Troubleshooting of Start-up for

Old Steam TurbineDECEMBER 14-16, 2021

Presenter/Author B ios

Yusuke Oishi yusuke.oishi.er@mhi.comTeam Leader, Turbine Engineering & Design Section, Mitsubishi Heavy Industries Compressor Corporation, Hiroshima, Japan. He has 12 years of experience as a turbine engineer. Mr. Oishi graduated from Tokuyama College of Technology (Mechanical & Electrical Engineering).

Tomoaki Nogami tomoaki.nogami.r8@mhi.comEngineer, Turbine Engineering & Design Section, Mitsubishi Heavy Industries Compressor Corporation, Hiroshima, Japan. He has 7 years of experience as a turbine engineer. Mr. Nogami graduated from The University of Tokyo.

Takuro Koda takuro.koda.k2@mhi.comManager, Turbine Engineering & Design Section, Mitsubishi Heavy Industries Compressor Corporation, Hiroshima, Japan. He has 15 years of experience as a turbine engineer. Mr. Koda graduated from Kyoto Institute of Technology.

Ayush Singh ayush.singh.p3@mhi.comEngineer, Turbine Engineering & Design Section, Mitsubishi Heavy Industries Compressor Corporation, Hiroshima, Japan. He has 0.5 years of experience as a turbine engineer. Mr. Ayush graduated from Indian Institute of Technology Kanpur, India.

Problem StatementD u r i n g t h e s ta r t - u p o f a n o l d s t e a m t u r b i n e ( a b o u t 3 0 ye a rs o l d ) , t h a t wa s i n t e r n a l l y re va m p e d , i t wa s t r i p p e d d u e t o h i g h ro t o r v i b ra t i o n s .

S i t e i nv e st i ga t i o n wa s d o n e t o f i n d o u t t h e ro o t c a u s e . A b n o r m a l c a s i n g d e fo r m a t i o n a n d r u b b i n g b e t w e e n l a b y r i n t h a n d ro t o r wa s fo u n d d u r i n g t h e i nv e st i ga t i o n .

I n t h i s s t u d y w e w o u l d l i ke t o i n t ro d u c e t h e d e ta i l p h e n o m e n o n , t h e ro o t c a u s e a n a l y s i s , w h a t w e l e a r n e d a n d w h a t w e s h o u l d h av e d o n e . We h o p e t h i s w o u l d b e b e n e f i c i a l fo r E P C a n d t h e e n d u s e r t o k n o w t h e i m p a c t i n c a s e t h e o l d s t e a m t u r b i n e wa s p a r t i a l l y re va m p e d .

Contents1. Background2. S i te Observat ions3. Root Cause Analys is (RCA)4. RCA Summary5. S i te Countermeasure6. Lessons Learned

1. BackgroundD u r i n g s ta r t - u p o f o l d t u r b i n e s , a p p rox i m a t e l y 3 0 ye a rs o l d ,• S t e a m t u r b i n e wa s t r i p p e d d u e t o h i g h v i b ra t i o n s .• M u l t i p l e s ta r t - u p t r i a l s w e re u n s u c c e s s f u l d u e t o h i g h ro t o r

v i b ra t i o n s .• D u e t o t h i s re a s o n , t h e t u r b i n e s ta r t - u p wa s p ro b l e m a t i c .

T h e t u r b i n e s p e c fo r t h i s c a s e s t u d y i s g i v e n i n Ta b l e - 1 .

Table-1 : Turbine Spec

Service Synthesis Gas

Model Extraction Condensing Turbine

Max. Output Approx. 28,000 kW

Max. Speed Approx. 12,000 rpm

Inlet Steam 106 ata x 505 deg-C

• O p e ra t i o n h i s t o r y fo r t h e t u r b i n e i s d e s c r i b e d i n Ta b l e - 2

1. Background

Year 1986/3 ～ 2020/9 2020/9,10

ActionShipment of

original turbine

Continuous Operation

Internal revamp(To decrease the steam consumption and

increase the performance)

Site operationafter internal

revamp

Newly Designed

Parts

Steam turbine assembly - Rotor, blade, nozzle,

diaphragm, labyrinth seal -

Design Philosophy Old → Latest →

Note -More than 30

years of operation

[Reused parts]Casing, governing valve, extraction control

valve, trip & throttle valve etc.

Combination of old design philosophy ( casing & reused parts) and new design philosophy

(internal parts)

High vibrations were observed

during start-up in multiple trials.

Table-2 : Operation History

1. Background

Figure-1 : Internal Revamp Modifications

Rotor (New)

Casing (Reused)

GV (Reused)

TTV (Reused)

ECV (Reused)

• I n F i g u re - 1 , t h e h i g h l i g h t e d p a r t s ( ye l l o w ) a re re va m p e d , a n d t h e re m a i n i n g p a r t s a re re u s e d .

