GT-1 LIQUID FUEL PRIMARY SPILL VALVE AND REVERSE PURGE PRESSURE DRAIN MONITERING FAULT

FAILURE ANALYSIS REPORTPrepared by Adnan Ahmad&Checked by Sohaib Adil18th July, 2013.

TABLE OF CONTENTS

1. BACKGROUND

2. INTRODUCTION

3. METHODOLOGY

4. DISCUSSION

5. CONCLUSION

6. RECOMMENDATIONS

7. REFFERENCES

BackgroundOn 22nd June 2013 early in the morning GT-1 was running smoothly on 2870 kW load. Around 5.55am suddenly the turbine tripped on Liquid fuel primary spill valve not closed fault (ZT-91).At the same time Liquid fuel Pump spill valve not open (ZT-92) alarm also occurred.On 29th June 2013 at 9.57 pm the turbine tripped on Liquid Fuel reverse purge drain pressure monitoring fail fault. All the parameters associated with CN-1044, CN-1045, CN-1046 and CN-1047 I/0 cards were also out of order due to this fault.

IntroductionAlstom Gas Turbine (GT-1) was installed in March, 2001 at Soda Ash Works. Alstom gas turbine can be operated on both Natural Gas and diesel fuel. Normally natural gas is used as fuel for gas turbines in works. On 22nd July the GT-1 tripped on liquid fuel primary spill valve not closed fault.Normal operations of Liquid fuel primary spill valve and liquid fuel pump spill valveThe liquid fuel primary prime valve SOL-292 is de-energized closed. The liquid fuel Pump spill valve SOL-293 is de-energized open. In normal turbine operation on Gas fuel the Liquid fuel primary fuel pump spill valve will remain closed. During Liquid Fuel the Liquid Fuel Primary spill Valve will be closed and liquid fuel pump spill valve will be opened.When Natural gas is used as fuel then the Liquid Fuel block valve SOL-8 will be in closed position. Liquid fuel prime valve SOL-292 will be closed and the liquid fuel pump spill valve SOL-293 will be opened.When Liquid fuel is used then the Liquid fuel prime valve (SOL-292) and the liquid fuel pump spill valve (SOL-293) will be in closed position.

Liquid fuel prime sequenceWhenever gas fuel is selected (Turbine stopped or running), periodic liquid fuel prime control will be initiated to ensure that liquid fuel lines are primed ready for a change over to liquid.The liquid fuel prime valve will be opened (SOL-292).The liquid fuel pump spill valve (SOL-293) will be closed.The off skid liquid fuel boost pump (MCC-6) will be started.

Liquid reverse purge pressure drain monitoring

The purging of liquid burners during gas fuel running is required to prevent carbon build up on nozzles. Purging is also used for cooling purposes. The system allows the burners to be purged by either instrument air or gas fuel. Instrument air is used to purge the burners when the turbine is at rest and during the startup sequence if required. Gas fuel from gas burners system is used to purge the liquid burners when the turbine is running on gas fuel. During the reverse purge, the reverse purge drain pressure (PT-163) is monitored for rise and subsequent fall of pressure.

Liquid fuel primary spill valve Liquid fuel pump spill valve

Methodology

After shut down the turbine, following methodology was adopted to investigate the Liquid fuel primary spill valve and reverse purge drain pressure monitoring fault.1 Understand the operation and working of liquid fuel circuit.2 Inspection of liquid fuel circuit thats includes SOVs, Pressure transmitters and Position transmitters.3 Inspection of liquid fuel circuit IO Modules.4 Manually operate SOL-293, SOL-292 and SOL-8 multiple times to ensure their integrity.

DiscussionThis portion discusses in detail all the activities carried out to determine the root cause of the Liquid Fuel primary spill valve not closed and liquid fuel reverse purge drain pressure monitoring failed fault.The troubleshooting started with opening liquid fuel circuit. Liquid fuel circuit that includes SOVs, Pressure transmitters and position transmitters were inspected. After inspection it was observed that The SOL-293 of liquid fuel pump spill valve was leaked. The Instrument air to SOL-292 and SOL-293 is supplied from common header. Due to leakage at SOL-293 the instrument air supply pressure dropped at SOL-292 of liquid fuel primary spill valve, due to which SOL-292 status changed to false safe condition. Due to this reason the turbine tripped on liquid fuel primary spill valve not closed fault. When Natural gas is used as fuel then the Liquid Fuel block valve SOL-8 will be in closed position. Liquid fuel prime valve SOL-292 will be closed and the liquid fuel pump spill valve SOL-293 will be opened. The faulty SOV was replaced and complete liquid fuel circuit was checked.SOL-292, SOL-293 and SOL-8 was operated multiple times. But after all this the fault did not clear. Liquid fuel circuit Pepperell & Fuchs I/O cards were inspected. The fault was cleared after resetting the bus isolator power supply. At this stage turbine was ready to run.Turbine was started on Gas fuel but it did not light up and tripped on no light up fault. Several attempts were made but the turbine did not light up and it was decided to start the turbine with liquid fuel. When turbine was attempted on liquid fuel the Electronic control unit common fault tripped it. After proper consultation and assessments it was decided to bypass the ECU and to start the turbine on liquid fuel. Turbine was attempted on with liquid fuel but it tripped on high top temperature. It was decided at that point that turbine wash up process should be carried out. Turbine was handed over to maintenance team for wash up. Maintenance team carried out wash up process in two hours.After wash up it was decided to start turbine with liquid fuel. ECU was already bypassed and turbine was started with liquid fuel successfully. After online fuel changeover the ECU jumper was removed. On 29thJune at 9.57 Pm the turbine tripped on Liquid fuel reverse purge drain pressure monitoring failed fault. All the parameters associated with Pepperell &Fuchs I/O Cards CN-1044, CN-1045, CN-1046, and CN-1047 were also out of order. It was very much cleared that the bus isolator is faulty. Bus isolator card was replaced. The TCM was reset and turbine was ready to run. Turbine was started on first attempt on gas fuel.

CONCLUSION

The Liquid fuel primary spill valve not closed annunciation occurred due to instrument air leakage from SOL293 and Bus isolator fault. So SOL-293 was replaced & Bus isolator module was restored after resetting. On the later tripping (29thJuly, 2013) Bus isolator card was also found faulty and it was replaced.

RECOMMENDATIONS

Action A proper annual Preventive Maintenance Routine of field instrumentation should be established in SAP and followed.EDC:ResponsibilityTo be Agreed AA/TMM/Adnan AhmadActionThe Electronic control Unit (ECU) common fault should be properly investigated in order to resolve this problem for ever.EDC:ResponsibilityTo be agreed AA/Adnan Ahmad

REFERENCESRustronic Mark II Control System Manual

O:\Engineering\E&I\Instrumentation\Sohaib\GT1-ECULiquid Fuel System P&IDO:\Engineering\E&I\Common\Manuals nd Drawings\Manuals & Drawings\GT1 E&I Drawings\Drawings\P&ID\T99-40681 - Liquid Fuel System