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1.1 This standard practice establishes procedures for ultrasonic testing (UT) of butt fusion joints in polyethylene pipe. 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.

1.2 This standard practice does not address ultrasonic examination of electrofusion joints (coupling joints), socket joints, or saddles.

1.3 This practice provides two ultrasonic examination procedures. Each has its own merits and requirements for examination and shall be selected as agreed upon in a contractual document.

1.4 The practice is intended to be used on thicknesses of 9 to 60 mm (0.375 to 2.4 in.) and diameters 100 mm (4 in.) and greater. Greater and lesser thicknesses and lesser diameters may be tested using this standard practice if the technique can be demonstrated to provide adequate detection on mockups of the same wall thickness and geometry.

1.5 This practice does not specify acceptance criteria.

1.6 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.

1.7 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 and health practices and determine the applicability of regulatory limitations prior to use.

5.1 This practice is intended primarily for the automated or semi-automated ultrasonic examination of butt fusion joints used in the construction of polyethylene piping systems.

5.2 Polyethylene piping has been used in lieu of steel alloys in the petrochemical, power, water, gas distribution and mining industries due to its readability and resistance to corrosion and erosion. Recently, polyethylene pipe has also been used for nuclear safety-related cooling water applications.

5.3 Two ultrasonic techniques have proven useful to provide examination of fusion joint integrity; Ultrasonic time-of-flight-diffraction (TOFD) and phased array ultrasonic testing (PAUT). These techniques are often considered complementary but may be used independently of each other. The choice of the technique used may depend on a variety of parameters including diameter, thickness, surface access, detection capabilities near surfaces, and quality level required.

5.4 The joining process can be subject to a variety of flaws including, but not limited to: lack of fusion, particulate contamination, inclusions, and voids.

5.5 Polyethylene material can have a range of acoustic characteristics that make butt joint examination difficult. Acoustic velocity of the material is similar to that commonly used for ultrasound wedge materials, making it difficult to use these materials to achieve appropriate refraction of sound at the interface. 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. The table notes the wide range of acoustic velocities reported in the literature. This makes it essential that the reference blocks are made of the same cell classification as that examined. This shall be confirmed by measuring the acoustic velocity of the pipe being examined. When using PAUT as the examination technique, the acoustic velocity of the reference block shall be within ±50 m/s of the examined pipe material being examined.

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 are carried out using shear mode (6).6

5.7 Due to the wide range of applications, joint acceptance criteria for polyethylene pipe are usually project-specific.

5.8 A typical butt fusion joint in polyethylene pipe has a pronounced bead profile similar to that illustrated in Fig. 1 where the bead is shown on the outer and inner surface of the pipe.

5.9 TOFD, when used on polyethylene, is simplified in that mode-converted signals are virtually eliminated due to the high attenuation of the shear mode. However, the near surface and far surface dead zones associated with TOFD may be considered limitations if determined to be excessive for the detection requirements.

5.10 PAUT can be used to address the near surface dead zone that occurs with TOFD.