STANDARD SPECIFICATION FOR ULTRASONIC ANGLE-BEAM EXAMINATION OF STEEL PLATES¹

1. Scope*

1.1 This specification² covers an ultrasonic angle-beam procedure and acceptance standards for the detection of internal discontinuities not laminar in nature and of surface imperfections in a steel plate. This specification is intended for use only as a supplement to specifications which provide straightforward ultrasonic examination.

1.2 Individuals performing examinations in accordance with this specification shall be qualified and certified in accordance with the requirements of the latest edition of ASNT SNT-TC-1A or an equivalent accepted standard. An equivalent standard is one which covers the qualification and certification of ultrasonic nondestructive examination candidates and which is acceptable to the purchaser.

1.3 The values stated in either inch-pound units or SI units are to be regarded separately as standard. Within the text, the SI units are shown in brackets. The values stated in each system are not exact equivalents; therefore, each system must be used independently of the other. Combining values from the two systems may result in nonconformance with the specification.

1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

2. Referenced Documents

2.1 ASTM Standards:³

• E317 Practice for Evaluating Performance Characteristics of Ultrasonic Pulse-Echo Testing Instruments and Systems without the Use of Electronic Measurement Instruments
• E1316 Terminology for Nondestructive Examinations
• E2491 Guide for Evaluating Performance Characteristics of Phased-Array Ultrasonic Testing Instruments and Systems

2.2 ASNT Standards:⁴

• SNT-TC-1A Recommended Practice for Personnel Qualification and Certification in Nondestructive Testing

3. Terminology

3.1 Definitions—For definitions of terms relating to nondestructive examinations used in this specification, refer to Terminology E1316.

4. Ordering Information

4.1 The inquiry and order shall indicate any additions to the provisions of this specification as prescribed in 12.1.

5. Examination Conditions

5.1 The examination shall be conducted in an area free of operations that interfere with proper performance of the examination.

5.2 The surface of the plate shall be conditioned as necessary to provide a clear, easily interpreted A-scan on the screen of the ultrasonic instrument. Any specified identification which is removed to achieve proper surface smoothness shall be restored.

6. Apparatus

6.1 Ultrasonic Instruments:

6.1.1 The ultrasonic instrument shall be a pulse echo type instrument capable of addressing either a mono-element probe or a phased-array probe and shall be equipped with a standard-sized dB gain or attenuation control stepped in increments of 1 dB minimum. The system shall be capable of generating and displaying A-scans.

6.2 Vertical and horizontal linearity and amplitude control linearity shall be checked in accordance with Practice E317, Guide E2491, or another procedure approved by the users of this specification. An acceptable linearity performance may be agreed upon by the manufacturer and purchaser.

6.3 The search unit shall be a 45-deg (in steel) angle-beam type with active transducer length and width dimensions of a minimum of ½ in. [12.5 mm] and a maximum of 1 in. [25 mm]. When phased-array systems are used, focal laws using an equivalent active aperture shall be used. Search units of other sizes and angles may be used for additional exploration and evaluation.

7. Examination Frequency

7.1 A nominal test frequency of 5 MHz is recommended. Thickness, grain size, or microstructure of the material and nature of the equipment or method may permit a higher or require a lower examination frequency. The ultrasonic frequency selected for the examination shall permit detection of the required calibration notch, such that the amplitude of the indication yields a signal-to-noise ratio of at least 3:1.

8. Calibration Reflector

8.1 A calibration notch, the geometry of which has been agreed upon by the purchaser and the manufacturer, with a depth of 3 % of the plate thickness, shall be used to calibrate the ultrasonic examination. The notch shall be at least 1 in. [25 mm] long.

8.2 Machine the notch or notches on the surface of the plate so that they are perpendicular to the long axis at a distance of 2 in. [50 mm] or more from the short edge of the plate. Locate the notch not less than 2 in. [50 mm] from the long edges of the plate.

8.3 When the notch cannot be machined in the plate to be tested, it may be placed in a calibration plate of ultrasonically similar material. The calibration plate will be considered ultrasonically similar if the height of the first back reflection of a straight-beam through its thickness is within 25 % of that through the plate to be tested at the same instrument calibration. The calibration plate thickness shall be within 1 in. [25 mm] of the thickness of plates to be tested, for plates of 2 in. [50 mm] thickness and greater and within 10 % of plates whose thickness is less than 2 in. [50 mm].

8.4 For plate thicknesses greater than 2 in. [50 mm], machine a second calibration notch as described in 8.2 or 8.3, as applicable, on the opposite side of the plate.

9. Calibration Procedure

9.1 Plate 2 in. [50 mm] and Under in Thickness:

9.1.1 Place the search unit on the notched surface of the plate with the sound beam directed at the broad side of the notch and maximize the response from the first vee-path indication. Adjust the instrument gain so that this reflection amplitude is at least 50 % but not more than 80 % of full screen height. Record the location and amplitude on the screen.

