【国外标准】 Standard Practice for Phased Array Ultrasonic Testing of Polyethylene Electrofusion Joints

5.1 This practice is intended for the semi-automated or automated ultrasonic examination of electrofusion joints used in the construction and maintenance of polyethylene piping systems.5.2 Polyethylene piping has been used instead of steel alloys in the petrochemical, power, water, gas distribution, and mining industries due to its reliability and resistance to corrosion and erosion.5.3 The joining process can be subject to a variety of flaws including, but not limited to: lack of fusion, cold fusion, particulate contamination, inclusions, short stab depth, and voids.5.4 Polyethylene material can have a range of acoustic characteristics that make electrofusion joint examination difficult. Polyethylene materials are highly attenuative, which often limits the use of higher ultrasonic frequencies. It also exhibits a natural high frequency filtering effect. An example of the range of acoustic characteristics is provided in Table 1.6 The table notes the wide range of acoustic velocities reported in the literature. This makes it essential that the reference blocks are made from pipe grade polyethylene with the same density cell class as the electrofusion fitting examined.(A) A range of velocity and attenuation values have been noted in the literature (1-9).5.5 Polyethylene is reported to have a shear velocity of 987 m/s. However, due to extremely high attenuation in shear mode (on the order of 5 dB/mm (127 dB/in.) at 2 MHz) no practical examinations can be carried out using shear mode (6).5.6 Due to the wide range of applications, joint acceptance criteria for polyethylene pipe are usually project-specific.5.7 A cross-sectional view of a typical joint between polyethylene pipe and an electrofusion coupling is illustrated in Fig. 1.FIG. 1 Typical Cross-Sectional View of an Electrofusion Coupling Joint1.1 This practice covers procedures for phased array ultrasonic testing (PAUT) of electrofusion joints in polyethylene pipe systems. Although high density polyethylene (HDPE) and medium density polyethylene (MDPE) materials are most commonly used, the procedures described may apply to other types of polyethylene.NOTE 1: The notes in this practice are for information only and shall not be considered part of this practice.NOTE 2: This standard references HDPE and MDPE for pipe applications defined by Specification D3350.1.2 This practice does not address ultrasonic examination of butt fusions. Ultrasonic testing of polyethylene butt fusion joints is addressed in Practice E3044/E3044M.1.3 Phased array ultrasonic testing (PAUT) of polyethylene electrofusion joints uses longitudinal waves introduced by an array probe mounted on a zero degree wedge. This practice is intended to be used on polyethylene electrofusion couplings for use on polyethylene pipe ranging in diameters from nominal 4 in. to 28 in. (100 mm to 710 mm) and for coupling wall thicknesses from 0.3 in. to 2 in. (8 mm to 50 mm). Greater and lesser thicknesses and diameters may be tested using this standard practice if the technique can be demonstrated to provide adequate detection on mockups of the same geometry.1.4 This practice does not specify acceptance criteria.1.5 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.1.6 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.1.7 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.