Material selection can be a difficult decision when you don’t understand the differences between two materials with almost the same cost.
Have you ever asked for Hastelloy C-276 material and been recommended Hastelloy C-22 instead? Have you wondered what the difference is between them, and why one should be preferred over the other?
Here are few reasons why C-22 is a better choice than C-276:
Hastelloy C-22 has a better overall corrosion resistance compared to Hastelloy C-276.
The life of the material—and eventually the costs—depends on its ability to withstand different environments. Looking at the chemical composition of these two materials, C-22 is about 22% chromium and C-276 is 16% chromium. This 6% difference provides C-22 with a better corrosion resistance than C-276 in oxidizing environments, improving the life of the material by 5-10 times.
Now, where would you find the oxidizing environments? Some of the severe oxidizing mediums are sodium chloride (NaCl), hydrochloric acid (HCl), and sulphuric acid (H2SO4). C-22 also shows outstanding resistance to ferric and cupric chlorides, acetic anhydride, formic and acetic acids, hot contaminated organic and inorganic acids, brine solutions, seawater, etc.
C-22 has been found to have outstanding resistance to pitting, crevice and stress corrosion cracking when compared to C-276.
Both C-22 and C-276 have been tested in the oxidizing mediums for pitting and crevice corrosion. It has been proven that C-22 is more resistant to the oxidizing media, even at higher temperatures, than C-276. However, in the reducing environments both C-22 and C-276 behave the same. A few of the reducing agents are oxalic acids (C2H2O4), formic acids (HCOOH), phosphorous acid (H2PO4), etc.
C-22 weld filler materials provide better weldability and over alloying ability, thus improving the corrosion resistance.
Many customers complain about the corrosion in their welds, but C-22 weld filler materials have been very successful in addressing these concerns. Not only is C-22 resistant to oxidizing and reducing environments, but also to the inter-granular corrosion in the heat-affected zone (HAZ) of weldments.
Upon exposure to oxidizing sulphuric acid solution, C-22 faced very nominal corrosion attack. Conversely, C-276 suffered severe base metal, weld metal, and HAZ attack.
When tested in the saturated wet chlorine environment as a function of temperature, C-276 corroded very severely in the weldments during the vapor phase as well as the liquid phase. C-22 withstood higher temperatures in the same phases.
Each of these factors support the fact that Hastelloy C-22 should be the choice for longer life and better performance when selecting the material for your process.
