Corrosion Resistant Nickel Alloys
Paul Crook -- Haynes International Inc.There are five main categories of usage for Nickel based corrosion resistant alloys.
1) Chemical Processing (in situations where stainless steels don't work.
2) Pollution Control - particularly in flue gas desulfurization.
3) Pharmaceuticals
4) Agrichemicals
5) Waste management (particular radiactive waste management).
In a hierarchy of corrosion resistant alloys the "nickel alloys" together with "zirconium alloys" and "titanium alloys" serve in special situations where stainless steels cannot perform and greater expense is justified. The ultimate in corrosion resistance is reached with "tantalum" but due to high cost, its use is restricted to the most critical of situations.
The main attributes of the Corrosion-Resistandt Nickel Alloys include:
-- high resistance to stress corrosion cracking
-- many resist aggressinve reducing acids (ie. hydrochloric, hydroflouric, and medium concentrations of sulfuric.
-- some withstand both strong reducing AND strong oxidizing acids.
-- Many exhibit high resistance to alkalis
-- Some have high resistance to pitting and crevice corrosion.
-- All are ductile, and easily formed and welded.
The main groups and used of corrosion-resistant nickel alloys are:
-- Ni alloys (for alkalis)
-- Ni-Cu alloys (for reducing acids)
-- Ni-Mo alloys (for reducing acids)
-- Ni-Fe-Cr alloys (for oxidizing acids)
-- Ni-Cr-Si alloys (for super-oxidizing acids)
-- Ni-Cr-Mo alloys (for alkalis and all acids)
Mr. Crook then when on in considerable detail explaining the development of a "Decision Tree" which selects an appropriate alloy for various specific application environments. Included in the decision are acid types, concentrations, purity, temperature, presence of other ions (impurities) etc.
This decision tree is to become available soon at the Haynes International web site www.haynesintl.com.
The entire presentation (including the "decision tree") is also available in printed form by request to the speaker (800) 354-0806.