【国外标准】 Standard Practice for Conventional Pulse-Echo Ultrasonic Testing of Polyethylene Electrofusion Joints

5.1 This practice is intended primarily for the manual ultrasonic scanning 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 This practice is not intended to provide 100 % joint examination. This practice specifies a minimum scanning grid that represents only a portion of the welded interface. As such, there exists a possibility of omitting flaws. In addition, selected areas of the welded interface may not be accessible. The extent of examination shall be specified in the contractual agreement.5.4 The joining process can be subject to a variety of flaws including, but not limited to, lack of fusion, particulate contamination, short-stab depth, inclusions, and voids.5.5 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 pipes with the same Specification D3350 density cell classification as the electrofusion fitting examined.(A) A range of velocity and attenuation values have been noted in the literature (1-9).5.6 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/inch] at 2 MHz) no practical examinations can be carried out using shear mode (6).5.7 Due to the wide range of applications, joint acceptance criteria for polyethylene pipe are usually project-specific.5.8 A cross-sectional view of typical electrofusion joints between polyethylene pipe and coupling and between pipe and saddle are illustrated in Fig. 1 and Fig. 2, respectively.FIG. 1 Typical Cross-Sectional View of an Electrofusion Coupling JointFIG. 2 Typical Cross-Sectional View of an Electrofusion Saddle Tee Joint1.1 This practice establishes a procedure for ultrasonic testing (UT) of electrofusion joints in polyethylene pipe systems. This practice provides one ultrasonic examination procedure for ultrasonic pulse-echo straight beam contact testing, using straight-beam longitudinal waves introduced by direct contact of the search unit with the material being examined.1.2 The practice is intended to be used on polyethylene electrofusion socket (for example, couplings) and saddle (for example, tees) fittings for use on polyethylene pipe ranging in diameters from nominal 0.5 in. to 12 in. [12 mm to 300 mm] with pipe dimension ratios (DR) ranging from 6.3 to 17. Greater and lesser thicknesses and greater and lesser diameters may be tested using this practice if the technique can be demonstrated to provide adequate detection on mockups of the same wall thickness and geometry.1.3 This practice does not address ultrasonic examination of butt fusions. Ultrasonic testing of polyethylene butt fusion joints is addressed in Practice E3044/E3044M.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 materials for pipe applications defined by Specification D3350.1.4 This practice does not specify acceptance criteria. Refer to Specification F1055 and Practice F1290 for destructive 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.