By:
K.K. Tandon – Director (Technical)
M/s Bhotika Pipeline Services Co. Pvt. Ltd.
Ex. G.M., Engineers India Limited (EIL)
ICEPIM 2015
International Conference on Pipeline Integrity management
Pipeline as a large pressure vessel.
Conventional NDT not feasible.
Hydro-testing limitations:
◦ Only a fail/ no fail test
◦ Interruption in supplies
◦ Availability of large amount of clean water
◦ Disposal of contaminated water
◦ Safety of public at large
Hydro-testing continues to be practised:
◦ For new pipelines
◦ For large scale rehabilitation projects
No provision for Launchers/ Receivers
Reduced bore mainline valves & check valves
Low flow conditions resulting in reduced velocity
Miter bends
Less than 3D bends
Large diameter unbarred Tee
ECDA & ICDA (Ref. NACE Standards RP0502-2002,
SP-0208-2008)
CPL Survey
DCVG Survey/ other Corrosion Control Surveys
Corrosion Probes
Guided Wave Inspection Technique
OISD GDN-233 Guidelines on inspection of on land non-
piggable pipelines.
Longitudinal guided waves
are induced into the pipe
body.
When these waves intersect
any pipe anomaly, mode
conversion takes place into
laminar waves and reflect
back to the tools original
location.
Reflected signals are digitally
captured and processed.
Teletest equipment hardware
and software developed by
TWI, UK on this principle.
The basic TeleTest system based on Long Range
Ultrasonic Testing (LRUT) comprises of the following:
◦ A low frequency flaw detector, the Teletest Focus pulser receiver
unit.
◦ Transducer ring or tool that wraps around the pipe.
◦ A laptop computer that contains the software controlling the
system.
◦ Cable connector between the Teletest Focus unit and tool.
◦ Communication between the Teletest Focus unit and laptop
through ethernet.
Contd…
Figure-2:
The TeleTest Equipment System
To determine the health of the pipeline in quantifiable
terms:
◦ To determine if any defect detected by the online inspection would
fall at the uprated pressure.
◦ To determine if any existing defect can extend and cause failure
at the uprated pressure.
◦ To consider all other factors (e.g. cracks, extensive fracture
propagation) which could conceivably influence the integrity of the
pipeline at the uprated pressure.
Imperfection:
◦ May cause failure above the pressure that causes nominal yield
of the pipe.
Defect:
◦ Will fail at or below the pressure that causes nominal yield of the
pipe.
Critical Defect:
◦ Will fail at or below the maximum allowable operating pressure.
Metal Loss (corrosion and gouges)
Metallurgical (hard spots, inclusions, laminations, and
weld porosity)
Cracks (axial)
Cracks (circumferential)
Dents and buckles with or without metal loss
Figure-3: Imperfection and defect sizes
(36-inch-diameter × 0.375-inch wall thickness X60)
Design & construction of intelligent pig tools
with specific emphasis on Magnetic Flux
Leakage (MFL) technology.
Ideal pipeline would be:
◦ Be perfectly straight from end to end
◦ Have a constant ID with no weld penetration
◦ Be perfectly round
◦ Have an inside surface which was polished or epoxy coated
◦ Have no off-takes
◦ Contain no valves or any other device
◦ Be pumping a light, refined oil at a speed of about 1m/sec.
◦ Should be equipped with suitably designed pig Launchers/
Receivers.
Can be defined as the pigging that generates and
records some data for analysis for establishing the
health of the pipeline segment in quantifiable terms.
Contd…
PIGGING
UTILITY PIGGING INTELLIGENT PIGGING
For Pipeline Cleaning
Hydro-testing
Drying
Internal Coating
Condensate Removal
Product Separation
(Batching)
Decommissioning
Geometry Pigging Corrosion Monitoring
Based on
MFL Principle
Based on
Ultrasonic Principle
Conventional Pig Tool
High Resolution
Pig Tool
Transverse Field
Inspection Pig Tool
The objective is to find the location and size of dents
and ovalities in the cylindrical geometry profile of
pipelines.
