Underestimated Threat To Metal Durability
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<div><p><strong><span style="font-size: 12pt;"><span xml:lang="EN-US" data-contrast="auto">Hydrogen Embrittlement </span> <span xml:lang="EN-US" data-contrast="auto">(a.k.a. Hydrogen Damage)</span></span></strong><span data-ccp-props="{"134233117":false,"134233118":false,"201341983":0,"335559738":240,"335559739":240,"335559740":279}"> </span></p></div><div><p><span xml:lang="EN-US" data-contrast="auto">Hydrogen embrittlement is an engineering consideration with high-strength steels, titanium, and other high-strength specialty metals. </span><span data-ccp-props="{"134233117":false,"134233118":false,"201341983":0,"335559738":240,"335559739":240,"335559740":279}"> </span></p></div><div><p><span xml:lang="EN-US" data-contrast="auto">Hydrogen blistering can occur when hydrogen enters metal because of the reduction reaction on a metal cathode. Single-atom, nascent hydrogen atoms diffuse through the metal until they meet and bond with another nascent hydrogen, usually at inclusions or defects in the metal. </span><span data-ccp-props="{"134233117":false,"134233118":false,"201341983":0,"335559738":240,"335559739":240,"335559740":279}"> </span></p></div><div><p><span xml:lang="EN-US" data-contrast="auto">The resultant stable diatomic hydrogen molecules are then too large to permeate the metallic grain structure to outgas and become trapped. Eventually, a gas blister builds up and may split the metal, as shown in the photo below.</span><span data-ccp-props="{"134233117":false,"134233118":false,"201341983":0,"335559738":240,"335559739":240,"335559740":279}"> </span></p></div><div><p><strong><span xml:lang="EN-US" data-contrast="auto">Intergranular Corrosion</span></strong><span data-ccp-props="{"134233117":false,"134233118":false,"201341983":0,"335559738":240,"335559739":240,"335559740":279}"> </span></p></div><div><p><span xml:lang="EN-US" data-contrast="auto">Intergranular corrosion occurs at or adjacent to the grain boundaries of an alloy. A highly magnified cross-section of commercial alloys shows a granular structure. Each grain has a clearly defined boundary that chemically differs from the metal within the grain center. Heat treatment of stainless steel and aluminum alloys accentuates this problem. </span><span data-ccp-props="{"134233117":false,"134233118":false,"201341983":0,"335559738":240,"335559739":240,"335559740":279}"> </span></p></div><div><p><strong><span xml:lang="EN-US" data-contrast="auto">Pitting Corrosion</span></strong><span data-ccp-props="{"134233117":false,"134233118":false,"201341983":0,"335559738":240,"335559739":240,"335559740":279}"> </span></p></div><div><p><span xml:lang="EN-US" data-contrast="auto">Passive metals like stainless steel resist corrosive media and can perform well over long periods. However, if corrosion does occur, it forms pits randomly. </span><span data-ccp-props="{"134233117":false,"134233118":false,"201341983":0,"335559738":240,"335559739":240,"335559740":279}"> </span></p></div><div><p><span xml:lang="EN-US" data-contrast="auto">Pitting is most likely to occur in the presence of chloride ions combined with depolarizing agents such as oxygen or oxidizing salts. </span><span data-ccp-props="{"134233117":false,"134233118":false,"201341983":0,"335559738":240,"335559739":240,"335559740":279}"> </span></p></div><div><p><span xml:lang="EN-US" data-contrast="auto"><strong>Uniform Corrosion </strong></span><span xml:lang="EN-US" data-contrast="auto">(a.k.a. General Corrosion, Uniform Etch Corrosion)</span><span data-ccp-props="{"134233117":false,"134233118":false,"201341983":0,"335559738":240,"335559739":240,"335559740":279}"> </span></p></div><div><p><span xml:lang="EN-US" data-contrast="auto">Uniform corrosion is a surface effect resulting from a uniform chemical etching of the metal surface. Etching can be caused by any chemical agent that attaches to the metal surface. </span><span data-ccp-props="{"134233117":false,"134233118":false,"201341983":0,"335559738":240,"335559739":240,"335559740":279}"> </span></p></div><div><p><span xml:lang="EN-US" data-contrast="auto">This type of corrosion on polished surfaces first manifests as dulling, followed by roughening or a 'frosted' appearance of the once polished metal