The Best Oxygen Analyzers for Welding (Expert Analysis)

Oxygen Analyzer, Oxygen Purge Monitor, Weld Purge Monitor, Welding Analyzer -

The Best Oxygen Analyzers for Welding (Expert Analysis)

Oxygen analyzers are used in welding to confirm an inert environment for best welding results. The Oxygen purge analyzers continuously operate to confirm low levels (100ppm) of oxygen. Oxygen Analyzers typically include a probe, pump, oxygen sensor, and display. Oxygen analyzers for welding have reduced in price over the past few years, now retailing for less than $500.

Pros

Cons

  • O2 analyzer prices have reduced as low as $500.
  • Reducing oxygen improves weld joints.
  • Simply, fast and small units.
  • Oxygen can be displaced and becomes dangerous to life when less than 19.5%. Care must always be taken.
  • Oxygen analyzers can get very expensive.
  • Electrochemical oxygen sensors have a limited life from 2 to 3 years.

Why is reduced Oxygen so important for Welding?

The objective when welding is to remove as much oxygen as possible. The best welding occurs when there is no oxidation taking place. Hence, the reason why we want as minimum oxygen as possible. Since oxygen naturally exists in the air at 20.9%, sometimes it is not a trivial task to eliminate oxygen in a small volume of space. 

Weld oxidation will degrade the mechanical properties of a pipe and reduce its resistance to corrosion. To reduce oxidation, the oxygen content must be dramatically reduced.

For welding, inert gases are used to displace and remove the oxygen so minimum oxygen remains. So this is where confirmation and confidence is important. A oxygen analyzer for welding, does exactly that. It confirms what the exact oxygen level is when welding. 

Benefits of using an Oxygen Purge Analyzer?

The most important benefit of using an oxygen purge analyzer is to track oxygen so that O2 levels remain low to reduce oxidation and oxide thickness when welding.

Many academic studies show the relationship of welding oxygen content and resulting oxide thickness (oxidation). For example:

  • One study showed when the oxygen was at 30ppm, the oxide thickness was about 0.7 μm compared to about 1.5 μm when oxygen was at 280ppm.
  • The combination of the oxidation was responsible for the crack of the specimens welded under high oxygen content.
  • This results in decreasing the corrosion resistance of the welding specimens.

Studies like this show the importance of very low oxygen detection down to 100ppm when welding.

The image below visually shows the correlation between oxygen content and oxidization. The darker the weld, the more oxidization. See more here.

purge monitor oxygen

Other benefits of using a Portable Trace Oxygen Analyzer:

    • Reduces time as there is no need to depend on time to purge estimates.
    • Reduces gas consumption when purging and easier to control the amount required.
    • Ensures quality as welding can begin when oxygen depletion has occurred, so no need to worry about welding too early.

What does an Oxygen Analyzer for Welding do?

Oxygen analyzers are sometimes called:

    1. Inert Shielding Gas Monitor
    2. Weld Purge Monitor
    3. Oxygen Analyzer for Welding
    4. Trace Oxygen Analyzer
    5. Oxygen Purge Monitor

They all refer to an oxygen measuring instrument that detects oxygen and provides the user with a quantitative concentration of the detected oxygen gas for welding application.

A Oxygen Analyzer tracks the oxygen concentration and provides the user with a unit value of % or part per million (ppm) reading.

For welding, O2 analyzers present the user with a % or ppm concentration display. 

How is Oxygen Gas Detected?

Oxygen is detected using an oxygen sensor. Within the oxygen analyzer, an oxygen sensor senses the oxygen molecules. The reaction produces an electronic signal that then represents the oxygen concentration. A small electrochemical oxygen sensor is shown below.

oxygen sensor

How does an Oxygen Analyzer Work?

An oxygen analyzer for welding works by using an oxygen sensor cell to detect oxygen concentrations. For electrochemical sensors, the oxygen gas reacts with a working electrode triggering an electrochemical redox reaction. Current is generated proportional to oxygen levels that is then converted to a representative oxygen concentration (related via a calibration curve). For more extensive information, see here.

What is the difference between an electrochemical and zirconia oxygen sensor?

O2 Sensor Technology

Working Principle

Pros

Cons

Electrochemical 

Cells (100ppm)

The gas reacts with a working electrode triggering an electrochemical redox reaction. Current is generated proportional to oxygen levels.
  • Small & Cheap
  • Easy to integrate with electronics
  • Immediate ON
  • Limited life from 24 to 36 months
  • Influenced by temperature and humidity
  • Limited down to 100ppm.

Zirconia 

Sensors (<100ppm)

Zirconia allows  oxygen ions to travel, so when exposed to gases at different concentrations, an electrochemical voltage is generated.
  • Very accurate in ppm (good for down to 1ppm)
  • Large Detection Range
  • Expensive
  • Requires heating and power

What are Safe Oxygen Levels?

When welding, low levels of oxygen levels are desired in a tube or a gas chamber, which in most cases are small volumes. With that said, it is worth mentioning that having an inert gas leak and oxygen being depleted in your breathing environment can be dangerous.

Various government agencies and associations have recommended oxygen gas limits. Some examples are in the below table.

Agency

Recommendation / Requirement

Occupational Safety and Health (OSHA)

Air is considered oxygen-deficient below 19.5%

National Institute for Occupational Safety and Health (NIOSH)

Air is considered oxygen-deficient below 19.5%

American Conference of Governmental Industrial Hygienists (ACGIH)
<18% is minimum partial pressure without the need for respiratory protection at normal atmospheric pressure

    How can I Test my Oxygen Analyzer?

