash tank through drain pipe with 2 manual valves. After carrying out the above

modifications, it was observed that the steam temp, before HPBP valve is about 480 deg C when

the unit is running with main steam temperature around 540 deg C. This establishing that the warm

up iine system is satisfactory while valve is on standby condition. Two numbers thermocouples are

being provided for temperature measurement before HP bypass valve and on the warm up drain

line. The performance during cold/warm start up will be assessed after collecting feed back on

steam temperature during cold start ups in the near future.

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