2. 2
PRESENTATION COVERS
•VARIOUS INSPECTION TESTS INCLUDING LATEST EQUIPMENTS
•HOW TO HANDLE A PRESSURE PART FAILURE
•VARIOUS TYPES OF TUBES FAILURES , CAUSES & REMEDIES
3. 3
• Visual inspection By Torch Light
• Thickness measurement Where & which orientation
• DPT/MPT/UT At what areas
• NDT Test Selection: Knowledge of damage mechanism
• Modern testing equipment: Fibroscopy, RFET,LFET,IRIS
Insitu metallography
Methods for inspection
8. 8
PRINCIPLE
– THE PENETRATION OF A LIQUID MEDIUM INTO OPEN DISCONTINUITIES AND
BLEED OUT OF THE SAME TO STAIN A DEVELOPER COATING ON SURFACE.
– DIRECT INDICATION BY VISUAL OBSERVATION OF STAINS.
PRECLEANING TEST SURFACE
APPLICATION OF PENETRANT AFTER PENETRANT DWELL TIME
APPLICATION OF DEVELOPER
AFTER DEVELOPER DWELL TIME
DYE PENETRANT TEST ( DPT )
9. 9
PRINCIPLE
– CHANGE IN MAGNETIC PERMEABILITY OF MATERIALS AND
ACCUMULATION OF MAGNETIC PARTICLES AT THE
RESULTANT LEAKAGES OF THE MAGNETIC FLUX.
FERROMAGNETIC MATERIAL MATERIAL MAGNETISED
...
MATERIAL MAGNETISED
SHARP SURFACE DEFECT
MATERIAL MAGNETISED
SUB-SURFACE DEFECT
MAGNETIC PARTICLE TEST ( MPT )
10. 10
Steam Drum - Ligament cracking Main Steam Line Piping - Joint MSSV
after grinding
MAGNETIC PARTICLE TEST ( MPT )
11. 11
Single Transducer Double Transducer Through Transmission
PRINCIPLE
REFLECTION OF ULTRASONIC
PULSES / WAVES FROM IN-
HOMOGENEITIES IN A SPECIFIC
MATERIAL, BASED ON
DIFFERENCE IN EITHER DENSITY
OR VELOCITY OF SOUND WAVES IN
THAT MATERIAL OR BOTH
APPLICATIONS
– VOLUMETRIC TESTING OF
WELDS, FORGINGS, RAW
MATERIALS.
– THICKNESS AND CORROSION
MONITORING FOR IN-SERVICE
INSPECTION
ULTRASONIC TESTING ( UT )
13. 13
PRINCIPLE
– DIFFERENTIAL ABSORPTION OF
PENETRATING RADIATION IN THE
COMPONENT AND THE RECORD OF
THESE DIFFERENCES ON A FILM /
SCREEN / VIDEO.
APPLICATIONS
– HOMOGENEITY OF WELDS,
CASTINGS, ASSEMBLED
COMPOSITE PRODUCTS.
Source
Object
Film
RADIOGRAPHY ( RT )
14. 14
• Pre heat removes moisture content from base metal which
can lead to poor welding quality.
• Distortion of base metal due to internal stresses developed
during welding.
• Reduces hardness of weld metal
• Control cooling rate to avoid cracking
WHY PRE-HEATING OF BASE METAL?
15. 15
• Visible external porosity
in addition to internal
porosity.
• Moisture can cause slag
removal difficult, a rough
weld surface and cracking
WHY BAKING LOW HYDROGEN ELECTRODES?
16. 16
• To ensure proper working of instrument / equipment
• Improper working of baking oven can result in over/
under heating of electrode
• Improper working of welding equipment can lead to
wrong operation characteristics of m/c resulting in
welding defects
• Improper working of measuring instrument can lead to
failure during assembly
WHY CALIBRATION?
17. 17
Components - Accessible
internal surface of Tubes &
Header
Visual inspection - Photographs of
inspected object taken
Fiberscope carried out where :
-Specimen may not be removed
because it would weaken or
otherwise render it useless for
service.