Figure-4: Electronic Geometry Pig Tool
Drive-Cup
Locator-Unit
Odometer-Wheel
Digital-Data-Recorder
Pushing-Flange
Sensing-Finger
Transmission-Disc
Figure-5: Basic principle of
Magnetic Flux Leakage (MFL)
Figure-6: Principle of Ultrasonic (UT) Metal Loss
Detection Technique
Table 1: Types of ILI Tools and Inspection Purposes
ILI PURPOSE METAL-LOSS TOOLS CRACK-DETECTION
TOOLS
CALIPER
TOOLS
MAPPING
TOOLS
Magnetic Flux Leakage (MFL) Ultrasonic
(compressi
on wave)
Ultrasonic
(shear
wave)
Transverse
MFL Standard-
resolution
(SR) MFL
High-
resolution
(HR) MFL
METAL LOSS (CORROSION)
External corrosion
Internal corrosion
Detection, (A)
sizing, (B) no
ID/OD (C)
discrimination
Detection, (A)
sizing (B)
Detection, (A)
sizing (B)
Detection, (A)
sizing (B)
Detection, (A)
sizing (B)
No
detection
No
detection
NARROW AXIAL EXTERNAL
CORROSION
No detection (A)
No detection (A)
Detection, (A)
sizing (B)
Detection, (A)
sizing (B)
Detection, (A)
sizing (B)
No
detection
No
detection
CRACK AND CRACK-LIKE
DEFECTS
(Axial)
Stress corrosion cracking
Fatigue cracks
Longitudinal seam weld
imperfections
Incomplete fusion (lack of fusion)
Toe cracks
No detection No detection No detection Detection, (A)
sizing (B)
Detection, (A)
(D) sizing (B)
No
detection
No
detection
CIRCUMFERENTIAL
CRACKING
No detection Detection, (D)
sizing (D)
No detection Detection, (A)
sizing (B) if
modified (E)
No detection No
detection
No
detection
DENTS
SHAP DENTS
WRINKLE BENDS
BUCKLES
GOUGES
Detection (F) Detection (F)
sizing not
reliable
Detection (F)
sizing not
reliable
Detection (F)
sizing not
reliable
Detection (F)
sizing not
reliable
Detection (G)
sizing
Detection,
sizing not
reliable
In case of detection, circumferential position is provided.
LAMINATION OR INCLUSION Limited
detection
Limited
detection
Detection,
sizing (B)
Detection,
sizing (B)
Limited
detection
No
detection
No
detection
PREVIOUS REPAIRS Detection of steel sleeves and
patches, others only with ferrous
markers
Detection
only of steel
sleeves and
patches
welded to
pipe
Detection
only of steel
sleeves and
patches
welded to
pipe
Detection
only of steel
sleeves and
patches,
others only
with ferrous
markers
No
detection
No
detection
MILL-RELATED ANOMALIES Limited
detection
Limited
detection
Detection Detection Limited
detection
No
detection
No
detection
BENDS No detection No detection No detection No detection No detection Detection,
sizing (H)
Detection,
sizing
OVALITIES No detection No detection No detection No detection No detection Detection,
sizing (B)
Detection,
sizing (B)(I)
PIPELINE COORDINATES No detection No detection No detection No detection No detection No
detection
Detection,
sizing
(A)Limited by the minimum detectable depth, length, and width of the defects
(B)Defined by the specified sizing accuracy of the tool
(C)Internal diameter (ID) and outside diameter (OD)
(D)Reduced probability of detection (POD) for tight cracks
(E)Transducers to be rotated by 90°
(F)Reduced reliability depending on the size and shape of the dent
(A)Depending on the configuration of the tool, also
circumferential position
(B)If equipped to bend measurements.
(C)If the tool is equipped for ovality measurement
Shaped area indicates ILI technologies that can be used
only in liquid environments, i.e., liquids pipelines or in gas
pipelines with a liquid couplant.
MFL Technique
Based Tool
Ultrasonic Technique
Based Tool
Can be conveniently used for
liquid and gas transporting
pipelines.
Practically very cumbersome to
use for gas transporting
pipelines.
Indirect method of defect sizing Direct measurement of defects
Conventional MFL tool has relatively less number of
sensors and analog recording.
High resolution system is comprised of a greater number
of sensors and digital recording.
The sensor size and the axial sampling interval which
determines tool resolution and the ability to accurately
characterize the defect.
Contd…
Digital recording mandates that the continuous signals
from the sensors be sampled at discrete intervals. The
signal may be sampled as a function of time or distance
traveled. In the realm of in-line inspection, time based
sampling is undesirable due to the rather large
excursions in tool speeds encountered. The axial
sampling internal is preferred and is the distance along
the pipeline at which the analog waveform is sampled
and stored.
Contd…
A study was conducted utilizing the test setup depicted
in Figure-10 to determine the effect of sensor size on the
ability to resolve defects. The defect set was comprised
of three machined defects. The maximum depth of each
defect was 30% of bodywall. The axial separation
between the defects was 1.2 inches. The circumferential
separation between the defects was also 1.2 inches. It
should be noted that according to one of the typical
interaction criteria cited in Figure-1, these defects will not
interact and therefore need to be resolved by the sensor
system.
