Material selection for hydrogen chloride pipelines in vinyl chloride production units
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In the design documents provided by the design institute, the hydrogen chloride gas pipeline between the hydrogen chloride synthesis furnace and the vinyl chloride mixing and dehydration unit is made of UPVC. I’m not sure whether this is an appropriate material; I would appreciate advice from those with experience in this field. Thank you. This post was last edited by yhpsxj on 2009-2-15 09:12
Here’s a preliminary suggestion: The main materials currently used for hydrogen chloride pipelines are as follows: 1. UPVC, 2. CPVC, 3. PVC+FRP, 4. Metal-lined with non-metallic material. In my opinion, using UPVC for hydrogen chloride pipelines can lead to aging issues, and its strength is also relatively low； CPVC is relatively expensive ； Although steel-lined non-metals have good strength, they are also expensive, and it is difficult to repair them in the event of corrosion and leakage ； PVC+FRP has an average price and is also easy to maintain. Therefore, PVC+FRP is recommended.
The HCL pipes we use are made of PP, that is, polypropylene. PP possesses excellent chemical stability and remains inert to most acids, bases, salts, and oxidizing agents. For example, it is stable in concentrated phosphoric acid, hydrochloric acid, 40% sulfuric acid, and their salt solutions at 100°C; only a few strong oxidizing agents such as fuming sulfuric acid can cause it to change.
It was said upstairs that PP is stable at 100°C; it seems that PP can withstand up to 80°C. UPVC offers higher strength compared to PVC, but its price is too high; therefore we use UPVC pipes. A polytetrafluoroethylene compensator is installed every 50 meters, as temperature changes can damage the pipes, allowing for continuous and stable production. It is recommended that when connecting straight pipes, welding should not be used; instead, straight sections should be bonded first and then welded, while flanges should be joined using socket welding. It would be better if steel-lined PO could be used; it ensures the quality of the lining for large pipes, although the installation cost is higher.
On the 4th floor, the temperature of the mixture of acetylene and hydrogen chloride is mainly kept below room temperature; as for the high temperatures and explosions that can occur due to the presence of free chlorine, even lined steel pipes may not be able to withstand them. Of course, there are steel pipes all the way back from the preheater outlet. Now, the diameter of PP large pipes is also quite large, and there are prefabricated splices and elbows, which makes on-site processing and assembly easier.
The pipes used in our facility are made of PVC/FRP, and no problems have arisen after several years