Inspection of a Welded T-joint

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.


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.

Welded T-Joint

Scan Plan – Lack of fusion or penetration

 

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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.

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Scan Plan

 

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

Cracks

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.

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Scan Plan

 

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


CODES & STANDARDS

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

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WAVE Interactive Scan-Plan for T-Joint inspection

 

For further information or support, please contact the Sonatest Applications Team: applications@sonatest.com