1、UDC 621.643.2-034: 620.179.147 DEUTSCHE NORM February 1987 Non-destructive testing Eddy current testing of pipes and tubes Procedure DIN 54 141 Part 3 Zerstrungsfreie Prfung; Wirbelstromprfung von Rohren; Durchfhrung der Wirbelstromprfung in keeping with current practice in standards published by th
2、e international Organization for Standardization (ISO), a comma has been used throughout as the decimal marker. 1 Field of application This standard applies to the nondestructive testing of ferromagnetic and non-ferromagnetic pipes and tubes (shortened below to “tubes“) with a diameter between 4 and
3、 150 mm and 0,5 to 5 mm wall thickness, using external or internal concentric test coils and the single- frequency method. It is to be used for in-process control of tubes or for tubes as installed (e.9. condenser tubes or steam generator tubes). 2 Scope This standard specifies the procedure for edd
4、y current testing. The principles of determining the properties of test coils, the relevant diagrams and the procedure of determining the test parameters are given in appendix A, whilst in appendix B, by way of example, the specifica- tions given in appendix A are applied to a set task. Appendix C g
5、ives a table correlating the specifications of Parts 2 and 3 of DIN 54 141. 3 Principle An eddy current test includes the following steps: a) Calibration of test equipment for a set task, .e. selec- tion and arrangement of equipment (see clause 6) and setting of equipment (see clause 71, taking into
6、 account the specifications given in the relevant prod- uct standard (see subclause 4.1 ). Other test param- eters are at the discretion of the person responsible for the test (see subclause 4.2), while all rules of a general nature relating to the test procedure as speci- fied in clause 5,are to be
7、 complied with. b) Routine calibration checking and verification of test c) Preparation of a test report (see clause 9). (see clause 8). 4 Test specifications 4.1 Required information Product related test specifications shall at least include the following data in respect of the test: a) scope of te
8、st specification; b) condition of tubes to be tested; c) reference standards (e.g. holes, grooves); d) evaluation and assessment. In addition, details should be given on any additional dressing and retesting of tubes that may be necessary. 4.2 Other test parameters Where the eddy current test equipm
9、ent and the test frequency are not specified in the test specification and no information is given as regards the evaluation proce- dure, it is at the discretion of the person responsible for the test to select and set the test equipment. If this is to be successful, this requires a knowledge of the
10、 charac- teristics of the test equipment and awareness of the problems involved in the set task. Note. To solve the set task, the person responsible for the test must know the natural imperfections that may occur in the tubes (listed for example in a catalogue on defects) and be instructed in the de
11、tectability and the reliability of detection of such imperfections by means of eddy current testing. Continued on pages 2 to 12 Standards referred to DIN 54 140 Part 2 DIN 54 141 Part 1 DIN 54 141 Part 2 Non-destructive testing; inductive methods; concepts Nondestructive testing; eddy current testin
12、g of pipes and tubes; general remarks on testing using concentric test coils and the single-frequency method Non-destructive testing; eddy current testing of pipes and tubes; reference method for the deter- mination and calibration of the properties of eddy current test equipment using concentric te
13、st coils Explanatory notes This standard has been prepard by Working Group Wirbelstromprfung of Technical Committee 824 Elektrische und magnetische Prfverfahren of the Normenausschu Materialprfung (Materials Testing Standards Committee) of DIM Deutsches Institut fr Normung e. V. International Patent
14、 Classification G O1 N 27/90 4th Verlag OrnbH, Berlin, has the exclusive right of sale for German Standards (DIN-NormenJ. DIM 54 141 Part 3 Engl. Price group 9 Sales No. qlO9 .88 Page 2 DIN 54 141 Part 3 The characteristics of the test equipment deter- mined by means of calibration test pieces as sp
15、eci- fied in DIN 54 141 Part 2 can either be directly adopted for the set task, adopted for the set task by using a transfer function or redetermined for the tube to be tested by an analogous method (see appendix C). 5 Procedure The following shall be taken into account when carrying out an eddy cur
16、rent test: the tube and the test coil equipment shall be concen- tric (see subclause 6.3.2); end effects shall be minimized (see subclause 6.6); any deformation shall be avoided when producing calibration standards or reference standards (see sub- clause 7.7.2); the relationship between filter setti
17、ng and test speed shall be taken into account (see subclause 7.2.4); the required magnetic field strength shall be estab- lished (see subclause 7.3); calibration checks shall be made during and after test- ing (see clause 8). Equipment 6.1 Test coil 6.1.1 Types of coil A distinction is made between
