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NON-DESTRUCTIVE TESTING IN PRACTICE
Eng. Guy Rapaport
Asset Management, Bridges and Structures
NVF ANNUAL BRIDGE CONFERENCE 2013
BACKGROUND INFORMATION WHY DO WE NEED NDT ?
• Regular condition evaluation of concrete structures is based mostly on visual inspection according to which we choose locations for a small amount of destructive testing (DT) and sample taking.
Problems:
Lack of info what is happing deeper in the concrete str.
Pre-stressed structures tendon ducts are left non-evaluated
Opening of the deck surface structures is done quite blindly.
What is the depth of cracks?
DT and samples target only points of the structure. Do they give a true picture of the investigated structure condition ?
Guy Rapaport
MAIN BENEFITS OF NDT
• Optimizing the sample taking process by pinpointing logical locations for invasive testing
• Enables to evaluate the inside of the concrete structure – to discover what is hidden from the eye.
• Typical disadvantages of NDT:
High cost (systems, training process)
Useful as “advanced inspection tool for experienced inspectors”. Experienced inspectors are rare and costly.
Difficult to use correctly (NOT BLACK BOXES!).
=> Active concrete structures NDT experts in Europe are very scarce, not more than some dozens.
Guy Rapaport
NDT – THE GENERAL PRINCIPLE
• In order to know what is happening inside the concrete we need an “agent” that will penetrate into the object and will return us a message if there is something wrong.
• Suitable “agents” = mechanical waves which we can generate in a controllable manner by an impact or an ultrasonic pulse.
• No further introduction regarding the physics of waves will be given here due to time limit.
Guy Rapaport
SHORT INTRODUCTION : THE MAIN NDT SYSTEMS USUALLY USED The Ultrasound 3D tomographer system (commercial name: MIRA)
• A state-of-the-art instrument for creating a 3-D representation of internal interfaces (defects, steel…) that may be present in a concrete structure.
• The detection (scanning and interpretation) is done almost in real time (3 sec. delay) and in situ.
• Scanning: only from one side of the object surface.
• Effective scanning depth: up to 1 m in heavily reinforced structures (bridge decks, girders)
Guy Rapaport
The 3D Tomographer System Components:
1. Antenna composed of 40 dry point transducers arranged in an array and a control unit operating the trasducers.
2. Laptop with the MIRA software – responsible for data processing and graphical presentation (reflected interfaces within the object)
3. Antenna power unit with wireless net transmitter.
DPC transducers
Guy Rapaport ANTENNA
ANTENNA POWER UNIT
Principle • Based on the ultrasonic echo method using transmitting and
receiving transducers in a "Pitch-Catch" configuration, i.e. one row of transducers send out short duration ultrasonic pulses of stress-waves (S- waves) and the other transducers receive the reflected pulses.
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DEFECT
BACK WALL
RECEIVING TRANSDUSERS
Detection of a defect:
DATA PRESENTATION- THE VISUALIZATION SOFTWARE:
B- SCAN
B- SCAN (ZOOM)
C- SCAN IN DEPTH OF 170 mm
D- SCAN
3D
IMAGE
1 st.
SCAN
POINT
2 nd.
SCAN
POINT
PLAN VIEW
LAST
SCAN
POINT
DEPTH
DEPTH
DIRECTION OF SCANNING
CONCRETE
SURFACE
Colour scale: more red => the more intensive wave reflections
=> different material interfaces (such as steel, air…)
C- SCAN
DUCT
DUCT
SIDE VIEW
ZOOM OF
SIDE VIEW
DUCT
LONGITUDINAL VIEW
Guy Rapaport
SHORT INTRODUCTION : THE MAIN NDT SYSTEMS USUALLY USED The Impact-Echo system (commercial name: DOCter)
• Allows to obtain information on the depth of internal reflecting interfaces (defects) or thickness of a solid member.
• As with the MIRA- tomographer, the detection is done almost in real time, in situ and from one side of the object surface.
