B S I BSU433L PART*3 7 4 W L b 2 4 6 b î 0 0 6 0 3 4 2 O BS4331 :Part3:1974 UDC 620.179.16.089.6 (Reprinted, incorporating Amendment No. 1) CONFIRMED SEPTEMBER 1987 Methods for Assessing the performance characteristics of uItrasonic flaw detection equipment Part 3. Guidance on the in-service monitoring of probes (excIud ing immersion probes) British Standards Institution --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. BSI BS*1133L PART*3 1 i1 W Lb211667 00603113 2 W "his British Standard, having been approved by the Mechanical Engineering Industry Standards Committee, was published under the authority of the Executive Board on 31 December 1974. O British Standards Institution, 1974 ISBN: O 580 08029 3 British Standards Institution incorporated by Royal Charter, BSI is the independent national body for the preparation of British Standards. It is the U K member of the International Organization for Standardization and U K sponsor of the British National Committee of the International Electrotechnical Commission. Copyright Users of British Standards are reminded that copyright subsists in all BSI publications. No part of this publication may be reproduced in any form without the prior permission in writing of BSI. This does not preclude the free use, in the course of implementing the standard, of necessary details such as symbols and size, type or grade designations. Enquiries by post should be addressed to the Publications Manager, British Standards Institution, Linford Wood, Milton Keynes MK14 6LE. The number for telephone enquiries is 0908 220022 and for telex 825777. 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Any person who, when making use of a British Standard, encounters an inaccuracy or ambiguity, is requested to notify BSI without delay in order that the matter may be investigated and appropriate action taken. ï ñ e following BSI references relate to the work on this standard: Committee reference MEE/169 Draft for comment 73/37538 DC Co-operating organizations The Mechanical Engineering Industry Standards Committee, under whose supen4L.m this BI ish Standard was prepared, consists of representatives from the following Government departments and professional and indus& I organizations: Associated Offices Technical Committee Association of Consulting Engineers Association of Hydraulic Equipment Manufacturers Ltd. Association of Mining Electrical and Mechanical Engineers British Compressed Air Society *British Electrical and Aüied Manufacturers' Association British Gas Corporation British Gear Manufacturers' Association British Internal Combustion Engine Manufacturers' Association British Mechanical Engineering Confederation British Pump Manufacturers' Association British Steel Corporation *British Steel Industry Crown Agents for Oversea Governments and Administrations Department of Employment (HM Factory Inspectorate) Department of Industry (Mechanical Engineering) *Department of Industry (National Engineering Laboratory) Department of the Environment Department of Trade *Electricity Supply Industry in England and Wales 'Engineering Equipment Users' Association Federation of Manufacturers of Construction Equipment and Cranes Institution of Gas Engineers Institution of Heating and Ventilating Engineers Institution of Mechanical Engineers Institution of Plant Engineers *Institution of Production Engineers London Transport Executive Machine Tool Trades Association *Ministry of Defence *Ministry of Defence, Army Department *National Coal Board Process Plant Association Railway Industry Association of Great Britain Royal Institute of British Architects *Society of Motor Manufact.urers and Traders Ltd. Telecommunication Engineering and Manufacturing Association The Government departments and professional and industrial organizations marked with an asterisk in the above list, together with the following, were directly represented on the committee entrusted with the preparation of this British Standard: Aluminium Federation British Chemical Engineering Contractors' Association British Airways, European Division British National Committee for Nondestructive testing British Non-ferrous Metals Federation British Non-ferrous Metais Research Association Institute of Physics Institute of Quality Assurance Lloyd's Register of Shipping Ministry of Defence, Navy Department Ministry of Defence, Procurement Executive Non-destructive Testing Society of Great Britain Nondestructive Testing Centre, Harwell oil Companies Materials Association 8804-8-0.8k- B --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. BSI BS*433L PART*3 7 4 I p L b 2 4 b b î O 0 6 0 3 4 4 4 I BS 4331 : Part 3 : December 1974 UDC 620.179.1 6.0896 --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- Methods for a Assessing the performance characteristics of uItrasonic flaw detection equipment Part 3. Guidance on the in-service monitoring of probes (excluding immersion probes) CONFIRMED SEPTEMBER 1987 . Amendments issued since publication Amd. No. I 2755 I December 1978 I Date of issue 1 British Standards Institution Text affected Indicated by a line in the margin 2 Park Street London W I A 2BS Telephone O1 -6299000 Telex 266933 1 COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. BS 4331 : Part 3 : 1974 Contents Co-operating organizations Foreword Page Inside front cover 3 4 7 9 11 15 15 18 20 20 22 23 27 27 27 Appendices A. Recommended checking procedures B. Text deleted C. Control of ambient temperature 31 37 38 --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- Guide 1. Scope 2. References 3. Range of tests 4. Probe index 5. Beam angle 6. Beam profile 7. Dominant frequency 8. Pulse length 9. Deadzone 10. Near field 11. Signai-to-noise ratio 12. Overall system gain 13. Beam alignment (squint) 14. Resolving power (depth) 15. Resolving power (angular) 16. Frequency of checking 17. Actions after checking Figures 1. A2 calibration block 2. A4 block 3. Calculation of beam angie (alternative to visual estimation) 4. Block for checking beam angle: different test ranges 5. Principle for plotting beam profile (compressional waves) 4 4 4 5 6 8 9 10 Page 6. ‘Welding Institute’ block for checking beam profile and resolution (depth) (A5 block) 12 13 7. Dominant frequency checking 8. Examples of traces for probes having nominal frequency of (a) 2.5 MHz and (b) 4 MHz 14 9. Checking of shear wave probe using block shown in figure 7 15 10. Measurement of puise length (diagrammatic) 16 11. Block for checking dead zone (A6 block) 17 12. Examples of traces using block shown in 18 figure 11 13. Block for near field checks: miniature probes 19 14. Block for near field checks: shear wave probes 19 15. Signal-to-noiseratio 20 20 16. Check of overall system gain 17. Beam alignment (squint): shear wave probes 21 18. Beam alignment (squint): shear wave probes (alternative) 22 19. Angle of squint: visual check 23 20. Screen traces showing full and partial resolution 24 21. Block for checking resolvingpower (depth) 25 (A6 block) 26 22. Alternative block for checking resolving power (depth) 23. Block for checking resolving power (depth): 26 shear wave probes (A7 block) 28 24. Resolving power (angular) 29 25. Resolving power (angular): shear wave probes 32 26. Beam profile: beam edge technique: compressional wave probes 33 27. Beam profile: beam edge technique: shear wave probes 36 28. Beam alignment: compressional wave probes 37 29. Text deleted 2 COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. -=- BSI BSm933L P A R T * 3 79 Lb29669 006034b B a BS 4331 : Part 3 : 1974 --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- This British Standard, which has been prepared under the authority of the Mechanical Engineering Industry Standards Committee, is intended t o provide further guidance for assessing the performance characteristics of ultrasonic flaw detection equipment. Whereas Parts 1 and 2 of BS 4331 are concerned respectively with the overall and electrical performance of ultrasonic equipment, this Part essentially deals with the checking of probe characteristics. Experience gained from investigation of testing practice in industry, and also from training centres, has shown that there is a real need for the standardization of simple checking procedures and Calibration blocks which will enable testers to establish initial probe characteristics and monitor variations of performance arising from such factors as age, wear and conditions of service. The simpler and more directly informative the checks, the more likely is the tester to acquire the desirable habit of comparing probes with the above mentioned object in view. Hence, the chief aim has been to devise calibration blocks of limited size and weight and suitable for use on site. In certain cases, however, it has been found necessary to recommend blocks which can best be used only in a test room. Some recommendations cover oniy generic types of block, the choice of dimensions, test material and surface finish being left to contracting parties who wiil be guided by considerations of practical relevance such as test ranges and working sensitivity levels. Guidance in the use of certain blocks is given in appendix A, but it is anticipated that testers wiil occasionally need assistance from other personnel responsible for exercising technical control. For these in turn, this standard provides means of remote control as, for instance, in clauses 8,9,12,14 and 15 which cover pulse length, dead zone, overall system gain and resolving power. Where probes or instructions on-procedure are issued from a central source, it should be remembered that the characteristics of equipment on site may sometimes differ significantly from those of the master set. (See 3.2.) 