Fastener galvanizing passivation
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Do the fasteners used for equipment flanges and pipe flanges need to be galvanized and passivated? What is the purpose of galvanizing and passivating?
What is the purpose of galvanizing and passivating? It’s for corrosion prevention.
This post was last edited by zhangjuhua on 2017-5-21 at 13:50. I agree with what was said above: passivation involves the formation of an oxide layer on the surface to separate the base metal, thereby improving corrosion resistance. Stainless steel flanges definitely require this treatment; it’s not clear whether carbon steel flanges need it as well, maybe they’re painted more often. Carbon steel fasteners may require it, but main bolts with a diameter greater than 36 seem inappropriate for this purpose
Thank you to the two people above; do all the fasteners shown in those drawings need to have zinc plating and passivation indicated?
For high-strength bolts, galvanizing or zinc infiltration can cause hydrogen embrittlement in the container; therefore, some standards and specifications require that such treatment not be applied to bolts. Therefore, this issue has always been controversial, but most of the bolts used in offshore oil environments are required to undergo zinc plating.
Galvanized bolts involve immersing the rust-removed bolts in molten zinc at around 500°C, so that a zinc layer is formed on the surface of the screws, thereby providing corrosion protection. When the equipment is exposed to a humid environment for long periods, is frequently washed with water, and subject to rain, it is best to use stainless steel bolts. Galvanized bolts are generally used in ordinary dry environments.
This post was last edited by Forgetting = Forgetting on 2017-5-22 at 17:09. Carbon steel, which contains iron, is prone to corrosion in the environment; after galvanizing, an inert zinc oxide layer forms on its surface. Moreover, during the corrosion process, the zinc layer corrodes first. During the passivation of stainless steel, the transformation of Gr ions within the metal into higher-valent Gr ions occurs slowly. Through the passivation process, a Gr film is formed rapidly, which reduces corrosion. Therefore, it is necessary to prevent Fe ion contamination in stainless steel, in order to avoid the formation of microcells that could disrupt the state of higher-valent Gr ions. Of course, this is standard; the actual use depends on the conditions of the environment in which it is applied.
No need. The equipment flange studs have been blue-treated.
For ordinary connection bolts, galvanizing can be used to prevent rusting. However, for equipment flanges and pipe flanges, the standards specify blueing treatment for alloy steel fasteners; there are also questions regarding the treatment required for fasteners made of non-alloy steel.
Is the purpose of blueing treatment and zinc plating passivation the same?