1. Background

Figure-2 : Start-Up Diagram

• M u l t i p l e t r i a l s w e re c o n d u c t e d b y T T V s ta r t - u p( s p e e d i n c re a s e b y m a n u a l o p e ra t i o n ) .

• I n t h e 1 st t r i a l ( F i g u re - 3 ) t h e re wa s a s u d d e n i n c re a s e i n s p e e d a n d v i b ra t i o n ( S p e e d i n c re a s e u p t o 4 t i m e s t h e ta rg e t s p e e d ) .

• A f t e r e v e r y t r i a l , re s i d u a l u n b a l a n c e re c o rd s h o w e d va r y i n g ro t o r d e fo r m a t i o n .

• F ro m t h e 5 t h t r i a l s p a re ro t o r wa s u s e d i n s t e a d o f t h e w o r k i n g ro t o r ( u s e d fo r 1 st – 4 t h t r i a l ) .

2. Site Observations

Time

Rotor Vibration

When TTV opened ;Speed and vibration was increased suddenly.

Figure-3 : 1st Trial

Vibration (Exhaust Side) (1)

Vibration (Exhaust Side) (2)Vibration (HP Side) (2)

Vibration (HP Side) (1)

Speed

• D u e t o a b n o r m a l i n c re a s e i n ro ta t i n g s p e e d , t h e re i s a p o s s i b i l i t y o f ro t o r r u b b i n g w i t h s ta t i o n a r y p a r t s .

• L a b y r i n t h p a c k i n g c l e a ra n c e wa s i n c re a s e d t o p re v e n t a ny p o t e n t i a l r u b b i n g o f ro t o r.

• Tu r b i n e wa s t r i p p e d a ga i n d u e t o h i g h v i b ra t i o n( F i g u re - 4 : 5 t h t r i a l ) .

• D u e t o t h e d i f f i c u l t y fa c e d b y o p e ra t o r i n T T V s ta r t - u p , G V s ta r t - u p wa s a p p l i e d .

2. Site Observations

Figure-4 : 5th Trial

Rotor Vibration

Time

Vibration (Exhaust Side) (1)

Vibration (Exhaust Side) (2)

Vibration (HP Side) (2)

Vibration (HP Side) (1)

Speed

Turning1st Warming Up

Speed

• S p e e d wa s g ra d u a l l y i n c re a s e d ( G V S ta r t ) t o 2 n d wa r m i n g u p s p e e d w i t h o u t a ny i s s u e s ( F i g u re - 5 ) .

• At 3 rd wa r m i n g u p s p e e d h i g h v i b ra t i o n s o c c u r re d , s o t h e s p e e d wa s d e c re a s e d .

• V i b ra t i o n f l u c t u a t i o n s w e re o b s e r v e d a t d i f fe re n t s p e e d s .• S o, t h e t u r b i n e s p e e d wa s i n c re a s e d a n d d e c re a s e d b a s e d o n

t h e f l u c t u a t i o n s a n d f i n a l l y t h e o p e ra t o r wa s a b l e t o a c h i e v e M i n i m u m G o v e r n o r S p e e d ( M G S ) ( 9 t h Tr i a l ) .

2. Site Observations

Figure-5 : 9th Trial

Rotor Vibration

Time

Vibration (Exhaust Side) (1)

Vibration (Exhaust Side) (2)Vibration (HP Side) (2)

Vibration (HP Side) (1)

Speed

Turning

1st Warming-up Speed

2nd Warming-up Speed

2nd Warming-up Speed

3. Root Cause Analysis (RCA)

Repeated High Vibration During

Start-Up

Rubbing with Stationary Parts

Casing Deformation Accumulation of Drain

Temporary Rotor Deformation

Deformation Due to Sudden Increase of Speed

Labyrinth Clearance Low Clearance

Unbalance

Bending of RotorUnconventional Start-Up

Insufficient Turning Operation

Coupling/Moment Simulator Large Residual Unbalance

Instrument Sensor Error Calibration Error

BearingJournal Bearing Misalignment of Center Position

Thrust Bearing Out of Design Clearance

Phenomena Root Cause

Poss

ible

Cau

ses

Accumulation of Drain

Check for drain accumulation Due to no drain line, accumulated drain was observed. High

Possibility

Deformation Due to Sudden Increase of

Speed

Operation Record Check

Sudden increase in speed just after opening TTV. This might have caused high vibrations and rubbing with stationary parts.

High Possibility

Low Clearance Clearance Check Clearance is almost larger side, so the possibility is less. However, the sudden increase in speed caused vibrations higher than clearance limit.