3 COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. BS 4331 : Part 3 : 1974 ~ _ _ _ _ _ _ _ _ _ _ _ British Standard Methods for Assessing the performance characteristics of ultrasonic flaw detection equipment Part 3. Guidance on the in-service monitoring of probes (excluding immersïon probes) 1. Scope 1.1 This Part of this British Standard provides practical guidance for monitoring the parameters of ultrasonic probes which most strongly influence the integrity of flaw detection and assessment, in particular the nature of the sound field and the degree of signal resolution. 1.2 The standard applies to compressional wave and shear wave probes used in contact or gap scanning on surfaces which are essentially flat. It does not apply to probes used in immersion testing techniques for which more complex checks are required. NOTE.Although a fuller assessment of the sound field (or at least a more direct one) can be obtained by using laboratory equipment, e.g. a beam plotter or a simple optical (schlieren) visualizer, such techniques are regarded as beyond the scope of this standard. 2. References The titles of the British Standards referred to in this standard are listed on the inside back cover. 3. Range and conditions of tests 3.1 Using the appropriate recommended types of test blocks, the design and manufacture of which are described in BS 2704, the range of tests covered in this standard is as follows: probe index (shear wave probes) clause 4 beam angle (shear wave probes) clause 5 beam profile clause 6 dominant frequency clause 7 pulse length clause 8 dead zone clause 9 near field clause 10 signal-to-noise ratio clause 11 overall system gain clause 12 bean alignment (squint) clause 13 resolving power (depth) clause 14 resolving power (angular) clause 15 The order in which the tests are listed is not significant. The choice of checks and order of checking WUvary with the nature of the work in hand. (For frequency of checking and actions to be taken, see clauses 16 and 17.) 3.2 Since the properties here referred to as probe characteristics (see also BS 3683 : Part 4) are in fact influenced by the acoustical and electronic characteristics of the test system as a whole (and including certain characteristics of the workpiece), it is essential that all checks are carried out with the tester’s own flaw detector and under conditions which are as nearly as possible identical with those involved in the particular work in hand, e.g. type and length of probe leads, inethod of acoustical coupling, surface roughness. 3.3 In clauses 6, 8 and 9, the methodical choice of gain setting (i.e. working sensitivity) is important. 3.4 The tests in clauses 4 , s and 6 are regarded as the foundation of good testing practice. Every care should be taken to ensure inaximuin accuracy and reproducibility of readings and, where beam profdes are involved, accuracy of plotting. (See also appendix A.) 3.5 Attention is drawn to appendix C concerning control of ambient temperature. 4. Probe index 4.1 General purposes 4.1,l It is necessary to use block A2 (see figure i), which utilizes a representative cross section of the beam and provides a large target, in the manner described in BS 4331 : Part 1. 4 --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. BSI B S * 4 3 3 2 P A R T * 3 7 4 M 1 6 2 4 b b ï 00b034B I BS 4331 : Part 3 : 1974 I- * Slot at zero point 30 t 55 23 I 100 I 1k l 5 4 I I $= 1.5 Plastics I t Unless otherwise indicated aii dimensions correct to 0.1 m. 1 Figure 1. A2 calibration block COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- - B S I BS*4331 PART*3 7 4 W L b 2 4 6 6 9 0 0 6 0 3 4 9 3 = BS 4331 : Part 3 : 1974 o See note 1 Ail dimensions in millimetres. NOTE 1.12.5 mm or 20 mm. NOTE 2.1.5 mm or 5 mm. I Figure 2. A4 block --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards 6 Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. BSI B S X 4 3 3 L PART*3 Lb24669 0060350 T W 74 BS 4331 : Part 3 : 1974 As a result, the influence of anomalous features such as non-uniform pressure distribution in the sound field, or irregular beam profile, niay be masked by the integrating effect of reflection at a surface much larger than the beam cross section (see A.2). 4.1.2 Block A2 provides one test range of 100 mm. It is advisable to position a guide strip on one side face in order to ensure that probe movement is always parallel to the side faces. NOTE, The block cannot be used to calibrate probes designed for use on non-ferrous metals, unless appropriately engraved. 4.1.3 If persistent sidewail echoes appear or tiie target echo is weaker when a guide strip is used, the probe should be checked for beam alignment (see clause 13). 4.1.4 The position of the probe index should be repeatable witlùn f 1 mnl. It is the first, indispensable characteristic which should be determined before any comparisons of beam angle or beam profile are attempted. The index should be engraved on each side of the probe body. NOTE. n i e position of the maker's index mark on a shear wave probe is usuaUyodecided by the geometry of the probe shoe before assembly. It may be significantly inaccurate at high probeangles, e.g. 70 . 4.2 Special requireiiients. Miniature blocks. To meet cases where the specified procedure or the conditions of test call for continual checking on site, three virtually identical blocks are available, namely the A4 and those complying with the Netherlands standard NEN 251 1* and the German standard DIN 54-122t (March 1973 edition). With the exception of the A4 block which can be 12.5 or 20 mm thick, the miniature blocks are only 12.5 thick and are therefore prone to sidewall echoes if used with too large a probe. (Figure 2 illustrates the A4 block). 5. Beam angle I I I O 5.1 General purposes 5.1.1 It is necessary to use block A2 (see figure 1) in the manner described in BS 4331 : Part 1 and the recommendations given in 4.1 apply. 5.1.2 Additional recommendations are made in respect of the index positions engraved on the side faces of block A2. These index positions should be clearly visible when covered by the pouplant, but should have a depth not greater than 0.1 mm. Beam angle values stamped at index marks should be not less than 3 mm high. 5.1.3 At beam angles of 70 o or less, readings should be repeatable within 1.5 O . Unless the position of the probe index coincides wiîh one of the angle markings engraved on the blocks, the angle should not be judged by visual interpretation alone. This requirenienf is of special importance for flaw location in thick sections. 5.1.4 If, when the target echo is maximized, tiie index on the probe falls between two beam angie markings, the corresponding beam angle should be calculated, A simple procedure for this is shown in figure 3. * 5.2 Spechl requirements 5.2.1 Mirriature blocks. The recommendations given in 4.2 apply for checking beam angle, but since the interpolation of readings between the engraved markings cannot readily be checked by calculation or protractor, miniature blocks are not recommended for the accurate determination of beam angle. They are, however, quite suitable for the detection of drift in tlie value of an angle previously determined as in 5.1, provided that tlie original reading is referred to the miniature block and recorded before testing is commenced. NOTE. niese miniature blocks are graduated for beam angles in steel only. 5.2.2 Different test ranges 5.2.2.1 There are circumstances, for example tlie precise location of small flaws at critical positions, in which it is necessary to supplement a standard block with a block designed to detect tlie variations of effective beam angle which anse from the fact that a probe is likely to give different responses when used on targets lying at different ranges. Other possible sources of significant variation are an unusually rough surface (see note), undulating surface profile or variable velocity of ultrasound, i.e. in excess of the not uncommon variation (in one and the sanie workpiece) of k 0.5 %. NOTE. 