CLEANING OF EQUIPMENT FOR OXYGEN SERVICE - AIGA

9
AIGA 012/04
contamination and the cleaning procedure continued until the acceptance standard of cleanliness is
reached.
Methods of determining contamination can be by comparison of colour to reference sample,
fluorescence under ultra violet light, by analysis, or by evaporation. (See Section 4 Inspection). Glass
bottles are recommended to be used for containing check samples.
Due to the potential hazard caused by solvents in contact with oxygen, after the completion of any
method of solvent cleaning, all residual cleaning fluid must be totally removed from the components.
An assessment of the component or system to be cleaned shall be made to ensure there are no pipe
or other dead ends or pockets present from which it will be difficult to completely drain or blow out the
solvent. If not, then this method shall not be used, or alternatively the system can be modified to
accommodate this method. The component shall be thoroughly drained, purged, and dried with warm,
dry, oil-free air or nitrogen. Small components may be air dried only, if appropriate. A method of,
checking that residual solvents have been eliminated is by using a commercially available vapour
detector/analyser on completion of the purge and drying process following cleaning.
The unit used comprises an aspiration pump to measure the sample volume using disposable,
calibrated, colorimetric detector tubes. This test can be supplemented by carrying out a sniff test when
it is considered to be completely purged of solvent vapours.
Solvent cleaning methods used are described in the following sub-sections. However, components of
a simple shape and with all surfaces accessible may be cleaned by wiping with a solvent using a
lint-free clean cloth and followed by drying.
Potential users should determine whether the solvent has been declared acceptable by
national authorities. Solvents shall only be used in stabilised form.
4.2.3.1 Immersion in Solvent Method
Cleaning of individual components can be effected by immersing the component in a tank of solvent,
at ambient temperature, and applying a means of agitation.
Disassembled parts can be cleaned by this method. The process can be improved by the use of an
ultrasonic generator. Some methods utilising solvents are described in Appendix B Section 4.
4.2.3.2 Forced Circulation Method
Cleaning by forced circulation of a flow of the solvent liquid through the component can be carried out.
This is done with the solvent at ambient temperature.
The duration of cleaning by circulation shall be continued, using clean solvent, until the used solvent
emerges from the component as clean as the solvent pumped in.
This method is a highly specialised cleaning procedure and is applied principally to assemblies, which
cannot be disassembled, large size components and prefabricated circuits, pipe works, etc. The use
of this method is, however, limited by the ability of the solvent to reach contaminants present in a
complex system and its subsequent complete removal.
4.2.3.3 Vapour Phase Method
Solvent vapour phase cleaning of components consists of the removal of contaminants by the action
of continued condensation of solvent vapour on the component surfaces.
The procedure requires that the equipment or component is colder than the solvent boiling point.
A significant advantage of solvent vapour phase cleaning is that re-vaporised solvent is always clean
and contaminants remain in the evaporator liquid section, which will require periodic cleaning out.
A description of the method for one type of equipment is given in Appendix B.