Standard Practice for Conventional Pulse-Echo Ultrasonic Testing of Polyethylene Electrofusion Joints

Importancia y uso:

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 Joint

FIG. 2 Typical Cross-Sectional View of an Electrofusion Saddle Tee Joint

Subcomité:

E07.06

Referida por:

E0543-21, E0543-21

Volúmen:

03.04

Número ICS:

23.040.60 (Flanges, couplings and joints)

Palabras clave:

electrofusion; polyethylene; ultrasonic;