Metal corrosion issues are all over the areas of the national economy, such as oil and gas, petrochemicals, transportation, mechanical manufacturing, etc. It can be said that as long as it is used in metal materials, corrosion problems are existing. Corrosion has brought many losses and harm to social production. Today, I will share with you the knowledge about metal corrosion. Let's start with the harm of metal corrosion.

 

Economic losses

The economic loss caused by corrosion is amazing. According to domestic rough statistics, the economic losses caused by corrosion have reached 280 billion yuan, accounting for about 4%of the GDP (GNP). Looking at the global oil and natural gas production industry, according to the US Corrosion Engineer Association (NACE) estimates, the total annual corrosion cost of the world is 1.3 billion US dollars, about 8.6 billion yuan.

 

Environmental pollution

The waste of resources caused by corrosion and environmental pollution are extremely serious. Corrosion can lead to a large amount of rust, cause the metal material to fail prematurely, and also causes a lot of waste of resources and energy. Corrosion products and dirt will cause the heat transfer efficiency of boilers, heat exchangers and other equipment, and waste a large number of tons of standard coal. Burning the harmful gases such as SO2 produced by these coal have exacerbated environmental pollution.

 

Security risks

In 2011, a petrochemical plant was located at the push tank of the deoxyne tower of the gas distillation device. Suddenly, the explosion occurred, causing 4 people to die, 1 person seriously injured, 6 people were injured, and the direct economic loss was 8.69 million yuan. It was confirmed by the accident investigation that the cause of the accident was that the stress corrosion of hydrogen sulfurized caused a burst of the return tank and caused an explosion.

 

What is metal corrosion?

 

Metal materials are damaged by the action of peripheral media, called metalic corrosion.

 

How many categories are there in metal corrosion?

Due to the complicated corrosion phenomenon and mechanism, the differences in the state of material and environmental factors, that is, the state of force, are very different from the situation and characteristics of metal corrosion. Therefore, there are many classification standards and methods, but the common corrosion classification methods are classified according to the corrosion mechanism and classification according to the corrosion form.

 

How to classify the corrosion mechanism?

Classified by corrosion mechanisms can be divided into two types: chemical corrosion and electrochemical corrosion:

Chemical corrosion refers to the metal corrosion that occurs directly in the chemical reaction of metal and non -electrolytes.

Electrochemical corrosion is damage caused by electrochemical effects in metal and electrolyte solutions.

How to classify by corrosion form?

Classified by corrosion forms can be divided into two types: comprehensive corrosion and local corrosion:

Comprehensive corrosion occurs on the surface of the entire metal. It may be uniform or uneven.

Local corrosion is concentrated in part of the metal, while the other parts are almost not corrosive or slightly corrosive. There are many types of local corrosion, which are generally divided into the following:

Electric corrosion: In the electrolyte solution, when the heterogeneous metal contacts, the metal with a positive potential of the potential promotes the type of accelerated corrosion of the metal with negative potential;

Point erosion: Corrosion destruction is mainly concentrated on certain active points. The diameter of the perforated diameter is equal to or less than the depth of the perforated, which can cause the equipment perforation in severe cases;

Capital corrosion: Corrosion at the gaps such as riveting, thread connection, welding joints, sealing pads and other gaps;

Crystal corrosion: Corrosion is performed along the crystal, the binding force between the metal atoms is lost, and the metal mechanical intensity has decreased sharply. Destroy the appearance of the front metal often has no significant changes;

Stress corrosion: Under the combination of tensile stress and corrosive medium, a cracking destruction at a significant rate occurs at a significant rate; the common type is sulfide stress corrosion and cracking and hydrogen sulfide stress corrosion cracking.

Corrosion fatigue: The corrosion produced by the metal under the action of the corrosive medium and the stress.

 

How to reduce the impact of corrosion on applications in the actual application process?

1. Determine the type of corrosion

In on -site applications, the type of corrosion is judged according to the medium type, pressure, temperature and environmental conditions and corrosion positions, and the appropriate anti -corrosion method is selected. For example, in the oil and gas industry, the instrumental valve parts and the main process pipeline adopt products of different materials, which may lead to corrosion of electric puppets.

2. Select the right corrosion -resistant material.

When selecting the material, the internal corrosive media type, pressure and external environment need to be considered. If the environment exceeds a certain temperature limit, it is not recommended to use 316 stainless steel materials at sea.

3. Reduce the position where the gap corrosion may occur.

Reduce the contact of incompatible metals. At sea, when the metal card sleeve and metal card sleeve are used together, the risk of gap corrosion is high. It is recommended that when the stuck pipe supports the material, select the card cover with a cushion.

Corrosion is a high price. If you can quickly identify the type of corrosion and find the location of corrosion, you can greatly reduce the potential risks. Technicians who master professional knowledge can often predict the position that may occur and choose the appropriate metal material in advance to avoid the occurrence of corrosion. This will largely improve the performance of the production system and improve its integrity and safety.