-Part or structure too large to
bring to laboratory
-Object inaccessible
FIBEROSCOPY/ VIDEOSCOPY
19. 19
TOD
T
Ts
Oxide Scale
t = 0.010” to 0.03”
0.001” scale - 20 F increase in TOD
T
OD
=
20
0
F
to
60
0
F
OXIDE SCALE MEASUREMNT
• Tube Temperatures > 900o F
• Failure prone by Creep Fatigue
• Oxide Scale formed (Fe2O3)
• Metal temperature increase 1-2o F
increases creep damage
Creep - Due to thermal
activation, materials can
slowly and continuously
deform even under constant
load (stress) and eventually
fail.
[The time dependent,
thermally assisted
deformation of components
under load (stress)]
Stress Rupture
Corrosion Assisted
Erosion Assisted
20. 20
Field surface Replication is a process that permits obtaining an image
of a component surface with sufficient retention of fine structure, to
permit laboratory examination & evaluation without having to cut out
a portion of the component. The evaluation of grain size, precipitate
spacing using both optical & electron microscopy can establish
presence of microstructural damage or changes and assist in
understanding service conditions.
INSITU METALLOGRAPHY
Normal grain structure Damaged Structure
21. 21
Localised underdeposit corrosion
produces atomic hydrogen (H)
Small hydrogen atom diffuses into
the tube metal and reacts with
carbon in the steel
4H + Fe3C = CH4 + 3Fe
Large methane molecule (CH4)
becomes trapped in grain structure
Intergranular pressures lead to
microfissuring of steel
Remaining
Tube wall
0.160”
Hydrogen
Affected
Metal
0.074”
Total Wall Thickness 0.025”
Corroded
Metal
0.016”
Entrapped
Methane
HYDROGEN DAMAGE MEASURMENT
22. 22
OTHER MODERN FAST SCANNING TECHNIQUES
INTERNAL ROTARY INSPECTION SYSTEM ( IRIS) –
Ultrasonic based testing for scanning thickness from inside the tubes.
Area Covered : Boiler Bank, Economizer
PRINCIPLE:
The IRIS probe consists of a rotating
mirror that directs the ultrasonic
beam into the tube wall. The mirror is
driven by a small turbine that is
rotated by the pressure of water being
pumped in. As the probe is pulled the
spinning motion of the mirror results
in a helical scan path.
23. 23
OTHER MODERN FAST SCANNING TECHNIQUES
REMOTE FIELD EDDY CURRENT TESTING ( RFET)
Eddy Current based testing for scanning thickness from inside tubes.
Area Covered : Boiler Bank, Economizer
24. 24
OTHER MODERN FAST SCANNING TECHNIQUES
TIME OF FLIGHT DIFFRACTION (TOFD)
Eddy Current testing for scanning Welds
Area Covered : Welds
Principle : TOFD technique is based on diffraction of ultrasonic waves on the
tips of discontinuities instead of reflection on the interface of discontinuities..
27. 27
• Consider Pressure Parts failure as a serious lapse from either
designer, erector, commissioning engineer or O & M staff.
• Treat it as a crime and FIR must be logged with utmost care.
• Shut the unit as early as possible to minimize further damage.
• Gather as many as information possible related to failure , that
includes data prior to failure, at the time of failure and after
the failure
• Preserve the operating log sheet, DCS trends as early as
possible
• Spend minimum @ 15-30 minutes time for inspecting &
investigating the failure area with out disturbing the evidence.
HOW TO HANDLE PRESSURE PARTS FAILURE
28. 28
• Take Photograph of the failed and surrounding area along with
noting of critical observation.
• Inspect the adjacent tube condition with same zeal & attitude.
• Type of failure would more often suggest the cause.
• Cut down the failed tube of @ 500 mm length keeping failed spot at
centre. Cut the tube preferably with hack saw.
• Before cutting the sample , mark tube no., direction of fluid flow,
side facing flue gas flow
• Do not remove the internal deposit of cut tube and cover both the
ends of cut tube.
• Try to preserve the external deposit too.
HOW TO HANDLE PRESSURE PARTS FAILURE
29. 29
• If over heating symptoms are there, it is advisable to cut one
more sample from adjacent un failed tube.
• Send the tube sample to IJT H.O with proper packing along with
Data format filled.
• Carry out thorough Physical, chemical and metallurgical
analysis of both tubes.
• Carry out deposit analysis collected from failed tubes. Which
will indicate water chemistry condition.
• Based on the analysis, root cause can be concluded.
• Ensure that all the corrective actions on boiler are incorporated
at the earliest available opportunity.
