{"id":31043,"date":"2019-12-14T10:39:28","date_gmt":"2019-12-14T09:39:28","guid":{"rendered":"https:\/\/bolting.eu\/galvanic-corrosion-with-expansion-bolt\/"},"modified":"2025-02-11T14:17:27","modified_gmt":"2025-02-11T13:17:27","slug":"galvanic-corrosion-with-expansion-bolt","status":"publish","type":"page","link":"https:\/\/bolting.eu\/en\/galvanic-corrosion-with-expansion-bolt\/","title":{"rendered":"Galvanic corrosion with expansion bolt"},"content":{"rendered":"\n

Galvanic corrosion at expansion bolt<\/strong> is probably one of the greatest safety risks on climbing routes<\/strong>. It is often referred to as contact corrosion or bimetallic corrosion <\/strong>. It has a negative impact on the breaking load of the affected components. We therefore want to provide comprehensive information on this topic<\/strong>. Firstly, about the principle of this type of corrosion. Secondly, we present practical examples. And thirdly, we give you simple tips on how to prevent it. <\/p>\n\n

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Example of contact corrosion on a zinc plated expansion bolt to which a stainless steel lug and nut have been fitted. Diameter just behind the bracket is only approx. 7-8mm! Photo: bolting.eu <\/figcaption><\/figure><\/div>\n\n
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Galvanic corrosion principle<\/h2>\n\n
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In simple terms, galvanic corrosion occurs at expansion bolt for the following reason. Components with different precious metals<\/strong> have been processed. E.g. a zinc plated expansion bolt with a stainless steel bracket.<\/strong> The influence of water then causes electrons to migrate. From base metal to noble metal <\/strong>. In the process, the base metal is decomposed (“oxidized”)<\/strong>. To stay with our example. The zinc plated expansion bolt (= base metal) begins to “rust”. <\/p>\n\n

The precious metal, the positively charged cathode, is “reduced” in the process.This happens mainly just behind the bolt hanger in the drilling hole. This is because water can accumulate perfectly between the thread and the rock. It then acts as a so-called “electrolyte”. In other words, as a liquid through which the electrons can flow. <\/p>\n\n

This chemical process – which in simple terms works like a small battery – can therefore progress unhindered. Over the years, the breaking load of the base component steadily decreases and eventually becomes a danger. This is because the maximum breaking load values are significantly undercut. <\/p>\n\n

Estates and Rapid limbs also affected<\/h3>\n\n
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Unfortunately, galvanic corrosion at expansion bolt very often also affects the lower off \/ climbing anchors<\/a>. Here, a stainless steel lower off was\/is classically mounted on zinc plated expansion bolt. <\/p>\n\n

Please also note. Bimetal corrosion will also occur if you attach a zinc plated screw link-Rapid link<\/a> to a stainless steel bolt hanger or vice versa! <\/p>\n\n

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Galvanic corrosion on a zinc plated screw link \/ Rapid link hanging in a stainless steel bracket.<\/figcaption><\/figure>\n\n

With glue in bolt<\/a> there can be no contact corrosion. This is because a glue in bolt consists of only one type of metal! <\/p>\n\n

Stronger corrosion in “salty” environments<\/h3>\n\n
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In simple terms, contact corrosion at expansion bolt depends on the following factors:– Salt content of the “electrolyte”: The more “aggressive” the water, the stronger the reaction of the two different metals.– Ambient temperature: In the range of 25\u00b0-35\u00b0 C, salt water offers the best solubility for many salts and leads to accelerated corrosion in this temperature range.Consequently, the degree of galvanic corrosion can vary greatly at expansion bolt. On a shady and dry granite rock, it will be rather low. On a damp and sunny limestone rock, it will be rather high. The individual processes are explained in detail at the bottom of the article!<\/strong>Click here for the article on galvanic corrosion \/ contact corrosion on Wikipedia<\/a>. <\/p>\n\n

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Deceptive appearance of a zinc plated expansion bolt with stainless steel tab. “Wow!” on the outside, “pooh!” on the inside. The shaft is extremely affected by corrosion and its breaking load is impaired. <\/figcaption><\/figure><\/div>\n\n
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Practical causes of galvanic corrosion<\/h2>\n\n
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There are many practical reasons for processing components made of different metals. In the following, we would like to present the three most important causes from our point of view: <\/p>\n\n