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है”ह”ह

IS 11612 (2004): Code of practice for eddy current testingof non-ferrous seamless pipes and tubes [MTD 21:Non-Destructive Testing]

IS 11612:2004

wah5*YRdW%FJT

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lndian Standard

CODE OF PRACTICE FOR EDDY CURRENT TESTINGOF NON-FERROUS SEAMLESS PIPES AND TUBES

(First Revision)

ICS 77.040.20,23.040.15

Q BIS 2004

BUREAU OF INDIAN STANDARDSMANAK BHAVAN. 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

i)ecember 2004 Price Group 3

Non-destructive Testing Sectional Committee, MTD21

FOREWORD

This Indian Standard (First Revision) was adopted by the Bureau of Indian Standards, after the draft finalized bythe Non-destructive Testing Sectional Committee had been approved by the Metallurgical Engineering DivisionCouncil.

This standard was first published in 1984. While reviewing this standard the committee felt to revise this standardin view of the accepted current practice for eddy current testing of non-ferrous pipes and tubes.

In this revision following modifications have been made:

a) Scope has been modified;

b) Terminology clause has been modified; and

c) Clause 4.4 and 5.4 has been modified.

For the purpose of deciding whether a particular requirement of this standard is complied with, the final value,observed or calculated, expressing the result of a test or analysis, shall be rounded off in accordance withIS 2:1960 ‘Rules for rounding off numerical value (revised’. The number of significant places retained in therounded off value should be the same as that of the specified value in this standard.

IS 11612:2004

Indian Standard

CODE OF PRACTICE FOR EDDY CURRENT TESTINGOF NON-FERROUS SEAMLESS PIPES AND TUBES

(First Revision)

1 SCOPE

This standard prescribes the methods of eddy current

detection of defects in seamless pipes and tubularproducts of outer diameter from approximately 3.0 to50.0 mm. This standard is applicable only to non-ferrous pipes and tubes including cupronickel ofuniform cross-section and composition.

2 TERMINOLOGY

2.0 For the purpose of this standard, the followingdefinitions shall apply.

2.1 Depth of Penetration — For a given material andfor given conditions of test coil assembly, frequencyof alternating current supplied to coil etc. the magneticfield strength and consequently the intensity of inducededdy currents in the material decreases in value fromthe surface (close to the coil) towards the interior ofthe material. The depth of which the magnetic fieldstrength or the intensity of induced eddy current hasdecreased to l/e (or 37 percent) of its surface value iscelled ‘depth of penetration’ where e is the base ofneperian logarithm. Synonymous terms are ‘standarddepth of penetration’ and ‘skin depth’ (see Annex A).

2.2 Eddy Current — Electrical currents caused to flowin a conductor by the time or space variation, or both,

of an applied magnetic field.

2.3 Effective Depth of Penetration — Thoughtheoretically the intensity of induced currents reducedto zero at infinite depth, for practical purposesconsidering the test system and detection capability,the induced eddy currents in the material do reach zerovalue at infinite depth beyond which the test systemdoes not ‘see’ the material. This depth in the materialat which the induced eddy-current intensity practicallyreduces to zero is called ‘effective depth ofpenetration’. In effect, the test system does not detectany defect situated beyond the effective depth of

penetration in the material.

NOTE — The frequency of alternating current fed to the coilassembly shall be chosen that wall thickness of tbe material isless than the effective depth of penetration and the conditionstipulated in 5.4 is satisfied.

2.4 End Effect (or Edge Effect) — The effect of themagnetic field caused by the geometric boundaries of

1

the test specimen that makes it impractical to applyelectromagnetic test methods to the associated regionsof the test specimen. A large indication generallydevelops which masks the indication of discontinuitiesin this region.

2.5 Saturation — Magnetic saturation is needed tosuppress the effect the effect of permeability variation

due to ferromagnetism in cupronickel tubes. The levelof saturation the tube is to be decided by trial and errormethod so as to get best signal to noise ratio. Thesaturation unit should be capable varying saturatingcurrents. Precaution should be taken to avoid overheating of saturating coil.

3 PRINCIPLE OF TEST

The test is performed to passing the tube through orin the proximity of a coil(s) energized with alternatingcurrent at one or more frequencies. This alternatingcurrent induces eddy-currents to flow in the tube as aresult of electromagnetic induction. The test coildetects the resultant electromagnetic flux related tothese currents. The presence of discontinuities in thetube will cause change in flow of eddy-currents.Where a discontinuity is present, the eddy-currentflow is impeded and changed in direction, causing,significant changes in the associated electromagneticfield,

During the passage of the tube the changes inelectromagnetic response caused by the presence ofdiscontinuities in the tube are”detected by the test coilwhich are amplifted and modified in order to actuateaudio/or visual indicating device (such as a cathoderay oscilloscope/or a recorder), a mechanical markeror a combination of these.

