Discuss whether C-PVC/L material can be used for caustic soda pipelines

This post was last edited by quhong*ng80 on 2009-12-8 at 22:21. I think CPVC can be used with alkaline solutions at temperatures below 80 degrees and under a pressure of 2 kilograms; PVC, on the other hand, can withstand temperatures of no more than 60 degrees

Have anyone who has used it shared their opinions? According to relevant information, CPVC tends to crack when exposed to alkaline solutions.

We use CPVC for the alkali in our electrolytic cells; the temperature can reach over 89 degrees, and there’s no problem with that

PVC cannot withstand high temperatures and cannot be used. CPVC works fine in alkaline environments in the short term, but leaks occur at the welds after one year. There have been cases of pipes that weren’t reinforced with FRP bursting, but I’m not sure if this is related to the material itself, as some pipes had issues right from the time of installation yet were not detected. Once such a pipe leaks, it is very difficult to weld it shut. For the alkaline system surrounding the electrolyzer, PPH pipes that can be welded by heat fusion can be used; nickel pipes are preferable when they are located away from the electrolyzer, and 310 stainless steel can also be used as a fallback option.

CPVC itself has decent corrosion resistance to alkaline solutions; the key factor is the influence of temperature. Due to the high temperature of the catholyte, although CPVC is claimed to be resistant to temperatures up to 110 degrees, it still undergoes deformation over time as a result of continuous operation. This deformation affects the strength of the weakest welds, leading to leaks and cracks. High-temperature, high-concentration caustic soda that leaks can cause severe harm to humans. From the perspectives of investment and operational risks, I personally am not in favor of using CPVC pipes under such high-temperature caustic conditions.

However, C-PVC is still being used by some manufacturers in China. For example, it is used by a manufacturer in Shanghai, and another manufacturer in Jiangsu has also used it for many years, and so on.

The alkaline solution produced by wood electrolyzers uses CPVC, although imported materials are generally used with FRP reinforcement on the outside; however, it is increasingly apparent that this approach does not yield good results.

Whether it is CPVC, FRP/PPH, or other types of piping materials, they can be used in the short term under conditions of low pressure and low temperature involving liquid alkali, as they have good corrosion resistance and are inexpensive. However, with long-term use, factors such as the aging of the material itself, deformation, and weld cracking caused by thermal expansion stresses can pose risks to the operation and safety of the entire device; in mild cases this leads to shutdowns, while in severe cases it can result in catastrophic consequences. Products from abroad, such as those from Japan and Australia, are generally of better quality than domestic ones, but they also have these same issues. Therefore, it is personally recommended to consider a long-term perspective when choosing the material for liquid caustic pipelines; stainless steel pipes should be used. For the circulation lines at the electrolyzer outlet, 310S stainless steel is suitable, while 316L stainless steel can be used for the sections from the liquid caustic receiving tank to the storage tank.

On the 10th floor, it is personally recommended that, from a long-term perspective, stainless steel pipes should be chosen for the liquid caustic pipelines. For the circulation lines at the electrolyzer outlet, 310S stainless steel should be used, while 316L stainless steel can be employed for the sections from the liquid caustic receiving tank to the storage tank. ”I think the material grade should be upgraded; Ni should be used at the electrolyzer outlet, while 310S should be used for the liquid caustic receiving channel and storage tank.