A Brief Analysis of Ultrasonic Testing Methods for Stainless Steel Pipes

23 Aug,2019

A Brief Analysis of Ultrasonic Testing Methods for Stainless Steel Pipes
　　An A‑type pulse‑echo ultrasonic flaw detector is employed, and the transverse wave reflection method with a focused probe is used for flaw detection.
　　Applicable to ultrasonic testing of single‑layer seamless straight cylindrical stainless steel tubes with an outer diameter of 6–7 mm and a wall thickness of 0.5–6 mm.
　　It may also serve as a reference for ultrasonic testing of steel pipes made from other grades, but it is not suitable for non‑circular steel pipes or ultra‑thin‑walled steel pipes.
　　The purpose of nondestructive testing is to detect longitudinal defects that compromise the integrity of the pipe material.
　　The actual dimensions of defects on tubular materials, as well as their formation and characteristics, are outside the scope of this standard. Defect evaluation is based on the reflection equivalent of standard reference specimens.
　　1 Standard Sample
　　1.1 The standard test specimen shall be of the same specification as the steel pipe under examination and shall have similar chemical composition, surface condition, and heat‑treatment process. The standard test specimen shall be free from natural defects.
　　1.2 Artificial grooves on the inner and outer walls of standard specimens may be machined separately on two separate tubes. Standard specimens with artificial grooves on both the inner and outer walls may be joined by an appropriate method after the grooves have been machined; the assembled specimen shall comply with the requirements specified in Clause 4.1. For specimens with an outer diameter not exceeding 12 mm, the specifications for inner-wall artificial grooves shall be determined through mutual agreement between the supplier and the purchaser.
　　1.3 The artificial groove may be machined on the inner or outer surface at the mid-length of the standard specimen.
　　1.4 The artificial groove is a longitudinal groove, and its cross-sectional shape may be U‑shaped, V‑shaped (with the angle of the V‑notch clearly indicated), or rectangular. In the event of a dispute arising from differences in the cross-sectional shape of the artificial groove, the U‑shaped groove shall serve as the reference standard for evaluation.
　　1.5 According to the geometric dimensions of the artificial groove, there are five levels of flaw detection standards, ranging from Level 1 to Level 5.
　　1.6 The artificial groove shall be produced by electrical discharge machining or other methods. The dimensions of the groove may be measured using the optical sectioning method or other techniques.
　　2 Instruments and Equipment
　　2.1 During nondestructive testing, ultrasonic flaw detectors, transducers, standard reference specimens, and auxiliary equipment designed to maintain consistent inspection parameters (such as incidence angle and scan pitch) that have been periodically calibrated shall be used.
　　2.2 The flaw detector shall be a pulse‑reflection ultrasonic flaw detector, either multi‑channel or single‑channel, with stable performance. Its technical specifications shall comply with the relevant national technical requirements for pulse‑reflection ultrasonic flaw detectors.
　　2.3 Probe selection: Use a linear‑focus or point‑focus probe with a frequency of 5–10 MHz.
　　2.4 In addition to complying with the requirements of Clause 4.3, mechanical transmission equipment shall also possess adequate accuracy.
　　3 Operators
　　The operator shall be a person who has passed the assessment conducted by the relevant nondestructive testing certification authority and holds a Level III or higher technical qualification certificate.

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