As the name suggests, destructive weld testing involves the physical destruction of a completed weld to evaluate its strength and characteristics. This method of 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 typically involves sectioning or breaking the welded component and evaluating various mechanical and physical characteristics. Below are some of the most common methods for executing a destructive weld test.
Destructive weld testing methods.
Macros etch testing.
This method requires the removal of small samples from the welded joint. Depending on the base material, these samples are then polished at their cross-section and etched using a mild acid mixture. The acid etches a clear visual of the weld’s internal structure.
Inspection of the etched sample reveals the depth of penetration and 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 inspection is a snapshot of the overall weld-length quality used for sampling inspection production welds. Macros etch testing is also used in failure analyses to pinpoint welding problems such as crack initiation.
Fillet weld break test.
This testing involves breaking a sample fillet weld welded on one side. Next, 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 indicate discontinuities within the entire length of the weld tested (typically 6 to 12 inches) rather than a cross-sectional snapshot, like the macro etch test. This weld inspection can detect such items as lack of fusion, internal porosity, and slag inclusions.
Though the fillet weld break test is often used independently, it can also be used in conjunction with the macro etch test. The two methods complement each other by providing information on similar characteristics but with different detail.
Transverse tension test.
Because a large portion of the design is based on the welded joint’s tensile properties of the base metal, the weld metal, the bond between the base and the weld, and the heat-affected zone must conform to design requirements.
The transverse tension test checks all this by pulling specimens to failure and 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 test method involves bending a specimen to a specified bend radius. Various bend tests are used to evaluate the flexibility and soundness of welded joints. Guided bend tests are usually transverse to the weld axis and may be bent in plunger-type test machines or 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. Side bend test specimens are usually cut from the welded joint and bent with the weld cross-section in tension when bending thick testing plates.
The guided bend test is commonly used in welding procedures and welder performance qualification tests. This testing is particularly good at finding liner fusion defects, which often open up on the plate surface during testing.