18、the following types of coil which shall be selected so as to ensure the best pos- sible interference suppression: a) Absolute coils. These are to be used, for example, for detection of a continuous open weld or similar type of imperfection. The use of such coils normally depends on the disturb- ance
19、s present. Suppression of any interference signals generated is more effective, the smaller the leading edge gradient of the disturbance is, as compared with the effective coil width. The sensitivity for detecting imperfections increases in direct proportion to the leading edge gradient of the imper
20、fection and the effective coil width, and is at its optimum when the length of the imperfection and the effective coil width coincide . For a specific coil type, eddy current test coils are distin- guished by their effective coil width, which largely governs the limit imperfection length and the loc
21、alized resolution (as defined in DIN 54 141 Part 2). If these characteristics have been determined for a cali- bration test piece as specified in DIN 54 141 Part 2, they can be applied to a set task using the procedure described in appendix A or B, and permit an assessment to be made to what extent
22、imperfections can be detected using the coil concerned. 6.1.2 Filling factor To achieve a high test sensitivity the diameter of the test coil is to be matched to that of the tube. Normally, the filling factor, 7, for external test coils (as defined in DIN 54 140 Part 2) lies between 0.5 and 0,9, the
23、 limit values corresponding to the diameter range given in clause 1. b) Differential or multiple differential coils. Note. Filling factors related to the coil inside diameter and those for internal test coils differ from the above values. 6.2 Test equipment By way of example, DIN 54 141 Part 1 illus
24、trates the arrangement of an eddy current test equipment. General characteristics of such an equipment (including test coil assembly and tube transport equipment), deter- mined as specified in DIN 54 141 Part 2, may be applied directly. These are a) the characteristic of the sensitivity setting; b)
25、the characteristics of the phase adjustment, plotting the phase angle, the signal amplitude and the angle of phase difference against the setting of phase shifter. 6.3 Tube transport equipment 6.3.1 General The tube transport equipment (permitting rotation of the coil assembly in the case of externa
26、l coils and trans- lation in the case of internal coils) should ensure good concentricity of tube and test coil assembly, the relative movement of which should be maintained as far as pos- sible at the same speed, and without vibration. 6.3.2 Check of concentricity A reference tube having three hole
27、s of the same diameter, circumferentially displaced by 1200 and 100 mm apart along the axis of the tube shall be passed through the test coil at as uniform a speed as possible, and with the normal filter setting. The transport is to be considered concentric if the vector sums of the signals for the
28、three holes are equal. Note. The check of concentricity described here is equiv- alent to the procedure specified in DIN 54 141 Part 2. The diameter of the hole used as the calibration stand- ard shall be chosen so that the vector sum of the signal exceeds the normal noise level by at least a factor
29、 of 5. 6.4 Magnetic saturation equipment Magnetic saturation equipment shall be used in the case of tubes made of materials having ferromagnetic proper- ties (e.g. iron alloys or nickel alloys) and materials with a tendency to precipitate ferromagnetic or other ferritic phases. It shall be used for
30、suppressing fluctuations in permeabil- ity in the tube resulting from the manufacturing process and for increasing the depth of penetration. With a suffi- ciently high magnetic field strength, the incremental per- meability (see DIN 54 140 Part 2) is virtually equal to unity throughout the tube so t
31、hat interference signals resulting from the permeability gradients are largely sup- pressed. 6.5 Recording and control devices 6.5,l General In the case of automatic eddy current testing equipment, the recording and control devices shall be coordinated to ensure simultaneous operability of the whole
32、 test equip- ment (e.g. by masking out the end effect), proper record- ing of the indications and sorting of the tubes in accord- ance with the test results. DIN 54 141 Part 3 Page 3 6.5.2 Functional check A reference tube as defined in the test specification shall be passed through the test equipme
33、nt at the required test sensitivity and under test conditions. It is to be checked whether the indicating devices (e.g. optical and acoustic devices, recorders) and control equipment (e.g. for classifying tubes into acceptable and suspect catego- ries, or for any colour marking) respond properly. 6.
