What is Degassing? Ensuring Safety and Efficiency in Shutdown and Turnaround Operations

Are you facing challenges in safely conducting shutdown and turnaround operations? 

Do you understand the critical role of degassing in maintaining operational integrity and ensuring worker safety? 

Degassing is a critical process in the oil and gas industry, especially during shutdown and turnaround operations. In this article, we explore what degassing is, its importance, degassing methods and chemicals, and how degassing impacts the safety and efficiency of your operations. 

Whether you’re a seasoned professional or new to the field, this guide will enhance your knowledge and help you navigate the complexities of degassing in the oil and gas industry. 

What is Degassing?

Degassing refers to the removal of unwanted or potentially harmful gases or vapors. In petroleum processing and production, volatile hydrocarbon gases (LELs, Benzene), hydrogen sulfide (H2S), and mercaptans are produced.

These gases or vapors are present in process piping, storage tanks, and vessels. During shutdown & turnaround operations, gas concentrations must be reduced to safe levels to protect personnel and maintain operational integrity.

Degassing is also commonly referred to as Chemical Degassing, LEL Scavenging or Vapor Phase Cleaning. 

Why is Degassing Important?

Degassing is often used during shutdown and turnaround operations to remove hazardous gases and ensure safer environments for workers.

Degassing processes are critical during shutdown and turnaround operations where personnel may be required to enter process vessels for maintenance and inspection. 

High concentrations of toxic and flammable substances, and high LEL (Lower Explosive Limit) levels pose a substantial risk. The process of chemical degassing efficiently reduces or eliminates these hazardous elements, ensuring a safer environment for workers. Chemical degassing reduces the possibility of accidental ignition or explosion and enables personnel to carry out inspection or maintenance work in a safer environment. 

Where is Chemical Degassing Required?

Degassing is required prior to performing vessel entry for final cleaning and inspection. These components often require degassing during oil field shutdown and turnaround operations: 

  • Storage tanks 
  • Process vessels 
  • Reactors 
  • Piping 
  • Heat exchangers 
  • Compressors 
  • Columns 
  • Knock out drums 
  • Ammonia strippers 
  • Amine towers and contactors 
  • Treaters and separators 
  • Vacuum towers 
  • Other equipment used for storing and processing hydrocarbons 

What is Removed During Chemical Degassing Operations?

Chemical degassing operations remove unwanted and harmful gases and vapours including: 

  • Hydrocarbon Gases (LELs, VOCs, Benzene) 
  • Hydrogen sulfide (H2S) 
  • Ammonia (NH3) 
  • Mercaptans 

Many chemical degassing agents have a cleaning effect and remove liquid and solid hydrocarbon contaminants as well. It’s also common during chemical degassing operations to apply H2S scavengers (Sourguard) and iron sulfide (FeS) dissolvers (Ferrosol). H2S scavengers remove H2S while iron sulfide dissolvers remove any pyrophoric iron present. 

How are Chemical Degassing Agents Applied?

There are several application methods for chemical degassing agents. Your choice will vary based on the equipment, system, or process being degassed and equipment available for application. Most applications involve circulation, spray, or injection. Common application methods include: 

  • Liquid circulation 
  • Vapour phase steam or steam purge 
  • System injection 
  • Nitrogen injection 
  • Gamma jetting 
  • 3D nozzle jetting 
  • High or low pressure wand spray 
  • High pressure man door cannon 
  • Scrubber 

Is a Steam Purge the Same as Chemical Degassing?

While steam can assist in the process of degassing, a steam purge is not the same as chemical degassing. 

A steam purge removes harmful gases and contaminants by flowing high-pressure steam through the system. The heat from the steam helps volatilize some lighter hydrocarbons, aiding in removal. However, a steam purge may not be effective in dealing with certain types of gases or residues. 

Steam purges are enhanced by the addition of chemical degassing agents such as Purge C or Purge HF to the process. These chemical degassing agents emulsify harmful gases making them easier to remove. This process is effective with volatile hydrocarbon gases, hydrogen sulfide (H2S), mercaptans, and other hazardous gases that are commonly found in oil and gas operations. 

Purge C and Purge HF Chemical Degassing Agents

Increasingly challenging industrial applications led to the development of our degassing chemicals—Purge C, and Purge HF. These specialized products meet the unique needs of degassing operations, ensuring maximum safety and efficiency. 