4 EQUIPMENT

4.1 Electronic Unit

The main apparatus shall consist of a source ofalternating current of a fixed or variable frequencyapplied to a test coil assembly, and an electronicdetecting system to sense and indicate variations inthe output of the coil assembly. The detecting systemmay include a phase selector and filter circuit. Thefrequency, selected for the test shall be such that the

IS 11612:2004

effective depth of penetration is greater than the wallthickness of thetube under inspection. For guidance

of users, a graph indicating the variation of depth of

penetration with frequency of alternating currentthrough the test coil for various non-ferrous materialis given in Annex A.

4.2 Test Coil Assembly

One or more coils supplied with alternating current andplaced in proximity to and therefore, electromagneticallycoupled to the material being tested and responds tovariations in these eddy-currents caused by

discontinuities in the material. The coil maybe either aprobe coil or an encircling coil of the absolute ordifferential type.

4.3 Transport Assembly

A material transport and guiding system shall beprovided if necessary, which will advance the tube atthe required rate. There shall be no excessive vibration

or m is-orientation of the tube and the feed speed shallbe constant within +10 percent. The transport assembly

shal 1in no way damage the tubes being tested.

4.4 Filters

Itis a network that transmits energy at frequencieswithin one or more frequency bands and attenuates

energy at all other ti-equencies. The continuous variableHI PASS and LOW PASS filters are desired. For agiven speed optimum filter setting is to be done.

4.5 Saturation System

Saturation unit and saturation coil is needed to inspectthe (ferro magnetic) cupronickel tubes effectively. Theprovision to vary the saturation level should beprovided. Suitable demagnetization shall be providedto demagnetize the tube to an acceptable limit, namely.-—less than 8 Gauss. (The value of demagnetization

to be pre-decided by buyer and seller of tubes.)

4.6 Other Accessories

Either a recorder, an alarm or a marking system alongwith a sorting system shall be used along with the main

equipment to keep the records of inspection for furtherreference as decided by buyer and seller of tubes,

5 TEST PROCEDURE

5.1 Reference Standard

5.1.1 A reference standard free from natural defects

shall be prepared from a length of tube of the samesize, composition and metallurgical conditions of thetubes to be inspected.

5.1.2 The artificial discontinuities shall be introducedas follows:

a)

b)

Drilled holes — Three holes of the same

nominal diameter shall be drilled through thewall and perpendicular to the surface of the

calibration standard. The three holes shall bedisplaced circumferentially at 120° from one

another, and sufficiently apart from each other

axially and from the end of the tube to ensure

that signals from each can be easily resolvedand are not influenced by end effect (see Fig. 1).

The holes shall be drilled radially through the

wall using a suitable drill jig that has a bushing

to guide the drill, care being taken to avoid

distortion of the tube and the hole whiledrilling. The diameter of the drilled hole shall

be in accordance with Table 1 and shall not

vary by more than +0.025 mm, –0.000 mm

of the hole diameter specified.

Such a reference standard shall not be construed as ameasure of the size of any imperfection detectable byeddy-current testing.

NOTE — The reference standard should be frequentlyexamined for damages like scars and dents.

Itea—.—— ——. —.— ———— ——-

--!-- ‘-:?--- ~ -jf==?---’w--–-––– r—-----——.-—-—-——-—

A A A* ~ ~ ‘

A = Space to provide signal resolution adequate for interpretation.

Fm. 1 CALIBRAI ION STANDARD WITH THREE HOLES

2

5.1.3 The diameter of the holes may be as per theproduct specification and be subject to agreementbetween the contracting parties. Table 1 maybe usedas a guideline for the dimension of the reference holes.

Table 1 Diameter of Drilled Holes

(Clauses 5.1.2 and 5. 1.3)

All dimensions in millimetres,

Outside Diameter of Tube Diameter of DrilledHoles

F ~Over Up to and lnclud~g

(1) (2) (3)

3 6 0.506 19 0.65

19 25 0.8025 32 0.9532 38 1.0538 44 1.1544 50 1.30

5.~ End Effect

The end effect shall be determined by drilling a seriesof holes near one or both the ends of a specialcalibration tube and passing the tube through the testerto determine the distance from the tube and up to whichdiscontinuity is detected.