    The best way to test your oxygen detector is to expose it to an inert gas such as argon or nitrogen. Since air has 20.90%, perturbing this concentration and bump testing it to pure nitrogen or reduced levels is a good check. 

    What will happen if I breathe onto my Oxygen Analyzer?

    If you breathe onto your Oxygen Analyzer, it will quickly decrease in O2 reading as breath exhalation has depleted oxygen levels, about 17%. 

    What is the Best Oxygen Analyzer for Welding?

    There are many oxygen analyzers for welding on the market. The reputable brands include the following:


      How do I choose an Oxygen Analyzer for Welding?

      To select the best oxygen analyzer for welding make sure to ask these questions: 

          • Does the oxygen analyzer have a pump? Avoid using handheld aspirators. Hand aspirators create variable pressure (pulses) affecting the sensor readings. Continuous constant electronic micro pumps within the oxygen analyzer are much more desirable.

          • How low do you need to detect O2 ppm? Depending on your weld application and the metals being used, 100ppm may suffice. In this case, a oxygen analyzer with 0.01% (100ppm) resolution will work fine, usually made using electrochemical sensors. If your welding application requires very low oxygen levels (down to 10ppm or even 1ppm), you will need a 1ppm oxygen analyzer. For these extremely low concentration readings, you will need to employ a zirconia sensor-based analyzer.

          • What accessories do I need? Typically, an oxygen analyzer comes with tubing, filters, a carry case and stainless steel probes.
        • Budget? Oxygen Analyzers for welding range from $500 to $5000. Typically for electrochemical sensors that go down to 100ppm, they can be purchased for less than $500. For zirconia based sensors (1ppm), they are sold for over $3000.

        • Calibration Certificate? Ensure the unit is calibrated with National Institute of Standards and Technology (NIST) traceable sources to ensure the upmost accuracy and confidence. Ensure the calibration certificate mentions where it is calibrated, the calibration standard, and all technical details, including date of calibration.

        How long do Oxygen Analyzers last?

        O2 sensors with electrochemical sensor cells last from 24 to 36 months. Zirconia oxygen sensors last much longer but are more expensive.

          What is Oxygen Analyzer Bump Testing?

          • Bump testing is a procedure when one exposes the oxygen analyzer to a small amount of “blast” target gas to ensure the detector operates as expected. 
          • The function of this test is to verify detection operation and build user confidence, particularly in hazardous and critical user applications.
          • It is recommended to bump test when first purchased. Weekly thereafter, especially in LIFE-THREATENING and or DANGEROUS applications to verify detector operation. See video explanation here
          • For oxygen analyzers, we recommend to bump test to pure argon or nitrogen gas.

          How do I take care of my Oxygen Analyzer?

          • Store your oxygen analyzer at normal room temperature.
          • Store it away from electromagnetic or magnetic sources such as phones or electronic equipment.
          • Store it in a clean environment where no dust or particles exist. If it comes with a case, keep it in the case.
          • Store it away from any exhaust gas, concentrated vapors, harsh chemicals that may poison the sensor.
          • Store it in a stable place where there are no vibrations or continuous shaking. 

          How do I properly use an Oxygen Analyzer?

          When operating your oxygen analyzer for welding, there are some essential tips to consider. Be smart and read your product manual.

          Before starting, set up your weld purge system. Typically it is an inert purge chamber, otherwise known as a glove box. Or a pipe purge system arrangement. Other hardware setups also exist that create a volume of inert gas around the area of welding.

          1. Ensure the oxygen analyzer has been bump tested and validated operational.
          2. Turn it on and allow the analyzer at least 60 seconds to come to a stable reading (It may take longer for zirconia-based oxygen sensors).
          3. Check all tube connections via the filter and barbs. Extremely important to ensure there are no vacuum leaks, which will introduce oxygen and elevate the O2 readings.
          4. Place the probe at your sample location.
          5. Ensure the pump is running. You will soon see the oxygen values decreasing once the inert gas starts to displace the oxygen. 
          6. Make the necessary flow adjustments to your inert gas as to preserve gas (not being wasted), yet maintaining low oxygen levels desired.
          7. Once finished, allow the analyzer to draw fresh air.
          8. Allow the analyzer to recover until it reads 20.90%.
          9. Turn OFF and store the analyzer.

          What is the difference between a ppm and % Oxygen?

          The typical scale of concentration for oxygen is %. For low levels, less than 1%, the part per million scale is used (ppm).

          For welding, since we are most interested in low values to ensure an inert environment, the ppm scale is more often used. Conversion between ppm and % is easy. Here is a quick Oxygen concentration conversion:

          10ppm = 0.001%

          100ppm = 0.01%

          1,000ppm = 0.1%

          Final Words

          Oxygen analyzers are used in welding to confirm an inert environment for best welding results - just a few 100ppm difference can dramatically change a weld oxide thickness. An O2 analyzer is a valuable tool for welding, as it continuously operates to confirm low oxygen levels. Oxygen analyzers for welding have decreased over the past few years, now retailing for less than $500.

          About The Author

          Dr. Koz is the President of FORENSICS DETECTORS where the company operates from the scenic Palos Verdes Peninsula in Los Angeles, California. He is a subject matter expert on gas sensor technology, gas detectors, gas meters, and gas analyzers. He has been designing, building, manufacturing, and testing toxic gas detection systems for over 20 years.

          gas detector expert

          Every day is a blessing for Dr. Koz. He loves to help customers solve their unique problems. Dr. Koz also loves spending time with his wife and his three children going to the beach, grilling burgers, and having a cold beer. 

          Read more about Forensics Detectors here.

          Email:  drkoz@forensicsdetectors.com
          Phone: +1 424-341-3886


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