9.1.2 Move the search unit away from the notch until the second vee-path indication is obtained. Maximize the response and record the indication amplitude. Draw a line between the peaks from the two successive notch indications on the screen. This line is the distance amplitude correction (DAC) curve for this material and shall be a 100 % reference line for reporting indication amplitudes. Alternatively the second vee-path indication may be set to equalize its amplitude to the first vee-path signal using time-corrected gain.

9.2 Plate Over 2 in. to 6 in. [50 mm to 150 mm] Inclusive in Thickness:

9.2.1 Place the search unit on the test surface aimed at the broad side of the notch on the opposite surface of the plate. Maximize the one-half vee-path indication amplitude. Adjust the instrument gain so that this amplitude is at least 50 % but not more than 80 % of full screen height. Record the location and amplitude on the screen.Without adjusting the instrument settings, repeat this procedure for the 1½ vee-path indication.

9.2.2 Without adjusting the instrument settings, reposition the search unit to obtain a maximum full vee-path indication from the notch on the test surface. Record the location and amplitude on the screen.

9.2.3 Draw a line on the screen connecting the pointsestablished in 9.2.1 and 9.2.2. This curve shall be a DAC curve for reporting indication amplitudes. Alternatively the vee-path indication and ½ vee-path indication may be set to equalize theamplitudes to the one-half vee-path signal using time-correctedgain.

9.3 Plate Over 6 in. [150 mm] in Thickness:

9.3.1 Place the search unit on the test surface aimed at the broad side of the notch on the opposite surface of the plate. Maximize the one-half vee-path indication amplitude. Adjust the instrument gain so that this amplitude is at least 50 % but not more than 80 % of full screen height. Record the location and amplitude on the screen.

9.3.2 Without adjusting the instrument settings, reposition the search unit to obtain a maximum full vee-path indication from the notch on the test surface. Record the location and amplitude on the screen.

9.3.3 Draw a line on the screen connecting the points established in 9.3.1 and 9.3.2. This line shall be a DAC curve for reporting indication amplitudes. Alternatively the vee-path indication may be set to equalize the amplitude to the one-half vee-path signal using time-corrected gain.

10. Examination Procedure

10.1 Scan one major surface of the plate on grid lines perpendicular and parallel to the major rolling direction. Grid lines shall be on 9-in. [225 mm] centers. Use a suitable couplant such as water, oil, or glycerin. Scan by placing the search unit near one edge with the ultrasonic beam directed toward the same edge and move the search unit along the grid line in a direction perpendicular to the edge to a location two plate thicknesses beyond the plate center. Repeat this scanning procedure on all grid lines from each of the four edges.

10.2 Measure grid lines from the center or one corner of the plate.

10.3 Position the search unit to obtain a maximum indication amplitude from each observed discontinuity.

10.4 For each discontinuity indication that equals or exceeds the 100% reference line, record the location and length, and the amplitude to the nearest 25%. No indication with amplitude less than the 100% reference shall be recorded.

10.5 At each recorded discontinuity location, conduct a 100% examination of the volume under a 9-in. [225 mm] square which has the recorded discontinuity position at its center. Conduct the examination in directions perpendicular and parallel to the major rolling direction.

11. Acceptance Standard

11.1 Any discontinuity indication that equals or exceeds the 100% reference shall be considered unacceptable unless additional exploration by the longitudinal method indicates it is laminar in nature.

12. Report

12.1 Unless otherwise agreed upon between the purchaser and manufacturer, the manufacturer shall report the following data:

12.1.1 Plate identity including pin-pointed recordable indication locations, lengths, and amplitudes.

12.1.2 Examination parameters, including: couplant; search unit type, angle, frequency, and size; instrument make, model, and serial number; and calibration plate description.

12.1.3 Date of examination and name of operator.

13. Inspection

13.1 The purchaser’s representative shall have access, at all times while work on the contract of the purchaser is being performed, to all parts of the manufacturer’s works that concern the ultrasonic examination of the material ordered. The manufacturer shall afford the representative all reasonable facilities to satisfy him that the material is being furnished in accordance with this specification. All examinations and verifications shall be conducted so as not to interfere unnecessarily with the manufacturer’s operations.

14. Rehearing

14.1 The manufacturer reserves the right to discuss unacceptable ultrasonically examined plate with the purchaser with the object of possible repair of the ultrasonically indicated discontinuity before rejection of the plate.

15. Marking

15.1 Plates accepted in accordance with this specification shall be identified by metal stamping or stenciling “UT A577” in one corner of the plate, at a location within 6 in. [150 mm] of the heat number.

16. Keywords

16.1 angle beams; steel plates; ultrasonic examination