HOW TO HANDLE PRESSURE PARTS FAILURE
30. 30
General Test Carried out on Tube Sample.
• PHYSICAL TESTS :
Outside Diameter Thickness
Tensile Strength Ultimate Strength
Percentage elongation Percentage Weight loss
• CHEMICAL TEST:
Material identification
• METALLURGICAL TEST:
Microstructure
Hardness
• DEPOSIT ANALYSIS
Composition analysis
HOW TO HANDLE PRESSURE PARTS FAILURE
31. 31
TUBE FAILURE DATA FORMAT
Report By: Date:
Name of Customer
Boiler Specification
Capacity:
Pressure:
Temperature:
Fuel being fired:
Name of failed Pressure part
Location of tube sample:
Duration of service of boiler
Is the failed tube original or replaced?
Date of failure:
Tube material ( specified)
Tube OD X Thk ( specified)
Orientation of tube
Fluid media flow direction ( with marking)
• Visual Inspection Report with sketch /Nature of failure:
Boiler operating condition at the time of failure (attach Boiler operation log sheets supported by DCS trends of critical parameters, Fuel
fired and water chemistry reports)
Chemical dosing details.
Any other relevant information about the failure.
(Attach extra sheets, if required)
HOW TO HANDLE PRESSURE PARTS FAILURE
33. 33
• During Manufacturing
• During Transportation
• During Erection
• During Operation / In Service
• Idle period.
FAILURE STAGES
Any Pressure part can be grouped into 2 class.
• Water Cooled Tubing or Headers
• Steam Cooled Tubing and Headers
Failure mechanism of these parts differs marginally
35. 35
CREEP CURVE FOR CARBON & LOW ALLOY STEELS
SL-I
CP-II
CP-II +
CP-III
SL-IV
SL-II
CP-I
EXPOSURE TIME
CREEP
STRAIN
SL-III
STAGE -I STAGE -IV
STAGE -III
STAGE -II
NOTE- IT AN APPROXIMATE CURVE DRAWN WITH REPRESENTATIVE METALLOGRAPHIC
DEGRADATION LEVELS OF MATERIAL IN SERVICE . FIGURE IS NOT AS PER SCALE.
CREEP CURVE FOR CARBON STEEL
36. 36
• Visual Inspection-
– Thin edge failure. Pin hole leak
– The external surface appears
to be polished.
– Large loss of wall thickness
• Occurs in -
– Waterwall tubes
– Inbed tubes
– Economizer tubes
– Superheater tubes.
Microstructure
– Normal ferrite plus pearlite
grain structure
Erosion
37. 37
• Possible causes
– Coal/Ash content
– Local high flue gas velocities
– Improper setting of valves in blowers.
• Preventive measures to reduce failure
– Use of erosion resistance material (Inconel etc.)
– Shielding of Tube
– Gas / liquid flow velocity
Erosion
39. 39
• Visual Inspection
– Pin hole type rupture.
– Metal attack confined to
surfaces covered with soot
deposits.(Small pits)
– Soot deposits evident on
external surface
• Occurs in
– Economizer tubes
– Furnace tubes
– Air-preheater tubes
• Microstructure
– Normal ferrite plus pearlite,
sometimes oxidation on
grain boundaries seen.
Dew Point Corrosion
40. 40
– Possible causes
Low back end
Temperature
Low feed water
temperature
High sulfur in fuel
fired
Accumulation of
sulfur rich deposits
on tubes for
prolonged period
,during the boiler
idle time.
Preventive measures
• Feed water
temperature above
dew point
• Low sulfur fuel
• Frequent cleaning of
sulfur rich deposits
during shut down
• Reduce no of start &
stop.
• Use of cast grilled tube
Dew Point Corrosion
41. 41
• Visual Inspection-
– Pinhole initiated from ID surface in center of circular pit.
– Maybe pit has rusty appearance
• Occurs in -
– Waterwall tubes, Economizer tubes, Superheater tubes.
• Chances of pitting are more in horizontal tubes & at bends
Oxygen Pitting
42. 42
• Microstructure
– Normal ferrite plus pearlite
• Possible causes
– Water remaining in tubes during shutdown etc.
– Oxygen ingress / higher O2 in Feed water
Preventive Measures to reduce failures
– Strict adherence to the shut down & lay-up procedures for
protecting the tubes like maintaining alkaline pH, keeping
surface dry and clean
– regular sampling of tubes from specified zones for metallurgical
evaluation & internal deposit analysis
– regular wall thickness measurement at critical locations.
