Back to Application Notes

Ultrasonic NDT

Inspection of a Welded T-joint

Published on 2nd January 2021

Inspection of a Welded T-joint

The ABC’s of a T-joint

A T-joint consists of two plates welded at 90° to each other in the form of a T. Commonly used in the structural industry, T-joints generally use fillet or groove type welds which may be referred to as weld overlays. Inspection can be challenging due to the actual weld geometries and the undesirable (repetitive) echoes within the test piece. Hence, it’s difficult to accurately identify potential defects and of course their correct solution.

The Sonatest WAVE Digital Flaw Detector with its interactive scan plan provides optimal visualisation of the sound path through the weld, covering the weld cap and root. Thus, the A-Scan signal can be displayed on the sound path, helping to improve the localisation of the defect at a glance.

This unique feature makes Wave an ideal instrument for T-joint inspection.

Typical Defects in T-joints

The most common defects in T-joint welds are cracks, lack of fusion and lamellar tearing all of which can be inspected with conventional ultrasonic methods.

Lack of fusion or Penetration

A lack of fusion occurs when the base metal is not melted during welding resulting in a lack of cohesion. For T-joints, lack of fusion is commonly seen in between the plates and therefore the optimal way to detect such defects is utilising a straight beam configuration on the lower flange of the joint. However, this may not be accessible.

Scan Plan – Lack of fusion or penetration

Microstructure – Lack of fusion or penetration

Lamellar tearing occurs when there is a weld contraction combined with low ductility of the base metal. This generates a very high stress concentration, located in the base metal, outside or close of the heat affected zone (HAZ). The tearing is generally parallel to the weld fusion surface.

Unfortunately, T-joint as well as corner joint are affected by this type of defect due to high through-thickness strain.

Lamellar tearing can be easily detected by an inspection from the lateral web of the joint because of its predictable orientation.

Scan Plan

Microstructure. KOU, Sindo (2003) Welding Metallurgy. New Jersey, USA: John Wiley & Sons


A crack is a combination of metallurgical and mechanical failures. It usually occurs due to pre-existing stresses, generally caused by thermal expansion, solidification, shrinkage or both. For example, aluminium alloys have a high thermal expansion coefficient and solidification shrinkage.

On a T-Joint with fillet welds on both sides, the second side is more restrained mechanically. Hence, this side will be more susceptible to cracks, as seen in the figure below.

It is difficult to correctly predict the orientation of cracks, as they can be detected from many inspection angles based on the sample geometrical aspects.

Scan Plan

Microstructure. KOU, Sindo (2003) Welding Metallurgy. New Jersey, USA: John Wiley & Sons


Welded structures have to meet applicable codes and standards related to their intended use. The welding process, inspection technique and acceptance criteria vary.

For structural welding inspection to the American Welding Standard (AWS), the most important measurements are the indication level, reference level, attenuation factor and the indication rating. The Sonatest Wave has a built-in single touch application for inspecting to AWS requirements. Hence, after an AWS calibration, the user is able to select the AWS measurements associated with the corresponding gate. In addition, the indication rating is automatically calculated, which improves the reporting efficiency.

Sonatest WAVE instrument with pre-defined AWS & TKY set ups

WAVE Interactive Scan-Plan for T-Joint inspection


  • Structural Steel Fabrication
  • Bridge Manufacture
  • Pipe Manufacture
  • Marine

Typical Parts

  • T-joint in bridge decks
  • Nozzle welding on pressure vessels

Inspection Techniques

  • Interactive plan
  • 2D view ray tracer
  • A-Scan displayed over the sound path
  • AWS sizing technique

Features & Benefits

  • Straightforward parametrisation of the weld and T-joint
  • Optimal visualisation of the sound path in the weld, the weld caps and the part
  • Mitigation of false calls
  • Enhanced flaw localisation with interactive scan plan
  • Advanced reporting with accurate representation of the weld and the sound path

Recommended Tool Package

  • Sonatest WAVE
  • Sonatest WAVE Companion software
  • SSG and PSS failing (1 to 5 MHz; ¼ inch to 1 inch footprint)

                - SSG probe series for sensitivity

                - PSS probe series for resolution

                - All 45 60 70 wedges on demand

For further information or support, please contact the Sonatest Applications Team:

Join the Conversation


Tree PNG back


Tree PNG back




Tree PNG back


Application Notes