• Effective detection depth: up to about 1 m.
Guy Rapaport
The Impact-Echo System Components:
1. Mechanical spherical impactor source – generating short duration pulses
2. High fidelity displacement transducer responsible to measure the surface displacement
3. Laptop with the Impact - Echo software data acquisition, data storage and signal analysis.
Guy Rapaport
IMPACTORS
TRANSDUCER
LAPTOP+SOFTWARE
Principle • By mechanical impact we generate a short-duration P- wave
which penetrates into the test object and is reflected from the back side of a solid object / from a defect inside the object.
• The P-wave undergoes multiple reflections between the object surfaces => recorded by the Impact-Echo system as the “Wave-Form Domain” => mathematically transformed (FFT- algorithm) into the “Frequency Domain” => signal amplitude (“Amplitude Spectrum”).
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• In the “Amplitude Spectrum” we look for dominant frequencies (signal peaks) which possibly indicate of reflecting interface (defect / back side).
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DATA PRESENTATION OF A TEST POINT:
Wave-Form Domain
Frequency
Domain:
The Amplitude
Spectrum
Dominant peak
Test-points data
(dominant frequencies)
The main applications of the Tomographer and the Impact-Echo are:
- Locating of casting defects
- Internal cracking (delaminations)
- Grout injection evaluation in pre-stressed str.
Often used at same the task to back-up each other and to increase credibility of testing results.
Guy Rapaport
SHORT INTRODUCTION OF THE MAIN NDT SYSTEMS USUALLY USED: The Impulse-Response system (commercial name: s’MASH)
• A different principle than the Tomographer and the Impact-Echo! Measuring the behavior (vibration) of the structure due to an impact not detecting the wave reflections due to an impact.
• The Impulse-Response enables to perform rapid screening of plate-like structures => searching for flaws and identifying suspicious areas for further investigation (Impact-Echo, core drilling…).
• Detection is done almost in real time, in situ and from one side of the object surface.
• Effective testing depth: up to 0,3…0,5 m.
Guy Rapaport
The Impulse-Response System Components:
1. A low-strain impactor - hard rubber tipped hammer (~1 kg) with a built-in load cell capable of measuring dynamic forces
2. Velocity transducer for 360o testing (geophone) that responds to normal surface motion
3. Laptop with the s’MASH software (+Excel®) connected to an amplifier data acquisition, data storage, signal analysis and graphical presentation
Guy Rapaport
AMPLIFIER
GEOPHONE
LAPTOP+SOFTWARE
RUBBER TIPPED HAMMER
Principle • With the hammer impact we send a P- wave through the tested
object which causes the object to vibrate in a bending mode. The geophone measures the amplitude of the response (the object vibration).
• The data is processed by the computer (FFT- algorithm) to a frequency domain where the amplitude of the signals is presented in Mobility.
• Mobility = velocity (from the geophone) / force (from the hammer).
• The Mobility describes the resistance of a plate-like object to vibrate due to an impact. The higher mobility => the smaller resistance to vibrate
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DATA PRESENTATION: • Processed data is presented in graphics and contour plots
• According the analysis of the frequency domain and other parameters, we can estimate locations of delaminations, debondings, deterioration (F-T, ASR) and casting defects.
• Very useful for mapping the condition of bridge deck surface structures – done from the surface of the asphalt.