– Use of de-aerator (Mechanical / Chemical)
Oxygen Pitting
43. 43
• Visual Inspection
– Longitudinal crack on
external surface may be
present.
– Large loss of wall
thickness
– Thick hard/molten deposits
on external surface
• Occurs in -
– Waterwall tubes
– Superheater tubes
Microstructure
– Normal grain structure ,
sometimes grain boundary
oxidation may be seen
Fire side Corrosion
44. 44
• Possible causes
– Aggressive coals containing high levels of chlorine
– Residual oils containing high levels of vanadium ,
sodium & sulfur.
• Preventive measures
– Preventive Measures to Reduce Failure
– Regular thickness measurement
– monitor temperature at suitable location
Fire side Corrosion
45. 45
• Overheating failures
– Short Term:
– Long Term:
• Occurs in -
– Inbed evaporator tubes
– Common in Superheater tubes
– Furnace wall tube
– Convection banks
Overheating Failures
46. 46
• Visual Inspection-
– Short Term:
• Longitudinal fish mouth opening
• Violent rupture, bulging may occur
• Rupture edges may be thin. No oxide scale on internal &
external surface.
– Long Term:
• Longitudinal fish mouth opening with thick lip fracture.
• Rupture may be with a bulge.
• Oxide scale evident on internal or external surface.
• Secondary cracks may be evident near the primary
rupture.
Overheating Failures
50. 50
Microstructure
– Coarse grains at the failure with voids at grain
boundaries or cracks.
– Surface decarburization may be evident.
Overheating Failures
51. 51
• Probable Causes -
– Tube starvation
– Flame impingement
– Upset in water chemistry
– Improper material selection
– Steam bubble on horizontal
tubes, Departure from
Nucleate Boiling (DNB)
conditions
Preventive Measures to
Reduce Failure overheating
– Avoid tube blockages by
cutting debris,weld spatter
– Proper coolant flow rates,
– Maintain drum-water levels
and control firing rates
– Modify Tube design with
internal ribbing or rifling
– Remove internal scale
– Upgrade metallurgy
Overheating Failures
58. 58
Visual Inspection
– Thin edge pin hole
rupture.
– Excessive deposits
& loss of thickness
on water side.
Occurs in -
– Waterwall tubes,
– Inbed tubes.
Microstructure
– Normal ferrite plus
pearlite structure
Caustic Gauging
59. 59
• Possible causes
– High levels of caustic
in boiler water
– Excess weld
penetration
– DNB conditions, dirty
boiler ID surfaces &
flame impingement
exacerbate the
problem .
Preventive measures to reduce
failure
– monitoring of heat flux using
proper thermocouples
– Stringent control on feed
water chemistry particularly
on pH and other Oxygen
scavenger additions
– Regular sampling of tubes
from high heat flux zones for
metallurgical & internal
deposit analysis
– Periodic inspection of proper
burner alignment
– Use of rifle tube
Caustic Gauging
60. 60
• Visual Inspection-
– Rupture in the form of window
type opening.
– Thick lip fracture.
– Fracture always brittle in nature.
– Excessive deposits on water
side.
– Failure always on fire side.
– Sometimes thickness reduction
is seen.
• Occurs in -
– Waterwall tubes,
– Inbed tubes.
Microstructure
– Cracks along the grain
boundaries & sometimes
decarburization observed.
Hydrogen Damage
61. 61
• Possible causes
– Upset in water
Chemistry
– Dirty boiler ID
surfaces
– Flame impingement
may exacerbate the
problem.
Preventive measures to reduce failure
- Monitoring of heat flux using proper
thermocouples
- Stringent control on feed water
chemistry particularly on pH and
other Oxygen scavenger additions
- Regular sampling of tubes from high
heat flux zones for metallurgical &
internal deposit analysis and
flattening test
- Periodic inspection of proper burner
alignment
- In-situ hydrogen embrittlement
analysis using Ultrasonic methods
- Use of rifle tube
Hydrogen Damage
62. 62
• Visual Inspection-
– Usually,
Circumferential
thick edge brittle
failure exactly at
the interface
between the 2 tube
weld.
• Occurs in -
– Superheater
– Reheater tubes
Dissimilar Metal weld ( DMW) failure
