An Introduction to Destructive Weld Testing

An Introduction to Destructive Weld Testing

Destructive Weld Testing Tips

The present article covers an introduction to destructive weld testing, various methods of destructive testing, their applications, and their significance. 

Destructive weld testing, as the name suggests, involves the physical destruction of a completed weld to evaluate its strength and characteristics. The testing procedure is conducted to understand a specimen’s material behavior, strength, quality of the welded joint, and the skill of the welder.  

Destructive weld testing is frequently used for the following applications: 

  • Welding procedure qualification 
  • Sampling inspection 
  • Research inspection 
  • Welder performance qualification testing 
  • Failure analysis work 

Destructive Weld Testing Methods 

Methods of destructive weld testing typically involve sectioning or breaking the welded component and evaluating various mechanical and physical characteristics. Check out some of the most common methods for executing a destructive weld test below. 

Macro Etch Testing 

This method requires the removal of small samples from the welded joint. These samples are then polished at their cross-section and etched using a mild acid mixture, depending on the base material used. The acid etch provides a clear visual of the weld's internal structure. 

Inspection of the etched sample reveals the depth of penetration, as well as evidence (if any) of lack of fusion, inadequate root penetration, internal porosity, and cracking shown at the fusion line (which is the transition between the weld and the base material). 

This type of inspection is a snapshot of the overall weld-length quality when used for sampling inspection of production welds. Macro etch testing is also used successfully in failure analyses to pinpoint welding problems such as crack initiation. 

Fillet Weld Break Test 

This type of testing involves breaking a sample fillet weld that is welded on one side only. The sample has a load applied to its unwelded side, typically in a press, and the load is increased until the weld fails. The failed sample is then inspected to establish the presence and extent of any welding discontinuities. 

Fillet weld break tests provide a good indication of discontinuities within the entire length of the weld tested (normally 6 to 12 inches) rather than a cross-sectional snapshot, like the macro etch test. This type of weld inspection can detect such items as lack of fusion, internal porosity, and slag inclusions. 

Though the fillet weld break test is often used on its own, it can also be used in conjunction with the macro etch test, as the two methods complement each other by providing information on similar characteristics but with different detail. 

Transverse Tension Test 

A significant portion of the design is based on the tensile properties of the welded joint. Therefore, the below factors need to conform to the design requirements: 

  • tensile properties of the base metal and the weld metal 
  • the bond between the base and the weld 
  • heat-affected zone 

The transverse tension test checks all this by pulling specimens to failure and then dividing the maximum load required during testing by the cross-sectional area. The result is in units of tension per cross-sectional area. 

Guided Bend Test 

This is a test method that involves bending a specimen to a specified bend radius. Various types of bend tests are used to evaluate the ductility and soundness of welded joints. Guided bend tests are usually taken transverse to the weld axis and may be bent in plunger-type test machines or in wraparound bend test jigs. Face bend tests are made with the weld face in tension, while root bend tests are made with the weld root in tension. When bend testing thick plates, side bend test specimens are usually cut from the welded joint and bent with the weld cross-section in tension. 

The guided bend test is most commonly used in welding procedures and welder performance qualification tests. This type of testing is particularly good at finding liner fusion defects, which will often open up in the plate surface during testing. 

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