Odor Fade – Why We Pickle Pipe

 In Pipeline Pickling

Why it is possible you MAY not smell gas?

In certain situations, the Mercaptan added (the sulfur or rotten egg smell) to natural gas supplies, maybe either filtered out or absorbed, leaving little to no odor in leaking or vented natural gas.  Utility companies regularly conducts tests within their systems to ensure gas is delivered to customers that meet State and Federal odorization levels.  However, once it leaves the distribution system, the odor may be stripped out from the natural gas.  This phenomenon can become a safety hazard if personnel are purging new equipment or appliances into service or otherwise relying on their sense of smell to detect the presence of natural gas.


  • Odor Fade:  Loss of odorant so that it is no longer detectable.
  • Purging:  Removing air in a pipe and replacing it with natural gas

Some of the most common factors where odor fade may be experienced include large diameter, steel pipe with relatively low-flow conditions.   While it is possible that smaller diameters and other materials may be impacted, most situations appear to involve larger commercial/industrial applications.

What might cause the smell to fade?

There are many factors that could impact gas odor.

  • Some people may not be able to detect odorant because they have a diminished sense of smell (either permanent or temporary).
  • Odor fatigue could occur when exposed to natural gas odor for an extended period of time.
  • It could be masked by other strong odors in the area.
  • Large diameter new pipe (more pronounced in steel pipe).
  • Gas pressure, flow or lack of flow conditions
  • Oxidation
  • Absorption
  • Moisture, rust or other contaminants in the piping system
  • Piping configuration downstream of the meter

Could Odor fade impact outside gas leaks?

  • Yes – soil or concrete could absorb odorant reducing the intensity.
  • DO NOT RELY on Sense of Smell alone to detect natural gas.

Odor Fade Considerations for Designers, Contractors, Builders

What can you do to help prevent odor fade?

  • Design piping systems for expected flow rate, try to avoid upsizing.
  • Design piping systems in a loop that minimizes dead ends to keep gas flowing.

General Precautions:

  • Always use gas detection equipment (combustible gas indicators) when purging or if natural gas may be leaking or venting.
  • Do not purge natural gas into a confined space, vent it to the outdoors.
  • When purging, make sure area is well ventilated.
  • DO NOT RELY on Sense of Smell alone to detect natural gas.
  • Follow local plumbing, mechanical or fuel gas codes during purging operations.
  • Follow manufacturer’s instructions when installing appliances or other gas equipment
  • Purging operations should only be done be licensed qualified professionals.

(The above information was shared from National Grid.)

What is Pipeline Pickling?

Pipeline pickling is the process of conditioning a new gas pipeline before putting it into service. In new gas lines, it is common to experience odor fade in gas as the natural gas odorant reacts with rust and mill scale inside new steel pipes, thereby producing less odorous compounds. The process of conditioning the line ensures the safe delivery of odorized gas to the end users.

Why MRR Pipeline Conditioning?

As the industry experts, MRR designs a pickling strategy for each site’s requirements using state-of-the-art tools and the industry’s best practices.

  • We utilize a front-end odorizer for pickling and a tail-end odorizer to supplement the gas for proper make-up odorization. The OdorTracker mercaptan monitoring system assists with determining supplemental odorization at the back-end odorizer. The system employs built-in communications and triggers alarms by text and email and permits remote control through a computer or smartphone.
  • Active filtration systems are used in sensitive locations to avoid false leak call complaints. Additionally, our leak monitoring systems automatically trigger alarms to SCADA and filtration, if needed.

Proper pipeline conditioning prevents odor fade, so odorant remains at the correct levels minimizing the concerns of under-odorization and false leak-call complaints due to over-odorization. Whenever technically possible we design the process to enable gas to be sold rather than flared to the atmosphere.

The MRR pickling procedures ensure the highest standards of safety.

  • MRR designs pickling strategy for steel, plastic and internally coated pipelines.
  • Pipeline conditioning is an eco-friendly approach since it becomes possible to start-up with no venting or flaring of gas.
  • The pickling process is a turnkey operation and offers control of the pipeline start-up.
  • The odorant injection type is:
    • Continuous flow-proportional injection
    • Controlled volume injection
  • Process monitoring
  • Data collection and reporting
  • Odorant concentration measurement using:
    • MRR OdorTracker
    • Stain tubes
    • GC
  • Liquid and vapor injection technology
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