'iñe ferni 'rough' in this context refers only to unevenness resulting from the manufacturing process or from heat treatment, or from pitting due to pickling (steel) or to atmospheric corrosion. A surface roughened by dcep machine marks, regularly spaced, is basically unsuitable for ultrasonic flaw detection and should never be accepted. O * NEN 2511 'Reference block 2 for the ultrasonic examination of materials'. t DIN 54-122 'Non-destructive testing; reference block 2 and its use for the adjustnicnt and control of ultrasonic echo equipnicnt' --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards 7 Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. BS 4331 : Part 3 : 1974 Beam angi: --D 70 R Observed range /I II x70 Echo from P maximized. NOTE. At least one repeat reading to be taken. tan B I AU dimensionsin millimetres. Figure 3. Calculation of beam angle (alternative to visual estimation) 8 COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- ‘u-4 Time base already calibrated: 35 = sin ß R t 25 Time base uncaiibrated: x-35-- B S I BS*4331i P A R T * 3 74 Lb24bbï 0060352 3 M BS 4331 : Part 3 : 1974 5.2.2.2 A block of the type sliown in figure 4 is recommended, the target size and coverage of test ranges being chosen to suit the work in hand. For the reasons given in 5.2.2.1 it may be preferable to prepare the block from an off-cut of the. material under test. Otherwise, it should be made from a material specified in BS 2704. f I I f" Figure 4. Block for checking beam angle: different test ranges 5.2.2.3 The side and end faces of the block should be provided with permanent reference marks as at f, r', f', f" for recording the probe positions required for the subsequent protractor reading or calculation of beam angle (see A.1 on preferred system for taking readings). One or inore alternative sizes of target may be incorporated at appropriate ranges in order to simulate conditions in the workpiece, but the recommended iiiaxiiiiuni hole diameter is 5 mm. 5.2.2.4 The targets may be produced by spark erosion where this is economicallyjustifiable, but most technical requirements can be met by a small diameter side-drilled hole, the primary object being to ensure that any anoiiialy in the geometry or acoustics of tlie ultrasonic beam, e.g. eccentric beam axis, noii-uniform sound field, will be inade apparent before the probe under test is released for use. a I 6. Beam profile 6.1 Compressional wave probes 6.1.1 This is an important check, particularly for probes with square or rectangular crystals, e.g. twin-crystal probes. 6.1.2 Special purpose blocks are recommended. Recommendations converning special purpose blocks are given in appendix A of BS 2704 : 1978. 6.1.3 The target may be a cylindrical hole or a planar surface as shown in figure 5(a), (b) and (c), the choice being based on the purpose for which the profde is to be plotted. A planar reflector such as the slot seen in figure 5 should be used if, for example, the probe is to be used for assessing internal lamination in thick steel plate. 6.1.4 In any case, it is to be expected that variations due either to the differing wave frequencies to which tlie targets are sensitive, or to differing designs of probe, inay appear in profiles plotted from different targets and at different gain settings. When flaw detectors are fitted with separafe attenuator and amplification controls, it is recommended that beam profiles be plotted at two appropriate levels of working sensitivity. 6.1.5 It is recommended that the targets be so placed that they can be scanned from two ranges representing the minimum and maximum testing distances in the workpiece (i2$ R ' etc., see figure 5). Permanent reference marks should be provided to facilitate the recording of successive probe positions. (See also appendix A.) 9 COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- 5.2.2.5 The beam angle should be determined at the same gain setting as that used when examining the workpiece. B S I BS*L133L P A R T * 3 7L1 W L b 2 4 b b 7 0 0 b 0 3 5 3 5 --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- BS 4331 : Part 3 : 1974 I NOTE. For detailed sketch and plotting procedure see figure 26 and .k2.1. Figure 5. Principle for plotting beam profile (compressional waves) 10 COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. BS 4331 : Part 3 : 1974 6.2 Shear wave probes 6.2.1 Vertical plane I O 6.2.1.1 Calibration block A5 (see figure 6) introduced by the Welding Institute in 1965, is recommended for checking shear wave probes. Its dimensions of 50 mm X 75 mm X 305 mm are suitable for most probes, though for some probes the 50 mm dimension may be too narrow. The procedure is described in appendix A. 6.2.1.2 The location and spacing of the 1.5 mm diameter drilled target holes has to be adhered to in order to obtain the maximum number of approaches to them by direct and indirect scanning, i.e. one ‘bounce’. 6.2.1.3 The recommendations given in 6.1 apply regarding the need to plot beam profiles for more than one gain setting. 6.2.2 Horizontal plane 6.2.2.1 The horizontal profile is plotted in the same way as the vertical, but using the 50 mm X 305 mm face shown in figure 6(b). This procedure involves maximizing the echoes from the tips of the target holes and traversing the probe laterally to find the loll signal-drop position. 6.2.2.2 Since some uncertainty attaches to results obtained by working off the tip of a hole it is recommended that, if knowledge of the fuli horizontal profile is indispensable, a thick plate be used having one hole passing through its thickness. Two such plates are described in this standard, block A2 shown in figuje l(a) (1.5 mm hole) and the one shown in figure 25 for plotting resolving power (anelar). 7. Dominant frequency 7.1 General 7.1.1 The test block recommended for checking dominant frequency is a plain bar of dimensions approximately 50 mm X 25 mm X 150 mm, machined on the 25 mm X 150 mm faces and having a rectangular slot in one of them, cut to a depth equivalent to the distance travelled by ultrasonic waves in 1 ps (5.9 mm in steel for compressional waves). The slot can, if desired, be incorporated in a multi-purpose block which wiil cover the checks described in clauses 7 , 8 , 9 and 14. 7.1.2 The echoes from the slot and the bottom face respectively (see figure 7) are used to calibrate a sufficient length of time base with sufficient accuracy for evaluation of a probe under service conditions. (There is also a 6 mm slot in block As.) NOTE.Wave frequency and pulse length (see clause 8 ) are both checked in the same operafion. The combination of these two ‘characteristicsdetermines the result of the check for depth resolution (see clause 14). a 7.2 Procedures 7.2.1 Rectified display. There is some uncertainty attached to the assessment of rectified signals and therefore no recommendations can be made. 7.2.2 Unrectifieddisplay (compressional wave probes). The trace of a pulse reflected from a small target as at R (see figure 7(a)) is brought into the calibrated section of the time base so that the leading edge coincides with an appropriate graticule division (see figure 7(b)). The wave frequency is then estimated by counting the number of cycles occurring in a given time interval. Figures S(a) and (b) are examples of cathode ray tube traces for nominal 2.5MHz and 4 M E probes respectively. NOTE.When counting cycles, the parts of the trace which lie outside the lines y and y’ are to be ignored (see also figure 10). 