• Alloy steel pipe
  • Ductile Iron Pipe
  • Carbon Steel Pipe
  • OCTG Steel Pipe
  • Stainless Steel Pipe
Product
Contact us

Address:Beijing Road, Yunhe District, Shengji Building #1802 ,Cangzhou City, Hebei

Contact:Lucky

Phone:86-15003171886

Email:jinxiaolong0221@gmail.com


Corrosion of stainless steel pipes in offshore environments

Attention:     Issuing time:2020-05-20 10:28
Corrosion of stainless steel pipelines in offshore environments

 
Foreword
In an island power transmission project, 0Cr18Ni9Ti stainless steel seamless pipes are used for water system transportation. The surface treatment method of the outdoor pipeline is sandblasting. After the pipeline of this system was put into use for 10 months, it was found that the surface of the outdoor pipeline was corroded seriously, and more rust marks appeared. It was found on the site by treating the rust on the surface of the pipeline that this rust is floating rust, which can be removed by simply wiping with a brushed cloth. In order to thoroughly understand the cause of the corrosion of outdoor stainless steel pipes in a short time and solve the problem of the operating life of stainless steel pipes. This article conducts a comprehensive analysis of the causes of corrosion of stainless steel pipes in complex marine environments such as high temperature, high humidity, high salt sea breeze, salt spray, and sea water splash. Put forward some anti-corrosion measures to provide effective solutions for the implementation of similar projects in the future.
 


 
 
Comprehensive analysis of the causes of corrosion
2.1 Pipeline chemical composition analysis
Using a material analyzer to analyze the chemical composition of the stainless steel pipeline, the results show that the chemical composition of the pipeline meets the requirements of 0Cr18Ni9Ti.
 
2.2 Corrosion analysis of stainless steel pipelines in marine environment
There are many differences between the marine atmospheric environment and the inland atmospheric environment. When analyzing the corrosion of stainless steel pipelines, it is necessary to consider various factors such as high temperature, high humidity, high salinity, sea breeze, salt fog, and sea water splash.
 
2.2.1 High-salt sea breeze, salt fog, sea water splash
In the marine environment, sea breezes and waves are relatively frequent. The waves caused by the sea breeze cause a large amount of salt liquid in the sea water to mix with the atmosphere, resulting in a large amount of salt in the atmosphere, and a large amount of chloride ions in these salts. Ions have high electrical conductivity, and it is easy to form electrolyte solutions and form micro-batteries on the metal surface, which enhances the corrosion activity and destroys the passivation film on the metal surface.
In the marine environment, when the temperature is high, a large amount of seawater produces atomization phenomenon, forming a large amount of salt mist, and the main composition of salt mist is similar to seawater and it also corrodes the surface of stainless steel pipes. The main cause of corrosion is the large amount of chloride ions in the salt spray. The main form of salt spray corrosion on the surface of stainless steel pipes is electrochemical corrosion. The electrochemical corrosion process of the salt spray on the stainless steel pipeline is as follows: the salt spray contains a large amount of sodium ions and chloride ions. The corrosion of the salt spray on the surface of the stainless steel pipeline is caused by a large amount of chloride ions; the chloride ion has a strong penetration ability, It can easily penetrate the oxide layer and protective layer on the surface of the metal, and electrochemically react with the inside of the metal to form electrochemical corrosion. When the salt mist settles on the surface of the stainless steel pipe, because there is still a lot of water vapor in the salt mist, the salt water film is first formed to cover the surface of the stainless steel pipe. At this time, the surface of the stainless steel pipe is equivalent to being immersed in a sodium chloride solution containing oxygen. The surface of the pipeline will constitute the two poles of the primary battery, causing corrosion. Therefore, salt spray corrosion and salt water corrosion are different in mechanism, and salt spray corrosion is more corrosive.
 
