NDT TRAINING METHOD IN CHENNAI
ULTRASONIC TESTING METHOD
INTRODUCTION
The sound range above 20 KHZ (or) 20,000HZ is called as an ULTRASONIC SOUND (or) ULTRASOUND.
SOUND CLASSIFICATION
subsonic < 16HZ
Sonic 16HZ 20KHZ
Ultrasonic > 20,000 HZ
The sound energy is introduced & propagates through the materials in the form of waves.
Whenever the sound waves meet another interface of different acoustic impedance part of energy will be reflected back.
The same occurs when it meets cracks, lamination or any other discontinuities.
Sound generated above 20,000 HZ is called Ultrasound.
The reflected wave signal is transformed into electrical signal by the transducer & is displayed on a screen.
PROCEDURE
ASME Sec V Article: 4 (Weld) & Article: 5 (Raw Materials).
PRINCIPLE
Acoustic Impedance mismatch
Sound Resistance of material.
GENRATION OF ULTRASONIC AOUND ENERGY
Sound is created when something vibrates.
ULTRASONIC TRANSDUCERS
It converts Electrical Energy into ultrasonic energy by utilizing a phenomenon known as the PIEZOELECTRIC EFFECT.
CRYSTAL MATERIAL
Quartz or Silicon oxide (SiO3)
Lithium sulphate (LiSo4)
Lead Zirconate (Pb Zr O3)
Lead Zirconate Titanate (Pb Z1 O3 T1 O3)
Barium Titanate (Ba Ti O3)
CABLE
Lemo cable.
BNC.
TYPES OF PROBES
Normal probe.
T/R Probe.
Angle Probe.
ADVANTAGES
Portable – Inexpensive.
Immediate result.
Wide range of material thickness can be inspected.
DISADVANTAGES
High degree of skill required.
Materials are rough, irregular in shape are difficult to inspect.
Surface must be accessible to transmit ultra sound.
Linear defect – undetected.
Calibration needed.