7.2.3 Unrectifieddisplay (shear wave probes). Using a compressional wave probe on the slot described in 7.1.2, the time base is calibrated so that the graticule represents a known time interval. Without adjusting the time base control, a shear wave probe is then connected to the flaw detector and aimed at a small target as at R in figure 9. Using oniy the delay control to bring the signal from R on to the graticule, the number of cycles occurring in a given time is noted in the same way as described in 7.2.2. --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards 11 Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. BSI BS*433L PART*3 74 W Lb24bbî 00b0355 7 W --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- BS 4331 : Part 3 : 1974 In r- U s y.-3- . _-.- i;n -- c .n c 12 COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. B S I BS*Ll331 P A R T * 3 7Li = 1624669 0060356 O BS 4331 : Part 3 : 1974 1 --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- 13 COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- Figure 8. Examples of traces for probes having nominal frequency of (a) 2.5 MHz and (b) 4 MHz 14 COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. BSI B S * 4 3 3 1 P A R T * 3 7Y M Lb24669 0 0 6 0 3 5 8 4 m BS 4331 : Part 3 : 1974 Figure 9. Checking of shear wave probe using block- shown in figure 7 (see also 7.2.3) 8. Pulse length 8.1 General. The influence of pulse length is immediately detectable in the test for signal resolution (depth) (see clause 14) but, as with frequency, there is a case for its direct measurement as a means of speci&ing one characteristic of a probe intended for a specific purpose. 8.2 Rectified display (compressional and shear wave probes). The time base is calibrated over a range short enough to open out the envelope of the pulse. The length of the pulse is then estimated by inspection of the screen display, using the definition given in BS 4331 : Part 2 which defines the duration of a pulse as the interval in microseconds between the first and last instant at which the value of the pulse reaches 10 % of its peak amplitude. In the absence of a microsecond display, time lapse is derived from observed path length as explained in clause 7. 8.3 Unrectified display (compressional wave probes). The definition of pulse length given in 8.2 applies. The procedure described in clause 7 and illustrated in figure 7 should be used. A common requirement is that the pulse shall not occupy more than a stated number of millimetres in the material under test or last longer than a stated number of microseconds. An alternative requirement is that the effective duration of the pulse in cycles be essentially the same as that ciaimed by the supplier of the probe. In this case, the time base need not be calibrated and any convenient target may be used to provide the pulse echo. 8.4 Unrectified display (shear wave probes). For this check, the block shown in figure 9 should be used. 8.5 Typical screen traces. Figure 10 depicts a pulse before and after rectification and indicates the length of the pulse as defined in BS 4331 : Part 2. 9. Dead zone 9.1 General. ‘Dead zone’ is defined as the depth of the zone imnediately beneath the surface of the workpiece, i.e. distance along the time base from zero time, in which it is not possible to detect small flaws with certainty. NÖTE. ‘Dead zone’ should not be confused with ‘near field’, in which a smali flaw may also go undetected. A probe intended to confine the near field within a plastics shoe might stiU produce a dead zone in the workpiece. I 9.2 AU probes 9.2.1 For checking dead zone, a test block of the same dimensions as that used for checking frequency (see figure 7) can be provided with suitably placed transverse holes as in figure 11 (block A6). Alternatively, dead zone checkirig requirements can be included in a general purpose block for convenient use on site together with holes for testing resolution and a ‘2 microsecond‘ slot. (See also clause 14 and figure 21 .) 9.2.2 Figure 11 illustrates a typical arrangement of the holes the edges of which are at depths of say 1,2 , 3 , 5 , 1 0 and 15 mm, pitched about 10 mm apart. Figures 12(a) and (b) respectively depict the possibility that the signal from the edge of the hole at a depth of 2 mm (scanned from the lower face of the block in figure 11) might be masked by noise, whilst that from the edge of the hole at a depth of 3 mm could be recognized as significant, i.e..reproducible in position and amplitude on repeated testing. 9.3 Combined probes (special check) 9.3.1 These probes having separate transmitter and receiver crystals are frequently referred to as twin-crystal probes. Some types are designed primarily for wall thickness measurement. Others are intended for flaw detection in the zone immediately beneath the probe and/or for thickness measurement in very thin sections. --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards 15 Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. B S I BS*433L P A R T U 3 7 4 W Lb24667 0060359 6 BS 4331 : Part 3 : 1974 I Y i x us Figure 1 O. Measurement of pulse length (diagrammatic) (a) unrectified, (b) rectified (see 8.5) --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- . . COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards 16 Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. 4331 : Part 3 : 1974 O --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- O i +o Y e Y o O n (D a Y m Q> U o ci / o, X r- i0; mr: COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. B S I BS*4333 P A R T * 3 74 W 3624669 0060363 4 W BS 4331 : Part 3 : 1974 9.3.2 In the latter type, the axis of the emerging beam is tilted (towards the receiver side) in order to provide increased flaw sensitivity at a given depth. 9.3.3 It is important to verify whether the peak sensitivity has been achieved and to check the depth range over which it is effective. 9.3.4 In order to promote the better understandiag of twin-crystal probes and avoid their misuse, it is recommended that the dead zone is always checked before a probe is issued for use, i.e. that the sensitivity peak is identified and its location recorded on the history sheet for the probe. NOTE. See also 17.6. Ail dimensions in millimetres. Figure 12. Examples of traces using block shown in figure 11 I O . Near field 10.1 The near field (N) is defined as the zone immediately in front of the transducer in which wide fluctuations of sensitivity can occur, particularly in the first half of its length, as the result of wave interference. NOTE. In twin-crystal probes and angle probes, the field may all be contained within the probe shoe and consequently not overlap the dead zone described in clause 9. 10.2 Knowledge of the full extent of the near field is often less important than the assurance that flaw sensitivity within the field is reasonably uniform and, specifically, that there are no conspicuous minima (blind spots) which would affect the setting of sensitivity levels or the accuracy of flaw sizing by techniques based on signal height. 10.3 Blocks of the type shown in figures 13 and 14 can be used to explore the whole field or to ascertain whether an anticipated flaw zone happens to coincide with a region of minimal sensitivity. By traversing the probe across the block it can also be seen whether the target echo is unique or if it reappears for different probe positions. (There are inaxiina and minima of sensitivity across the axis as well as along it.) 10.4 Dimension H will be fured by the requirements of the job and the design of the probe. 10.5 If the probe is suspected of having a prolonged near field, the longest distance from transducer to target might be put at 2N or its calculated equivalent so as to cover possible anomalies. Normally, however, maximum sensitivity will be recorded at about 0.9N and will be more intense than any reading in the adjacent far field. 10.6 For miniature probes, several targets inay be drilled side by side in one block. Targets will show some variation of reflectivity from block to block, In this respect the flat-bottomed hole is rather more difficult to produce than the side-drilled hole; see figure 13(a) and (b). The saw-slit of figure 13(c) probably offers the greatest possibility of uniform finish combined with ease of production. 