Analysis of corrosion failure process and countermeasures of tinplate three-piece tank

analysis of corrosion failure process and countermeasures of tinplate three-piece tank
Corrosion of tinplate can

The corrosion of metal packaging products is caused by the electrochemical instability of the material in the corrosive content. The main corrosion-resistant materials of the tinplate three-piece tank are the coating of the tank body, the tinplate plating layer and the iron layer, and the top cover and the bottom cover containing the coating. Because the metal packaging products have a certain shelf life, when the tin can design corrosion life is greater than the shelf life can meet the requirements of production, to ensure the quality and safety of food and beverage in the shelf life period, too much corrosion margin is excess quality, increase the economic cost of products. In order to take into account the requirements of qualified design life and economic saving at the same time, the production of tinplate three-piece cans has precise requirements for raw materials and processes, and maintains the quality of products.

The experimental work shows that the coating, tinning layer and iron layer of tinplate are the main corrosion protection barriers of the tank. Stable raw materials and reasonable technology can meet the corrosion resistance requirements of most of the solid tank products. Related research also found that the corrosion in the tank of some products occurred earlier, due to the different types of corrosion and the location of the occurrence, its development rate is very different, some solid tanks have produced rust spots within a few weeks, serious corrosion even after a few months will appear corrosion perforation phenomenon, some solid tank corrosion can continue to the shelf life after the corrosion will not occur corrosion perforation. In the process of production and storage of tinplate cans, it is often found that there will be tank corrosion before reaching the shelf life of solid cans, and the main corrosion forms are divided into uniform corrosion and local corrosion. Local corrosion is harmful to the quality and safety of the tank, and can lead to corrosion and perforation leakage during the shelf life of the tank.

1. Uniform corrosion

Uniform corrosion, also known as comprehensive corrosion, the corrosion phenomenon is distributed on the entire metal surface, the corrosion rate of each part of the metal surface is roughly the same, the metal surface is more evenly thinned, and the metal surface has no obvious difference in corrosion morphology, such corrosion is easy to find and control because it occurs on all the surface. The more common corrosion phenomenon in tinplate can corrosion is uniform corrosion, which mostly occurs in the neck area at the top of the can body, the deformation area at the bottom of the can body and the position of the weld coating area.

2. Local corrosion

Local corrosion, also known as non-uniform corrosion, is caused by the formation of local battery corrosion due to the non-uniformity of electrochemical performance, such as dissimilar metals, surface defects, concentration differences, stress concentration or environmental non-uniformity. The negative and anode of local corrosion can be distinguished, the local corrosion is concentrated in a specific location, occurs rapidly, the material is rapidly corroded, and the local corrosion of the tinplate can easily lead to the perforation leakage phenomenon. Local corrosion presents a variety of characteristics, according to the damage form of local corrosion, such corrosion can be divided into electric corrosion, pore corrosion, seam corrosion, intergranular corrosion, wear corrosion, stress corrosion, fatigue corrosion or selective corrosion.

The local corrosion of tinplate cans is mostly concentrated in the weld area or the expansion ring of the bottom cover of the tank, of which the bottom corrosion is the main area of corrosion perforation, as shown in the figure below, the center of the black uniform corrosion area appears corrosion holes, compared with the uniform corrosion area, the corrosion hole area is very small, is a typical local corrosion phenomenon, the continued development of corrosion will lead to the tank corrosion perforation.
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