EXPERIMENTAL SETUP OF INFRARED TESTING

Experimental Setup

Concrete test pieces, 80x400x100mm with known maximum crack widths of 0.5 and 1 mm, are mounted vertically and heated by a uniform output heating element. The concrete mix complies to British Standard BS8110 specification and is designed to an approximate cube strength of 40 MPa. This is a generic mix which is meant to represent many of the concrete structures in the UK and EU, hence adding realism to the experiments. The concrete mix can be procured from most contractors for industrial use. The surface temperature distribution of the specimen is registered by the IR camera which has a resolution of 240 x 360 pixels, and a sensitivity of 0.15 °C. The IR camera is capable of capturing consecutive images using a Frame Grabber through an image acquisition expansion card for PC. Appropriate software is used to control the grabber, and many frames of recorded images may be displayed simultaneously in pseudo-colours. A schematic diagram of the experimental set-up is shown in Fig. 1.

Fig 1: The Schematic of the Experimental Set-up

Experimental Results

The experimental results are analysed using a bespoke software package. Surface temperature distribution is presented in the form of the images. Results for cracks with a width 1 mm are shown in Fig. 2 (images 1-8).

Fig 2: A Set of Infrared Images Which Show the Extent of Heat Flow Blocking due to Surface Discontinuity Caused by A Mechanical Crack. Image 7 is at Steady-State Condition after 394 Minutes of Test Starting

The heat 'front' is allowed to propagate at various time intervals and its progress recorded as isotherms by the Frame-Grabber software. The temperature field variation graph indicates the sharp change in temperature between the leading and the lagging crack-tip, due to interference with the natural heat conduction of the continuum. Images 1-6 are taken at given intervals in Table 1 for a total time lapse of 354minutes. This constitutes a transient heat flow condition. Image 7 and 8 are at steady-state after 394 minutes. Table 1 includes the complete time and image recording details for this experiment at which the images were taken.


Image Number	1	2	3	4	5	6	7	8
Lapse time ts in minutes(t start = t 0 = 0 )	0	26	90	210	266	354	394	¥
Transient (Tn)Steady-state (Ss)	Tn	Tn	Tn	Tn	Tn	Tn	Ss	Ss
Table 1: Image and Time Lapse Specified

Numerical Modelling

Fig 3: Typical FE Crack Geometry Mod

Fig 4: Temperature Distribution for a T dimensional Model

A commercially available finite element (FE) software is used to model the geometry of the test specimens as well as determine the temperature variation field in the material due to a specified heat source (ANSYS, Release 5.4, 1997). There are standard text books discussing the use of FE method for heat transfer, for example see Bonet and Henwood[9], Zienkiewicz[10].
All present analytical models are formulated in two-dimensions, see Fig. 3. The 2-D model which includes the crack, is generated automatically using 2480 triangular FE's from which the temperature distributions are obtained. Material parameters such as the thermal conductivity k, specific heat C, and the heat transfer coefficient a are used based on the referenced literature such as Carslaw[11], Chapman[12], DeWitt and Incropera[13], Jaluria and Torrance[14], and Minkowycz et al [15]. The density of the specimen is obtained accurately from the standard laboratory measurements.
The characteristic of the temperature distribution is identical to the images gained from the experiments. Figure 4 is an example representing the shape of the predicted temperature field. As the heat is continuously delivered by the source, the temperature distribution along the concrete surface, at steady-state conditions, can be plotted by a single curve. A group of such curves are shown in Fig. 5. This shows surface temperature distributions due to a concentrated heat source (generating heat) as multiples of the ambient temperature (T). Similar results are shown in Fig. 6, where each curve represents the surface temperature variation due to input of heat, in this instance assumed to be uniformly distributed as a plateau, also as multiples of the ambient temperature (T).


