Caustic soda stress corrosion cracking titanium

Titanium has gained acceptance in many media where its corrosion resistance. Carryover of caustic soda naoh in the steam path caused. It occurs in piping and equipment exposed to caustic, primarily adjacent to non pwht welds. Caustic stress corrosion cracking inspectioneering. Alloys for caustic soda service by corrosion resistance. These alloys can however suffer from caustic stress corrosion cracking at caustic concentrations above 70% at temperatures above 290crmo c 550f.

Titanium alloys can be resistant up to about 40% concentration and below. Metalenvironment combinations susceptible to cracking are specific. Although it has been demonstrated in laboratory tests that titanium alloys are susceptible to hot salt stress corrosion cracking, no service failures have ever been reported, even though titanium alloys have been used in aerospace applications at temperatures as high as 600c. Caustic cracking is a form of stress corrosion cracking most frequently encountered in carbon steels or ironchromiumnickel alloys that are exposed to concentrated hydroxide solutions at temperatures of 482f 250c. Caustic embrittlement or caustic cracking occurs when the alloy material cracks under the action of tensile stress and corrosion medium in alkaline solution. It becomes increasingly more corrosive with increasing temperature and concentration. Temperature and concentration of caustic soda that can cause scc of carbon steels. The first known report of stress corrosion cracking of titanium alloys in room. Pdf caustic soda is used in several refinery processes. An iron alloy with 3% ni was found to be immune to caustic cracking. Stress corrosion cracking of titanium alloys ntrs nasa. Isocorrosion chart for aisi 304 and 316 stainless steels in sodium hydroxide, with stress cracking.

Other higher nickel stainless alloys like alloy 20, 800 and 825 also resist caustic corrosion and caustic cracking better than the 300 series stainless steels. This means that all environments do not cause scc on all of the alloys. Carryover of caustic soda naoh in the steam path caused catastrophic. It is one of the most prevalent afflictions in the industry and one of many environmental cracking mechanisms that typically occur in carbon steel equipment, but it can also afflict low alloy and austenitic stainless steel. Caustic stress corrosion cracking, also referred to as caustic embrittlement, is a form of degradation that is caused when a component operates in a caustic environment. Which alloy material is most resistant to caustic soda. Commercially pure ni is the most resistant material for caustic applications both from the general corrosion and the stress corrosion cracking scc perspectives. Caustic stress corrosion cracking caustic embrittlement. The first known report of stress corrosion cracking of titanium alloys. For example, methyl alcohol can cause stress corrosion cracking in. Caustic alkali generally refers to caustic soda and caustic potassium, namely sodium hydroxide and potassium hydroxide. Resourcestechnical newsletterscorrosion in caustic solutionstable 1 alloys for caustic soda service by corrosion resistance category composition wt. It can lead to unexpected sudden failure of normally ductile metals.

Stress corrosion cracking scc is the formation and growth of crack through materials subjected to tensile stress and a specific corrosive medium. Most caustic soda is produced as a coproduct in the production of chlorine by the. Siconversionunits inviewofpresentacceptedpracticeinthistechnologicalarea,u. It is a form of stress corrosion cracking characterized by surface initiated cracks. These alloys can be candidates for service in caustic exposure when corrosion from cooling waters is a concern. In addition, cring specimens of these same grades of titanium were subjected to a stress corrosion cracking test as specified in astm g3873 standard recommended practice.