Compressed air pipes are rusting
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Our company’s compressed air pipelines are made of carbon steel pipes; there are filters and regenerative dryers at the compressor outlet, with a dew point of -20°C. They have been in use for 10 years, but recently rust has started to appear in large quantities. The solution proposed by our engineering department is to replace the carbon steel pipes with stainless steel pipes. However, I still have some questions: 1. If rust appears suddenly after 10 years of use, when it never happened before, I don’t think natural corrosion would cause such issues to show up only after 10 years ； 2. The compressed air is purified; if the dew point meets the specifications of the dryer, the humidity should be very low, making rusting less likely. Therefore, I speculate that abnormal operation of the dryer at some point could also be one of the causes. I wonder if there are any similar experiences shared in the forum, or if any experts in this area can help identify the cause. Thank you!
It’s not just the dryer that needs to be considered; if the nitrogen seal is not properly in place during shutdowns for maintenance, corrosion and rusting can occur. It’s already quite good that carbon steel materials can last for 10 years
The sudden appearance of a lot of rust is definitely abnormal. I wonder where you noticed the rust?
This post was last edited by 955559 on 2018-7-16 at 16:02. Flanges are required; you can contact us via private message for pipe fittings.
Carbon steel pipes and galvanized pipes are prone to rusting anyway
This post was last edited by 955559 on 2018-7-23 at 14:32. Hello, Sichuan Tailande Technology, which specializes in gas analysis and dew point detection – we see many cases like yours. The following points need to be clarified: 1. The corrosion rate is not constant; there is randomness involved, and carbon steel pipes also undergo surface treatment. The corrosion rate varies depending on the time period and season, so there is no need to worry about differences between 10 years ago and 10 years from now ； 2. There are too many factors that affect corrosion; pipeline material and moisture are just two aspects. Changing the material is also a solution, and cathodic protection can be employed when necessary ； 3. Many dryer manufacturers, considering costs, make mistakes in the selection and installation of dew point meters, resulting in test values that may not be accurate. I’d like to ask gently: is the dew point meter located behind your compressors sent for inspection every year? What brand is it? Additionally, do you currently have a dedicated portable dew point meter for online comparison? If such measures are not in place, the purification of your compressed air may not meet the required standards.
The last edit to this post was made by 955559 on 2018-7-23 at 14:32. Corrosion prevention is essentially a systematic issue; changing the material is a good solution. However, the problem right now is that you haven’t identified the cause yet. Based on my experience, your dew point measurements may not be accurate, and the compressed air may not meet the required standards ；
Currently, plastic PVC pipes are used as compressed air pipelines in the market. The joints are connected using heat fusion. For long-distance transmission, proper fixed support is sufficient. Stainless steel pipes are relatively expensive.
1. The dew point temperature is not necessarily accurate (it needs to be corrected and verified). 2. The moisture content of the air drawn in is not fixed; it can be high during rainy weather. 3. Changing the material used is a good solution (if stainless steel is used, care must be taken to ensure there are no chloride ions around, as this could lead to pitting). 4. Sudden rusting… it seems that such situations were never checked before… (at least that’s what happened in our unit in the past)
Carbon steel pipes used in compressed air pipelines will inevitably rust; even galvanized pipes can rust. For applications with high requirements for air quality, filters can be installed or stainless steel pipes can be used instead