2.2.2 High temperature and high humidity environment
The temperature and humidity in the marine environment are much larger than those in the inland environment. The high temperature and high humidity environment accelerate the evaporation of seawater, and the large amount of evaporated water vapor has a great influence on the corrosion of stainless steel pipes. As a good medium, water vapor aggravates the transmission speed of various ions and acts as a good corrosive medium. As the carrier's large amount of chloride ion moisture penetrates into the pipeline, electrochemical corrosion or chemical corrosion occurs
 
2.2.3 Other factors
The impact of the ocean wave has stirred and renewed the electrolyte solution on the surface of the stainless steel pipe. At the same time, the erosion of the ocean wave has rusted off the rust layer, accelerating the corrosion progress. The growth of marine organisms on the surface of stainless steel pipes can seriously damage the protective layer of the original objects (such as the passivation film on the surface of the polished pipeline), which causes the pipeline to be damaged by corrosion. At the same time, the metabolites of marine organisms (containing sulfides) make the corrosion environment of stainless steel pipes Further deterioration, leading to increased corrosion. If the area where the pipeline is located is an acid rain area, the corrosion rate of the pipeline is also proportional to the PH value of the acid rain.
 

 
Stainless steel pipeline anti-corrosion measures
3.1 Start with the material of the pipeline and strictly control the quality of raw materials.
Strict entrance inspection of stainless steel pipes and fittings. To ensure that the material meets the requirements. In terms of material selection, both economical and functional considerations are considered. Under special operating conditions, austenitic stainless steel with high corrosion resistance, high nickel content, duplex stainless steel, titanium and titanium alloys, and glass steel can be considered.
When selecting materials, appropriately increase the corrosion allowance of pipes and fittings to meet the service life requirements of the pipeline system.
 
3.2 Surface coating protection
At present, in view of the corrosion of stainless steel pipes in the environment, in addition to selecting materials with strong corrosion resistance, the corrosion resistance can also be improved by coating the surface of the stainless steel pipe. Aiming at the problem that the surface of stainless steel pipe substrate is relatively smooth and the adhesion of conventional anti-corrosion coatings on its surface is relatively poor, an effective stainless steel anti-corrosion coating for marine environment-epoxy powder coating has been developed. The paint is a new type of paint which is completely free of solvent and sprayed into a film in powder form.
 
3.3 Electrochemical protection
The electrochemical protection methods are mainly provided with protector protection, cathodic protection and anode protection methods.
(1) The protector protection method refers to connecting the metal with lower electrode potential and the protected metal together to form a primary battery. The metal with the lower electrode potential is dissolved as the anode, and the protected metal is used as the cathode to avoid corrosion.
 
(2) The cathodic protection method refers to the addition of a DC power supply, connecting the protected metal to the negative electrode as the cathode, so that the potential of the protected metal is adjusted negatively, and enters the non-corrosive area of ​​the E-pH diagram; the waste metal is connected to the positive electrode As a method for the anode to corrode the waste metal and protect the cathode.
 
(3) The anode protection method refers to the use of an external DC power supply to connect the protected metal to the positive electrode as the anode. The electrode potential moves in the positive direction (ie, anode polarization) and enters the passivation area of ​​the E-pH diagram to protect it. The metal is "passivated" and protected.
 
 
 
Summary
Under the premise that the material meets the requirements, the corrosion of stainless steel pipes in complex marine environments such as high temperature, high humidity, high salinity, sea breeze, salt fog, and sea water splash is mainly caused by chemical corrosion and electrochemical corrosion caused by chloride ions. The corrosion of stainless steel pipes can be suppressed or eliminated by changing the surface treatment of the pipes, selecting materials with stronger corrosion resistance, coating the surface of stainless steel pipes, or electrochemical protection. I hope the above method will be of great help to similar problems encountered by similar projects in the future.

 

HOME |  Company |  Product |  News |  KnowLedge |  Equipment |  Contact | 

Technical Support:CZWLWL.COM  Address:Beijing Road, Yunhe District, Shengji Building #1802 ,Cangzhou City, Hebei

Phone:86-15003171886   站长流量统计