PAUT of CRA Cladded Pipe Circumferential Dissimilar Welds

Abstract

Ultrasonic testing (UT) is a technical way of communicating with materials, but what does that mean? To be able to understand this, we should think about how people communicate with each other—by talking. Humans have vocal cords in their throats, also known as vocal folds, a band of highly elastic connective tissue. When someone wants to talk, their brain sends a signal to the vocal fold, and after receiving the electrical signal, the folds start to vibrate and cause the air molecules flowing around them vibrate as well. This vibration flows through the air molecules to the ears of the other people, causing tiny bones within the ear to vibrate. This mechanical vibration is converted into an electrical signal by stimulation of the sensory cells in the ear and nerve impulses sent to the brain. Through this complex conversion of electrical signal to vibration, and then vibration back to the electrical signal, two human beings talk to each other. In general, the human ear can detect sounds with frequencies between 20 and 20 000 Hz, which is called an audio range. (Frequency means the number of vibrations against the unit time and is expressed in cycles per seconds). Frequencies below 20 Hz are called infrasound and above 20 000 Hz are called ultrasound. The industrial application of ultrasound is the answer to the question, “How can we talk to material?”, which forms the basis of UT. UT is widely used as a nondestructive testing method to examine materials and welds, as well as bondings between the materials. In this article, UT of dissimilar welds shall be discussed.