【国外标准】 Standard Practice for Use of the Ultrasonic Time of Flight Diffraction (TOFD) Technique

4.1 This practice provides general principles for the application of the Time-of-Flight Diffraction Technique as a tool for detection and sizing of discontinuities.4.2 TOFD is a nondestructive ultrasonic examination technique that is not based on amplitude response. However, sufficient sensitivity is required to identify indications for evaluation.4.3 TOFD techniques are typically applied to welded joints in carbon steel, but the principles may be applicable to other applications including other materials with suitable validation procedures agreeable to the contracting parties.4.4 In addition to a stand-alone ultrasonic detection technique, TOFD may be used in conjunction with weld examinations such as those described in Practices E164 and E1961 where it may be used to improve sizing estimates of flaws detected by the manual or mechanized pulse-echo techniques and help discriminate between flaws and geometric reflectors.4.5 The technique has proven effective on thicknesses from 9 to 300 mm [0.375 to 12 in.]. TOFD has been used on thicknesses outside of this range but special considerations are necessary. Techniques developed outside of this range of thickness shall be demonstrated as capable of meeting the required detection and sizing requirements of the specification used.1.1 This practice establishes the requirements for developing ultrasonic examination procedures using the ultrasonic technique known as Time-of-Flight Diffraction (TOFD).1.2 Consistent with ASTM Policy, TOFD may be regarded as an ultrasonic test method whereby the qualities and characteristics of the item tested are evaluated, measured, and, in some cases, identified. Measurements may be subject to precision and bias that may be determined statistically or as a function of some parameter(s) such as wavelength. This practice may be used for applications that would be quantitative examinations as well as quantitative tests.1.3 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.5 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.