Advance NDT

8/10/2019 Advance NDT

1/28


2/28

Advanced NDT

Long Range Ultrasonic Testing (LRUT)

Acoustic Emission Testing (AET)

Time of Flight Diffraction (TOFD)


3/28

LONG RANGE ULTRASONIC TESTING


4/28

Long Range Ultrasonic Technique (LRUT)

HOW IT WORKS Torsional or longitudinal guided waves are induced into

the pipe body and propagated along the pipe segment

being inspected. When these guided waves identify ananomaly or Pipe feature, the waves convert into laminar

waves and reflect back to the LRUT Toolsoriginal location.

We use a laptop computer to digitally capture the results.

The time-of-flight for each signature is calculated to

determine it's distance from the tool.


5/28

5

Conventional UT measures the wall thickness at a spot,

while Guided Wave Ultrasonics can identify locations of

metal loss along a length of the pipe

WeldMetal loss Metal loss

FlangeConventional

Ultrasonic Test

Weld Metal loss Metal loss

Guided Wave

100%

Inspection

LocalizedInspection

Convent ional ult rasonic inspect ion prov ides a local th ickness measurement

GWUT Inspect ion p rovides d etect ion of b oth in ternal and

external corrosion typically for 100 or more down the pipe.


6/28

6

Guided waves, typically between 3075 KHz, are

introduced into the pipe

An array of piezoelectric crystals arepositioned in modules that typically

hold two transducers each. The

modules are spaced around the pipe

under an air bladder which whenpressurized forces the units against

the surface. The individual crystals

oscillate at the frequency at which

they are excited and transmit the

wave into the pipe.


7/28

7

The power and durability of todays electronics

has made it possible to field the GWUT system

in a compact package

Pressurized bladder

containing the array of

piezoelectric crystals

Laptop

computer

Field

electronics

Umbilical cableconnecting

electronics to

transducers


8/28

LRUT - APPLICATIONS

Road and river crossings

Risers

Offshore topsides pipe work Jetty lines

Refinery pipe work

Chemical plant pipe work Tank farm link lines


9/28

LRUT - Features

o Diameters if 1.5 to 48.o 100% Coverage

o Test Range Typical 30m

180m in Ideal conditions

o Production rate approx. 600m per day under ideal conditions

o Service temperature up to 120 C


10/28

LRUT - Performance


11/28

11

Advantages of LRUT

Can test long distances of pipe from a single access point

Has developed into an effective screening tool useful in locating and rankingareas of corrosion; thereby minimizing the amount of follow-up inspectionneeded to determine the integrity of piping.

Can be used on in-service pipelines

Both internal and external corrosion can be identified

Current commercial systems are packaged in a small number of durablecomponents. The systems are easily transported and quickly setup in the fieldwith preliminary results available at the time of the test


12/28

12

Limitations of LRUT

Complicated evaluation of data by highly trained operators is required becauseof the complex signals involved

Dimensions of corrosion (wall loss, longitudinal length, profile) cannot bedirectly determined

Significant corrosion can be missed, especially localized damage

The scattered signal cannot be directly equated to a specific area or volume ofloss due to a lack of an absolute calibration standard

Many field conditions exist that limit the distances that can be effectivelyinspected and that cause artifacts which can complicate analysis.


13/28

13

Example of corrosion that would not have been noted with

Guided Wave on a buried piping segment

This is a photograph of the

corroded area which caused

the leak in a buried 6 line.

Along the line drawn, the

cross-sectional area of the

walled pipe is approximately

9.62 square inches, while the

area lost to corrosion through

the hole is 0.5 square inches.

This is a loss of approximately

5.2% of the cross-section. It

would not been seen in a scan

since the section was buried.

However, if this line was

above-grade and exposed the

corrosion probably would have

been noted as a minor

anomaly


14/28


15/28

AET

Acoustic Emission examines the behaviour of

material under stress.

Acoustic Emission is the spontaneous release

of energy when material undergoes

deformation for ex: erosion, corrosion,

leakage, plastic deformation etc.

