Stress Corrosion Cracking (SCC) is a common problem in the engineering world. It is a slow failure mechanism that occurs in a corrosive environment, and it affects many ductile metals and alloys each year. In this article, we will explore the basics of SCC and its causes.
Factors Contributing to Stress Corrosion Cracking: Tensile Stress, Corrosive Environment, and Material Susceptibility
The process of stress corrosion cracking can be divided into three major factors: tensile stress, corrosive environment, and material susceptibility. The presence of these factors can lead to premature failure in a component. We will explore each of these factors in detail.
The Role of Temperature and Time in Stress Corrosion Cracking
Temperature and time are two additional elements that can contribute to stress corrosion cracking. The temperature of the environment in which the material is placed can affect the rate of corrosion, and the time the material is exposed to the corrosive environment can also affect the development of cracks. We will discuss these factors and their impact on SCC.
Stress Corrosion Cracking in the Steel Industry: A Form of Intergranular Corrosion
Stress corrosion cracking is a significant threat to industrial systems such as pipelines, power plants, chemical industries, and bridges. In the steel industry, SCC can result in crack formation in a corrosive environment, and it is a form of intergranular corrosion. We will explore the implications of SCC in the steel industry and its impact on industrial systems.
Examples of Stress Corrosion Cracking and its Symptoms
Stress corrosion cracking can initiate and propagate with little or no outside warning of corrosion. Cracks usually start at surface flaws by corrosion, wear, or other processes. We will provide examples of SCC and its symptoms, as well as how to detect and prevent it.
Stress corrosion cracking is a complex phenomenon that is specific to the material and environment in which it occurs. It is a slow failure process that can cause significant damage to industrial systems. Understanding the factors that contribute to SCC and taking preventive measures can help prevent premature failure in components.
Types, Characteristics, and Materials Susceptible to Attack
Stress Corrosion Cracking Types Stress corrosion cracking (SCC) is a failure mechanism that can occur in materials exposed to a corrosive environment and tensile stress. Here are some common types of SCC:
- Chloride Stress Corrosion Cracking: This type of SCC occurs in austenitic stainless steels when exposed to a high-temperature environment containing chloride ions and oxygen.
- Caustic Embrittlement: This type of SCC is prevalent in stainless steels exposed to a high hydrogen concentration in caustic environments.
- SCC Cracking of Steels in Hydrogen Sulfide Environment: This type of SCC commonly occurs in oil and chemical industries when steel is exposed to hydrogen sulfide environments.
- Seasonal Cracking: This type of SCC is prevalent in brass when exposed to ammonia environments.
- Craze Cracking: This type of SCC occurs in polymeric materials due to applied stress and environmental reaction.
Characteristics of Stress Corrosion Cracking SCC has distinct characteristics that distinguish it from other types of corrosion:
- Failure occurs at stress levels lower than the material yield stress.
- Ductile materials are susceptible to brittle failure through SCC.
- Cracks in SCC are typically caused by corrosion.
- SCC cracks are often intergranular or transgranular, and the propagation of cracks depends on the material and environment.
Materials Susceptible to Stress Corrosion Cracking Many materials can be susceptible to SCC under certain conditions. Here are some examples:
- Stainless Steels: Stainless steels are vulnerable to SCC when exposed to chloride, caustic, and polythionic acid environments within the temperature range of 415°C to 850°C.
- Carbon Steel: Carbon steel can be susceptible to SCC in carbonates, strong caustic solutions, nitrates, phosphates, seawater solutions, acidic H2S, and high-temperature water environments.
- Copper and Copper Alloys: Copper and copper alloys can be susceptible to SCC in environments containing ammonia, amines, and water vapor.
- Aluminum and Aluminum Alloys: Aluminum and aluminum alloys can be vulnerable to SCC in environments containing moisture and NaCl solution.
- Titanium and Titanium Alloys: Titanium and titanium alloys can be susceptible to SCC in exposure to seawater, fuming nitric acid, and methanol-HCl environments.
- Polymers: Polymers can be vulnerable to SCC in aggressive acid and alkali environments.
- Ceramics: Ceramics can be susceptible to SCC in certain environments.
Understanding the types and characteristics of SCC and the materials susceptible to attack is critical for identifying and preventing SCC failures in industrial systems.
Stress Corrosion Cracking in Welding: Causes and Effects Stress corrosion cracking (SCC) in welding occurs due to the residual stress generated during the welding and fabrication processes. The non-uniform temperature changes during welding and the transformation of austenite to martensite during cooling create significant residual stresses. This type of SCC is caused by the uneven distribution of stress in welded components.
Mechanisms of Stress Corrosion Cracking: Understanding the Process Depending on the type of material and environment, various different mechanisms of SCC can be found in the industry. The mechano-electrochemical model explains how pre-existing regions become sensitive to anodic dissolution. The film rupture model is well-known for alloys that have a passive layer on their surface, while the adsorption phenomenon considers the material embrittlement in the vicinity of a corroding area. The pre-existing active path model shows how intermetallics and compounds are formed in already existing paths like grain boundaries which are prone to SCC attack.
How to prevent Stress Corrosion Cracking?
Best Practices Although the mechanism of stress corrosion cracking is not yet fully understood, several empirical experiences can help prevent SCC. Lowering stress levels in components, such as by providing annealing treatment, can reduce the potential of an SCC attack. Eliminating or decreasing aggressive species from the environment where the component is installed will serve as one method of reducing SCC attacks. Selecting more stress corrosion cracking-resistant materials will protect the product from SCC. Cathodic protection, adding inhibitors, applying a protective coating, using the shot-peening method, and controlling temperature and electrochemical potential can also prevent SCC.