How can you select materials to optimize pipeline corrosion resistance?

Materials and Chemical engineers have a course about corrosion in university, in which they study the basics of some deterioration mechanisms such as uniform, pitting, crevice or galvanic corrosion. However microbially influenced corrosion (MIC) can accelerate these in various ways. As MIC is a multidisciplinary area which has recently gained more attention, we may need retraining in this field. On land, underground and submarine pipelines in many industries such as oil and gas and water treatment are susceptible to MIC. It can damage different materials but high Cr-Ni alloys such as some austenitic and duplex SS grades are considered to be more resistant. mechanical cleaning of surfaces can mitigate biofilm formation in early stages.

Fluid Compatibility Understand the type of fluid the pipeline will carry (e.g., water, gas, oil, or multiphase streams). Carbon steel is commonly used due to its cost-effectiveness, but it’s susceptible to corrosion in the presence of CO2 and H2S. Conduct detailed corrosion assessments to determine the predicted corrosion over the pipeline’s lifetime. Consider a corrosion allowance, which is a sacrificial thickness of steel that can be safely lost during service without compromising pipe strength.

To optimize pipeline corrosion resistance, the first step is to understand the corrosion mechanisms that affect pipelines. Corrosion results from a chemical or electrochemical interaction between metal and its environment, leading to metal degradation. Pipelines can experience various corrosion types, such as uniform, pitting, crevice, galvanic, stress corrosion cracking, and microbiologically influenced corrosion. Each type has distinct characteristics, causes, and impacts, requiring specific prevention and mitigation techniques. By understanding these mechanisms, you can select appropriate materials and implement effective protection strategies.

To optimize pipeline corrosion resistance, the second crucial step is to assess the material properties that affect their corrosion behavior. Key properties to consider include chemical composition, mechanical strength, ductility, toughness, weldability, and coating compatibility. These factors influence how the material interacts with corrosive environments, withstands mechanical stresses, and can be joined and protected. For example, carbon steel is commonly used for pipelines but requires coatings or cathodic protection to prevent corrosion, while stainless steel, with its chromium content, offers greater corrosion resistance but is costlier and susceptible to stress corrosion cracking.

In many research articles, we observe that corrosion tests are conducted in a 3.5%wt NaCl solution. This environment is chosen to simulate seawater conditions and appears to serve as a reference for result comparison. However, this approach can be misleading since many engineering materials do not come into direct contact with seawater during service. In the oil industry, it is essential to conduct corrosion resistance tests under conditions closer to what structures and pipelines encounter in reality. For instance, facing a mixture of water and oil (internal pipe surfaces) or creating an environment to simulate soil and atmospheric fluctuations in humidity and temperature (external pipe surfaces).

Identify the type and concentration of corrosive substances present in the transported fluid. Consider external factors such as soil conditions, temperature, humidity, exposure to chemicals. Look for materials with inherent corrosion resistance properties, as stainless steel, corrosion-resistant alloys, and non-metallic materials like fiberglass reinforced plastics or high-density polyethylene .Consider the susceptibility to localized corrosion mechanisms as pitting, crevice corrosion, and stress corrosion cracking. Assess mechanical strength, toughness, and ductility of materials to withstand operational stresses, including pressure, temperature fluctuations, and mechanical loads. Seek advice from corrosion engineers, material scientists