CLEANING OF EQUIPMENT FOR OXYGEN SERVICE - AIGA

The amount of contaminants in a sample can be determined in three ways.
- weight of residue (laboratory test)
- volume of residue (laboratory test)
- light transmission (laboratory test for qualitative figures)
26
AIGA 012/04
This method is accurate in determining low amounts of oil or grease residues with small tolerances.
6.2.4.1 Weight of Residue
A known quantity (MS) of a representative sample of unfiltered used solvent is contained in a small
weighed beaker and is evaporated to dryness being careful not to overheat the residue and the
weight (m2) of the residue established. In the same manner the weight (in, ) of residue from a similar
quantity of clean unused solvent is determined.
The difference in weight between the two residues and the quantity of representative sample used is
related to the total quantity (Mv) of solvent used and can be taken to compute the amount of residual
contaminant removed per square metre (mc) of surface area (A) cleaned.
m
c
=
m2
− m ) mv
/ m
A
( 1
s
m1 = weight of residue (clean solvent)
m2 = weight of residue (used solvent)
ms = weight of representative sample (used solvent)
mv = total weight of solvent used
A = surface area of component cleaned
Mc = weight of contamination present per area cleaned.
6.2.4.2 Volume of Residue
A measured quantity of a sample of the unfiltered used solvent can be placed in an Imhoff cone and
evaporated to dryness. The volume of residue can be measured directly and used to compute the
volume contaminant extracted per square metre of surface area cleaned. Greater sensitivity can be
achieved by successive evaporation of quantities of the same extracted solvent batch in the same
Imhoff cone.
6.2.4.3 Light Transmission
A sample of the unfiltered used solvent is compared a reference sample of unused solvent by
comparing light transmission through the two samples simultaneously. The difference in colour or light
absorption of the solvents is a qualitative indication of the amount of contaminants dissolved. The
quantity of any contaminant in a sample can be estimated by analysis techniques e.g. making use of
V or infrared light.
6.2.5 Water Break Test
Drinking or distilled water is sprayed on a surface as horizontal as possible. If the amounts of oil or
grease are very small an unbroken layer of water stays for some seconds. If higher amounts of oil or
grease are on the surface the water quickly contracts and forms small beads or droplets between
water free areas.
6.2.6 Spectrometric, Chromatographic and other Special Methods
The measuring instruments used for these methods are very different. For their use special operating
instructions are necessary. By some of them low amounts of oil or grease contamination can be
detected and measured. In some cases the tolerances are low.
Another method is the Total Organic Carbon Analysis-TOC". The technique is based on oxidation of
the samples in furnace in flowing oxygen. The COZ-concentration gives an accurate quantitative