10.7 In soine designs of shear wave probe, the near field is almost entirely confined to the plastics shoe of the probe. Where calculation indicates that this is not the case, the principle employed in 10.2 can be applied as in figure 14. See A.6 for method of estimating whether the near field is likely to be contained within the plastics probe shoe. In view of the probability of a change of angle due to probe wear, the side-drilledhole is the best choice of target. NOTE. Economies may be achieved by designing large, inulti-purpose blocks to cover the combined requirements for checking for instance near-field, dead-zone and depth-resolution, provided that the material available is uniform in respect of attenuation (see appendix B). --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards 18 Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. BSI BS*L133L PART*3 7L1 L b 2 4 6 b î ûûbû3bZ -b BS 4331 : Part 3 : 1974 n Al I holes 2 f 0.02 mm dia. For a probe 15 dia. of frequency 2.5 M H z ~ / '/ //I Vf =f =24 in steel iI ;I (a 1 I I I' II Il I I I! II II I I --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- I 4p 2 E0.02 dia. l width slot 2 t 0 . 0 2 Ail dimensions in millimetres. NOG. A block with a target at 2Nwill sometimes be necessary (see 10.5). To prevent the block shown in figure 13(a) from being excessively heavy, this should be driiied in a separate piece of material. Figure 13. Block for near field checks: miniature probes (see 10.6) dia. Ail dimensions in millimetres. NOTE.Hat-bottomed holes of comparable reflectivity can be easily produced by machining the initial hole to the bottom limit on diameter. 'Ihe reflectivity of such a hole may then be increased by increasing its diameter, within the limits given, using a series of cutters, until the required reflectivity is achieved. Figure 14. Block for near field checks: shear wave probes (see 10.7) COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards 19 Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. B S I BSU433L PARTm3 7 4 W Lb24bb7 00b0363 B BS 4331 : Part 3 : 1974 11. Signal-tonoise ratio 11.1 This test is of particular importance in cases where it is necessary to ensure that s m d flaws do not go --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- undetected. 11.2 The determination of noise level can be carried out quantitatively as follows. (a) Set the noise suppression control (sometimes marked ‘reject’) to zero. (b) Apply the probe to the workpiece and set the target echo (or bottom echo) to a predetermined height, e.g. 20 % full screen height (see figure 15(a)). Take attenuator reading. (c) Adjust the attenuator until the probe noise reaches the same height as the target echo (see figure 15(b)). Take further attenuator reading. (d) Express the result as the difference between the two attenuator readings in decibels. NOTE. Noise from the metallurgical structure of the workpiece, e.g. grain size, may reveal unsuspected differences of effective wave-frequency between probes. ia) (b) Figure 15. Signal-to-noise ratio 12. Overall system gain 12.1 The test described below provides a simple but none the less valid check on equipment performance on the basis of day-to-day comparison of results. 12.2 Block A2 is used, the target being the 1.5 mm hole shown in figure 16 and the procedure is as follows. (a) Set the noise-suppression control (sometimes marked ‘reject’) to zero. (b) With a compressioqal wave probe positioned as shown in figure 16, the echo from the 1.5 mm hole is maximized and adjusted to, say, mid-screen height. (c) With the uncalibrated gain control set at maximum and with at least 35 dB inserted by means of the calibrated attenuator, the echo from the hole should remain at least as high as the echo height obtained when the instrument was previously calibrated. NOTE. The choice of height for the target echo and the appropriate number of decibels to be inserted are determined by a series of checks on a master flaw detector of the particular type under test, The value of 35 dB represents practical possibility and is believed to be lower than the value attainable with some flaw detectors. It is also possibly less than is needed for critical flaw detection in test materials whose attenuation is high. ö Figure 16. Check of overall system gain 20 COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. BSI BSm1133L - ~ PART*3 7Li U L b 2 4 6 6 7 0060364 T BS 4331 : Part 3 : 1974 7 y-- Y -8 n Cu 6 21 COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. B S I BS*i.1331 P A R T * 3 7i.1 W 1 b 2 Y b h ï 0 0 6 0 3 b 5 I BS 4331 : Part 3 : 1974 13. Beam alignment (squint) 13.1 Compressional wave probes 13.1.1 The same type of calibration block and the same plotting system are used as when plotting beam profile (see figures 5 and 26). 13.1.2 If, when maximizing a target echo, the relevant reference line marked on the probe casing does not coincide with the target reference line marked on the surface of the calibrating block, the axis is out of alignment. The extent of its deflection has to be ascertained by offering each probe reference point in turn to the target reference line and plotting the probe displacements (‘shifts’)’ as described in appendix A. 13.1.3 The above procedure should be repeated when the probe has been repaired. 13.2 Shear wave probes 13.2.1 Three methods are available, two for use in the test room and one on site. In the first it is assumed that the deflection of the beam is to be expressed in degrees for the guidance of those who wiil repair the probe. A smoothly finished block is required, such as ‘the A2 block, having one edge accurately machined at 90 o to the face on which the probe is placed. A straight-edge and protractor having a radius of at least 75 mm are also required (see figure 17). 13.2.2 The echo of the edge and corner of the block is maximized by swivelling the probe. The straight-edge, preferably magnetic, is laid against the probe shoe and its position is marked. The angle between the line so drawn and a line drawn at right angles to the edge of the block is the angular deviation or squint of the acoustical axis of the beam. It can be measured with sufficient accuracy with a protractor placed as shown, provided that the pencilled lines L and L’ are carefully drawn. NOTE.With a 60 probe, the corner echo wiii be approximately 15 dB down due to mode change. 13.2.3 In the second method, a piece of plate with side- or bottom-driiled target is used, a protractor not being needed. The echo from the target hole is maximized from each side of its axis and probe index positions are marked, together with the distance D separating the’ probes (see figure 18). The ratio D/P is the tangent of the angle of misalignment, 8. k - J y ,Index line P ---. i : Index line Figure 18. Beam alignment (squint): shear wave probes (alternative) (see 13.2.3) --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards 22 Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. B S I BSX4331 P A R T * 3 7 4 W 3624669 00603bb 3 BS 4331 : Part 3 : 1974 13.2.4 As a third method, a convenient on-site check for squint can be made using a piece of plate with a saw-cut in one edge, and a steel rule. Probe positions are noted when the target is scanned at two different beam path distances, for instance haíf- and full-skip, the echo being maximized in each case. This method is illustrated in figure 19. Saw cut --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- Emission point - - Straightedge or steel rule Figure 19. Angle of squint: visual check I) 14. Resolving power (depth) 14.1 General. The probability that any two reflectors in a workpiece may be separated by much less than the length of a pulse makes it desirable to provide a test'block in which the distance between targets is of the order of COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards 23 Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. BS 4331 : Part 3 : 1974 two wavelengths. At this degree of separation, overlapping portions of the two reflected wave trains are liable to cancel each other, due to interference, but it is stiU possible to achieve sufficient resolution t o recognize two discrete echoes in the reflected pulse. (See also clauses 7 and 8, and appendix A.) 14.2 Recommended procedure 14.2.1 The probe is placed so that the axis of the beam impinges upon the edge of the step between one target and the next, and its position is adjusted so that the echoes from the two targets are of the same height and approximately half full graticule height. The steps are said to be resolved when their echoes are clearly separated at half maximum echo height or lower (see figure 20). I I 14.2.2 In cases where the foregoing degree of resolution is not apparent, or not required, the presence of two target holes can often be confirmed by rotating the probe through a small arc about the beam emission point and observing the rise and fail of the highest peaks in the envelope of the reflected pulse. 