Guy Rapaport
Frequency domain
M
O
B
I
L
I
T
Y
TEST CASES – Usage of the NDT systems in inspection and quality control tasks
TEST CASE 1 AIM: ESTIMATION OF TENDON DUCTS GROUT INJECTION. BRIDGE INSPECTION TASK. OBJECT: PRESTRESSED CONCRETE BOX-GIRDER BRIDGE. OVERALL LENGTH: 102 m USED NDT- SYSTEMS: MIRA TOMOGRAPHER AND IMPACT-ECHO
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LOCATION 1
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UPPER DUCT
LOWER DUCT
LOCATION 2
UPPER DUCT
LOWER DUCT
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LOCATION 3 (MID SPAN)
OK
(CONFIRMED)
-E UPPER DUCT
124 mm =>
SUSPICIOUS
I-E LOWER DUCT
NON-SUSPICIOUS
Guy Rapaport
IMPACT-ECHO
MIRA
TEST CASES – Usage of the NDT systems in inspection and quality control tasks
TEST CASE 2 AIM: ESTIMATION OF TENDON DUCTS GROUT INJECTION. CONSTRUCTION QUALITY CONTROL. OBJECT: STEEL ARCHED BRIDGE, PRESTRESSED CONCRETE DECK. OVERALL LENGTH: 163 m USED NDT- SYSTEMS: MIRA TOMOGRAPHER AND IMPACT-ECHO Guy Rapaport
DUCT 1
DUCT 2
DUCT 5
DUCT 6
DUCT 1 DUCT 2
DUCT 5 DUCT 6
MIRA
IMPACT-ECHO
Guy Rapaport
TEST CASES – Usage of the NDT systems in inspection and quality control tasks
TEST CASE 3 AIM: ESTIMATION OF CASTING DEFECTS AND PREVIOUS DEFECTS PATCHING. BRIDGE INSPECTION TASK. OBJECT: PRESTRESSED CONCRETE GIRDER BRIDGE. OVERALL LENGTH: 59 m USED NDT- SYSTEMS: IMPULSE-RESPONSE AND IMPACT-ECHO
Guy Rapaport
Guy Rapaport
IMPACT-ECHO
IMPULSE-RESPONSE
TEST CASES – Usage of the NDT systems in inspection and quality control tasks
TEST CASE 4 AIM: INTEGRITY ESTIMATION OF CONCRETE SLABS. INSPECTION TASK. OBJECT: GROUND SUPPORTED AIRPLANES PARKING CONCRETE SLABS. USED NDT- SYSTEMS: IMPULSE-RESPONSE AND IMPACT-ECHO
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PEAK ~220 mm = THICKNESS OF
SLAB => OK
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LOCATION 1
IMPULSE-RESPONSE
IMPACT-ECHO
PEAK ~220 mm = THICKNESS OF
SLAB => OK PEAK ~165 mm =>
SUSPICIOUS
Guy Rapaport
LOCATION 2
IMPULSE-RESPONSE
IMPACT-ECHO
TEST CASES – Usage of the NDT systems in inspection and quality control tasks
TEST CASE 5 AIM: CONDITION EVALUATION OF BRIDGE DECK SURFACE STRUCTURES (AC SURFACE) BRIDGE INSPECTION TASK. OBJECT: CONTINUOS CONCRETE SLAB BRIDGE. OVERALL LENGTH: 92 m USED NDT- SYSTEMS: IMPULSE-RESPONSE AND IMPACT-ECHO
Guy Rapaport
OK - CONFIRMED
LOOSED WATERPROOFING AND
CONCRETE DETERIORATION
CONFIRMED
Guy Rapaport
IMPULSE-RESPONSE
TEST CASES – Usage of the NDT systems in inspection and quality control tasks
TEST CASE 6 AIM: INVESTIGATION OF CRACKS - MEASURING THE DEPTH AND WIDTH OF CRACKS BRIDGE INSPECTION TASK. OBJECT: CONTINUOS CONCRETE GIRDER BRIDGE. OVERALL LENGTH: ~200 m USED NDT- SYSTEMS: IMPACT-ECHO, SURFER, CRACK WIDTH GAUGE
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DEPTH OF CRACK, BY IMPACT-ECHO
DEPTH OF CRACK, BY SURFER
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WIDTH OF CRACKS :
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THANK YOU CONTACT DETAILS:
Guy Rapaport
Senior Consultant , Civil Eng. (Tech. University)
Ramboll Finland Oy
Asset Management, Bridges and Structures
M +358 40 824 5622
www.ramboll.fi
Guy Rapaport