Stress Corrosion Cracking: Necessity, Mechanisms, and Prevention

Stress corrosion cracking (SCC) in the chemical, petrochemical, and power industries is a hidden form of corrosion that causes financial loss and loss of life. This phenomenon involves a combination of cyclical, environmental and metallurgical specifics. 

During stress welding, a large portion of the metal or sheet is successfully separated, while fragments of hair and branches are scattered throughout most of the material. 

This fracture can have serious consequences as it can occur at an effective stress level below the design stress and cause material and structural failure. Stress corrosion cracking begins in the corroded portion of the product and evolves into brittle material.

Stress corrosion cracking requirements

1. Materials (Stainless steel, Copper & Copper alloys, Aluminum & Aluminum alloys, Corrugated iron, Titanium alloys). 
2. Environments 
3. Stress

Stress Corrosion Cracking Mechanism

SCC failure refers to a combination of mechanical, physical, and chemical/electrical factors that cause magnetic separation of the crack, which increases the rate of cracking. 

Three mechanisms have been proposed for SCC: 

1. preexisting activation pathway mechanisms 
2. stress-induced activation pathway mechanisms 
3. adsorption-related phenomena

Prevention of:

1. Use post-weld heat treatment to reduce tensile stress in welded area.
2. Tensile stress reduction by injection peening is also recommended.
3. Remove, demineralize or distill materials that decompose in the environment.
4. If the atmosphere or pressure cannot be changed, metal changes can occur. For example, the application is to use Inconel (nickel plus elements) under normal conditions. We are not interested in 304 stainless steel.
5. Use cathodic protection: I am impressed with the current cathodic protection methods for preventing SCC in steel.
6. Add blockers to the body if possible: High levels of phosphate used have been effective.
7. Coatings are sometimes used, depending on keeping the surface metal-free.

Example: 

Stress corrosion cracking initiation of high alloy materials Corrosion-resistant stainless steel and other alloys may cause localized corrosion (pitting, cracking, intergranular corrosion) in certain areas under certain conditions. 

Stress corrosion cracking (SCC) is difficult to predict and can occur in tanks, pipelines, equipment, etc. and can be very damaging. Hydrothermal tests are recommended to test the hydrothermal resistance of SCC materials at high temperatures (100-300°C). 

Water Resistance Testing (DET) can be used to compare and evaluate the resistance of stainless steel and other materials to stress-induced corrosion cracking in chloride-containing water. 

This test is based on failure results in the following scenarios: The evaporation of the surrounding water (temperature, boiler, steam) releases the internal anion (chloride). to the surface and may form salts (soluble) on the material. surface. 

During the DET process, it is possible to monitor the onset and propagation of pitting corrosion and cracks on the sample surface. Thermal fatigue and corrosion techniques are applied in SCC in the initiation and propagation phases of short cracks, especially in the initiation and propagation phases of short cracks. 

A condition in which the temperature difference between the drop and the heated sample is large. DET also simulates the local corrosion effects of heat transfer from the material to the environment under ambient conditions.

This project aims to study the onset and short-term corrosion crack propagation of duplex steels.

Conclusion 

In collaboration, the cracking resistance of duplex steel against stress corrosion cracking was evaluated. The results confirm the validity of the study and the comparison of the effects of metal materials on corrosion cracking. 

Droplet Evaporation Testing (DET) is a simple method for evaluating small cracks subjected to high-temperature evaporation and can also be used to test for pitting corrosion or thermal fatigue corrosion. 

An important advantage of this method is that microcrack initiation and small propagation can be monitored in the center of the sample. From the tests, it was determined that duplex steel was less susceptible to corrosion cracking than austenitic steel. 

The resistance of a material to corrosion cracking is usually measured based on the expected corrosion cracking rate and stress cracking time in the test specimen.