14.3 Compressional wave probes 14.3.1 For site work the A6 block in figure 21 is recommended, This is the same block as illustrated in figure 7 , but now provided with two pairs of concentric drill holes 9 mm and 3 mm diameter and 6 mm and 3 mm diameter respectively, in addition to the 2 microsecond slot and the dead zone targets referred to in clauses 7 and 9. 14.3.2 The 9/3 combination provides a 3 mm step. This represents two wavelengths in steel at 4 MHz and is a reasonable test for a flaw detector system in good repair. 14.3.3 A block which provides larger targets at any desired range and is therefore possibly better suited to the test.room than to site work, is illustrated in figure 22. If a less severe test is required, the step distances may be increased to 2% wavelengths. 14.3.4 A third block, also possibly better suited to test room use, is shown in figure 23. This is the dual purpose block specified in BS 2704 and designated A7, and provides four steps within the range 60 mm to 69 mm. 14.4 Shear wave probes 14.4.1 The block described in 14.3.4 (see also figure 23) is recommended. The 4 mm step represents 2% wavelengths at 2 MHz, the 3 mm step represents 2% wavelengths at 2.5 MHz and the 2 mm step represents 2% wavelengths at 4 MHz. I 14.4.2 An alternative block (designated A5), which has the advantage that it can also be used for checking beam profile, is that illustrated in figure 6, which is provided with a row of three side-drilledholes 1.5 mm in diameter pitched at 2.5 mm centres on a 10 o slope. 14.4.3 It is recommended that two more holes be added, 4 mm apart, and that, if required, a second set of holes should be arranged at the diagonally opposite corner of the block, spaced to suit the user?s needs. 14,4.4 The test range varies from 65 mm (45 o probe) to 180 mm (70 o probe) and for any given hole spacing the test becomes more severe with increasing beam angie. 14.4.5 This block is not recommended for use at beam angies above 60 o unless the user?s own choice of spacing makes clear resolution practicable. 3 mm step Echoes resolved 2 mm step Echoes not resolved Figure 20. Screen traces showing full and partial resolution --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards 24Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. B S I BS*4331 PART*3 7 4 1624669 0060368 7 BS 4331 : Part 3 : 1974 ò 9 x - c "f I L --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- I COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards 25 Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. BSI B S * 4 3 3 L P A R T * 3 74 M L b 2 4 b b î 0 0 b 0 3 b î î U BS 4331 : Part 3 : 1974 Appropriate range Each step 2 X at 6MHz (2) Each step 2 1 at 4 M H r (3) AU dimensions in millimetres. Figure 22. Alternative block for checking resolving power (depth) (see 14.3.3) Probe .a U- /ci @ 148 ____ -- 1 I I _ _ _ _ _ _ _ _ L_ _ _ _ _ _ - - - - I I I AU dimensions in millimetres. Figure 23. Block for checking resolving power (depth): shear wave probes (A7 block) (see 14.3.4) --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards 26Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. s s 1 SS*4333 PARTm3 74 l b 2 4 b b 9 00b0330 5 m BS 4331 : Part 3 : 1974 15. Resolving power (angular) 15.1 General 15.1.1 The true resolution of echoes from smali reflectors lying side by side at approximately the same distance from the probe is not possible, chiefly on account of interference effects. 15.1.2 It is possible, however, to select the most suitable probe from a batch by exploring the cross section of the beam between the region of maximum intensity (the acoustical axis) and a point at which this value has dropped by, say, 6 dB, e.g. by observing the loss of echo height from a suitable target (hole or slit) as the beam is swept over it. The result can be expressed either as an observed lateral displacement of the probe or, more meaningfully, as an angular relationship involving the beam axis and a line joining the beam emission point and the ‘-6 dB’ point. NOTE.For the purpose of this test, it may be assumed that the point of intersection of the longitudinai axis of a shear wave probe with a line joining the two probe index marks w i l l coincide with the beam emission point. It is also assumed that the probe index positions are marked on opposite sides of the probe casing. O 15.2 Compressionalwave probes 15.2.1 The procedure for identifying the ‘-6 dB’ point is in principle the same as that described in clause 6 for locating the -20 dB point (echo amplitude ratios 211 and loll respectively); see also appendix A. 15.2.2 The index of angular resolution is expressed as tan 8 , i.e. probe shift D/range R (see figure 24). 15.3 Shear wave probes 15.3.1 The recommended procedure is as shown in figure 25. A thick plate permits the use of a shear wave probe of any angle at any of several different ranges chosen to suit the work in hand. 15.3.2 The target echo is maximized and the position of the probe is marked, preferably on a guide strip. The probe is then moved successively to the left and to the right until the echo height has dropped by the agreed amount, and its new positions noted. 15.3.3 The index of angular resolution is expressed as tan 6 , i.e. probe shift Dlrange R (see figure 24). --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- 16. Frequency of checking For equipment in regular use, the probe performance checks should be carried out at the intervals recommended as follows. Probe index: Daily. On very rough surfaces, e.g. castings, twice daily. Beam angle: Alignment of beam (squint): Beam profde: Dominant frequency: Pulse length: Dead zone: Near field: Signal-to-noise ratio: Overall system gain: Resolving power, both depth and angular: Monthly, and whenever large variations in the probe index position or the beam angle are observed. I I Monthly, and whenever repairs have been made to either the probe or the flaw detector; also, if the flaw detector in use is replaced by another. Daily, and after repairs, as above, Monthly, and after repairs or replacement as above. 17. Actions after checking A probe with substandard performance need not necessarily be discarded as it may usefully serve some other purpose. The following courses of action are recommended in cases where checking reveals significant deviations of any one characteristic from the reputed or required value. 17.1 Probe hidex. If the revised index is more than k 1 mm distant from the original one, mark the position of the revised index indelibly. Preferably also cover the original index. 27 COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. I B S I BSm4332 PART*3 74 Lb24bbî 00b037L i m BS 4331 : Part 3 : 1974 Q hole waves) --dD bNormal probe: view in side elevation. Angle probe: view in plan. Resolution index = tan 8 = D/range R. Figure 24. Resolving power (angular) o --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. BSI B S % 4 3 3 1 P A R T * 3 7Li 16246bï 0060372 7 M BS 4331 : Part 3 : 1974 Appropriate test ranges Steel plate thickness < 2 5 4 i ,--1--, r-- Guide strip ___ I --i *+ I --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- AU dimensions in millimetres. Figure 25. Resolving power (angular): shear wave probes 17.2 Beam angle. Consider the implications of the error in relation t o the work in hand. Assuming a test range of 100 mm: 70 probe: a deviation o f t 2 o will introduce an error o f f 3.3 mm in the estimated depth (below surface) of a flaw; 60 o probe: deviation t. 2 o ,depth error t 3 mm; 45 o probe: deviation f 2 O , depth error f 2.5 mm. If these tolerances are unacceptable, the probe shoe should be reground. 17.3 Beam profde. If the beam spread is significantly different from the calculated value (using the reputed wavelength and diameter of crystal), the frequency should be checked. Where precise flaw location is of primary importance, it is advisable also to plot the beam profile in reverse. (See also A.2.) 17.4 Dominant frequency. Check signal resolution (depth) and plot beam profile if not already known. (See also A.3.2, A.3.3.) 17.5 Pulse length. Check resolution (depth) and dead zone. (See also A.4.) 17.6 Dead zone. Check pulse length. With twin-crystal probes, examine for deterioration of acoustical barrier, both at working face and within the probe shoe. 17.7 Near field. Consider the implications of the test in relation t o the work in hand. For instance, even in the absence of any inconveniently situated blind spots, knowledge of the position of the sensitivity maximum adjacent to the far field may be valuable. (See also 10.2,) 17.8 Signal-to-noiseratio. If unacceptablylow, check probe on alternative similar flaw detector or arrange for overhaul of equipment. 