Stress corrosion cracking

Stress corrosion cracking or SCC is a cracking procedure that needs the simultaneous action of corrosive agent and residual tensile stress. It isolates the corrosion reduced areas damaged by quick cracking. It also isolates the intercrystalline or transcrystalline attack that can damage the alloy without applied or remaining stress. The stress corrosion cracking sometimes occurs with hydrogen embrittlement.

Phenomenon

Stress corrosion cracking is a combined action of three factors—a sensitive material, special chemical materials and tensile stress. For instance, copper and its alloys are prone to attack in ammonia compounds, mild steels are sensitive to alkalis and stainless steels are attacked in chlorides.

There is no combined mechanism of SCC. Several models have been made that include the following:

Absorption model: special chemical materials enter in the crack surface and decrease the fracture stress.

Film cracking model: stress ruptures the oxide layer and creates an active passive cell. Innovatively produced security layer is cracked again in the stress and cycle continues until damage occurs completely.

Embrittlement: Hydrogen embrittlement is a chief mechanism of stress corrosion cracking for steels and alloys of titanium. Hydrogen atoms combine to rupture the metal.

Hydrogen embrittlement

Different metals and alloys particularly few steels, obtain a considerable loss in ductility and tensile strength when atomic hydrogen enters into their crystalline structure. Usually the reason for this kind of entrance is a chemical corrosive reaction, normally the oversecurity mechanism in the cathodic protection, electroplating, pickling operations, and pickling of steels in sulfuric acid such as high temperature applications like heat processing and welding with a wet electrode in availability of hydrogen-containing conditions such as water vapor or sour gas conditions. These entire treatments cause the production of hydrogen atoms on the material surface, causing these atoms to be taken into holes into metal and combine to produce hydrogen gas and deposit, resulting into increasing volume and pressure value because hydrogen molecule is larger in size than two individual hydrogen atoms and the molecules do not diffuse as that occur with hydrogen atoms. This mechanism is stated as hydrogen embrittlement describing the hydrogen-induced cracking and hydrogen stress cracking that are used to display this type of attack.

Hydrogen embritllement is a kind of damage that occurs by residual tensile stress. Fracture takes place quickly as cracks develop and disperse fast. An atomic hydrogen unlike to molecular hydrogen diffuses interstitially across the crystal lattice and concentrates mildly in many parts per million of it can cause fracture. If metal is free of stress, few hydrogen atoms which did not combine to produce their molecules diffuse back out.

Hydrogen embrittlement is equivalent to stress corrosion cracking in that standard ductile metals obtain brittle fracture when are subjected to tensile stress and corrosive conditions. Although, these mechanisms are differentiated depending on their interactions with applied electricity. When cathodic security decreases or causes end of stress corrosion, it incepts or accelerates the hydrogen embrittlement. Additionally the hydrogen based cracks are usually transangular however the intergranular fracture is found in few alloy matrices.

What We offer?

The nickel based Inconel alloy 601 are recommended for use in preventing such types of corrosion. Contact us to determine the most suitable alloy for use in the specific hydrogen embrittling corrosive conditions. 

As the family of alloys together named as nickel based alloys continue to expand with their significant applications in the industry, Heanjia Super-Metals is also striving in achieving the maximum expertise in meeting your application needs. Normally is the competence to withstand corrosion by severe chemicals that develop a large demand for these alloys in the chemical as well as petrochemical industrial units.

In the recent time, the demand of high alloy nickel grades has enabled to compete with titanium base alloys for applications in the severe conditions. We are experienced in producing the high yielding and plant friendly materials that offer the maximum service reliability. Advanced methods are used to emphasize the material engineering and bringing large interest in the high corrosion resistance alloys to cope with a large array of raw crudes. 

Nickel-Inconel-Incoloy-Hastelloy-Titanium-Duplex stainless steel.