When holes are made at one end only, pass the tubethrough the coil twice, once each with holes at theleading and trailing ends.

The end effect shall be determined only once for eachsize, gauge, speed and test frequency. It need not berepeated during each calibration check.

5.3 Surface Preparation

The surface of the tube shall be free from such metallicparticles, other foreign materials and roughness thatmay interfere with the interpretation of the test results.

5.4 Temper Condition

Eddy-current testing of tubes should be conducted on

tubes in drawn condition prior to final heat treatmentin absence of special agreement between the supplierand the purchaser.

The tubes are either pre-straightei~ed or made to passin straight position while testing is performed. The

automation for handling the tubes is to be decided bythe purchaser and the supplier of eddy-current tester.

5.5 Adjustment of the Instrument

The reference standard shall be passed through or inthe proximity of the test coils at the same speed and inthe same manner as the tubes would be passed duringinspection. The instrument settings and frequency andthe speed of the test shall be optimized to consistentlydetect all the three reference defects, the instrument

1S 11612:2004

should be set to mark such detected effects. This setting

of the instrument shall not be altered during testing ofthe lot. The alarm level and the marking mechanismshall be so set that an alarm or a mark is given eachtime a defect passes the test coil.

5.6 Mode of Testing

5.6.1 The tubes shall be passed through or in theproximity of the test coil with speed being maintainedwithin +10 percent of its nominal value. Wobbling,vibrations and the mis-orientation of tube axis withrespect to coil axis shall be kept minimum. Any sectionor length of tubing giving a defect indication equal toor greater than that produced by the reference standardshall be segregated from the material producingindication of lesser electrical magnitude.

5.6.2 Unless otherwise specified amplitude (all phase)mode of inspection shall be used. The phase sensitiveand sector mode may be used by mutual consent oftube manufacture and the user.

5.7 The proper functioning of the equipment shall bechecked:

a) at the beginning of the test,

b) every one hour during production run or after

a batch of 50 tubes,

c) after finishing test, and

d) whenever malfunctioning is suspected.

If malfunctioning is confined all the tubes which havebeen tested since the last satisfactory calibration shallbe retested.

6 LEVEL OF ACCEPTANCE

6.1 The acceptance standard shall be based on thesetting of the instrument to a sensitivity adequate todetect all the 3 artificial defects of the reference sample.

7 REPORT OF TEST RESULTS

7.1 The test report shall contain the followinginformation:

a)

b)

c)

d)

e)

f-)

g)h)

j)

3

Component drawing reference number whereapplicable;

Specification of material, including itsdimension;

Surface condition of the tubes;

Make of the instrument;

Description of the coil assembly, includinginner diameter of test coil, method ofmagnetic saturation;

Frequency used and instrument setting;

Location size and extent of defects;

Recorder chart where available; and

Any unusual occurrence encountered duringthe test.

IS 11612:2004

ANNEX A

(Clauses 2.1and 4.1)

VARIATION OF DEPTH OF PENETRATION WITH FREQUENCYOF ALTERNATING CURRENT

A-1 Figure 2 indicates the variation of depth of wherepenetration with frequency of alternating currentthrough the test coil forvarious non-femous metals.

S = depth of penetration in mm;

Figure 3 indicates the same for different type of alloys. p = resistivity of the type, being tested, in ohm-

cm;For theoretical estimation of depth of penetration, thefollowing formula may be used:

u = magnetic permeability ( 1 for non-magneticmaterial); and

S= 50292 ~~ J = frequency in hertz.

4

IS11612:2004

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FREQUENCY (f) IN HERTZ

FIG. 3 VARIATION OF DEPTH OF PENETRATION WITH FREQUENCY oF ALTERNATINGCURRENI

THROUGH THE TEST COIL FOR VARIOUS NON-FERROUS ALLOYS

61

—

.

—

—

i

—

72

—

—

—

—

—

.

6108

.

Bureau of Indian Standards

BIS is a statutory institution established under the Bureau oflndian Standards Act, 1986 to promoteharmonious development of the activities of standardization, marking and quality certification of goodsand attending to connected matters in the country.

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Review of Indian Standards

Amendments are issued to standards as the need arises on the basis of comments. Standards are also reviewed

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This ]ndian Standard has been developed from Doc : No. MTD 21 (4347).

Amendments Issued Since Publication

Amend No. Date of Issue Text Affected

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