QUALITY ASSURANCE ON WELDED JOINTS WITH THE MECHANISED LINEAR SHEAR TEST (LST)

Papers # 2018 Las-Vegas

A testing apparatus for determining the mechanical properties of electrofusion and heated tool sleeve welded joints with the mechanized linear shear test (LST) was developed. The LST-apparatus allows the recording of the force as a function of the extension / shear length. It has been proved that the linear shear test represents a very good possibility for analyzing electrofusion and heated tool sleeve welded joints. The testing method has been implemented in the technical codes of the German Association for Welding and Related Procedures (DVS) (DVS 2203-6 supplement 1).

Testing the quality of welded joints in plastic pipe systems is of essential importance, especially in the field of water and gas supply. Currently used test methods for characterizing the mechanical properties of electrofusion and heated tool sleeve welded joints are mainly manual test methods which do not produce a mechanical characteristic value, e. g. the torsion shear test or radial peeling test. The assessment of the welding zone is done with the naked eye of the operator. Furthermore, these test methods can unintentionally be influenced by the operator. 

In cooperation with WIDOS GmbH, SKZ developed a testing apparatus for determining the mechanical properties of electrofusion and heated tool sleeve welded joints with the mechanized linear shear test (LST). Parallel prepared samples from the welding zone are loaded with a linear shear force in the test application. Two hydraulic clamping devices fix the sample. One clamping device fixes the pipe section of the sample and the other one fixes the fitting / coupler section of the sample. An electronic powered linear device moves the upper clamping device and shears the sample. The LST-apparatus allows the recording of the force as a function of the extension / shear length. 

The LST has proven to be a reproducible test procedure for the assessment of electrofusion and heated tool sleeve welded joints. It is very suitable for detecting defects in electrofusion and heated tool sleeve welded joints. In addition to frequent and obviously incorrect preparations it was possible to detect defects which, with the manual radial peeling and torsion shear tests, could not be recognized at all, like e. g. contaminations of the welding surface or incorrect welding parameters. Due to its reliability the LST allows the optimization of welding parameters and further developments (e. g. testing of glued connections). 

Related keywords : Electrofusion Welding (HM), Heated Tool Sleeve Welding (HD), Quantitative results, Welding Defects.
Please note that the whole article content is available on PPCA website onlySource : 2018 Las-Vegas


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