ghazlan unit#4 ip turbine blade shroud...

3 RD ANNUAL TECHNICAL EXCHANGE MEETING OF ROTATING EQUIPMENT King Fahad University of Petroleum & Minerals

Dhahran , Saudi Arabia 9th and 10th April 2014

BY Agil A. Al-Jamaan

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GHAZAN UNIT# 4 IP TURBINE BLADE SHROUD

FAILURE

GHAZAN UNIT#4 IP TURBINE BLADE SHROUD FAILURE

Agenda Introduction

Ghazlan Power Plant (GPP) GPP Unit (1-4) Turbine HP-IP rotor Turbine Blade Shroud U-4 Turbine Operation Parameter

Incident and findings Failure Events Description Major Findings

Proposed Renovation - (Blade Shroud) Damaged blade removal Replacement of damaged blades Replacement of complete blades row

Conclusion

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Ghazlan Power plant (GPP) is located in Juaymah on the Arabian Gulf Coast in the eastern province of Saudi Arabia. It is a major power plant having a production capacity of about 4000 MW from 8 eight units. The first four units (1-4) are fitted with Siemens- Westinghouse turbine generator with a capacity of 400 MW each. They were put in service between 1979 & 1982.

The other four units (5-8) are fitted with Mitsubishi turbine generator with a capacity of 632 MW each and they were put in service between 2002 & 2003.

Ghazlan Power Plant (GPP)

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GPP Turbine (1-4)

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The turbine of each unit is a Westinghouse tandem compound, double flow exhaust , condensing, reheat type, 3600 rpm. Each consist of one HP-IP element and one LP element having a maximum calculated net power of 418 MW.

The turbine of each unit is a Westinghouse tandem compound, double flow exhaust , condensing, reheat type, 3600 rpm. Each consist of one HP-IP element and one LP element having a maximum calculated net power of 418 MW.

GPP Turbine (1-4)

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The HP-IP turbine rotor is machined from a solid alloy steel forging. The blading path include an impulse element operating with partial admission control followed by reaction blading in the HP (Rows 1 to 8 ) and IP (Rows 9 to 13).

Turbine HP-IP Rotor

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Turbine Blade Shroud

Several rotor blades are shrouded and held together by one plate and between each plate a gap is provided for thermal expansion . The shroud is fitted over tenons on the end of the blades and secured to turbine blades by riveting.

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Turbine Blade Shroud

Several rotor blades are shrouded and held together by one plate and between each plate a gap is provided for thermal expansion . The shroud is fitted over tenons on the end of the blades and secured to turbine blades by riveting.

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Unit # 4 Turbine Operation Parameters

Rated Output: HP Steam Conditions: IP Steam Conditions: In Service Date: On line duration : (running hours) No of starts:

430 MW 1800 psig, 950 deg F 427 psig, 950 deg F 1982 210360 hours 426 starts

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1- Ghazlan Unit#4 tripped on the protective reverse power due to all turbine valves closed.

Failure Events Description

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2- Plant started trouble shooting for the cause of valve closing by checking electrical anti-motor , O/speed signal, vibration wiring, trip signal and everything was found normal.



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3- The turbine is started.



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4- At speed 1000 rpm, unit tripped due to hi-hi vibration on bearing 1 & 2 (reaching trip level-10 mils) , abnormal sound noticed in the bearing side.



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5-Turbine bearings were dismantled and inspected after cooling down and stopping the turning gear, Preliminary bearings inspection findings did not reflect the real cause of such high level of vibration.



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5-Turbine bearings were dismantled and inspected after cooling down and stopping the turning gear, Preliminary bearings inspection findings did not reflect the real cause of such high level of vibration.

6- It is was decided to dismantle HP-IP turbine. disassembly of HP-IP turbine revealed that the shroud of one group of blade of HP-IP Rotor Blade Row#9 came off during unit operation causing consequent damages to other parts of the turbine.

Major Findings

IP Rotor Blade Row#9 Shroud Failure

The shroud of one group IP Row-9 Rotating Blades was found detached and mostly rubbed-off completely. Only two small pieces of the shroud were found at stage location and a lot of small metallic particles deposited on shrouds of the next IP stages and at the condenser hot well.

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HP-IP Rotor Blade Row#9 Shroud Detachment

Deposits of Metal Particles Collected Metal Particles

Major Findings

IP Rotor Blade Row#9 Shroud Failure

The shroud of one group IP Row-9 Rotating Blades was found detached and mostly rubbed-off completely. Only two small pieces of the shroud were found at stage location and a lot of small metallic particles deposited on shrouds of the next IP stages and at the condenser hot well.

