How does corrosion spoil a stale pipe?

February 20, 2018 | Views: 54 |

Situations are not uncommon when pipe metal products can be stored in a warehouse for a long time until they are sold. However, it happens that products do not go into use for too long and lose a number of their properties. In such cases, such a pipe from the new category falls into the used category, namely the old one, and cannot be used without undergoing special restoration work.

What kind of negative changes might happen?

The main and most significant is corrosion. Corrosion is the spontaneous destruction of metals and alloys as a result of chemical, electrochemical or physico-chemical interaction with the environment. Iron is present in the alloy of any rolled steel. When interacting with water and oxygen, it begins to oxidize. This causes the formation of iron oxide, or more simply, rust. At first, this layer does not exceed a micron. However, the longer the product is under the negative influence of moisture and temperature, the larger this layer becomes. Over time, the rusting process penetrates deeper and can cause quite serious damage, up to through holes. Seamless pipes are less susceptible to corrosion than those with a welded seam, which is why they are more expensive welded. It is in the places of welding that corrosion processes occur more often than usual.

Corrosion classification

The main classification is based on the mechanism of the rusting process. There are two types: chemical and electrochemical corrosion.

  1. Chemical corrosion is a process in which an oxidative reaction occurs when a metal interacts with an aggressive environment. This type of corrosion occurs not under the influence of electric current, but due to the fact that the destructible material (metal) is also a reducing agent for the elements of the environment.
  2. If we talk about electrochemical corrosion, then in this case, the destruction of the metal is caused by its contact with conductive materials.

About 30 types of corrosion are known. However, for pipe metal products, namely old pipes, 4 can be distinguished:

  1. slit - enhanced destruction in gaps, crevices, cracks;
  2. local - damage process that is difficult to see with the naked eye;
  3. surface - characterized by uniform destruction over the entire surface and is determined by the thickness of the layer (in mm) destroyed during the year;
  4. pitting - corrosion leading to the formation of pits, that is, ulcers, cavities starting from its surface. Externally, pitting manifests itself in the form of depressions on the surface of the metal;
  • slit - enhanced destruction in gaps, crevices, cracks;
  • local - damage process that is difficult to see with the naked eye;
  • surface - characterized by uniform destruction over the entire surface and is determined by the thickness of the layer (in mm) destroyed during the year;
  • pitting - corrosion leading to the formation of pits, that is, ulcers, cavities starting from its surface. Externally, pitting manifests itself in the form of depressions on the surface of the metal;
  • It is not difficult to guess that all these processes have an extremely detrimental effect on the condition and quality of stale products.

    Ways to protect pipes from corrosion

    There are many methods of protection, the timely application of which can significantly extend the life of products. The most popular are:

    • use of corrosion-resistant materials in production;
    • apply electrical protection;
    • isolation of the pipe surface from environmental factors;
    • influence on the environment to reduce its negative impact on pipes.

    The first option can only be implemented at the stage of rolled products production, which makes it quite expensive.

    The second option is no less cheap, since it consists in closing the electrical circuit to any other metal sample near the old pipes. In this case, corrosion occurs on the surface of another metal, bypassing the products placed in storage. To organize such protection, a constant source of energy is needed, which requires additional costs.

    In the third option, a special coating of mastic, varnish, enamel, or a zinc, magnesium, or aluminum alloy is applied to the surface. As it dries, the layer hardens and acts like a shell, depriving the surface of moisture, temperature or chemicals.
    The last option involves treating the surface of the rolled products with inhibitors - substances that “attract” molecules that slow down the corrosion process. The processing of the product (water, oil, gas, etc.), which will be further transported through the pipeline, also contributes to minimizing the negative impact of the external environment.
    As we could see, Selecting old used pipes requires no less attention than choosing and buying refurbished used products. The employees of our metal warehouse will be happy to help you understand all the intricacies of used pipe and help you find the best solution.


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