Fig 5: Surface Temperature Distribution due to Different Temperatures of an Applied Point Heat Source (curves relate to various source temperatures, from T to 5T), S/d = 0.5

Fig 6: Surface Temperature Distribution due to Different Temperatures of the Distributed Heat Source Applied (S is the distance of the leading edge of heat source to crack centre, refer to Fig. 1), S/d = 0.5

A series of calculations are carried out with both heat source models in order to study the effect of varying geometric parameters of the crack on heat flow characteristics. As an example, the temperature distributions along the specimen for different widths of the cracks are presented in Fig. 7, where the source temperature is 3T due to a plateau-type heat source.


Fig 7: Surface Temperature Variation for Different Crack Width (S = leading edge heat source to crack centre, refer to Fig1)

It is surmised that if there were no cracks present, the temperature distribution on the concrete surface would be expected to be symmetrical and continuous. In the section of the surface with at least 1 crack, there would be a sharp local change in the temperature distribution. The temperature value is seen to reduce with the increase of distance from the heat source. To summarise, the theoretical study indicates that:

1. As expected, the temperature distribution on the surface is symmetrical relative to the source centre-line, in the absence of surface discontinuities (assuming that the edge effects are negligible).
2. Even very small cracks have significant effects which interfere with the heat flow.
3. The difference of crack geometry would have a varying impact on the temperature difference between the leading and trailing edges across the crack width.
4. Geometrical parameters of the crack influence surface temperatures only in close vicinity of damage.
5. It can be seen in Fig 6 that on the left side of heating element temperature variation has a fixed variation irrespective of different crack widths.
6. Increasing the source temperature (within limits) exaggerates the temperature difference across the crack width, for the same damage geometry.

Comparison contd................

APPLICATION OF INFRARED THERMOGRAPHY IN NDT

Applications
Electrical
A/C Package Unit Switch		Burned Phase "B" wire
Often Overlooked - Motor Connections		T/F Connection

Mechanical
Motors	Bearings
Energy Loss
Heat Loss	Un-insulated Heating Duct
Building Envelope Roof Moisture
Saturated Roof of Office Building

A Brief Background
Infrared energy is radiated by every physical object in an amount proportional to its temperature. While such energy is invisible to the human eye, it can be measured, recorded and visually presented in a variety of useful formats through the use of today's advanced technology IR cameras and image enhancement computer programs. The resulting information has proven itself invaluable in identifying hidden physical, electrical and mechanical defects, and has been employed within the building management industry for well over a decade. Properly applied, IR technology provides a secondary benefit through its ability to reduce unnecessary maintenance by predicting the occurrence of future operating problems. Typically, an infrared inspection will provide advance warning of an equipment failure or fire threat months to years prior to its normal occurrence. In electrical systems, loose, corroded or poor connections produces heat. Heat, in return, raises electrical resistance - thereby creating additional heat. This runaway cause and effect condition eventually results in an electrical failure and often fire and/or explosion. For mechanical equipment, shaft misalignment, inadequate lubrication, or some other frictional defect is typically the cause of the heat generated. The resulting heat product further deteriorates any lubricants, bearings, seals, or other mechanical components, and again leads to an inevitable failure of the component. Such mechanical failures typically have secondary and costly consequences.
For building management interests, the benefits of IR testing are many. Infrared thermography can quickly expose hidden stresses, damaged components, loose connections, unbalanced loads and other faults in electrical equipment. IR can diagnose problems in rotating machinery by permitting the inspection of the motor shell, motor bearings, load bearings, and other transmission components under physical load. In electrical applications, loose, dirty, corroded or oxidized connections or contacts will produce infrared energy proportional to the amount of heat generated and dissipated due to their increased electrical resistance. In friction generating equipment, heat buildup will show prominently over the ambient surroundings.

