Asset Integrity Management

Electromotive Force Series (corrosion)

Electromotive Force (EMF) Series: A Guide for Oil & Gas Professionals

The Electromotive Force (EMF) Series, also known as the Galvanic Series, is a fundamental tool used in the oil and gas industry to understand and prevent corrosion. It plays a critical role in selecting materials for pipelines, storage tanks, production equipment, and other components exposed to corrosive environments.

What is the EMF Series?

The EMF Series is a list of elements arranged in order of their standard electrode potentials. This potential measures the tendency of an element to lose electrons and become oxidized (corroded). Elements at the top of the series are more likely to oxidize and corrode, while those at the bottom are less likely.

How does the EMF Series relate to corrosion?

When two dissimilar metals are in contact in an electrolyte (like seawater or acidic fluids), a galvanic cell is formed. The metal higher on the EMF Series will act as the anode, corroding, while the metal lower on the series will act as the cathode, remaining protected. The further apart the two metals are on the EMF Series, the greater the potential difference and the more severe the corrosion.

Example:

Consider a steel pipe (iron) buried in the ground. If a copper wire is attached to the pipe, the copper will act as the cathode, while the iron will act as the anode. Iron will corrode faster due to the galvanic effect.

Using the EMF Series in Oil & Gas Applications:

The EMF Series is used extensively in oil and gas operations to:

  • Material Selection: Choosing compatible metals for pipelines, tanks, and other components to minimize corrosion.
  • Cathodic Protection: Implementing cathodic protection systems to protect structures by applying an external current to make them cathodic, preventing them from corroding.
  • Corrosion Mitigation: Understanding the potential for galvanic corrosion and implementing preventative measures like using protective coatings, isolating dissimilar metals, and using sacrificial anodes.

Importance of the EMF Series in Oil & Gas:

Corrosion in oil and gas infrastructure can lead to leaks, spills, equipment failures, and even explosions. Using the EMF Series helps engineers and technicians make informed decisions to prevent corrosion, ensure safe operations, and reduce environmental impact.

EMF Series List (Common Metals in Oil & Gas):

More Active (Anodic)

  • Magnesium
  • Aluminum
  • Zinc
  • Iron
  • Nickel
  • Tin
  • Lead
  • Copper
  • Brass
  • Bronze
  • Silver
  • Gold
  • Platinum
  • Graphite

Less Active (Cathodic)

Important Considerations:

  • The EMF Series is a guide, and actual corrosion behavior can be influenced by environmental factors like temperature, pH, and the presence of impurities.
  • It is crucial to consider the specific conditions when applying the EMF Series to real-world situations.
  • Consulting with corrosion specialists is essential for complex projects.

By understanding and applying the EMF Series principles, oil and gas professionals can contribute to the safety, efficiency, and environmental sustainability of their operations.


Test Your Knowledge

Quiz: Electromotive Force (EMF) Series

Instructions: Choose the best answer for each question.

1. What is the primary function of the EMF Series?

a) To determine the electrical conductivity of metals. b) To predict the tendency of metals to corrode in different environments. c) To measure the strength of an electric current. d) To classify metals based on their melting point.

Answer

The correct answer is **b) To predict the tendency of metals to corrode in different environments.**

2. Which of the following statements is TRUE about the EMF Series?

a) Metals at the top of the series are less likely to corrode. b) The further apart two metals are on the series, the weaker the galvanic effect. c) The EMF Series is only applicable to metals. d) The EMF Series is a definitive guide and does not require consideration of environmental factors.

Answer

The correct answer is **b) The further apart two metals are on the series, the weaker the galvanic effect.**

3. In a galvanic cell, which metal acts as the anode?

a) The metal higher on the EMF Series. b) The metal lower on the EMF Series. c) The metal with the highest electrical conductivity. d) The metal with the lowest melting point.

Answer

The correct answer is **a) The metal higher on the EMF Series.**

4. How is the EMF Series used in oil and gas applications?

a) To select materials for pipelines and tanks. b) To implement cathodic protection systems. c) To mitigate corrosion risks. d) All of the above.

Answer

The correct answer is **d) All of the above.**

5. Which of the following metals is the most likely to corrode when in contact with iron in a saltwater environment?

a) Copper b) Gold c) Magnesium d) Silver

Answer

The correct answer is **c) Magnesium.** Magnesium is higher on the EMF Series than iron, making it more prone to corrosion when in contact with iron.

Exercise: Choosing Compatible Materials

Scenario:

You are tasked with designing a storage tank for a crude oil processing facility. The tank will be constructed from steel and will be exposed to the corrosive environment of the surrounding soil.

Instructions:

  1. Refer to the EMF Series provided in the text.
  2. Identify two metals that are compatible with steel in this environment.
  3. Explain your reasoning, considering the EMF Series principles and the need for corrosion prevention.

Exercice Correction

The most compatible metals for a steel storage tank in a corrosive environment are:

  • Nickel: Nickel is lower on the EMF Series than steel, making it less likely to corrode when in contact with steel. This means steel will act as the anode, but the corrosion rate will be significantly reduced due to the small potential difference.
  • Lead: Similar to Nickel, Lead is also lower on the EMF Series than steel and offers good corrosion resistance in this scenario. It will act as the cathode, preventing steel from corroding rapidly.

It is crucial to note that while these metals are compatible with steel, other factors like temperature, pH, and the presence of impurities can influence the actual corrosion behavior. Implementing protective coatings and proper maintenance procedures are essential for ensuring the long-term integrity of the tank.


Books

  • Corrosion Engineering by Mars G. Fontana and Norbert D. Greene: A classic textbook covering all aspects of corrosion, including the EMF Series.
  • ASM Handbook, Volume 13A: Corrosion by ASM International: A comprehensive reference on corrosion science and engineering, providing detailed information on the EMF Series and its applications.
  • Corrosion Control in the Oil and Gas Industry by R.N. King and J.L. Crolet: A practical guide focusing on corrosion issues specific to the oil and gas sector, including the EMF Series and its role in materials selection.

Articles

  • "The Galvanic Series and Its Application to Corrosion Control" by A.W. Peabody: A seminal article explaining the EMF Series and its importance in corrosion prevention.
  • "Corrosion in Oil and Gas Pipelines: A Review" by A.K. Mohanty and M.R. Sridhar: An overview of corrosion in oil and gas pipelines, including the role of the EMF Series in materials selection and cathodic protection.
  • "Galvanic Corrosion: A Practical Guide for Engineers" by NACE International: A practical guide covering the principles of galvanic corrosion and its mitigation, including the use of the EMF Series.

Online Resources

  • NACE International: (https://www.nace.org/) A leading corrosion control organization providing extensive resources, including information on the EMF Series, corrosion prevention, and materials selection.
  • Corrosion Doctors: (https://www.corrosiondoctors.com/) A website dedicated to corrosion science and engineering, featuring articles, tutorials, and a comprehensive glossary.
  • ASM International: (https://www.asminternational.org/) A materials science and engineering society offering valuable resources on corrosion, including the EMF Series and its applications.

Search Tips

  • "EMF Series corrosion" OR "Galvanic Series corrosion" - Find general information on the EMF Series and corrosion.
  • "EMF Series oil and gas" OR "Galvanic Series oil and gas" - Focus your search on applications within the oil and gas industry.
  • "EMF Series materials selection" OR "Galvanic Series materials selection" - Search for information on using the EMF Series to choose compatible materials.
  • "EMF Series cathodic protection" OR "Galvanic Series cathodic protection" - Find resources on how the EMF Series informs cathodic protection systems.

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