African Fusion March 2018

SAIW bulletin board

Consumable testing and diffusible hydrogen

D espite it being a subject that has been intensely researched over the decades, hydrogen in steel weldments, particularly high tensile and high yield strength low-alloyed steels, continues to limit the performance of components due to the negative effect on the properties of the metal, which typically include em- brittlement, cracking and pore formation. Hydrogen-induced cracking, also known as cold cracking, is a well-known and dreaded phenomenon. Cold cracks in welded joints can be caused by hydrogen that enters the material during the fusion welding process. Sources of hydrogenmay arise from the filler materials’ humidity whenwelding at ambient atmosphere, ad- ditives in the filler wire or from condensed water near the welding zone. For the SMAW, FCAW and SAW welding processes, flux is used in the consumable to shield the weld pool from oxidation duringwelding. The flux consists of several ingredients including chemically bonded water. During welding the water (H 2 O) will dissociate to form hydrogen ions H + , which enter the weld pool. At high welding temperatures the solubility of hydrogen in

steel increases, allowing large amounts of hydrogen into the weld pool. However during cooling the solubility significantly decreases and faster cooling rates will result in hydrogen entrapment, causing very high local stresses that result in the weld and its heat-affected zone be- coming prone to cold cracking. In 2018, SAIWmaterials testing labora- tory (MTL) extended its testing scope to include diffusible hydrogen testing. Unlike the traditionalmercurymethod, SAIWMTL’s newly commissioned Bruker G4 PHOENIX diffusible analyser uses the carrier gas hot extraction method. The basic principle for the determination of diffusible hydrogen is made using the carrier gas (Nitrogen at 99,999% purity) with hot extraction in a tube furnace, followed by detection of the evolved hydrogen with a thermal conduc- tivity detector. Welding consumable testing has long been required by industry. Over the past few years, however, the demand for consumable testing has increased with industry also requiring EN 10204 type 3.2 inspection certification, where an impar- tial and independent body is appointed to

SAIW’s MTL assistant, Nicolene Kgoedi, testing for diffusible hydrogen in a weld metal sample using the laboratories new Bruker G4 PHOENIX analyser. verify thematerials’ chemical andmechani- cal properties. SAIW is at the front line of testing weld- ing consumables with a fully equipped material testing laboratory with all the re- quired equipment and skills. With qualified welders onsite, aheat treatment furnace, an NDTandmechanical testing laboratory and a newly commissioned diffusible hydrogen tester, SAIWoffers a one-stop-shop for con- sumable testing and verification. “Our material testing laboratory is ac- credited by SANAS as conforming to the re- quirements of ISO17025 inorder toprovide our customers with assurance of reliable consumable testing results,” says SAIW welding consultant, Confidence Lekoane. info@saiw.co.za

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March 2018

AFRICAN FUSION