Essential Series on Pump Selection and Piping（2）

                                                 Essential Series on Pump Selection and Piping（2）

II. The Impact of Corrosion

Corrosion has always been one of the most vexing hazards for chemical equipment, where even the slightest oversight can lead to minor damage or severe accidents, potentially triggering disasters. According to relevant statistics, approximately 60% of chemical equipment failures are caused by corrosion. Therefore, the scientific selection of materials is the primary consideration when choosing chemical pumps. There is a common misconception that stainless steel is a "universal material," suitable for any medium or environmental condition, which is highly dangerous. Below are key points for material selection when dealing with some commonly used chemical media:

Sulfuric acid, as one of the highly corrosive media, is a crucial industrial raw material with extensive applications. The corrosion effects of sulfuric acid vary significantly with different concentrations and temperatures. For concentrated sulfuric acid with concentrations above 80% and temperatures below 80°C, carbon steel and cast iron exhibit relatively good corrosion resistance. However, they are unsuitable for high-speed flowing sulfuric acid and are not ideal materials for pump valves. Common stainless steels such as 304 (0Cr18Ni9) and 316 (0Cr18Ni12Mo2Ti) also have limited utility in sulfuric acid environments. Therefore, pumps and valves for sulfuric acid transportation are typically manufactured from high-silicon cast iron (with significant casting and machining challenges) or high-alloy stainless steel (Grade 20 alloy). Fluoroplastics demonstrate excellent resistance to sulfuric acid, making lined fluorine pumps (F46) a more cost-effective option. The company's applicable products include: IHF lined fluorine pumps, PF (FS) highly corrosion-resistant centrifugal pumps, and CQB-F fluorine plastic magnetic pumps.

2. Hydrochloric acid: Most metal materials are not resistant to corrosion by hydrochloric acid (including various stainless steel materials), and high-molybdenum silicon iron can only be used for hydrochloric acid below 30% at temperatures of 50°C or lower. In contrast, the vast majority of non-metal materials exhibit excellent corrosion resistance to hydrochloric acid. Therefore, rubber-lined pumps and plastic pumps (such as polypropylene and fluoroplastics) are the best choices for conveying hydrochloric acid. The company's applicable products include: IHF fluorine-lined pumps, PF(FS) highly corrosion-resistant centrifugal pumps, CQ polypropylene magnetic pumps (or fluoroplastic magnetic pumps), etc.

3. Nitric Acid  Most common metals are rapidly corroded and destroyed in nitric acid, while stainless steel is the most widely used corrosion-resistant material against nitric acid, exhibiting excellent resistance to all concentrations of nitric acid at room temperature. Notably, molybdenum-containing stainless steel (e.g., 316, 316L) does not necessarily outperform ordinary stainless steel (e.g., 304, 321) in nitric acid resistance and may sometimes be inferior. For high-temperature nitric acid applications, titanium and titanium alloy materials are typically employed. The company's applicable products include: DFL(W)H chemical pumps, DFL(W)PH shielded chemical pumps, DFCZ process pumps, DFLZP self-priming chemical pumps, IH chemical pumps, CQB magnetic pumps, and others, with materials such as 304.

4. Acetic Acid  It is one of the most corrosive substances among organic acids. Ordinary steel will severely corrode in acetic acid of any concentration and temperature, while stainless steel serves as an excellent material resistant to acetic acid. Molybdenum-containing 316 stainless steel is also suitable for high-temperature and dilute acetic acid vapor. For demanding conditions such as high-temperature, high-concentration acetic acid or environments containing other corrosive media, high-alloy stainless steel or fluoroplastic pumps can be selected.

5. Alkali (Sodium Hydroxide)  Steel is widely used in sodium hydroxide solutions below 80°C and within 30% concentration. Many factories still employ ordinary steel at temperatures up to 100°C and concentrations below 75%, despite increased corrosion, due to its cost-effectiveness. Ordinary stainless steel offers no significant advantages over cast iron in resisting alkaline corrosion, and stainless steel is not recommended unless trace iron content is permissible in the medium. For high-temperature alkaline solutions, titanium and titanium alloys or high-alloy stainless steel are typically employed. Most cast iron pumps in the company can handle low-concentration alkaline solutions at room temperature, while stainless steel or fluoroplastic pumps are used for special requirements.

6. Ammonia (Ammonium Hydroxide)  Most metals and non-metals exhibit minimal corrosion in liquid ammonia and ammonium hydroxide, with the exception of copper and copper alloys, which are unsuitable for use. The majority of our company's products are suitable for the transportation of ammonia and ammonium hydroxide.

7. Saltwater (seawater)  Ordinary steel has a relatively low corrosion rate in sodium chloride solutions, seawater, and brine, but typically requires coating protection. Various types of stainless steel also exhibit very low uniform corrosion rates, but may suffer from localized corrosion due to chloride ions. Generally, 316 stainless steel is preferable. The company's range of chemical pumps are all configured with 316 material.

8. Alcohols, ketones, esters, and ethers  Common alcohol-based media include methanol, ethanol, ethylene glycol, and propanol. Ketone-based media include acetone and methyl ethyl ketone. Ester-based media include various methyl esters and ethyl esters. Ether-based media include methyl ether, ethyl ether, and butyl ether. These substances are generally non-corrosive and compatible with most common materials. Specific selection should be made based on the properties of the medium and relevant requirements. Additionally, it is noteworthy that ketones, esters, and ethers can dissolve various types of rubber, so care should be taken to avoid errors when selecting sealing materials.