Contd…
In figures 11-13 the results of this study are shown. An
inspection of the results reveals that resolution in the
circumferential direction is indeed dependent on sensor
size.
Both the .25” wide sensor and the .5” wide sensor were
clearly able to resolve the machined defects both in the
axial and circumferential direction.
The .75” wide sensor and the 1” wide sensor displayed
increasing difficulty in resolving the defects in the
circumferential direction.
Contd…
Figure-7: Test Setup
Figure-8: .25 Inch Wide Sensor
Figure-9: .5 Inch Wide Sensor
Figure-10: .75 Inch Wide Sensor
Axial sampling interval affects defect characterization.
Axial sampling interval must be less than or equal to .10”
for accurate peak amplitude measurements.
Contd…
Axial interaction may occur if L3 is less than L1 and L2
Circumferential interaction may occur if W3 is less that W1 and W2
Axial interaction may occur if L3 is less than 1”
Circumferential interaction may occur if W3 is less than 6t, where t is
the wall thickness
Figure-12: Typical criteria for interaction
Figure-13: Axial Sampling Interval Versus Peak Amplitude
Figure-14: Typical High Resolution MFL Tool
Figure-15: Typical Transverse Field Inspection Tool
Drive System
Power System
Magnetization System
Sensor System
Data conditioning and recording system
Tool design parameters
Pipeline design & operating parameters
Magnetization Level
Sensor System
Figure-16: Typical Magnetization Curve
Figure-17: Flux Leakage at Three Magnetization Levels
Sensors between the magnet pole pieces measure the
flux leakage field. The purpose of sensor systems is to
convert the flux leakage field into a signal that can be
stored and analyzed.
Induction Coil System:
◦ The most commonly used type of sensor on MFL tools is an
induction coil. Induction coils incorporate several turns of fine
wire.
◦ A changing magnetic field induces a voltage across the wire.
◦ Therefore, no voltage will be induced when no defect is present.
When a imperfection causes flux to leak into the air, a voltage is
induced because the flux density is changing.
Contd…
Figure-18: Coil Sensor Basics
Hall-Effect Sensors:
◦ A charged particle moving (flow of electrons in a charged
conductor) in a magnetic field (leakage magnetic flux)
experiences a potential difference (voltage). This effect is known
as “Hall-Effect’ and voltage is called Hall Voltage.
◦ A magnetic field sensor directly measures the magnetic field. The
most common type is a Hall-effect sensor, which directly converts
the magnetic field level to an output voltage.
◦ Hall-effect sensors are also temperature sensitive, with a drift in
output voltage on the order of a tenth of a percent per degree
Celsius (-0.06 percent/degree F).
◦ Hall effect sensors require power to operate, of the order of tenth
of a watt.
Figure-19: Hall-Effect Sensor
An MFL tool contains a system that magnetizes a length
of the pipe wall. Typically, sets of magnets are used to
provide coverage around the circumference of a pipe.
Either permanent magnets or electromagnets are used.
Permanent magnets have a constant charge, and they
require no power to operate.q
Figure-20: Magnetizing Systems
The magnetization system in an MFL tool should
produce a magnetic field that is:
◦ Strong enough to cause a measurable amount of flux leakage at
defects,
◦ Uniform from inside to the outside surface of the wall thickness
so that changes in the magnetic field do not skew the results, and
◦ Consistent in magnitude along the length of a pipe so that
measurements can be compared at different locations during an
inspection run.
Permanent magnets Vs Electro-magnets
ALNICO Magnets
Rare earth magnets
Temperature sensitivity of magnets
Data generated is large:
Data points = (number of sensors) x (the number of
samples per unit distance) x (the distance traveled)
Data points = (2*24*pi) x (120 samples per foot) x
(100*5280) = 9,504,000,000 10 Billion data points
Tool designers use data conditioning systems to
compress the data and reduce storage requirements.
Figure-21: Data generating system
The data conditioning and data storage devices that are
used in an MFL tool require power to operate, as well as
some sensors. So, the battery power that is available
limits the mileage that can be inspected at any time.
The force exerted by gas or liquid pushing on a cup or
set of cups at the front of the tool pulls the tool through
the line. Differential pressure acting between the front
and back of the drive cups provides a force along the
pipe axis. This force propels the drive cups, which in turn
pull the rest of the tool
Figure-22: Drive System
The intelligent pigging should be considered as a multi
disciplinary project.
Expensive
Pre-inspection activities.
Field activities during intelligent pig run.
Post intelligent pig run activities including data
assessment.
