Why does chloride corrode stainless steel?

Wet and humid environments containing chloride ions can cause pitting corrosion and crevice corrosion of austenitic stainless steel components. (i) Higher chloride level than the bulk solution because negatively charged chloride ions migrate into the pit to balance the positively charged metal ions.

What causes chloride stress corrosion cracking?

Chloride stress corrosion cracking (CSCC) is a type of intergranular corrosion. Chloride stress corrosion involves selective attack of a metal along its grain boundaries. It occurs in austenitic stainless steel under tensile stress in the presence of oxygen, chloride ions and high temperature.

What stainless steel group has the best chloride stress corrosion cracking resistance?

Austenitic grades with relatively high nickel and molybdenum contents such as alloy 20, 904L, and the 6\% molybdenum super austenitic grades have substantially better chloride SCC resistance. The ferritic family of stainless steels, which includes grades such as type 430 and 444 is very resistant to chloride SCC.

What is caustic stress corrosion cracking?

Caustic cracking is a form of stress corrosion cracking most frequently encountered in carbon steels or iron-chromium-nickel alloys that are exposed to concentrated hydroxide solutions at temperatures of 482°F (250°C). Caustic cracking is also known as caustic embrittlement.

What is stress corrosion cracking testing?

The crack plane is indicated by the direction normal. Tests for Stress-Corrosion. Stress-corrosion cracking is a time-dependent process in which a metallurgically susceptible material fractures prematurely due to the synergistic interaction of a corrosive environment and sustained tensile stress at the metal surface.

What is pitting corrosion of stainless steels?

Pitting corrosion is a form of localized corrosion, which produces attacks in the form of spots or pits. Pitting corrosion may occur in stainless steels in neutral or acid solutions containing halides*, primarily chlorides (Cl-), such as seawater.

What are the causes of crevice corrosion?

Crevice corrosion is caused on contact of metals with metals or metals with nonmetals, for example, gaskets, couplings, and joints. It may occur also at washers, under barnacles, at sand grains, under applied protective films, and at pockets formed by threaded joints.

Does chlorine corrode stainless steel?

Chlorine is a powerful oxidising agent. It normally occurs as a gas, but can be liquefied under pressure at ambient temperatures. As a dry gas it does not tend to be aggressive towards stainless steels, but as either a damp gas or dissolved in water it can be a corrosion hazard.