Why does a copper pipe leak prematurely? FILAB expertise

A leak in a copper network is almost never an isolated event. In most cases, it reveals a degradation mechanism already active in the installation: copper pitting, erosion-corrosion , defective passivation layer, internal contamination, brazing residues, excessive flow velocity, local stagnation, a physicochemical imbalance in the water or even a galvanic couple between dissimilar materials.

The issue is therefore not merely to seal a leak, but to establish a rigorous DHW or CW network diagnosis in order to determine whether the cause is related to the material, installation or service conditions.

The perforating corrosion in copper piping often takes the form of a highly localized attack. Type I pitting is classically associated with cold water and the presence of films or deposits that promote local corrosion cells.

Type II pitting is more often observed in domestic hot water systems, with a possible role played by temperature, water composition, and the internal surface condition. In both cases, the visible breach is minimal, but the mechanism is deep and progressive.

FILAB laboratory then looks for the morphology of the pits, the condition of the internal surface, the nature of the corrosion products, and the presence of aggressive or inhibiting elements in order to guide the diagnosis.

The diagnosis begins with a visual and microscopic examination of the sampled section. The laboratory locates the origin of the degradation, observes the geometry of the perforation, compares sound and affected areas, and looks for signs of propagation.

Metallographic cross-sections may be carried out to study the remaining thickness, microstructure, surface condition, and the immediate environment of the pit.

Elemental analysis makes it possible to verify the material composition and identify any heterogeneities, contamination, or deposits. This step is essential to distinguish an intrinsic pipe problem from a phenomenon initiated by the environment or the installation.

For a copper failure analysis, the laboratory uses complementary techniques: optical microscopy for the morphology of the attacks, SEM-EDX for detailed observation and semi-quantitative identification of deposits, chemical analysis by ICP for composition, surface examinations by XPS or other suitable methods, as well as electrochemical tests such as OCV, LSV and EIS.

Depending on the case, studies of galvanic coupling, simulations of specific environments, comparisons of failed and sound areas, or investigations into the metallurgical state may be carried out.

The goal is not to accumulate measurements, but to produce a coherent interpretation of the degradation mechanism.

The expertise approach consists of reasoning like a forensic materials scientist. The laboratory examines the tube at the perforation, compares sound and degraded areas, identifies the corrosion mode, characterizes the deposits, and looks for triggering factors.

The goal is to distinguish between type I or II pitting, under-deposit attack, biofilm-related corrosion, erosion-corrosion due to hydraulics, or galvanic interaction. This approach makes it possible to impartially arbitrate between several hypotheses: copper quality, local brazing defect, network contamination, water quality, temperature, flow rate, network design, or unsuitable maintenance.

A properly conducted pipe laboratory expertise (piping) thus makes it possible to decide on the corrective actions needed before large-scale replacement or recommissioning.

A premature leak can also result from erosion corrosion when the flow velocity is too high, when there are hydraulic singularities, abrupt changes in direction, constrictions, or turbulence zones.

To this may be added installation defects: poorly controlled brazing, residual flux, local overheating, contamination during assembly. Finally, the coexistence of different metals in the network can create a galvanic couple and accelerate the dissolution of the most unfavorable area.

The analysis must therefore never be limited to the observed hole: it must include the operating context, the network architecture, and the material interfaces.

The laboratory then uses methods suited to corrosion: optical microscopy, SEM-EDX to observe and identify corrosion products, surface chemical analyses, elemental determination and, as required, electrochemical tests such as OCV, LSV, EIS or galvanic coupling studies. .

These tools make it possible to assess the metal’s spontaneous behaviour, estimate the corrosion rate, detect protective film defects and understand interactions between materials and the environment.

At the same time, testing for chlorides, halogens, deposits, flux residues, oxidizing agents or organic contamination helps establish a technically substantiated conclusion.

This approach addresses very concrete challenges for the construction sector: securing real estate assets, avoiding unnecessary replacements, guiding network rehabilitation, substantiating an insurance claim, validating a design office hypothesis, or determining technical liability. The laboratory acts as a neutral arbiter to determine whether the failure is attributable to the material, the installation, the operation, or the water quality.

For DHW networks, this interpretation is particularly strategic, because temperature, recirculation, local velocities, and the possible presence of biofilm and corrosion can accelerate invisible degradation before the leak occurs.

Having a corroded section assessed makes it possible to avoid reproducing the cause of the leak on a new installation.

If the root cause is related to water, hydraulic sizing, an installation detail, a material combination, or internal contamination, simply replacing the pipe will not solve anything.

On the contrary, the assessment helps guide targeted actions: correcting flow velocities, reviewing metal interfaces, adapting soldering and flushing procedures, checking water quality, treating high-risk areas, or prioritizing replacements.

To carry out a useful investigation, it is recommended to keep and submit several representative sections, indicating the flow direction, position in the network, operating temperature, and leak history.