Oxygen cleaning is a high quality cleaning process used on equipment and pipework utilised in the handling, storage and transport of oxygen.
Equipment that comes into contact with >23.5% oxygen should be cleaned to remove contaminants that could lead to a fire. An oxygen-enriched / pressurized environment will result in much more vigorous combustion and can cause ignition in materials that would not normally burn in atmospheric air. Therefore, combustible contaminants on the surface must be removed. This includes hydrocarbon oils and greases, or anything that could ignite or spark, for instance metal swarf, dust and lint.
There are various recognised specifications detailing the methodology that should be used, the permissible levels of contamination and the associated testing protocols used to certify the process.
CGA G-4.1 and ASTM G-93 are known internationally. More locally, BOC, Air Products and EIGA have their own specifications, but they’re all very similar.
The EIGA Oxygen Cleaning specification can be found here.
Dust, paper and swarf, are flushed / blown out before the cleaning process begins. Loosely-adhered debris such as rust, or tightly-adhered material such as mill-scale or excessive weld oxide, can be removed with a chemical cleaning process such as pickling. Stainless steel equipment should be passivated to ensure there is no free-iron contaminantion and ensure a corrosion-resistant finish.
Thorough degreasing is critical and it is the effectiveness of this which is quantified during the inspection phase.
The choice of cleaning agent and method of application will be determined by the following:
The surfaces should be thoroughly dried after oxygen cleaning to ensure that there is no moisture left within the system. This is often done using filtered clean air or nitrogen. The air/gas is blown through the equipment until it is dry. A dewpoint meter can be used to determine when this has been achieved.
The system is inspected after drying in order to validate the process. There are four method, and are either qualitative or quantitative.
Easy to access areas (vessel walls, large bore pipework, valve bodies, etc.) can be tested in one of three ways.
The simplest inspection is of course to just look at the cleaned surfaces. This should be done under a bright white light (ideally, natural light), above 500 lux. Any visible debris or staining will result in the components being re-processed.
A white lint-free cloth wetted with demineralised water or perchloroethylene is lightly wiped over the surface. This is then visually inspected for evidence of discolouration. Any dirty marks on the cloth would indicate a ‘fail’ and therefore the cleaning was unsuccessful..
Many hydrocarbons fluoresce beneath an ultra-violet light. Inspecting the components/surfaces/swabs in a dark environment with a UV light will immediately identify any hydrocarbon contamination.
Harder to reach areas, such as the internal surfaces of pipework, will need inspecting in a different manner. With short runs of pipe, it may be possible to pass a small, wetted plug (or soft pig) through the pipe and inspect it, much like the swab test described above. In most cases however, this can be tricky. It won’t work if the line is made up of different diameter pipe because the swab will either be too loose or too tight.
A section of pipe is selected and a quantity of perchloroethylene is swilled through and collected. The solvent will drag out any hydrocarbon debris. The collected sample is then evaporated, leaving the hydrocarbon debris behind which is weighed to give an accurate measurement in mg/m2.
Acceptable mg/m2 limits are identified in each of the recognised specifications. Again, this will be determined by the type of equipment and nature of the service.
INOX Passivation Ltd are able to carry out all of the requirements detailed in the recognised specifications.
We will audit your system and select the most appropriate/effective methodology in order to produce the necessary RAMS and testing protocol. Once complete, we shall carry out the required inspections before certifying the system/equipment as fit-for-use.
All of our documentation is produced in accordance with cGMP guidelines