17.9 Overall system gain. If unacceptably low, check probe on alternative similar flaw detector or arrange for overhaul of equipment. COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards 28 Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. B S I BS*433L PART*3 74 m Lb24b69 0060373 O m BS 4331 : Part 3 : 1974 17.10 Beam alignment (squint). Assuming an out-of-line error of 2 O , then, at a working range of 100 mm, the lateral displacement of the beam will be 3.5 mm. Assuming also that wear is the cause and that it has taken place in a direction at right angles to the longitudinal axis of the probe, the above mentioned error would be acconpanied by an out-of-square error at the working face of 1 in a compressional wave probe and 1% o in a shear wave probe. 17:11 Resolving power (depth). If resolution fails to meet the requirements of the blocks shown in figure 21,22 or 23, or, alternatively, those specified in the contract, check both frequency and pulse length. 17.12 Resolving power (angular). Consider the implications of the result in relation to the work in hand. Any failure to give the desired degree of resolution will derive from the sound field characteristics of the probe itself, which should then be exchanged for a more suitable one. --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards 30 Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. B S I BS0433L PART*3 7 4 9 1624669 0 0 6 0 3 7 4 2 BS 4331 : Part 3 : 1974 Appendix A Recommended checking procedures This appendix supplementsthose clauses of the standard in yhich, for reasons of brevity, the test procedures are not described in detail or where further background information is considered necessary. A.1 Beam angle (see 5.1 and 5.2) A.l.l In this, as in ail checks which involve the reading of probe shoe or probe index positions, it is important to keep strictly to a clear convention as t o how reference marks are to be made, e.g. with scriber or sharp pencil, and how they are to be read. Rule measurements between clearly defined reference points (e.g. edge of block and casing of probe) are to be preferred to those involving wax pencil lines. Where the latter are unavoidable, they should be drawn so as to provide one clean continuous edge for reference. A.1.2 The use of a straightedge, preferably magnetic, for the control of probe movement,-isrecommended. A convenient size is 150 mm X 25 mm X 3 mm. A.1.3 A suitable background for pencil lines onthe test blocks is a coat of contrast aid paint, such as is used in magnetic particle testing (see BS 5044), applied from an aerosol. A.2 Beam profile (see clause 6) A.2.1 Compressionalwave probes (see 6.1) A.2.1.1 Figure 26 shows a block with a target hole so placed that the profde can be determined a t four different depths, 20 mm, 30 mm, 60 mm and 90 mm. (The probe position for 20 mm depth is not shown irr figure 26.) The hole need not be drilled right through. A slit, sawn or spark-eroded,may be used instead but the profile can then only be checked at two depths, 30 mm and 90 mm. The choice of depths is of course fured by the needs of the job. A.2.1.2 The width will depend on the need to avoid sidewall echoes, particularly with rectangular crystals where the beam wiii be much wider in the direction parallel to the smaller side, the cross section of the beam being virtually elliptical. A.2.1.3 The probe is first marked at four numbered reference points 90 o apart. With twin-erystal probes it may be necessary to identi@ the transmitter. This should already be known if the probe has been in use for flaw detection as distinct from wail thickness measurement. A.2.1.4 Next, the position of the acoustical axis of the beam (A in figure 26(b)) has to be checked by maximizing the echo from the deepest target for ail four reference points. (For use with miniature probes, it should be possible t o driil more than one hole in the block.) If the maximum echo position does not coincide with the reference line on the face of the block (centre line of target) within 2 mm, the axis is probably not centrally aligned and has to be checked at other (i.e. intermediate) reference points and the probe, if necessary, set aside for repair. NOTE. Even with the beam out of alignment, there wiU always be two positions, 180 apart, at which the acoustical axis and target wiü lie in the same plane and produce a standing signai at constant range throughout probe movement along the reference he. A.2.1.5 With the axis checked and the echo maximized, the position of the edge of the probe is marked on the block (position p in figure 26(b)). The probe is then drawn back at right angies to the target reference line untii the signal has dropped to one tenth of its original height and the edge is marked again (position p’ in figure 26(b)). Measurement of the probe shift gives the half-width of the beam at this level, which is plotted as distance X in figure 26(b) and (c), A.2.1.6 The probe is rotated through successive intervals of 90 o for points 2 , 3 and4 and the procedure is repeated. The completedplot for four levels is shown in figure 26(c). A.2.2 Shear wave probes (vertical plane) (see 6.2) A.2.2.1 The method employed and the apparatus used are the same as before, namely a block with target holes at different depths and means of measuring probe shift about a fixed reference point which in this case is usually the probe index as already determined with the A2 block. The loll amplitude drop is used, thesequence of operations being a$ shown in figure 27. A.2.2.2 For the fmal plot, the reputed beam index is taken as the master reference point whilst the axis (also as determined on the A2 block) is drawn through the points indicated b y the maximum echo positions. If these do not lie close t o the line the check should be repeated. A.2.2.3 Daily checks for drift of the beam index should be carried out using the 100 mm quadrant of the A2 block (see clause 16). --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards 31 Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. B S I BS*433L PART*3 7 4 Lb24bbî 00b0375 4 BS 4331 : Part 3 : 1974 --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- A.2.2.4 A useful cross check on reproducibiiity of results can be made by reversing the plotting procedute. To do this, the reputed index is ignored and one edge of the probe shoe is used instead as the reference point for the cross check. A line drawn through the maximum echo positions should intersect the work surface line at a point k 1 m m from the reputed index point, whilst the angle measured between the new axis and the vertical through the new index should be within f 0.5 o of the angle originally determined; If the foregoing conditions are not met, it will be necessary to establish which of the two results is to be considered valid for the job concerned, namely the one based on the A2 block or the one based on very small targets.. Reference I n Numbered positions indelibly marked ! I (bl Recorded reading for position I 6 1.5 or 3 Au dimensions in millimetres. Figure 26. Beam profile- heam edge technique: compressional wave probes 32 COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. B S I BS*:4333 PART*3 74 L b 2 4 b b ï 00b037b b BS 4331 : Part 3 : 1974 (a) Target echo maximized. (b) 10/1 drop. Forward shift Y marked on final plot to the tear of the axis. /-:-- (d) Final plot (for all targets). I (A Reputed 2 block) beam angle / O O' Q Figure 27. Beam profile: beam edge technique: shear wave probes COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards 33 Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- (cl l O / l drop. Backwardshift X plotted in front of the axis. BSI BS*4332 P A R T x 3 74 = Lb24b69 0060377 B --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- BS 4331 : Part 3 : 1974 A.3 Dominant frequency (see clause 7) A.3.1 If the test block shown in figure 2 is the only one available, the time base may be calibrated for 50 mm range (O to 10 on scale) and marked off in pencil in units of 6 mm. The 5 inm hole in the block will serve as a target (unrectified display). When the cycles are counted, any marking error is unlikely to result in a counting error of more than Ys 'cycle. NOTE.Under the convention by which the timebase is calibrated for range, 6 mm represents 12 mm total path length and a travel time of 2 ps in steel. A.3.2 Deviation from a reputed frequency may have a detrimental effect upon flaw