Report No FR0079
AN INVESTIGATION INTO THE SIGNIFICANCE OF WATER
AND QUALITY IN THE OCCURRENCE OF 'PEPPER-POT'
CORROSION OF COPPER TUBE
- To determine the role, if any, of water treatment or water quality in the recent
outbreak of pepper-pot corrosion of copper tube in Scotland.
- To advise on any changes in treatment necessary to avoid problems while maintaining
acceptable water quality.
A new variety of copper pitting has broken out in hospitals and other institutional
buildings in Scotland. Any changes in the recent past, in either the copper tube or in
water quality, may be implicated in the occurrence of this new problem.
III RESUME OF CONTENTS
The different forms of copper pitting are outlined as are the different aspects of the
current problem being investigated by various research organisations. The results of the
WRc investigations into changes in water treatment and water quality that have taken place
in the last 10-15 years are then presented. Attempts to develop a laboratory
electrochemical test cell for pepper-pot corrosion are outlined.
- This work has found no changes in water treatment practices or water quality that can be
directly correlated with the occurrence of pepper-pot corrosion in Scotland.
- It has not proved possible, by the application of techniques previously used with
success on Types I and II copper pitting, to develop an electrochemical cell to mimic
- Results from a Mattsson-type corrosion cell suggest that pepper-pot corrosion is a
distinctive form of attack from Type II pitting.
- The evidence collected during this work suggests there can be no direct and immediate
link between water quality and the occurrence of pepper-pot corrosion.
- Until the cause of pepper-pot corrosion of copper is identified more clearly, there can
be no justification for changing treatment practices or water quality solely for the
purpose of alleviating or avoiding the problem.
- The results from the other investigations into this problem, currently being pursued at
various research organisations, should be reviewed by the copper pitting steering group
set up under the chairmanship of the National Physical Laboratory.
- In the light of the collective findings from the different research programmes, any
further work required should be identified and water utilities advised on the current best
practice to avoid the problem. (It is anticipated that this will be possible by January
Copies of the report are available from FWR, price £15.00, less 20% to FWR Members.