Blade Failure on an Axial Compressor Caused by Unexpected...
Transcript of Blade Failure on an Axial Compressor Caused by Unexpected...
Blade Failure on an Axial
Compressor Caused by
Unexpected Operating at Choke
Y. Bidaut & Ch. Müller - MAN Diesel & Turbo Schweiz AG
Contents
1 Background
2 Description of the machine
3 Findings
4 Root Cause Failure Analysis (RCFA)
5 Actions
6 Conclusion
2 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
Background
3 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
Two parallel trains consisting of axial air compressors driven by steam turbines
Application: blast furnace
In operation since more than forty years (trouble free)
Recently : shutdown (planed) of one train with inspection of the compressor.
After three months of operation break-down of this compressor.
Blades damaged
RCFA performed:
Reasons of the damage
Countermeasures
Description of the machine
4 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
Axial compressor, 19 stages
gas handled : wet air
ps= 1.0 bara
pd= 5.5 bara
V = 450,000 Nm3/h
P = 40.7 MW
noperation = 3,200 rpm
nmin = 2,856 rpm (89%)
nmax = 3,360 rpm (105%)
1 Background
2 Description of the machine
3 Findings
4 Root Cause Failure Analysis (RCFA)
5 Actions
6 Conclusion
5 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
Findings
6 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
Rotor: Major damages on stages 16 to 19
Findings
7 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
Stator: Major damages on stages 16 to 19
minor damages on blade carrier & lever system
1 Background
2 Description of the machine
3 Findings
4 Root Cause Failure Analysis (RCFA)
5 Actions
6 Conclusion
8 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
Root Cause Failure Analysis
9 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
In order to clear up the compressor break down cause,
following investigations were performed:
on-site inspection
RCFA
laboratory analysis
timeline and operation data evaluations
aerodynamic investigations
Root Cause Failure Analysis - Overview
10 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
Blade bushes
Manufacturing report
Blade Machining
Geometry of blades
Foreign object
Operation below
choke line/stall !
Metallurgical
Investigation
Material
Properties
Vibration Trends
Response line
Campbell diagram
Gas bending stress
(normal operation)
Low flow operation
Blade natural
frequency
Design clearances
Normal operation
Adjusting cylinder
Rotating stall
Hardness test
Fatigue fracture
Raster lines ?!
Surge Protect°
Coating report
Coating
Coating
Corroded / Eroded blades
Alignment review
Start / stop
References
Material suitable for
actual conditions
Field Service works
7. Site Layout
Process layout
Layout changes
Instrument arrangemt
3. Blade design
2. Manufacturing
& Assembly
1. Site & Work-
shop Inspection
Corrosion
4. Material
Inspection
5. Compressor
Controls
6. Operation
Assembly report
Blade Failure
Surge
no contribution ?! possible contribution ! important contribution
Perform. control
Set Point
changes
Compressor
envelope
?!
Cracks
in other
Blades
Axial displacemt
silencer
incident !
RCFA – Laboratory analysis
11 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
Blades failed/fractured in stage 18 & 19 (blades of stage 18
failed by material fatigue)
Fracture initiation and propagation always on/from the back-
side of the blades (transition area airfoil-blade root)
RCFA – Laboratory analysis
12 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
Deposits with corrosive potential
In all deposits,
remarkable sulphur and
chloride - enrichments in
various concentrations.
Deposits contain dilutable
elements
corrosion of blade material
(with moisture)
Local corrosion reduces material fatigue
resistance
corrosion fatigue caused by cracks with
simultaneous influence of mechanical
alternating load and of attacking medium.
RCFA – Timeline Evaluation, Operation Data Analysis
13 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
February: completion of compressor installation
(new blading installed)
May : termination of commissioning
July 11th : silencer failure
July 31st : compressor breakdown
ASV
Operation data during
compressor breakdown
RCFA – Operation Data Evaluation
14 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
May – June :
operation at
chokepoint 1
for several hundred
hours
standstill of
compressor
Reason : warm-up of compressor
RCFA – Operation Data Evaluation
15 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
ASV silencer
July 11th : silencer failure
RCFA – Operation Data Evaluation
16 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
discharge pressure
4.2 barg
0.2 barg
Silencer failure leads to a sudden pressure drop and a resulting
negative pressure wave hits the compressor blading.
RCFA – Operation Data Evaluation
17 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
Result of silencer failure:
operation at
chokepoint 2
for approx. 8 hours
(cumulative) from
June 12th until
July 31st
Choke Point 2
- 100% Speed (1.5h)
- Increasing of backpressure (1s)
- Opening of IGV (4 min)
- Silencer incident
- Dropping of backpressure to 0.2 barg
RCFA – Aerodynamic Investigations
18 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
choke operation: explanation
actual inlet
volume flow
actual discharge
volume flow
static inlet
pressure
static discharge
pressure
1 bara
140 m3/s
4 bara
1.2 bara
120 m3/s
50 m3/s
exemplary values only (qualitative)
pressure
volume flow
RCFA – Aerodynamic Investigations
19 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
choke operation: explanation
R17 S17 R18 S18 R19 S19
specific flow
conditions (stall),
which can
stimulate the
natural
frequencies of the
blades
RCFA – Aerodynamic Investigations
20 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
choke operation: first bending mode (B1)
RCFA – Aerodynamic Investigations
21 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
airfoil cross section
with highest bending
moment
choke operation:
first bending mode (B1)
RCFA – Breakdown causes
22 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
long standstill / operation
@ warmup speed 1
punctual corrosion
- reduction of material
fatigue resistance
- fracture starting points
failure of silencer
choke operation
High dynamic blade
loading with excitation of
B1-mode during choke
fractures in rotor blades
#18
switching compressor to
BF
increase of blade load
blade overload #18
blade failure #18 DOD #16 - 19
1 Background
2 Description of the machine
3 Findings
4 Root Cause Analysis (RCFA)
5 Actions
6 Conclusion
23 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
RCFA – Countermeasures
24 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
In order to avoid any further compressor breakdown due
to above mentioned reasons, 3 countermeasures were
implemented:
1. realization of a choke control system
(see next slide)
RCFA – Countermeasures
25 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
ISO-Valve
1. realization of a choke control system:
Choke line
Alarm line
RCFA – Countermeasures
26 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
2. improved resistance against overload and fatigue
fractures with modified rotor blade design
3. avoidance of corrosion attacks by
application of an inorganic aluminum
coating with chromate/phosphate inert
sealant (rotor blades only)
1 Background
2 Description of the machine
3 Findings
4 Root Cause Analysis (RCFA)
5 Actions
6 Conclusion
27 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
Conclusion
28 < > Y. Bidaut / Ch. Müller METS III – Case Study – Blade Failure 01.12.2014
The encountered case was the consequence of the
concatenation of many factors:
Choke operation
o High load on blades
Corrosion
Not only the surge but also the operation in (deep) choke is
an issue for the reliability of an axial compressor
To prevent any future damage appropriate countermeasures
are necessary:
Choke control system
o Increased blade thickness
Application of coating
All data provided in this document is non-binding.
This data serves informational purposes only and is especially
not guaranteed in any way. Depending on the subsequent
specific individual projects, the relevant data may be subject
to changes and will be assessed and determined individually
for each project. This will depend on the particular
characteristics of each individual project, especially specific
site and operational conditions.
Disclaimer
Thank you very much
for your attention
Questions ?