Residual oxygen measuring devices
Overview of residual oxygen measuring devices
Residual oxygen content during moulding: Measurement, significance and effects
The residual oxygen content during forming plays a decisive role in the quality of weld seams. Even small amounts of oxygen in the shielding gas can lead to oxidation, pore formation and other welding defects. Precise measurement and control of the residual oxygen content is therefore essential, especially in demanding industries such as aerospace, medical technology or the chemical industry.
Effects of residual oxygen on the welding result
Too high an oxygen content can lead to considerable metallurgical and mechanical changes in the weld seam. These include
- OxidationThe formation of oxides on the surface impairs the seam quality and reduces the corrosion resistance.
- Pore formationDiffusing oxygen can be trapped in the melt and lead to the formation of pores, which reduces the strength of the seam.
- BrittlenessOxygen ingress can cause undesirable embrittlement effects, especially with high-alloy steels or titanium.
Required residual oxygen limit values
The requirements for the residual oxygen content vary depending on the material and area of application:
- Stainless steels & titanium<10 ppm required for high quality weld seams
- Pressure vessels & pipework20-50 ppm acceptable
- Aerospace, medical technology: Values below 5 ppm required
International standards define specific requirements for the shielding gas atmosphere for various welding processes:
- ISO 14175This standard specifies requirements for the categorisation of gases and mixed gases used for joint welding and related processes. It is valid for various welding processes in the metal industry. Source: ISO 14175:2016
- ASME Section IXThis section of the Boiler and Pressure Vessel Code contains rules for the qualification of welding, brazing and joining processes and for the qualification of the relevant personnel. It is applicable in industry and energy technology. Source: ASME BPVC Section IX
Methods for measuring the residual oxygen content
There are various measuring methods for determining the residual oxygen content during moulding:
- Electrochemical sensors (oxygen measuring cell)
- Precise measurement of the O₂ content in the ppm range
- Ideal for automated welding processes
- Sensitive to moisture and contamination
- Optical sensors
- Measurement of light absorption by oxygen molecules
- Cost-effective and easy to use
- Lower accuracy than electrochemical sensors
- Residual oxygen analysis by means of gas sampling
- Sampling and analysis with external measurement technology
- Highest accuracy, but not applicable in real time
Choosing the right residual oxygen meter
Selecting the right measuring device is crucial for ensuring weld seam quality. It is important to select the device according to the specific requirements of the application:
- Electrochemical sensorsHigh accuracy, ideal for precision welding (e.g. aerospace, medical technology). Devices such as the Oxy EVO offer continuous measurements with an accuracy of less than 5 ppm, but are more cost-intensive.
- Optical sensors: Less expensive, but less accurate. However, it may not be suitable for critical welding processes.
- Devices with lower accuracy: Measuring devices with an accuracy of 100 ppm or 1000ppm as well as devices with percentages are not recommended for professional forming processes, as they do not offer sufficient precision for high-quality weld seams.
Oxy EVO vs. Oxy Smart - Which residual oxygen meter is right for you?
If you have a Residual oxygen meter for your welding applications, there are various models with different properties available. Two tried and tested devices are the Oxy EVO and the Oxy Smart from Orbitec. Both offer reliable measurement of the residual oxygen content, but differ in their accuracy, speed and possible applications.
Oxy EVO - Highest precision for demanding applications
The Oxy EVO was specially developed for high-precision welding applications where an extremely low oxygen content must be ensured. It measures with an accuracy of ±2 ppm in the range below 30 ppm and is therefore ideal for industries with highest quality requirementssuch as the Aerospace, pharmaceutical industry or high-precision Orbital and inert gas welding.
One of the outstanding features of the Oxy EVO is its Fast response time of approx. 2 secondswhich is almost Continuous monitoring of the residual oxygen content. It can also Record and document measured valueswhich guarantees quality assurance and traceability in accordance with international standards such as ISO 9001 considerably easier.
Oxy Smart - The economical solution for general welding applications
The Oxy Smart is a more cost-effective alternativewhich is particularly suitable for applications in which a Very high precision not absolutely necessary is. It also uses a Zirconium oxide measuring cellHowever, its accuracy is not as high as that of the Oxy EVO.
Comparison table: Oxy EVO vs. Oxy Smart
Feature | Oxy EVO | Oxy Smart |
---|---|---|
Measuring method | Zirconium oxide measuring cell | Zirconium oxide measuring cell |
Measuring range | 5 ppm to 21 % O₂ | 5 ppm to 21 % O₂ |
Measuring accuracy | ±2 ppm below 30 ppm | Manufacturer information not specified |
Measuring time | Very fast (approx. 2 seconds) | Slower, discontinuous |
Logging | Yes, for quality management and traceability | No |
Recommended application | High-precision applications: Aerospace, pharmaceutical, orbital welding | General welding applications |
Mobility | Stationary | Mobile and flexible |
Price level | Higher | More favourable |
Technical challenges with low ppm values
Residual oxygen values below 10 ppm or 20 ppm are technically difficult to achieve, as the forming system must ensure uniform gas distribution throughout the forming chamber. The Holzer moulding systems have been specially developed to overcome these challenges. One particularly innovative process is the Shock mouldingwhich uses specially developed bubble and barrier systems to efficiently reduce the residual oxygen content. The ASS® Prime forming system can reduce the oxygen content to as low as 5 ppm and thus create optimum welding conditions. This is particularly important for applications in the pharmaceutical, food and aerospace industries. Further information on this process is available at the following link: Impact purging with ASS® Prime.
In addition to choosing the right measuring device, it is also essential to use the right forming system in order to achieve the desired low ppm values. A high-quality forming system such as the ASS® Prime contributes significantly to the reduction of oxygen ingress and thus supports flawless weld seam quality.
Summary
Checking the residual oxygen content is crucial for high-quality welded joints, especially in critical industrial areas. The choice of the appropriate measuring method depends on the specific requirements of Accuracy, speed and costs from. By using modern measuring devices such as Oxy EVO or Oxy Smart, the oxygen content can be precisely monitored to avoid welding errors and ensure optimum seam quality in the long term.
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