Oil & Gas Pipeline Survey

Pipeline corrosion is the deterioration of pipe material and the related system due to its interaction with the working environment. It affects pipeline and accessories made of both metals and non-metals. Pipeline corrosion—and the related catastrophic failures thatit can cause—cost billions of dollars to the economy.

Corrosion Underwater Pipeline

• The oxygen content or reactivity of liquids and gases carried
  

• The use of dissimilar metals within the piping system
  

• The temperature, flow rate and pressure of the fluids and gases
  

Types of Pipeline Corrosion

1. Uniform Pipe Corrosion. This type of corrosion causes uniform loss of the material along the surface of the pipe, resulting in a continuous thinning of its solid structure. The rate of reaction is measured by the depth of penetration of the surface in millimeters per year. By selecting a suitable piping material and a combination of corrosion protection methods such as cathodic protection as well as surface coatings, it is possible to prevent this type of deterioration.
   

2. Pitting Corrosion. This is a severe, localized deterioration of a limited surface area, leading to cavity formation, or pits, on a pipe’s surface. In some cases, these pits may puncture the pipe. The reasons for pitting corrosion include pipe material defects or surface defects, mechanical damage to the protective passive film, and penetration by an aggressive chemical species, such as chlorides. This type of corrosion is frequently found in passive metal alloys and metals, such as aluminum or even stainless steel. Pits normally vary in shape and depth. Improper material selection for piping can be one of the causes.
   

3. Selective Leaching. Selective leaching, or graphitic corrosion, occurs when a noble metal and a more reactive element form an alloy. This may result in the loss of the reactive element from the pipeline’s surface, causing loss of strength and premature failure. A typical example of this is the removal of nickel, cobalt or zinc from copper alloys. This can result in color changes or changes in density in the affected material. The addition of aluminum or tin can, in some cases, provide protection from leaching.
   

4. Galvanic Corrosion. occurs when dissimilar alloys or metals of different corrosion potentials are connected electrically. In this case, only the metal working as an anode with respect to the other will deteriorate. This reaction can be prevented by using a combination of metals that are closer in the galvanic series, and by placing insulation between the two. Coating of the cathodic surface will also help.
   

5. Crevice Corrosion. Caused by an accelerated reaction at joints and other crevices of a pipeline due to differential oxygen availability. The surfaces starved of oxygen become the anode in an electrochemical reaction. Replacing riveted joints with welded joints can help overcome such problems.
   

6. Intergranular Deterioration. Refers to the selective deterioration at a surface’s grain boundaries (due to high temperature) when the grain boundary reaches high activity, which is prone to corrosion. Heat treatment and welding heat can cause this transformation, leading to corrosion. This problem can be prevented by selecting extra-low carbon stainless steel materials.
   

7. Stress Corrosion Cracking. Stress corrosion damage is the growth of pre-existing cracks in corrosive conditions. It can lead to the sudden failure of ductile metal pipes under tensile stress, particularly at higher temperatures. Cracks grow rapidly in the case of alloys, but failure occurs only if the amount of stress exceeds a specific threshold level. Therefore, preventive measures for stress corrosion cracking include limiting the loads to ensure they are below threshold stress levels.