An Overview of Ultrasonic Weld Testing

Ultrasonic testing encompasses many different methods of non-destructive techniques where ultrasonic waves are sent through a material or an object. By transmitting high frequency sound waves into materials, we can detect flaws and characterise the material. This is an extremely popular method for evaluating the quality of a weld.  

While carrying out ultrasonic weld testing, an ultrasonic energy beam is directed towards the weld to be tested. Under normal circumstances, the beam travels through the weld without any significant loss. However, if there is any discontinuity, the waves get intercepted and reflected. 

The testing technology utilises the ability of high-frequency oscillations be reflected from surface voids, scratches, and other types of discontinuities. When diagnostic waves reach the surface of the weld, if there is a defect, the waves tend to deviate from their normal propagation. Graphical and parametric readings are used to identify the nature of the defect. For example, propagation time of the ultrasonic wave provides an indication of distance to the fault. On the other hand, amplitude of the reflected pulse is the measure of relative size of the defect.  

Inspection Procedure: 

A typical weld inspection process comprises of the following steps. 

  • Removal of rust and paints from the welding seam.
  • To ensure accurate results, the weld seam and the metal surface around it should be treated with a couplant.  
  • Depending on the specific task, the device should be pre-configured. 
  • Move the transducer along the seam in a zigzag manner while turning it around the axis by an angle of 10-15 degrees.
  • Move the transducer repeatedly at the occurrence of stable flaw signal. Ascertain the position at which the flaw signal is at its maximum.
  • Try to ensure that no reflection of the oscillations is caused by the welding steam itself.
  • Weld seam inspections are generally performed in one or two approaches.
  • Check the T-joints by echo method. 

Defects You Can Identify:  

  • Cracks present in and around the weld zone
  • Stratified weld metal
  • Pores within the weld 
  • Welded joints with lack of fusion
  • Weld joints with incomplete fusion and discontinuities
  • Presence of slack metal in the weld’s lower zone.
  • Corrosion affected areas
  • Areas with  chemical composition mismatch
  • Areas with distorted geometric size


  • Allows for flaw detection deep within a weld because of high penetration power
  • Very small flaws in weld can be detected because of the high sensitivity of ultrasonic testing 
  • This method can be used even when just one side of the weld is accessible
  • Higher accuracy compared to most other non-destructive testing methods
  • Allows ascertaining the shape, size, nature, and orientation of defects.
  • The method is completely non-hazardous to nearby materials, equipment, and personnel.
  • Possibility of highly portable and automated operations.
  • Helps make quick decisions by delivering immediate results. 

If want to find out more about ultrasonic weld inspection, please contact us at Coating Management Solutions. We offer highly specialised welding inspection and NDT services using the most advanced testing equipment.