These failures are usually the result of poor commissioning practice although a significant number are initiated by flux left in the bore after assembly of soldered joints.
[1] Prior to about 1970 the most common cause of Type 1 pitting was carbon films left in the bore by the manufacturing process.
Research and manufacturing improvements in the 1960s virtually eliminated carbon as a cause of pitting with the introduction of a clause in the 1971 edition of BS 2871 requiring tube bores to be free of deleterious films.
Type 1 pitting is relatively uncommon in North America and this may be a result of the lower population density allowing a significant proportion of the potable water to be obtained from surface derived sources.
When a copper tube is initially filled with a hard water salts deposit on the wall and the copper slowly reacts with the water producing a thin protective layer of mixed corrosion products and hardness scale.
Stagnation and flux residues are the most common initiation mechanisms that have led to Type 1 pitting failures in the last ten years.
If the carbon is left in the bore of the tube then it disrupts the formation of the protective scale and allows the initiation of pits in the wall.
The presence of deleterious films, such as carbon, has been prohibited by the British Standards in copper tubes since 1969.
Particles of scale that do not adhere to the walls and are not washed away tend to fall into the bottom of the tube producing a coarse porous deposit.
Then, even after the tube has been put back into service, the pit will continue to develop until the wall has perforated.
Once a system has been commissioned it should be either put immediately into service or drained down and dried by flushing with compressed air otherwise pitting may initiate.
Tubes greater than 10 mm in diameter made to this standard will always be marked the number of the standard, the nominal size, wall thickness and temper of the tube, the manufacturer's identification mark and the date of production at least every 600 mm.
A small quantity should be painted over the areas to be joined and any excess removed after the joint has been made.