Pinhole leak
| Pinhole leak | |
| Type | Leak type |
|---|---|
| Usual cause | Pitting corrosion |
| Affects | Metallic pipe, most often copper |
| Characteristic | Small continuous loss rather than sudden failure |
| Tube standard | BS EN 1057 |
A pinhole leak is a very small perforation of a pipe wall, usually the result of pitting corrosion, that passes a small but continuous volume of water. It is the most common form of failure in copper tube, which is specified by BS EN 1057,[1] and it is distinguished from a burst by rate rather than by kind: a pinhole may lose a few litres a day for months, where a burst loses that in minutes.
Why pinholes are hard to find[edit]
Every property that makes a leak easy to find is absent in a pinhole. The escape is too small to produce a strong acoustic signal. There is no visible damage at first, and by the time damp appears the water has usually tracked along a joist, under a screed or across a membrane, so the wet area is not above the pipe. On a sealed heating system the only symptom for a long period is a pressure gauge that needs topping up.
The loss is also small enough to be dismissed. A pressure drop over a week reads as a system that needs bleeding rather than as a leak, which is why pinholes are commonly found late and after damage has accumulated.
Detection[edit]
Because the acoustic signal is weak, tracer gas is often the method that resolves a pinhole: gas escapes through an opening far too small to produce useful noise. Thermal imaging can narrow the area on a heating circuit where the water is warm enough to produce a surface pattern, and moisture mapping bounds the wetted area, though it shows where water arrived rather than where it left.
Pressure testing an isolated section establishes that a loss exists and roughly how fast, which is what separates a pinhole from a passing valve or a failed expansion vessel before any search begins.