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Metal Particles & Damaged Seal strips collected from different areas of the turbine

Major Findings

IP Turbine Seal Strips Damage

All seal strips of IPT stages were found completely damaged. Some seals were rubbed smashed and some seals either completely or partially peeled off from their locations. Many seal strips and caulking strips pieces were collected from IPT downstream stages and at LPT first stage.

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Metal Particles & Damaged Seal strips collected from different areas of the turbine

Major Findings

IP Turbine Seal Strips Damage

All seal strips of IPT stages were found completely damaged. Some seals were rubbed smashed and some seals either completely or partially peeled off from their locations. Many seal strips and caulking strips pieces were collected from IPT downstream stages and at LPT first stage.

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Major Findings

HP-IP Rotor Bearing# 1 & 2

Scoring in the Bearing pads and babbit material was wiped and turbine rotor journal scoring.

Bearing Bottom Pads and Journal Scoring

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Major Findings

Extension Shaft / Turbine Main Oil Pump (MOP)

Heavy rubbing and overheating

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Major Findings

LP turbine

heavy scoring in turbine bearings journal along with seals rubbing.

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Major Findings

LP turbine

Broken pieces of IP Turbine seal strips were found trapped in 1st.stage stationary blades. Many trailing edges of 1st stage stationary blades became serrated due to striking of solid metal particles

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Removing the newly seen failed group blades along with 6 more blades in exactly opposite direction to avoid unbalance during operation. This action is treated as temporary repair and risky to shorten the shutdown period and return the unit as soon as possible .

Proposed Renovation - (Blade Shroud)

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Other Plant Experience


Several large sections of shrouding and few blades liberated without plant notice. Replaced the entire rotor with the planned upgraded rotor. There is no repairs were made to the failed blade row.

Another plant has experienced shrouds loosening on the LPs and the feed pump turbine. (Not tried running without portion of blades).

Removed blades from the row 180 deg . from the damaged blades but not on shrouded rows ……only free standing.

Experienced shroud lifting on the 3rd stage of IP turbine but it never came off (Repaired during outage).

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Turbine lost L-0 and L-1 shrouds. Damage was severe and full rotor overhaul was chosen and the complete row is replaced.

we lost a shroud on the L-P turbine, we cut off all four blades in that group and four blades at 180 degrees and run the turbine with no operating issues until new blades could be ordered and installed, approximately six months later.

we have removed(cut the blade off just above the root) opposite of blades that had cracked to balance out the rotor on the L-0 row.



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As a summary Several plants stated that as a temporary measure, they did remove the blades with damaged shrouds and also, an equal amount of blades 180 degrees opposite. This may not be an ideal solution and can lead to additional problems but as a temporary measure, it could be effective.



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OEM Concern : Not recommending removal any group due to followings: Balancing issue: not necessary each group has the same number of blades and the rotor has to be first be slow speed balanced before installation and further balance shots when placed into operation.

Removal two groups (12 blades) equivalent to about 25 % of the blades in row. This will change the pressure distribution in blade path with temperature increase down stream.

Steam will flow into the two large gaps causing the steam to flow into different directions to the next stage and changing the incident angles and this may cause new and unaccounted for vibratory excitation.


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Higher running speed excitation will be created on the downstream stationary row forming new vibratory excitation force on the blades and will almost act as a double shock.


OEM Concern : Not recommending removal any group due to followings:

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Replace the damaged shroud segment with the blades (riveted).

During the process of blades replacement for the row # 9 that lost its shroud during operation, it has further been seen that other shroud appear to have some amount of lifting and blade tip gaps.

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Removal and replacement of the whole blades row with integrally shrouded blades to eliminate rivet inspection and long-term maintenance issues

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The plate (shroud) is a part of the blade. The plates of several blades, which are in contact with one another, form an integral shroud.


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Conclusion and Recommendation

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The importance of returning the unit with high reliability without a risk was the main aim of SEC.


Continue and ensure performing the turbine components inspection by qualified personals in every overhaul.

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Study and analyze the cause of such failure including the review of last operational data, last overhaul report and metrological analysis of the failed blades and shrouds.

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Install online historical vibration monitoring system (under execution).

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Consult other plants for any experienced such shroud failure.

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Adaption of new technologies in blades shrouds design for new steam turbine rotors. (ongoing project as a replacement of HP/IP rotor in Ghazlan Plant)

Consult other plants for any experienced such shroud failure.

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ghazlan unit#4 ip turbine blade shroud...

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