AE detects defects only when crack grows.

A static defect will not be detected by AE


16/28

AET


17/28

AE Testing of Pressure Vessels

Example of Transducers Distribution on Vessel's Surface Typical Results Representation of Acoustic Emission Testing


18/28

Advantages of AET

Inspect 100% of the part/vessel (global

inspection)

Detect discontinuities significant to the part's

structural integrity

Can be applied in-service

Little/no disturbance to insulation

Wide temperature range (Cryogenic to High

temperature )


19/28

Limitations of AET

Cannot size discontinuities (depth, length)

Cannot detect flaws if improper stressing

method is applied

Cannot detect dormant discontinuities, notassociated with an active damage mechanism

AE testing is sensitive to process noise exceedingthe detection threshold

Evaluation criteria do not exist in form ofcommonly accessible data ; service providerdependent.


20/28

TIME OF FLIGHT DIFFRACTION


21/28

TOFD

The TOFD technique is a fully computerized system able toscan, store, and evaluate indications in terms of height,length, and position with a grade of coverage, accuracy andspeed not achieved by other ultrasonic techniques.

The TOFD technique is based on diffraction of ultrasonicenergy from tips of discontinuities, instead of geometricalreflection on the interface of the discontinuities.

This phenomena makes TOFD effective for identifyingcracks and lack of fusion located along the vertical axis ofthe weld (in particular for narrow gap preparation) or withany other orientations, because defect detection is notaffected by unfavourable orientation to the primary soundenergy angle


22/28

TOFD Principles

Four different types of waves are involved in theconstruction of a TOFD image:

longitudinal wave generated by the transmitterand partially transformed in spherical wave whenthe beam crosses the tip of a defect

the lateral wave that propagates near the surfacebetween the two transducers

the longitudinal wave reflected by the backwall

the shear waves generated by the modeconversion L/T on the interface of discontinuities


23/28

Two probes of opposite beam directions are used in a transmitter-receiver arrangement

Emitter Receiver

Case of an embedded crack

1

2

3

2

scanning

Time of flight

amplitude1

2 2 3

2 : bottom diffraction

scanning

time

1 : lateral wave

3 : backwall echo

2 : top diffraction

TOFD

60 L-Waves inspection

2.25 MHz frequency

TOFD (Time of Flight Diffraction Technique) use in NDT to detect and characterize flaws.

Echoes are used to size the defect


24/28

Transmitter Receiver

Surface breaking crack

1

2

3

Transmitter Receiver

Backwall breaking crack

1

3

2

surface breaking flaw will prevent lateral wave

to be transmitted: interruption of the lateral

wave

Depending on size and position of the flaw shadowing effects can be observed

Shadowing effect may arise to backwall echo as

the beam will be partially reflected by the flaw

TOFD inspection principle


25/28

Application Pre Service inspection partly and fully welded welds, 6-... mm (experience

up to 350mm)

Diameters from DN 100 (4 inch)

In Service Inspections (up to 450C)

Piping (weld) inspections

Root corrosion and erosion inspection Detection and monitoring of hydrogen damage


26/28

Advantages

Detection is independent of the orientation of the indication,resulting in a higher probability of detection (POD )

The reliability of the technique notably reduces the chance that animportant error is missed. The missing of an important error canlead to an unplanned shut down

Reproducibility and measuring errors proved < 0.5 mm deviation Consistent results before and after PWHT

Electronic and/or hard copy available

Immediate result

NO radiation, so weld and construction activities can continue,

because there is no need to evacuate large zones for performingthe inspection

Defect monitoring is possible (during production)


27/28

Limitation

Only applicable on fine-grained steel (low or

non alloyed steel)

Starting thickness of 6 mm

Starting diameters of 4

Death zone at the surface, this dead zone is

dependant on the inspected wall thickness

Some geometries are impossible (has to be

reviewed case by case)


28/28

THANK YOU

Advance NDT

Documents