Pull Through Test
Information review
Pipeline cleaning & geometry assessment
Placement of aboveground markers
The proposed intelligent pigging tool shall be calibrated
through pull through test at tool owning agencies works.
Test pipes shall have comparable wall thickness as the
actual pipe to be inspected.
Tool velocity during pull through.
Pull through test data regarding known defects should
coincide within acceptable tolerance limits with the
actual size of the defects including relative position.
TYPICAL PULL THROUGH TEST REPORT
Figure-23: Pull Test — Feature length comparison
Figure-24: Pull Test — Feature width comparison
Figure-25: Pull Test — Feature wall loss comparison
All pipeline features should be known & evaluated.
Presence of non-return/ check valves.
Presence of internal corrosion monitoring probes.
Internal cleaning is a must before launching the
intelligent pig tool.
Special cleaning pigs such as magnetic cleaning pigs
should be deployed.
Electronic geometry pigging is most advisable.
Marking systems are essential to have reference
locations which establish a relationship between the
locations of significant defects on the pipeline & those on
the survey charts.
The following two types of markets systems are currently
in vogue:
◦ Magnet marker system
◦ Aboveground market coils
Permanent magnet markers are placed at approximately
1 km interval.
The system is most effective.
Figure-26: Proper placement of a horseshoe marker magnet
Electro magnetic coils are provided by intelligent pig
manufacturers which can be placed directly over the
ground.
Pipeline Cleaning
Electronic Geometry Pigging
Launching
Pig Tracking
Receiving
Of late, pipeline owners require XYZ mapping data
acquisition preferably to be done concurrently with the
MFL tool run.
XYZ mapping was developed to determine
3-Dimensional graphical pipeline coordinates. Inertial
navigation unit is attached with the MFL tool.
The major advantage of XYZ mapping is that all the
anomalies detected on the pipeline can be located with
XYZ coordinates assigned to these features. This
facilitates defect identification in the field very accurately
without any hassles.
Figure-27: Typical Launcher/Receiver Arrangement
Defect Verification
Data Analysis
Reporting
Flaw selection
Flaw verification procedure
Figure-28: Defect verification
Figure-29: Data analysis
The typical final inspection report shall consist of the
following information:
◦ Tool operational data,
◦ Pipe tally,
◦ List of features,
◦ Summary and statistical data,
◦ Fully assessed feature sheets, and
◦ Defect assessment method.
Data sampling frequency or distance;
Detection threshold;
Reporting threshold, normally taken at 90 percent POD,
if not specified otherwise;
A tool velocity plot over the length of the pipeline;
Optionally, a pressure and/or temperature plot over the
length of the pipeline; and
In case of MFL pigs, the magnetic field strength H in
Am-1.
The pipe tally list shall contain the parameters:
◦ Log distance, in m;
◦ Joint number giving log distance at upstream girth weld;
◦ Joint length, in m; and
◦ Description of installation.
The list of features shall contain the following
parameters:
◦ Log distance;
◦ Joint number;
◦ Nominal pipe wall thickness or reference wall thickness as
measured by the tool;
◦ Feature description adjacent to girth weld;
◦ Distance to upstream girth weld;
◦ Orientation;
◦ Feature length, width and depth;
◦ ERF (Estimated Repair Factor); and
◦ Internal/external/mid-wall indication.
Total number of metal loss features,
Number of internal metal loss features,
Number of external metal loss features,
Number of general metal loss features,
Number of pits,
Number of axial and circumferential grooves,
Number of metal loss features with depth 0-9 percent,
Number of metal loss features with depth 20-29 percent,
Contd…
Number of metal loss features with depth 30-39 percent,
Number of metal loss features with depth 40-49 percent,
Number of metal loss features with depth 50-59 percent,
Number of metal loss features with depth 60-69 percent,
Number of metal loss features with depth 70-79 percent,
Number of metal loss features with depth 80-89 percent,
Number of metal loss features with depth 90-100 percent,
Number of metal loss features with 0.6 ≤ ERF ≤ 0.8,
Number of metal loss features with 0.8 ≤ ERF ≤ 0.9,
Number of metal loss features with 0.9 ≤ ERF ≤ 1.0, and
Number of metal loss features with ERF ≥ 1.0.
Fully assessed feature sheets shall contain the following
information to the full sizing specification:
◦ Length of pipe joint and orientation of longitudinal seam (when
present),
◦ Length and longitudinal seam orientation of the 3 upstream and 3
downstream neighbouring pipe joints,
◦ Distance of upstream girth weld to nearest upstream marker,
◦ Distance of upstream girth weld to nearest downstream marker,
◦ Distance of metal loss feature to upstream girth weld,
◦ Distance of metal loss feature to downstream girth weld,
◦ Orientation of metal loss feature,
◦ Feature description and dimensions, and
◦ Internal/external/mid-wall indication.
