Why Special Alloys?
 
While 316L / 1.4404 will hold for most applications, some factors such as high chloride media, acidic
pH levels, high temperature, time of contact, and equipment design can affect the corrosion of stainless
steel.
 
With this in mind, the NEUMO Ehrenberg Group offers a wide range of special alloys.
From 316L / 1.4404 and 1.4435 to 904L / 1.4539, AL-6XN® / 1.4529 and Hastelloy C22® /
Alloy C22 / 2.4602 as well as Alloy 59 / 2.4605.
 
These alloys are commonly used in the biotech, pharmaceutical, personal care, home care, food, dairy,
and beverage industries worldwide. The main concerns of end users, architects and engineers (A&E’s)
when choosing a special alloy are microbial contamination, system reengineering, maintenance
downturns, production loss and safety of its employees and the environment.
 
Stainless Steel and Corrosion

The uniqueness (secret) behind the corrosion resistance of stainless steel is the formation of a durable
and spontaneous ultra-thin film that covers the surface. This film consists mainly of chromium oxides
and ensures the metallic steel (base metal) is never in contact with the environment.
 
As long as the surface is clean and free of contamination, this film protects the steel in a process known
as passivation. The resistance of this film is dependent on the steel grade chosen and the conditions to
which it is exposed.
 
If the conditions become aggressive, the oxide film breaks down resulting in corrosion. Finding the
proper chemical composition steel will result in a stable oxide film that will be resistant to the relevant
type of corrosion.
 
The main types of corrosion affecting hygienic and high purity application in aggressive chloride
environments are pitting, crevice, and stress corrosion.
 
Optimum performance is obtained by the use of alloying elements, chromium, molybdenum, and
nitrogen, all of which are very effective in improving resistance to pitting and crevice corrosion,
and high nickel and nitrogen contents for stress corrosion cracking.
 
When a part of process equipment breaks down, it is vital to determine the cause of the failure to
prevent future replacement and production losses. For example, if the piping system is made from
316L and it fails in an aqueous salt environment with high temperature, a special alloy with higher
molybdenum could provide a lifelong solution to the system.