Coupon Holder

Description

Corrosion Coupon Holder Assembly is a simple yet effective tool for providing a quantitative estimation of corrosion rates occurring in an operating system. They also provide a visual indication of the type of corrosion that may be occurring in the monitored system. This Holder is part of the product. In a word, if you want to know more about Coupon Holder, please contact our professionals to answer them for you.

Pipeline corrosion and anti-corrosion measures

1. Corrosion type of steel pipe

The corrosion forms of buried metal pipelines include uniform corrosion and local corrosion. Most of them are local corrosion. And its harm is also the greatest. The corrosion process of steel pipe in soil is mainly electrochemical dissolution process. Corrosion and perforation of pipes due to the formation of corrosion cells. According to the size of the distance between the anode area and the cathode area of the corrosion cell. We can also divide the corrosion forms of steel pipes into two categories: micro cell corrosion and macro cell corrosion.

The so-called micro cell corrosion refers to the pipe corrosion caused by the action of micro cells composed of anodes and cathodes only a few millimeters or even a few microns apart. Its shape features are very uniform. Therefore, it has another name, “uniform corrosion”. Because the micro anode is very close to the micro cathode. Therefore, the corrosion rate of the micro cell does not depend on the soil resistivity. This only depends on the electrode process of the micro anode and micro cathode. Micro battery corrosion is less harmful to buried steel pipes.

Corrosion pipe

So called macro cell corrosion. It refers to the pipeline corrosion caused by the macro cell action composed of anode and cathode areas several centimeters or even several meters apart. We also call macrocell corrosion as local corrosion. Since the anode region is far from the cathode region. Therefore, the soil dielectric resistance accounts for a considerable proportion of the total resistance of the corrosion battery circuit. Therefore, the corrosion rate of the macrocell is related to the electrode processes of the anode and cathode. It is also related to soil resistivity. The soil resistivity is large. This can reduce the rate of macro cell corrosion. The plaque or hole corrosion on the surface of buried steel pipe is caused by macro cell corrosion. Its harm is quite great.

To sum up, buried pipelines are mainly subject to electrochemical corrosion in soil. The corrosion is divided into three processes: anode process, cathode process and current flow. They are independent and connected with each other. One of the processes is blocked. The other two processes are the same. The corrosion of the battery will stop and slow down. This provides a theoretical basis for us to take anti-corrosion measures.

2. Anti-corrosion method of steel pipe

Three processes of electrochemical corrosion of buried pipelines. The anti-corrosion method of steel pipe also starts from inhibiting one of the processes. For example, add anti-corrosion coating on the outer wall of the pipeline. The circuit resistance can be increased and the corrosion current can be reduced. External DC power supply. This makes the steel pipe cause negative potential to the soil and form cathodic protection. It can eliminate the potential difference between anode and cathode. It fundamentally stops the progress of the anode and cathode process. Anti corrosion coating is the rule of law, while cathodic protection is the root cause.

The exposed iron part will accelerate local corrosion. Therefore, the combination of anti-corrosion coating and cathodic protection is the most effective anti-corrosion method at present. The United States and other countries have clearly stipulated this. If anti-corrosion coating is used, cathodic protection must be used at the same time.

But for urban gas systems. And because the underground pipe network is dense. Therefore, the external power supply for cathodic protection has great interference on other pipelines. This will benefit itself. While other unprotected pipelines cause corrosion interference. This kind of situation will not occur in the sacrificial anode protection law that uses a metal material with a negative potential than the steel pipe to connect with the steel pipe. Therefore, the anti-corrosion method of combining anti-corrosion coating and sacrificial anode should be adopted for the main gas transmission pipe of urban gas. For other non main pipelines with low pressure. We generally adopt the anti-corrosion coating method directly.

Corrosion

Three-layer PE composite structure and epoxy powder anti-corrosion coating have excellent performance. Therefore, it is also the main anti-corrosion coating for buried pipelines in Europe and America. In China, comprehensive economic factors such as service life and maintenance cost are considered. Generally, three-layer PE composite structure anticorrosive coating is preferred.

In the sacrificial anode protection method, magnesium alloy is generally used as the sacrificial anode to protect the pipeline. Due to damage during the output current. Therefore, the design service life of magnesium alloy sacrificial anode should match the service life of the pipeline. It neither generates waste nor increases maintenance cost. However, it should be noted that when the soil resistivity is too high and the protected pipeline crosses the water area. At this time, we should not use sacrificial anode protection.

In consideration of economic rationality, two points should be paid attention to: ① the primary anti-corrosion investment during the construction of the gas pipeline network; ② the maintenance cost after the operation of the gas pipeline network. Because the urban gas pipeline network is located in the urban area. Therefore, it is difficult and expensive to maintain and repair after putting into operation. Therefore, one-time investment should be appropriately increased. This can reduce the daily maintenance workload of the pipeline after it is put into operation.