Destructive Testing (Mechanical)

Destructive (Mechanical) and Non-destructive (NDT)

 

Destructive (Mechanical) Test

The tests applied may include all or some of the following tests.

The destructive tests (as related to welding), in each case the acceptance criteria is the same as that for the parent material.

  • Tensile Test

To stretch a sample of the test weld and parent material to failure and compare with parent material specification.

  • Bend Test

To bend the steel around a former of a diameter used on the parent material, this is a test of ductility, thickness's up to 10 mm the face and root are put in tension. Greater than 10mm and the sides are put in tension.

  • Macro Etch

The weld is sectioned,  polished then etched to make the weld stand out, it enables the examiner to see the degree of fusion into the parent material and between passes. Defects within the weld are assumed to extend the full length.

  • Hardness Survey

A series of indentations made with a tool of known size and load from the parent material on one side across the weld to the parent material on the other side. This tells how hard the material is, and shows the difference between Parent Material, Heat Affected Zone and weld metal.

  • Corrosion Test

Some parent materials are chosen for their resistance to corrosion, in which case this resistance to corrosion must include weld metal and heat affected zone (HAZ )

  • Impacts

Sometimes known as Charpy or IZOD,  At low temperature some steels become brittle, the parent material must show resistance to brittle failure at the working temperature and the weld must show equal resistance. The desired is a ductile failure in which the material distorts before failure. The most famous case of brittle failure was the sinking of the Titanic, after hitting the iceberg a crack torn down the length of three compartments without warning.

  • Metallographic

This is a test to check the Micro structure, what is acceptable depends on the material being examined. It is similar to a macro-examination except it is polished and examined under a powerful microscope.

  • CTOD

Crack Tip Opening Displacement, a test to establish the resistance to fatigue failure.