GB2397878A

GB2397878A - Identification of coating defects using thermography

Info

Publication number: GB2397878A
Application number: GB0229964A
Authority: GB
Inventors: Peter Edmond Chandler; Michael Bernard Coupla Quigley
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-12-20
Filing date: 2002-12-20
Publication date: 2004-08-04
Anticipated expiration: 2022-12-20
Also published as: GB2397878B; GB0229964D0

Abstract

Apparatus and method used to identify and locate defects in coatings 6, which may be used in-situ where the coatings are applied, utilises transient (pulsed, flash) thermography whereby a heat source 1 is used to generate a thermal pulse. The response of the coated substrate 6 is monitored using an array of photodiodes 2. The results generated are displayed such that any anomalous behaviour within the coating can be identified and such areas located, by means of a corresponding array of light emitters 3 whose amplitude corresponds to the maximum output of the corresponding photodiode 2. Thus "hot-spots" may be located.

Description

Apparatus and method and for in-situ identification of coating defects

using thermography.

Background

Infrared (JR) transient (pulsed, flash) thermography is an established non-destructive testing technique that utilises heat transference through an object to provide information on the structure and integrity of that object. Since the passage of heat through an object is changes in the thermal properties of the material and defects within the object can be revealed as localised 'hot spots'. This technique has thus found application for the detection of defects in objects. This technique may also be used where the surface of an object has been coated. The presence of defects within coatings such as cracks, lack of adhesion to the surface etc can also be identified.

Basically, this technique involves heating the surface of an object and recording the temperature changes over time. In previous Infrared (JR) transient (pulsed, flash) thermography systems, the recording and analysis of these temperature changes has been achieved by complicated data handling, data storage and data processing which makes such systems difficult to use especially on site where coatings are applied.

Furthermore, such systems are often over-complicated and provide detailed information on the defects. Often all that required is a method for detecting the presence of a defect without the need for a detailed or complex characterization.

Description

The application of coatings to protect or enhance components and structures is of major industrial importance. Coatings of almost every material type may be produced and can be applied within every sector of industry. Examples range from ceramics applied to components in gas turbines, paints applied to the bodies of automobiles through to corrosion protection of bridges and oil platforms.

In many cases, the functionality of a coating relies upon the lack or minimisation of defects within the coating. Defects such as pores, oxides, poor bonding etc may lead to premature coating failure.

The use of transient, pulsed or flash thermography to detect defects in coatings has been used since the early 1980's. Such systems have evolved into very sophisticated apparatus which have found use in a number of industries. However, such systems can be difficult to operate and their use is largely confined to operation within the laboratory environment. Furthermore, such systems are overcomplicated for most applications where all that is required is the identification and location of defects in a qualitative manner ie are they present or not.

The aim of this invention is to provide an apparatus which can be used in any location especially where the coatings are applied and which can be used to provide a simple visualization of a coated surface whereby identification of defects can be made. It is known that defects such as pores, oxides, poor bonding etc can interrupt the heat flow and act as local hot spots.

The apparatus is shown in drawing 1. It consists of a heat source (1) which can be pulsed an array of photo-diodes (2) a corresponding array of light emitters (3), a measurement device (4) which measures the maximum output from each photo-diode, a variable power supply (5) which provides power to each light emitter which is directly proportional to the maximum output from the corresponding photo-diode.

The array of light emitters is used as the display from which a visualization of the location of any areas of the coating (6) which exhibits anomalous behaviour ie hot spots.

A detail of the relationship between each photodiode and its corresponding light emitter is shown in figure 2 which shows that each photo-diode (7) is linked via the measurement device (4) and variable power supply (5) to one light emitter (8).

In operation, a heat pulse is generated and directed into the coated surface and the resultant response from the photo-diodes is measured. The maximum signal from each photo-diode is measured and is used to drive a variable power supply for each corresponding light emitter. The power delivered to each light emitter is directly proportional to the maximum signal measured for the corresponding photo-diode.

The utilisation of the maximum photo-diode output signal contributes to the overall simplicity of the apparatus. For a sound coating the display will exhibit a varying intensity of light which is maximum at the position of the heat source and decreasing gradually with increasing distance. However, should a defect be present, the display will show an area of localised higher intensity. The display will thus provide a visualization of the location of coating defects. The apparatus can be re- set for the next measurement run.

The apparatus will be capable of operation within any environment especially where the coating is being applied.

Claims

Claims What is claimed is: 1. An apparatus which identifies and locates

defects within a coated layer.
2. An apparatus which is portable and can be used in-situ were the coatings are applied
3. An apparatus which comprises of pulsed heat source, an array of photo- diodes, a corresponding array of light emitters, a measurement unit and a variable power supply.
4. A measurement unit which determines the maximum signal from each photodiode within the photodiode array.
5. An apparatus, as in claims 1, 2, 3 and 4, which is portable and can be used in- situ where the coatings are applied

5. A variable power supply which provides power to the light emitters in direct proportion to the maximum signal measured from the corresponding photodiode.

6. A method whereby a visualization of the array of light emitters can be used to locate abnormal coated areas which give rise to a hot spot.

Amendments to the claims have been filed as follows What is claimed is: 1. An apparatus which identifies and locates defects within a coated layer using a pulsed heat source, an array of photo-diodes, a corresponding array of light emitters, a measurement unit and a variable power supply.

2. A measurement unit, as in claim 1, which determines the maximum signal from each photodiode within the photodiode array. ' 3. A variable power supply, as in claims 1 and 2, which provides power to the light emitters in direct proportion to the maximum signal measured from the corresponding photodiode.

4. A method using the apparatus in claims 1, 2 and 3, whereby a visualization of the array of light emitters can be used to locate abnormal coated areas which give rise to a hot spot.