Stainless steel formulas—especially those in the 300-series—are widely regarded as the standard for hygienic and high-purity process piping in a wide variety of applications. They’re the most popular formulas in the industry, but they’re not perfect.
For more severe applications requiring better corrosion resistance and performance at higher temperatures, specialty steel formulas are required.
AL-6XN is one such formula. With much higher concentrations of chromium, nickel and molybdenum, the formula is preferred for the transmission of fluids corrosive enough to eat through traditional stainless steel. As you’ll see, selecting AL-6XN for your process piping application comes with some extra considerations.
AL-6XN was developed for performance in severe environments, including high heat and low-pH processes in a wide variety of industries such as pharmaceutical, medical (sterilization), chemical processing, oil & gas and power generation.
With 2-4% more chromium and around twice the nickel content compared to 316L stainless steel, AL-6XN boasts good stress cracking resistance in the presence of chlorides. The higher molybdenum content imparts better resistance to chloride pitting; slightly more nitrogen provides better strength.
To better visualize how corrosion-resistant AL-6XN is, consider its pitting resistance equivalent number (PREN). Using the PREN formula that accounts for the alloying elements chromium, molybdenum and nitrogen, AL-6XN registers at 44.48. For comparison, the PRENs for 316L and 304 stainless steels are 29.5 and 21.6, respectively.