This article was originally published on November 15, 2021, and updated on March 24, 2025
In your most challenging applications, prioritizing safety is critical. For instance, in environments with high oxygen levels, you need to ensure your pressure instruments are free of contaminants to prevent a fire. Even though oxygen itself is not flammable, it can cause other materials like dust, oils and lingering residue to easily ignite and burn with intensity. Cleaning for oxygen service is an effective safety precaution you can take to prevent this from happening in your application.
As a product sales leader at Ashcroft, a leading authority in pressure and temperature instrumentation, I am often asked if we offer this service to our customers. The answer is yes, depending on the application. However, before you decide if it's right for you, take a few minutes to see what the service involves.
Read this article to learn more about the benefits of cleaning for oxygen service and the process we use to be sure your instruments are safe to use in high-purity gas or pure oxygen systems. You will also see additional articles and resources that are relevant to pressure gauge selection and care.
Why perform oxygen service cleaning on your pressure instruments?
When cleaning pressure gauges for use in pure oxygen environments, you must be sure the instrument is free of any lingering contaminants to prevent potential reactions or oxidation. This is particularly important in applications involving high-purity gases, semiconductor processing, chemical processing, and other scenarios that require "oxygen-cleaned" instruments.
At Ashcroft, our manufacturing process for pressure instruments includes calibration through pressurization. During machining, fabrication, and calibration, residual oil may remain on the instrument components. The oxygen service cleaning process, which adheres to the ASME B40.100 Cleanliness Level IV standard, effectively eliminates these contaminants.
Figure 1: ASME B40.100 Cleanliness Level IV standard
Cleaning for oxygen service process
Generally speaking, the cleaning process removes all traces of hydrocarbons such as methane, butane, oil and petroleum from wetted surfaces. This includes materials such as solvents, fiber, dust, weld slag and dirt. Here's how it's done at Ashcroft for different instruments:
Bourdon tube gauges, low-pressure electronic gauges, and pressure transducers
- Use a low-pressure solvent extraction process
- Pump solvent into the pressure gauge up to 15 psi to dissolve hydrocarbons and remove particles/fibers
- After pressurizing the gauge, the solvent is removed under a vacuum
- Repeat the process of applying and draining solvent multiple times depending on the gauge's size, type and contamination
Bleed cap gauges
- Remove the bleed cap from the bourdon tube
- Allow the solvent to flow through
- Purge with dry gas
Instruments that cannot be pressurized or allow flow through
For fasteners, diaphragms, and other equipment that can’t be pressurized or have anything flow through them, the solvent immersion technique is used whereby we fully submerge the instrument in a tank of solvent. This tank can also have ultrasonic vibration if needed.
After each of these cleaning processes, the instruments are tested for cleanliness and then dried in an oven to evaporate any remaining solvent. The pressure port is then capped, and the instrument is packed in a sealed plastic bag. The instruments are then labeled “for oxygen service – use no oil".
How to test for residual contaminants after oxygen service is complete
Once the cleaning process is complete, there are a few ways to verify an instrument has no remaining dust, particles, or non-volatile residue.
1. UV-VIS Spectroscopy. Take a sample of the last flush of liquid and test it with a UV spectrophotometer (UV light absorption). If the results are lower than a calibrated standard limit, then it passes – otherwise, the instrument must be flushed and tested again.
2. Gravimetric Determination. Take the last flush of liquid and evaporate the solvent in a container of known weight. The weight difference before and after adding the solvent will allow you to compare cleanliness against the allowed NVR level set in ASME B40.100.
3. Particle Size Analysis. Take the last flush of liquid and run it through a particle size analyzer. This equipment is set to detect the amounts and sizes of particles that flow through. Compare the size and count to the level IV standard for cleanliness verification.
4. Blacklight Inspection. If you see any fluorescent particles in the solvent effluent sample, this indicates the presence of residual contamination, and the instrument will need to be cleaned again.
5. Solvent Ring Test. Place a sample of the solvent effluent on a glass slide and allow it to evaporate. Then inspect the slide under magnification to determine if there is contaminant residue left behind.
Ready to learn more?
Now you know why cleaning for oxygen service is so important and the process that is used to ensure instruments will be safe to use in high-purity gas or pure oxygen applications. You can also be confident that Ashcroft cleaning technicians are highly qualified with a combined experience of over 30 years. We can help ensure that your instrumentation keeps your operators safe and your equipment functioning reliably.
If you want to learn more about pressure gauges and the other services we offer for them including Ashcroft's Critical Application Solutions Expert® (CASE), here are a few articles that may interest you:
- 4 Important Benefits of Critical Application Instrument Audits
- 6 Reasons Pressure Gauges Fail Instrument Audits
- How To Identify Your Pressure Gauge and Get the Proper Replacement
- How Can I Order Custom Dials for Pressure Gauges?
Feel free to contact us today to talk to one of our industry experts and get all your pressure gauge questions answered.
