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है”ह”ह

IS 12782 (1989): Guidelines for Using Thermography forMonitoring of Industrial Components [MTD 21:Non-Destructive Testing]

Indian Standard

IS 12782 : 1989

: GUIDELINES FOR USING THERMOGRAPHY FOR MONITORING OF INDUSTRIAL

COMPONENTS

UDC 536’5’087’6

Sj BIS 1990

BUREAU OF INIJIAN SYANDAHDS MANAK BHAL’AN, 9 HAHADUK SHAH ZAk’AK MAKG

NEW DELHI 110002

March 1990 Price Group 1

Non,destructive Testing Sectional Committee, MTD 21

FOREWORD

This Indian Standard was adopted by the Bureau of Indian Standards on 6 September 1989, after the draft finalized by the Non-destructive Testing Sectional Committee had been approved by the Metallurgical Engineering Division Council.

This standard is intended to be a guide for using thermography for monitoring of industrial components.

Indian Standard

iS i27iii : 1085,

GUIDELINES FOR USING THERMOGRAPHY FOR MONITORING OF INDUSTRIAL

COMPONENTS

1 SCOPE

1.1 This standard covers application of heat sensing devices to detect non-uniform temperature and also to detect undesirable distribution of heat ~during service by mapping of isotherms. This standard is applicable for monitoring industrial components, such as metal casings, and metal composite bonds, and also for monitor- ing of furnaces and boilers in power stations for detecting hot spots.

2 METHODS OF TEST

2.1 The following methods are generally used depending on thermally generated electro mag- netic energy by infrared radiation :

a) Direct contact method, and

b) Non-contact method.

3 PRINCIPLES OF THERMAL INSPECTION

3.1 Work pieces that are inspected by thermal inspection are considered either passive or active.

3.2 Passive piece artificially heated or cooled during inspection to obtain a thermal profile. Presence of imperfection is indicated by an abnormal temperature in the vicinity of imperfec- tion.

3.3 -Greater the impedence of the material to heat flow better will be the detection of the imperfection present. Higher resistance to heat flow changes temperature more slowly under fixed thermal input. Greater temperature difference is observed near surface imperfection.

3.4 Work pieces that are inspected using heating or cooling effects inherent in normal service are considered active The purpose of inspecting active work pieces during service usually to detect and measure harmful hot spots rather than to detect only flaws.

4 DIRECT CONTACT METHOD

4.1 The surface is coated with a material that react to changes in temperature by changes in colour. The reaction may be reversible or non- reversible. The choice of coating is governed by

characteristics of work piece. This system enables interpreting hidden phenomena through high resolution thermal images.

4.2 Calibration and Checking

The equipment for direct measurement of tempe- rature has to be calibrated with the known temperature source for determining exactly the temperature of material especially in a process plant.

5 NON-CONTACT METHOD (PULSE VIDEO THERMOGRAPHY)

5.1 Non-contact method (Pulse video thermo- graphy) involves the use of TV-video compatible infrared imager to continuously monitor the temperature distribution in a visible surface. A sudden but modest change in temperature of the surface (or its opposite face1 is induced brief exposure to a high power heat source or by contact with another material at a different temperature. Sub-surface defects such as dela minations, inclusions and voids affect the diffusion of the heat through the material, pro- ducing the variations in surface temperature. The changing surface temperature patterns are scanned with the infrared imager and followed on a TV display, and the results are recorded on video tapes for further analysis or image enhance- ment. The technique is rapid with d&et detcc- tion time as short as a few scgconds. The deve- lopment of WT inspection technology is under- pinned by extensive experimental and theoretical work on defect detectability and defect image resolution.

5.2 PVT is developed to detect defects in carbon glass or kevlar resins.

6 APPLICATION

6.1 Portable equipments are regularly used in monitoring electric furnaces used in heat treat- ment, and checking water wall and, furnace walls in power plants, and in control rooms For check- ing control panels for hot spots. The over-head transmission lines are checked for power losses. This condition-monitoring helps in preventing breakdowns and to forecast preventing mainte- nance in time.

1

-. . -.._ I

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Comments on this Indian Standard may be sent to BIS giving

Dot : No. MT-D 2 1 ( 3363 )

Amendments Issued Siuce Publication _ _ . ..-_ - ----.---~-----.-- .-.- - --.- --_.- -.._ - .__.._ - - ____--

Amend No. Date of Issue Text Affected

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