Moderate Possibility

Unconventional Start-up

Operation Record Check Large increment in speed, which is not suitable for start-up. Moderate

Possibility

Insufficient Turning Operation

Operation Record Check

Turning operation stopped in about 15 minutes. Due to this the lower half of shaft may be heated up by sealing steam.

Moderate Possibility

Large Residual Unbalance

Residual Unbalance Record Check Residual unbalance was within the criteria. Not Possible

Sensor Calibration Error

Calibration Record Check Calibration record showed no problem. Not Possible

Misalignment of Center Position

Operating Data Check

Shaft center position deviation was within criteria from our experience of similar turbine. Not Possible

Out Design Clearance Clearance Check Bearing clearance was within the acceptance criteria at assembly stage. Not Possible

3. Root Cause Analysis (RCA)Root Cause Verification Result JudgementHow to Verify

Poss

ible

Cau

ses

Accumulation of Casing Drain

Rotor Temporary Deformation Due

to Sudden Increase of Speed

3. Root Cause Analysis (RCA)Root Cause Research / Evaluation Judgement

Long Term Operation (30 Years)

No Casing Drain Line

(Old Design Philosophy)

Unexpected Temporary

Casing Deformation

Sudden Increase in

Turbine Speed

Insufficient Warming-

Up of Rotor & Casing

Sudden Increase in

Speed Near 1st

Critical Speed (High Possibility

of Rubbing)

Repeated Rubbing

with Increasing Intensity

Unexpected Temporary

Rotor Deformation

High Possibility

High Possibility

4. RCA Summary

High Vibrations

• Rubbing of rotor with stationary parts

• Less clearance compared to original case (Latest Design Philosophy) with no drain line

Sudden Increase in Operating

Speed

• Speed control by manual TTV start-up was difficult due to sensitive rotor & insufficient operator skills

• Sudden increase in speed and repeatedly increasing rubbing resulted in temporary rotor deformation

After 1st

Revamp

• Internal parts were revamped

• Existing Casing was reused

Drain Accumulation

• Gradual accumulation of casing drain during the long-term operation resulted in thermal bending of casing

5. Site CountermeasuresFo l l o w i n g c o u n t e r m e a s u re s w e re ta ke n fo r a ro b u st s ta r t - u p :

• T T V m a n u a l s ta r t - u p wa s d i f f i c u l t d u e t o s e n s i t i v e ro t o r a n d i n s u f f i c i e n t o p e ra t o r s k i l l s .

• G V a u t o m a t i c s ta r t - u p wa s a p p l i e d i n s t e a d o f T T V m a n u a l o p e ra t i o n .

• I f v i b ra t i o n i s i n c re a s e d d u r i n g t ra n s i t i o n , o p e ra t i n g s p e e d s h o u l d b e d e c re a s e d t o p re v i o u s o p e ra t i n g s p e e d .

• S u d d e n c h a n g e i n o p e ra t i n g c o n d i t i o n s s h o u l d b e av o i d e d exc e p t t h e c r i t i c a l s p e e d b a n d t o p e r fo r m t h e g ra d u a l wa r m i n g - u p .

6. Lessons LearnedPr

oble

m High Vibrations during Start-up

Temporary Casing Deformation due to drain accumulation

Installation of Casing Drain Line

Sudden increase in Rotation Speed

without warming up

TTV Manual Start-Up is hard to control due

to sensitive rotor

GV Automatic Start-Up to be applied

Phenomena Root Cause Solution

Permanent Solution

Permanent Solution

Figure-6 : Casing Drain

Pressure Gauge

Casing Drain Line added to pressure gauge line

6. Lessons LearnedF i n a l c o n c l u s i o n s f ro m t h e c a s e s t u d y :

• C a s i n g d ra i n l i n e i n s ta l l a t i o n s h o u l d b e c o n s i d e re d fo r t h e re va m p o f o l d s t e a m t u r b i n e s .

• Fo r t u r b i n e s w h i c h a re c u r re n t l y i n o p e ra t i o n a n d d o n ’ t n e e d re va m p s h o u l d a l s o c o n s i d e r a d d i t i o n o f c a s i n g d ra i n l i n e a s a c o u n t e r m e a s u re fo r a ny f u t u re i s s u e s .

• S u d d e n c h a n g e i n o p e ra t i n g c o n d i t i o n s s h o u l d b e av o i d e d t o p re v e n t a ny a b n o r m a l c h a n g e i n ro ta t i n g s p e e d .

• Fo r s e n s i t i v e ro t o rs t u r b i n e s ta r t - u p s h o u l d b e ro b u st t o p re v e n t ro t o r d e fo r m a t i o n d u e t o r u b b i n g w i t h s ta t i o n a r y p a r t s .