34、6 Determining the length of untested tube ends The length of untested tube ends can be determined by a) using a calibrated controller fitted on the test equip- ment for masking out the ends (.e. the adjustable length of the untested end is increased from zero until the amplitude of the signal repres
35、enting the end effect no longer exceeds that associated with the selected evaluation threshold): b) providing holes at the tube end. Note. The method described under item b) shall corre- spond to that specified in DIN 54 141 Part 2. 7 Setting of test equipment 7.1 Tube transport equipment The speed
36、of the tube transport equipment shall be kept constant as far as possible and be adjusted so that the tubes and the test coil can be moved relative to each other without vi bration. 7.2 Eddy current test equipment 7.2.1 Test frequency The test frequency shall be selected taking the following factors
37、 into account: a) the required influence of depth of imperfection; b) the required ratio of indications of internal to external imperfections; c) the required angle of phase difference between the various wanted signals and interference signals. If factors a) and b) above have been determined as des
38、cribed in DIN 54 141 Part 2 for a calibration test piece, they can also be determined for a set task by the procedure described in the appendix. The angles of phase difference between the indications from internal and external ring grooves can be taken from the diagrams shown in appendix A. Note. In
39、 a test using external test coils, the value of the ratio of the vector components of signal indica- tions received from internal and external imper- fections decreases in inverse proportion to the frequency. As a result, there is an increased sensi- tivity in the detection of small surface imperfec
40、- tions and a decreased sensitivity in the detection of internal imperfections, the angle of phase differ ence between the internal and external imperfec- tion signals increasing at the same time. In the case of internal test coils, the relative sensi- tivity is reversed. 7.2.2 Test sensitivity The
41、test sensitivity shall normally be established by means of a reference test piece containing reference standards. The test equipment must, under test condi- tions, produce a signal identifying the reference test piece as suspect. The test sensitivity may also be established by using a reference stan
42、dard to obtain a basic setting and then increasing or decreasing the sensitivity by a specified amount. Note. The reference test piece containing reference stand- ards in accordance with the test specifications, shall have the same dimensions and be of the same material as the tubes to be tested and
43、 should have the highest possible signal-to-noise ratio. Reference test pieces are primarily used to estab- lish the test sensitivity, whilst calibration test pieces (.e. tubes with dimensions and calibration standards as specified in DIN 54 141 Part 2) are used to determine the properties of the te
44、st equipment. 7.2.3 Evaluation method When evaluating the components (see DIN 54 141 Part 1) it is to be ensured that the indications of the imperfec- tions to be detected by eddy current testing come within the range of evaluation. 7.2.4 Filters The filter setting is a function of the test speed wh
45、ich may be selected in accordance with the manufacturers data. To optimize thesignal-to-noise ratio (see DIN 54 140 Part 2), different settings may be required. 7.3 Magnetic saturation equipment Ferromagnetic tubes should be magnetized to saturation in order to suppress interference signals resultin
46、g from variations in permeability. To achieve interference sup- pression, in the case of ferritic tubes, a tangential field strength at the tube surface of not less than 160 kA/m is required. 8 Calibration checking of test equipment Calibration checking shall be made with the settings as described i
47、n clause 7 unchanged. At intervals not exceed- ing four hours, at the end of each working period and after completion of testing, the reference tube shall be passed one or more times through the test equipment under test conditions. If, in calculating the vector sum, any reduction in sensitivity exc
48、eeds 2 dB, and in calcu- lating the phases or components, any change in the phase angle exceeds 9 5“. all tubes tested since the last check shall be retested with the settings corrected. 9 Test report The test report shall give at least the following details: a) make and type of eddy current test eq
49、uipment; b) sorting and marking device; c) details of test equipment: test method, coil type and designation, test frequency, auxiliary equipment (e.g. magnetic saturation equipment); d) information on equipment setting, adjustment and evaluation; e) test results; f) place and date of testing, test supervisor, tester. Page4 DIN 54 141 Part 3 Appendix A Test parameters and principles of determining the characteristics of test coils A.l A.l.l Definition To apply a limit imperfection length determined for a given tube size with a particular type of coil, to a set task, the effective
