Stress corrosion cracking (SCC) in pipelines is caused by a combination of factors that include tensile stress, a corrosive environment, and a susceptible material. Here are the primary causes:
- Tensile Stress: Residual or applied tensile stresses from manufacturing, welding, or operational loads can promote SCC. Stress can be due to internal pressure, thermal expansion, or external loads.
- Corrosive Environment: Exposure to specific corrosive agents, such as chlorides in coastal regions, sulfides in sour gas pipelines, or carbon dioxide in natural gas pipelines, can initiate SCC.
- Susceptible Material: Pipelines made from materials that are prone to SCC, such as certain grades of carbon steel or stainless steel, are at higher risk.
Other Contributing Factors:
- Temperature and Pressure: Elevated temperatures and pressures can accelerate the SCC process.
- Soil Conditions: In buried pipelines, soil composition, moisture content, and the presence of aggressive ions can influence SCC.
- Coating Defects: Damaged or improperly applied coatings can expose the pipeline to corrosive environments, increasing the risk of SCC.
Preventive Measures:
- Stress Relief: Apply stress-relief heat treatments to reduce residual stresses.
- Corrosion Control: Use corrosion inhibitors, protective coatings, and cathodic protection to mitigate the corrosive environment.
- Material Selection: Choose pipeline materials with high resistance to SCC for the specific operating conditions.