Accidents appear to fall into three main areas of
handling pressurized equipment, loading and unloading
of pigs and defective equipment such as pressure
gauges.
Pyrophoric materials
Hydrate precautions
Slug collection
Notwithstanding, the best of preparation and planning,
the occurrence of contingency situations cannot be
completely ruled out.
Contingency arising out of stuck pig
Contingency due to sudden stoppage of flow
Sudden failure of pipeline
Contingency arising due to excess amount of
condensate/water mixtures and/or black dust/iron oxide
coming out along with cleaning pig or Intelligent tool
shall be taken care.
Figure-30: Typical Line
Preparation/ Inspection
Programme
A changing magnetic field passing by an electrical
conductor will produce a current in the conductor. An
MFL magnetization system traveling down a pipeline
represents a changing magnetic field. The pipe is an
electrical conductor. Therefore, current will be induced in
the pipe.
Increasing the velocity of a tool reduces the applied field
strength by inducing eddy currents.
For the 10-mph case, the magnetic field in the pipe
drops 10 percent. So, the applied field is reduced, which
affects detection and characterization.
Figure-31: Calculated applied fields as a function of velocity
Stress in a pipeline arises due to gas pressure in the
pipe, residual stresses from the fabrication process, field
bends, ground shifts, etc. Metal-loss regions act as
stress risers that increase the effects of stress even
further.
Stress effects are complicated because stress affects
the overall (bulk) permeability of a steel, and it affects
the local permeability at a metal-loss region.
A change in the local permeability at a metal-loss region
can produce significant changes in the amplitude and
shape of the leakage field.
Contd…
As stress increases, the signal amplitude initially
decreases up to 25 percent, then increases passing the
initial amplitude, and continues to rise for practical
operating stresses.
Stress affects detection and characterization because it
affects applied flux densities and leakage fields.
Additional research is needed to better define the effects
of stress.
Remanent magnetization also affects the applied
magnetization level. Remanent magnetization is the
magnetization level left after a tool passes.
Pipeline steels exhibit a hysteresis effect when
magnetized; specially, when the applied field is removed,
a flux density is left in the pipe.
Complete data on pipeline.
Anticipate tool anomalies.
ILI is not the panacea of all the troubles.
Select appropriate (Fitness-for-Purpose) tool.
ILI is expensive & resource consuming activity.
Detection, Identification and sizing of the metal loss
features with a confidence level and probability of
detection are called Defect characterization. All the metal
loss features need to be characterized with at least 80
percent confidence level and 90 percent probability of
detection.
Pin Hole
Pitting
General Corrosion
Axial Grooving
Circumferential Grooving
Slotting
Figure-32: Geometrical representation of
metal loss feature definitions
Figure-33: Location and dimension of metal loss features
As per ASME B31G
There are four levels of evaluation mentioned in ASME
B31G – 2009 i.e. Level 0, Level 1, Level 2 and Level 3.
Contd…
Nomenclature:
Contd…
Nomenclature:
Contd…
As per original B31G:
Contd…
As per modified B31G:
Contd…
Level 0 Evaluation:
◦ ASME B31G provides tables of acceptable lengths of corrosion.
◦ The maximum depth of corroded area & longitudinal length is
measured corresponding to the size of pipe.
◦ It can be directly located in the tables corresponding to various
dia of pipelines
◦ Metal loss is acceptable if its measured length does not exceed
the value of L given in the corresponding table.
Contd…
Level 1 Evaluation:
◦ Measure the maximum depth of the corroded area & longitudinal
extent of corroded area.
◦ Define an acceptable safety factor, SF.
◦ The flaw is acceptable where SF is equal to or greater than
SF × So, or where PF is equal to or greater than SF x Po.
Contd…
Level 2 Evaluation:
◦ Level 2 evaluations are performed using what is known as the
Effective Area Method.
◦ The Effective Area Method is expressed as follows:
Contd…
Level 3 Evaluation:
◦ A Level 3 evaluation typically involves a detailed analysis, such as
a finite element analysis of the corroded region.
Contd…
Figure-34: Parameters of metal loss used in
analysis of remaining strength
Contd…
Axial interaction may occur if L3 is less than L1 and L2
Circumferential interaction may occur if W3 is less that W1 and W2
Axial interaction may occur if L3 is less than 1”
Circumferential interaction may occur if W3 is less than 6t, where t is
the wall thickness
Figure-35: Typical criteria for interaction