Infrared Thermography in NDT

Infrared Thermography (IR) has been successfully employed as a diagnostic tool in commercial applications since the early 1970's. Technological advancements in sensitivity, accuracy and data display have expanded its use throughout various industries at the same time its availability as a consulting service has brought costs within every operating budget.
With occupant safety, the protection of capitol equipment, and energy conservation all being synonymous with proper electrical and mechanical maintenance, IR has established itself a leading tool of successful building operation and management. Infrared thermography's non-contact, non-destructive form of measurement provides a cost effective, real time and on-line analysis of any building's electrical, mechanical and physical operation.

 credit: east coast industries,inc ECI

 

WHAT YOU NEED TO KNOW ABOUT PHASED ARRAY ULTRASONICS

Phased array ultrasonics (PA) is an advanced method of ultrasonic testing that has applications in medical imaging and industrial nondestructive testing. Common applications are to noninvasively examine the heart or to find flaws in manufactured materials such as welds. Single-element (non-phased array) probes, known technically as monolithic probes, emit a beam in a fixed direction. To test or interrogate a large volume of material, a conventional probe must be physically scanned (moved or turned) to sweep the beam through the area of interest. In contrast, the beam from a phased array probe can be moved electronically, without moving the probe, and can be swept through a wide volume of material at high speed. The beam is controllable because a phased array probe is made up of multiple small elements, each of which can be pulsed individually at a computer-calculated timing. The term phased refers to the timing, and the term array refers to the multiple elements. Phased array ultrasonic testing is based on principles of wave physics, which also have applications in fields such as optics and electromagnetic antennae.

The PA probe consists of many small ultrasonic transducers, each of which can be pulsed independently. By varying the timing, for instance by pulsing the elements one by one in sequence along a row, a pattern of constructive interference is set up that results in a beam at a set angle. In other words, the beam can be steered electronically. The beam is swept like a search-light through the tissue or object being examined, and the data from multiple beams are put together to make a visual image showing a slice through the object.

 Principle of operation of phased array (PA). The PA probe consists of many small elements, each of which can be pulsed separately. In the figure the element on the right is pulsed first, and emits a pressure wave that spreads out like a ripple on a pond (largest semicircle). The second to right element is pulsed next, and emits a ripple that is slightly smaller than the first because it was started later. The process continues down the line until all the elements have been pulsed. The multiple waves add up to one single wave front travelling at a set angle. In other words, the beam angle can be set just by programming the pulse timings.

PROFESSIONAL DIPLOMA IN PIPELINE-INSPECTION AND Non-Destructive Test (NDT).

Name of Organization	PETRO-TRACKING SERVICES LIMITED
Address	12 Irhirhi Street, OKO ADP Off Airport Road, G.R.A Benincity,Edo State.
E-mail	E-mail:info@petrotrackingserviceltd.com.ng, petrotrackingservices@gmail.com
Name of Contact Person	Philip Asibor   Cell 08108927239, 08156210344
Position held	Program Co-coordinator
Project Title:	PROFESSIONAL DIPLOMA IN PIPELINE INSPECTION   AND NDT
Project Period	2 Months

 

Petro-Tracking Services Limited is offering a Professional Diploma program in PIPELINE INSPECTION AND Non-Destructive Test (NDT)with initial enrollment in January 2016.

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Dear All, We have multiple vacancies for the position "ANDT Inspector" Company Name: NDT Corrosion Control Services Location : Saudi Arabia/GCC Job Type : Permanent Required Nationality : India Below are the requirements for the said position 1. 4 years Technical Degree 2. PCN/CSWIP Certified PAUT Level II with at least 1 year of experience Please send your CVs to reddy@ndtcorrosion.com subject line must be " PCN/CSWIP PAUT Inspector" All educational / NDT Certificates must be attached with CV Selection Criteria: Round 1. Based on CVs Round 2. Technical Interview ( will be held in Chennai) Round 3. Training for 4 days Round 4. Final Examination after training (Theory and practical ) Interview date and location will be informed to Shortlisted candidates only

SHUTDOWN (45 Days) Need NDT technician Job Location: Gujarat offered by NDT SERVICES

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