surface. </span><span data-ccp-props="{"134233117":false,"134233118":false,"201341983":0,"335559738":240,"335559739":240,"335559740":279}"> </span></p></div><div><p><span xml:lang="EN-US" data-contrast="auto">Discoloration or dulling caused by exposure to elevated temperatures should not be confused with uniform corrosion. </span><span data-ccp-props="{"134233117":false,"134233118":false,"201341983":0,"335559738":240,"335559739":240,"335559740":279}"> </span></p></div><div><p> </p><h2><span style="font-size: 14pt;" xml:lang="EN-US" data-contrast="auto">Preventive Methods</span><span data-ccp-props="{"134233117":false,"134233118":false,"201341983":0,"335559738":240,"335559739":240,"335559740":279}"> </span></h2></div><div><p><span xml:lang="EN-US" data-contrast="auto">Now that the mechanisms of corrosion and the factors contributing to corrosion are understood, a meaningful examination of conventional preventative measures may be undertaken. Given that a single metallic body may act as both anode and cathode, there are effectively two basic methods of protecting metals from corrosion. </span><span data-ccp-props="{"134233117":false,"134233118":false,"201341983":0,"335559738":240,"335559739":240,"335559740":279}"> </span></p></div><div><p><strong><span xml:lang="EN-US" data-contrast="auto">Protective Coatings</span><span data-ccp-props="{"134233117":false,"134233118":false,"201341983":0,"335559738":240,"335559739":240,"335559740":279}"> </span></strong></p></div><div><p><span xml:lang="EN-US" data-contrast="auto">Protective coatings can effectively control corrosion by creating a physical film barrier that prevents contact between the metal and at least one corrosion factor, such as oxygen, water, and/or electrolytic salts (in water, create an electrolytic solution). However, these coatings are only effective if they maintain adherence to the metal and don't get scratched, develop holidays, or other coating breaches.</span><span data-ccp-props="{"134233117":false,"134233118":false,"201341983":0,"335559738":240,"335559739":240,"335559740":279}"> </span></p></div><div><p><strong><span xml:lang="EN-US" data-contrast="auto">Electronic Protection</span></strong><span data-ccp-props="{"134233117":false,"134233118":false,"201341983":0,"335559738":240,"335559739":240,"335559740":279}"> </span></p></div><div><p><span xml:lang="EN-US" data-contrast="auto">Transfers the electrons by electronic conduction to a location where the corrosion can occur without harm. Another method is the use of imposed electric potentials from external power supplies. However, this method is less common due to economic factors.</span><span data-ccp-props="{"134233117":false,"134233118":false,"201341983":0,"335559738":240,"335559739":240,"335559740":279}"> </span></p><p> </p><p> </p><p><em>This article was contributed by our expert <a href="https://www.linkedin.com/in/andrew-sokol-19b59a22/" target="_blank" rel="noopener">Andrew Sokol</a></em></p><p> </p><p> </p><h3><span style="font-size: 18pt;">Frequently Asked Questions Answered by Andrew Sokol</span></h3><p> </p><p>1. What innovative corrosion prevention techniques are being developed specifically for high-strength steels in industries such as aerospace, automotive, and construction? </p><p>Some of the innovative corrosion prevention techniques developed to address the unique challenges are :</p><p><strong>Advanced Surface Coatings</strong></p><p>These coatings may incorporate nanomaterials, polymers, or ceramic compounds to provide enhanced barrier protection against corrosive environments while maintaining the mechanical properties of the steel.</p><p><strong>Corrosion-Resistant Alloys</strong></p><p>Metallurgists are continually refining alloy compositions to improve the inherent corrosion resistance of high-strength steels</p></div><div><p><span data-ccp-props="{"201341983":0,"335559739":160,"335559740":279}"> <strong>Surface Modification Techniques</strong></span></p><p><span data-ccp-props="{"201341983":0,"335559739":160,"335559740":279}">These techniques can create a hardened surface layer that is more resistant to wear, abrasion, and corrosion, thereby extending the service life of components in harsh environments.</span></p><p> </p><p> </p><p> </p></div>
KR Expert - Andrew Sokol
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