Purge C leads the line with a unique low-foaming formula that chemically encapsulates hydrocarbons in both liquid and vapor forms. This reduces the explosive potential, removing harmful gases and liquids. And, it ensures a safer working conditions for personnel. 

Purge HF introduces more powerful cleaning capabilities to enhance the efficiency of shutdown and turnaround operations. Purge HF can remove low levels of hydrogen sulfide (H2S) without the addition of a dedicated H2S scavenger making it a single component solution for degassing operations. 


Chemical degassing is not just a process but a strategic commitment to safety, efficiency, and operational integrity. Our continuous research and development efforts aim to make this process simpler, safer, and more effective. With the right approach and the right tools, chemical degassing can reduce operational hazards, ensure the safety of your workforce and the efficiency of your operations. 

Making the Right Choice for Your Degassing Needs

Choosing the right degassing product is a decision that directly influences the success and safety of your operations. Every operation has unique needs, challenges, and risks. The chemical degassing process must be tailored to your operation. Our chemical degassing product line – Purge C, Purge HF, and H2S Scavengers – Sourguard, Sourguard SG, and Sourguard DSS are designed to suit a wide range of industrial applications. 

Our commitment to safety and efficiency is not limited to product development; it extends to helping our clients make the right choice. We’re dedicated to understanding the specific needs of your operations and recommending the most suitable products from our range.

When you’re ready, contact our chemical degassing experts and see how you Create a Better Future with Chemistry Done Better.  

Table of Contents

FAQ: Degassing in Shutdown and Turnaround Operations

How do I choose the most effective degassing agent for chemical tank cleaning?

The choice of degassing agent depends on the type of hydrocarbons and contaminants present. Each tank and its contents are different. Custom chemical tank cleaning and degassing solutions are often developed based on the information and contaminant samples provided. You can learn more about our custom chemical tank cleaning solutions in this case study. 

When you’re ready, contact our degassing experts to learn more or to have us develop a custom chemical tank cleaning solution for you. 

With large storage tanks, what is the best degassing application method for chemical tank cleaning operations?

The effectiveness of the application method can vary. For large tanks, 3D nozzle jetting or high-pressure man door cannon methods are often effective for degassing and tank cleaning. The choice depends on tank design, the nature of the residue, and the specific degassing agent used. 

How long is the degassing and chemical tank cleaning process?

The timeline varies based on tank size, contents, contamination level, and the method used. Chemical tank cleaning can take several hours to several weeks or even months. Efficient planning and the use of the right degassing and tank cleaning chemicals will reduce overall downtime. 

How can I monitor gas concentrations during the degassing process?

Advanced gas detection and monitoring equipment are commonly used to continuously measure gas concentrations. These devices should be calibrated and maintained regularly for accuracy.

Can the degassing process be automated to enhance safety and efficiency?

Automation can be implemented in certain aspects of the degassing process, such as the application of chemical degassing agents and monitoring of gas levels. This will reduce the need for vessel entry prior to inspection. Throughout the process, human supervision is crucial to manage unforeseen issues and ensure overall safety.

How is the effectiveness of the degassing process measured?

Effectiveness can be measured by testing gas concentrations before, during, and after the process.

What are the key differences between Purge C and Purge HF?

Purge C is designed as a low-foaming encapsulant for hydrocarbons in both liquid and vapor forms. It effectively reduces explosive potential by emulsifying volatile gases and liquids. Purge HF adds powerful cleaning capabilities and the ability to remove low levels of hydrogen sulfide (H2S), however it is higher foaming.

How do H2S scavengers and iron sulfide dissolvers integrate into the degassing process?

How do H2S scavengers and iron sulfide dissolvers integrate into the degassing process? 

H2S scavengers and iron sulfide dissolvers are typically integrated into the chemical degassing process during tank, vessel, or process piping cleaning. These specialized chemicals target specific compounds (H2S and iron sulfide) to enhance the overall effectiveness and safety of the degassing operation.

What factors should be considered when selecting a degassing application method?

When choosing a degassing method, consider the size and design of the equipment (like storage tanks or process vessels), the nature and concentration of the gases present, accessibility, and the potential impact on the environment. The method should maximize efficiency and minimize safety risks and environmental impact.

Originally published June 20, 2023. Updated with additional content and FAQ December 6, 2023.

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