RELIABILITY OF TEST METHODS FOR METALLIC PRODUCTS - FINAL REPORT TO THE DRINKING WATER INSPECTORATE
The development of a short term laboratory procedure to test a
metal's acceptability for use with drinking water would minimise the
costs involved as well as facilitate the development of new alloys or
the determination of limitations on use based on water compositions of
- To Pilot and Round Robin test a variant of the test procedure
used in the first Round Robin i.e. using disposal plastic centrifuge
tubes as the reaction vessels and a more stringent control of
- To develop a statistical based method to determine the outcome of a test.
The results of the first Round Robin test (see WRc-NSF report DWI
4079 July 2002) showed the good intra-laboratory and poor
inter-laboratory reproducibility observed in previous studies.
Significant correlations between the concentrations of metals leached
were observed a possible interpretation of which was competition for
the dissolved oxygen in the test water. To test this idea, a procedure
was devised using closed test tubes as the reaction vessels. By using
disposable plastic centrifuge tubes, the new procedure also
significantly reduced the cost of testing.
Although the Pilot established that the original ideas as to the
cause of the correlations between the concentrations of metal leached
was not correct, it was decided that a limited second Round Robin test
of the new procedure would be of value.
- This work has developed a test procedure, based on plastic
centrifuge tubes as the reaction vessels, that significantly increases
the practical convenience and significantly reduces the cost of
carrying out the testing of metals.
- Strong correlations have been found between the concentrations
of the major elements, i.e. copper, lead and zinc, that leach from the
copper alloys. All show an exponential increase in concentration with
time in the leachate water.
- The amount of metal leached showed little sensitivity to the
depth of immersion of the test coupon, suggesting little sensitivity to
the level of dissolved oxygen in the test water. This in turn suggests
that the contamination level achieved cannot be under the simple
control of the alloy corrosion rate.
- The exponential increases with time of a particular metal in
the leachate water, found by the different test laboratories, in most
cases do not appear to be going to the same equilibrium value. This
suggests that the contamination level achieved cannot be under the
simple control of the solubility of the corrosion product formed.
- The levels of copper and zinc leached in the tests were so far
below their respective PCV's that the acceptability for these elements
of the alloys tested could be made unambiguously. This was not the case
- Although the differences between measured lead concentrations
at the three laboratories were considerable, a statistical procedure to
decide the outcome of the test, that takes these 'between laboratory'
differences into account, can be suggested.
Copies of this report may be available as an Acrobat pdf download under the 'Post 2000 Reports' heading on the DWI website.