The problem of corrosion in liquid ammonia pipelines
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This post was last edited by wangqiande2oo8 on 2022-4-20 at 15:43. I would like to ask the experienced experts on this forum: during the special inspection, it was found that the liquid ammonia pipelines were severely corroded, while the gas ammonia pipelines were not as severely affected, and the high-pressure pipelines also showed little signs of corrosion. What could be the cause of this corrosion?
Corrosion caused by low-temperature condensate water. Ensure proper corrosion protection and insulation, and conduct regular inspections
If it is outer wall corrosion, the surface temperature of the liquid ammonia pipeline is relatively lower. If the pipeline insulation measures are the same under the three conditions, more condensation water forms on the surface of the pipeline at lower temperatures, leading to severe electrochemical corrosion.
It is necessary to check the insulation of the pipes. First of all, whether foam glass or polyurethane is used, it must be properly sealed; materials such as mastix should be used to prevent heat loss. Additionally, since summer is approaching, it is important to check whether there is freezing or frost on the surface of these two types of pipes, as moisture can cause corrosion of the outer walls.
Corrosion on the outer wall of liquid ammonia pipelines is definitely related to insulation. How is the corrosion of the inner wall? No introduction.
Typical corrosion under insulation: 1. Ensure proper anti-corrosion treatment for these pipelines, especially rust removal and application of primer; 2. Implement isolation using an anti-corrosion layer
If it is a pressure pipe, check the wall thickness. If it’s still in good condition, clean and polish it, then apply an anti-rust agent. Once the pipe turns white, an oxide layer will form; after that, apply anti-rust paint, which will make it less likely to rust. However, insulation still needs to be applied
In liquid ammonia pipelines, due to the low temperature of the medium, moisture in the air tends to condense on the surface of the pipes when cooled, or it may penetrate into the insulation layer, thereby causing corrosion of the outer wall of the pipes. This phenomenon is particularly evident in areas with humid air in the south. Gaseous ammonia is generally produced by heating and evaporating it in an ammonia vaporizer; the temperature in the pipelines is usually higher than that in the pipelines carrying liquid ammonia, and moisture in the air does not easily condense, so the corrosion conditions are generally much better. Previously, the material used for ammonia pipelines was generally 16Mn; however, through nearly 20 years of use and observation, it has been found that ammonia causes extremely mild intergranular corrosion in austenitic stainless steels at room temperature, and no external wall corrosion has ever occurred. It is recommended to use austenitic stainless steels such as 316 and 316L instead.
The material used is 09Mn2VDG; with a proper anti-corrosion coating in place, there is generally no issue
For localized treatment, using brush-on insulation materials for protection provides both waterproofing and insulation, achieving two goals at once; however, it is not suitable for application over large areas.
An anti-corrosion coating can be applied, followed by a thermal insulation layer