© Carina Hansen
Opening photo Application-related hydrogen-induced stress corrosion cracking may cause sudden system failure in functional components of wind energy units.
SPECIAL ON PROTECTIVE TECHNOLOGIES FOR THE ENERGY INDUSTRY
INNOVATIONS: PRESENT&FUTURE
United Against Hydrogen Embrittlement Klaus Gradtke DÖRKEN MKS - SYSTEME GMBH &Co. KG, Herdecke – Germany kgradtke@doerken.de
A
pplication-related hydrogen-induced stress corrosion cracking that is associated with the application may cause sudden system failure in
functional components of wind energy units (ref. Opening photo). The result: maintenance and repair work – and subsequent downtime for the units. Avoiding this calls for effective corrosion protection. Whether it is the construction of new plant or regular maintenance and repair work, to render the assembly process as efficient as possible and increase service life, the components of wind energy units should be coated effectively. Because it is not just red rust that is harmful to the components. Similarly dangerous is application-related hydrogen-induced stress corrosion cracking – a phenomenon that appears to occur “out of the blue”. It can even lead to sudden failure during the assembly of the subsequently highly-stressed components. Construction parts but also connecting elements can break at any time. In wind energy units this sudden loss means downtime and associated costs.
Interaction of various causes The risk of hydrogen embrittlement affects high-tensile steels above strengths of > 1,000 N/mm² and is favoured by, for example, structural defects, inclusions, impurities or mechanical stresses in working the steel. Further influencing factors arise in the manufacture of components from steel via measures such as forming, hardening or thermal processing. The coating of the component can also have an influence. In pickling or cleaning procedures and the galvanic coating of ferritic steel parts atomic hydrogen may arise in the process bath, which can diffuse into the steel surface. Finally, hydrogen charging may occur via corrosion hydrogen, i.e. when using the components. It is the critical interaction of various influencing factors that ultimately results in failure of a component without any prior damage being noted.
A gradual process The atomic hydrogen migrates to grain boundaries and areas of defect within the steel, where it enriches itself, weakening the metallic compound until a microscopically-fine crack is created. Although this eases tension in this zone, at the tip of the crack new tension concentrations arise, which in turn attract more atomic hydrogen, weaken and crack. Ultimately, the remaining
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N.31 - 2019 OCTOBER - ipcm® Protective Coatings