Turbine Seized

Eight years ago on 8 May 2001 was my first day I as a plant operator in Paiton unit 5&6.

I still remember what happen that was the night shift that we got the unit after trip and the turbine was stuck / seized caused labyrinth seal contact each other and the turning gear motor can not enough power to turn the turbine shaft. My boss ordered to us for turning the turbine shaft by big long stick manually, need three persons to turning that from pointer 0 degree to 180 degree every 30 minutes to avoid turbine shaft deflection cause not uniformly of temperature upper and lower side.

Click here for Turbine theory

Finding of the condition that may lead the turbine seized.
1.According to Turbine Stress Evaluator program in DCS, the turbine requirement for the main steam temperature should be 523C and turbine shaft temperature of 510C to get X5 criteria fulfilled.

2.Seal steam, condenser vacuum, bearing temperature, vibration was all right.

3.Soon after getting release from steam conductivity, the turbine HP stop valve (ESV) opened while the control valves were still remaining closed. The 439C main steam was ready at the upstream of the control valve when the turbine shaft temperature was still 453C and its casing was 458C (that was way the X5 criteria was not released). This condition was occurred for about 15 minutes until finally the turbine shaft temperature equal to the main steam temperature and its exhaust temperature was increased until 367C. By this fact, we suspect that there was small passing at turbine HP control valve that released the lower steam temperature into the turbine. This situation may lead thermal stress / shock to the turbine prior to the turbine seized.

4.There was also indication the steam temperature coming to the 2 legs of the turbine IP valves were not balance and caused high differential temperature alarm and warning, but it seems not give contribution to the turbine seized.


The Steps of turbine warm up.

Before open HP ESV
Main steam temperature a head by-pass valve should be more than main control valve inner metal temperature plus X1
T MS AHD BP > T 50% CV + X1

Saturation Temperature of main steam a head HP turbine should be less than main control valve inner metal temperature plus X2
T SAT AHD TURB < T 50% CV + X2 X3 is not applicable in Indonesia Before warm up to 500 RPM
Main steam temperature a head HP turbine should be more than saturation temperature head HP turbine plus X4
T MS AHD TURB > T SAT AHD TURB + X4

Main steam temperature a head HP turbine should be more than HP turbine casing inner metal temperature plus X5
T MS AHD TURB > T 50% HP + X5

Re-heater temperature a head by-pass valve should be higher than IP Shaft inner metal temperature plus X6
T RHT AHD BP > T 50% IP-SHAFT + X6


Before warm up to 300RPM
Main steam temperature a head turbine should be less than HP Shaft inner metal temperature plus X7A
T MS AHD TURB < T 50% HP-SHAFT + X7A Main steam temperature a head turbine should be less than HP casing inner metal temperature plus X7B T MS AHD TURB < T 50% HP-CSG + X7B Main steam temperature should be less than turbine main stop valve inner metal temperature plus X7C T MS < T MSSV (50%) + X7C Before Synchronise
Re-heater temperature a head by-pass valve should be less than IP Shaft inner metal temperature plus X8
T RHT AHD BP < T 50% IP-SHAFT + X8 Before Re-Load HP Turbine
Main steam temperature a head by-pass valve should be less than HP shaft inner metal temperature plus X9A
T MS AHD BP < T 50% HP-SHAFT + X9A Main steam temperature a head by-pass valve should be less than HP casing inner metal temperature plus X9B T MS AHD BP < T 50% HP-CSG + X9B During turbine warming, Spray Hood valve should be open for cooling LP Turbine last blade.