sensitivity (restriction on minimum detectable size), and also upon signal resolution and penetrating power. Resolution is affected in turn by pulse length, whilst penetrating power is affected by attenuation, i.e. the metallurgical structure of the workpiece. A.3.3 The positive identification of frequency'itself as a source of inefficiency depends upon knowledge of other factors, and a probe found to be substandard in respect of frequency should not be discarded before those factors have been evaluated. A.4 Pulse length (see clause 8) A.4.1 Since there is a direct connection between the nuinber of waves in a pulse, the length of each wave and the probability that the pulse, when intercepted by two reflectors lying close together, will return two clearly distinguishable echoes to the probe, the tester should regard the checks described in clauses 7 , 8 and 14 as inseparable. A.4.2 There should be no material interference between the trailing edge of the part of the pulse reflected at the top of the 2 microsecond slot and the part reflected at the bottom face of the test block (see figure 7). A.4.3 Ideally, the pulse length (in millimetres) should be not greater than twice the distance between the two reflectors whose echoes are to be separated. A.4.4 Thus, in the case of the commonly used pulse duration of 5 cycles, complete signal resolution requires that the distance between any two reflectors should be not less than 2%wavelengths. (In steel at, say, 4 MHz, the distance would be 3.7 min (compressional waves) or 2.0 mm (shear waves)). A.4.5 Even if the check shows that the pulse length does not meet this requirement, a practised tester should still be able to detect the presence of two reflectors at a separation of slightly less than two wavelengths (equivalent to visible separation, at the peaks only, of two overlapping echo signals). A.5 Dead zone (see clause 9) A.5.1 The depth of the dead zone is chiefly determined by the design of the probe, the pulse energy setting (where this facility is provided) and the gain setting. Other factors, external to the probe itself, also intervene, e.g. the performance of the amplifier and the metaliurgical structure of the workpiece. A 5 2 As with other checks, see clauses 7 and 8, it is advisable to check other attributes of the equipment before discarding a probe that is suspected of being substandard in respect of dead zone. The probe might not perform so badly on the workpiece as on the test block, or on a different flaw detector from that currently in use. A.6 Near field (see clause 10) A.6.1 In manual scanning, particularly with heavily damped short pulse probes, variations of sensitivity in the near field are generally not so wide as predicted from theory and the transition from near field to far field condition is less marked. The conventional formula for calculating the length of the near field (N) is: N= D2 inin 4X where D is the diameter of the transducer (mm), and X is the wavelength (mm). A.6.2 The formula in A.6.1 is not directly applicable in practice because the effective diameter of the transducer is not usually known and h is an approximation based on the dominant frequency. Also, square or rectangular transducers are quite common. Nevertheless the formula offers a convenient means of estimating the required dimensions of a test block. A.6.3 To ascertain whether the near field is likely to be contained within a plastics probe shoe, reduce the d u e of h in steel (compressional waves) by half (the precise ratio is 1/0.465),and calculate N. Compare N with the distance X in figure 14. A.6.4 For square transducers, the equivalent diameter is : side of square X two sides X 'ylo. 78, and for rectangular it is :mean of 34 COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. B S I BS*433L PART*3 74 1 6 2 9 b b ï 00b037B T W BS 4331 : Part 3 : 1974 a A.7 Alignment of beam (squint) (see clause 13) A.7.1 Compressional wave probes A.7.1.1 A check for beam alignment is an essential preliminary to the plotting of beam profde, the same system and the same block(s) being used for both. In figure 28(a) and (b) it is assumed that the be& axis is deflected in the 45 " direction along the line b-b'. If visible, it would be seen in plan as in figure 28(b) and would be of finite thickness as shown. A.7.1.2 At stage 1 (see figure 28(b)) the maximum signai will be received oniy when the probe has been drawn back from the target reference line (engraved on the block) through the shift distance s'. The point at which the beam axis strikes the target lies ahead of the 2-4 line and a line s' is drawn in this position on the master plot (see figure 28(f)). A.7.1.3 The probe is next rotated through 90" (stage 2) and the maximum echo obtained for probe reference-point no. 2 (for clarity, the target reference lines are omitted in figures 28(c), (d) and (e)). The striking point lies ahead of the 3-1 line and the corresponding probe-shift line s'' is &awn on the master plot, figure 28(f), where it is seen to intersect the line s'. A line (double-headed arrow in figure 28(f)) drawn from the probe centre to the point of intersection shows the direction and extent of the off-centre deflection of the beam axis. A.7.1.4 Consideration shows that at stages 3 and 4 the probe shifts s'" and s"" will coincide with the lines already drawn. NOTE.There will always be one piane (e.g. b-b' in figure 280)) which contains both the deflected axis and the target centre line and for which no probe shift WUbe observed. Beam axis checks should therefore always be made at more than one probe-reference position. A.7.2 Shear wave probes. Three possible ways of checking are described in sufficient detail in clause 13. 35 --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. . B S I BS*433L PART*3 74 m Lb24bbï 00b0377 L m Reference line target $ of A! / t I : I Target Stage 1 - Section through plane b b' (a 1 Stage 2 Stage 3 Stage 4 (Cl (d1 (e1 (f) Master plot Figure 28. Beam alignment: compressional wave probes COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards 36 Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- BS 4331 : Part 3 : 1974 ~ BSI B S * 4 3 3 L PART*3 74 1 6 2 9 b 6 7 0060380 8 BS 4331 : Part 3 : 1974 Appendix B Design and manufacture of test blocks Text deleted --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards 37 Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. . B S I BSx4331 PART*3 74 = Lb2qbbï 00b038L T W BS 4331 : Part 3 : 1974 Appendix C Control of ambient temperature C.1 Since the velocity of ultrasonic waves in plastics materials vanes with temperature, it is essential that checks on shear wave probes be carried out within a temperature range which is known and readily reproducible. C.2 In the case of a probe with a plastics shoe, transferred from a surface which is cool to the touch (e.g. 10 O C ) to one which feels warm (40 O C ) , there would be a reduction in velocity of the order of 3.5 %which, in turn, would result in an increase of beam angle of the order of 2 o in a 45 " probe and 6 o in a 70: probe. C.3 The recommended range for check testing in the United Kingdom is 15 "C to 20"C, but in some cases it will be necessary to test at a temperature within the range met within the workpiece itself, where this is significantly higher or lower than that recommended above. --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- 38 COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584. ~~ BSI BS*:L1331 P A R T * 3 74 H 1 6 2 L i b b î 0 0 6 0 3 8 2 _~ L i BSI publications referred to in this standard This standard makes reference to the following British Standards and Draft for Development: BS 970 Wrought steels in the form of blooms, billets, bars and for&@ Part 1 Carbon and carbon manganese steels including free cutting steels BS 2704 Specification for calibration blocks for use in ultrasonic flaw detectiori Bs 3683 Glossary of terms used in non-destructive testing --``,```,,`,,```,`,,,,`,`,,,`,,-`-`,,`,,`,`,,`--- Part 4 Ultrasonic flaw detection BS 4331 Methods for assessing the performance characteristics of ultrasonic flaw detection equipment Part 1Overali performance: on-site methods Part 2 Electrical performance BS 5044 Contrast aid paints used in magnetic particle flaw detection COPYRIGHT 2003; British Standards Institution on ERC Specs and Standards Document provided by IHS Licensee=BP Amoco/5928366101, User=, 04/17/2003 03:15:43 MDT Questions or comments about this message: please call the Document Policy Management Group at 1-800-451-1584.
