Mechanical testing

Mechanical testing or engineering test is performed to determine various mechanical properties of materials such as strength, hardness, ductility, toughness, brittleness, etc. There are several types of test to determine various mechanical and physical properties of material. The precision results of these tests is utilised to determine suitability of materials for the field application.

To approve a butt welding procedure most specifications such as ISO 15614 and ASME IX require Tensile tests, Impact tests, hardness and macro examination to be carried out.

Many application standards such as PD 5500 require tests additional to those required by, for example, ISO 15614-1. This must be remembered when procedure approval documentation is submitted for approval by the inspecting authority or the client.

Tensile tests

These are generally cross joint (CJ) tensile tests of square or rectangular cross section that, as the name suggests, are oriented across the weld so that both parent metals, both heat affected zones (HAZs) and the weld metal itself are tested.

While it is possible to measure the yield strength, the elongation and the reduction of area of CJ specimens the fact that there are at least three different areas with dissimilar mechanical properties makes such measurements inaccurate and unreliable, although this is sometimes carried out purely for information purposes.

Charpy Impact Test,

Also known as the Charpy V-notch test, is a standardized high strain-rate test which determines the amount of energy absorbed by a material during fracture. This absorbed energy is a measure of a given material’s notch toughness and acts as a tool to study temperature-dependent ductile-brittle transition.

Today it is used in many industries for testing materials used in the construction of pressure vessels and bridges and to determine how storms & Climatic conditions will affect materials used for construction.

Macroscopic examination:

Also called macro test or macro examination, is an extension of visual examination and evaluates quality and homogeneity of the test sample indicating the flow of material during the forming or welding process. Information on macrostructural features can be used to assess internal quality, presence of hydrogen flakes, chemical segregation, hard cases, flow lines and welds. A common macro test is weld cross section examination to reveal internal discontinuities, weld profile, weld passes and sequence, extent of penetration and the quality of weld. The macrostructural properties of a weldament can then be used as a component of weld procedure qualification or welder qualification.

Relevant specifications

• BS EN 10002 Methods of tensile testing of metallic materials.
• BS EN 876 Destructive tests on welds in metallic materials – longitudinal tensile test.
• BS EN 895 Destructive tests on welds in metallic materials – transverse tensile test.
• BS EN ISO 7500-1 Tension/compression testing machines. verification and calibration of the force measuring system.
• ASTM A370 Mechanical testing of steel products.
• ASTM E8 Tension testing of metallic materials.
• ASTM B557 Tension testing wrought and cast aluminium and magnesium alloy products.