How to Measure Pipe Wall Thickness Loss? FILAB Laboratory

Une tuyauterie qui s’affine sous l’effet de la corrosion, de l’érosion-corrosion, de la piqûration ou de l’usure canalisation constitue une menace invisible pour l’installation.

Dans les réseaux vapeur, les circuits d’eau, les chaufferies et les lignes de process, la perte d’épaisseur peut évoluer localement sans signe extérieur évident, jusqu’à compromettre l’aptitude au maintien en service.

Mesurer la perte d’épaisseur d’une tuyauterie ne consiste donc pas uniquement à relever une valeur : il s’agit de comparer l’épaisseur résiduelle à l’épaisseur nominale, de cartographier les zones aminciées, d’identifier le mode d’attaque et d’évaluer le risque de fuite ou de rupture.

Anticiper cette dégradation est une obligation de sécurité et un levier de décision pour planifier un remplacement, un chemisage, une réparation ou une correction des conditions de service.

The ultrasonic thickness measurement is the most suitable technique for monitoring piping in service or during a planned shutdown.

It makes it possible to quickly obtain remaining thickness values in accessible areas, detect localized losses and build a thinning profile.

Depending on the geometry and surface condition, the inspection can be carried out point by point or on a denser grid in order to identify minimum thickness values. This approach is particularly useful for periodic monitoring of networks subject to internal corrosion, abrasion or under-deposit attack.

A single value is not enough to assess the level of risk. The distribution of measurements, the presence of local minima, the shape of thinned areas and their position relative to line singularities must be analyzed: bends, welds, reducers, low points, turbulence zones or material interfaces.

The thickness profile helps distinguish uniform wear from more critical localized attack. This reading also helps guide the search for the cause, for example toward a water treatment issue, flow velocity, fluid chemistry, deposits or galvanic coupling.

A simple thickness reading answers the question “how much is left?” but not the essential question “why is it thinning?”. Without identifying the cause, the risk of recurrence remains after replacement or repair.

The expert assessment carried out by FILAB aims to link wall thickness loss to the mechanisms at work: fluid quality, presence of chlorides, oxidizing agents, deposits, insufficient deaeration, excessive velocity, material/medium incompatibility or differential corrosion. This approach makes it possible to address the root cause rather than only the visible consequence.

FILAB goes beyond being a simple provider of non-destructive testing (NDT). The laboratory combines ultrasonic thickness measurement on site, metallographic examination, surface analysis and chemical identification of deposits or corrosion residues to understand why the piping is thinning.

This approach makes it possible to establish a complete pipeline corrosion diagnosis for carbon steels, stainless steels, copper and specific alloys. The expert report then becomes a decision-support tool: it documents the corrosion profile, estimates the thinning rate, contributes to the corrosion rate calculation and sheds light on technical choices for keeping the installation in service or upgrading it.

When the situation requires it, the expert assessment can be supplemented by cross-sections and metallographic observations in order to directly measure the remaining thickness, characterize the morphology of the attack and distinguish corrosion that is general from localized attack.

Optical and electron microscopy, combined with elemental analysis of deposits, makes it possible to link thinning to a specific mechanism: pitting, under-deposit corrosion, galvanic corrosion, erosion-corrosion or material defect. This step is decisive for moving from simple measurement to understanding the cause.

The interpretation must then incorporate the corrosion rate calculation based on measurement histories or analytical indicators obtained from the expert assessment.

By comparing the current thickness with the initial thickness or previous readings, it becomes possible to estimate a thinning rate and approximate the remaining service life. This estimate must remain cautious, as localized corrosion can progress faster than uniform corrosion. The expert report then serves to rank priorities: continued monitoring, reduced operating conditions, targeted repair or replacement.

FILAB mobilise des moyens adaptés à l’expertise métallurgique tuyauterie et à l’analyse de corrosion : observations métallographiques, microscopie électronique avec analyse élémentaire, analyses chimiques, essais électrochimiques, caractérisation de surface et étude des résidus de corrosion.

Cette complémentarité est particulièrement utile lorsque plusieurs mécanismes coexistent. Le laboratoire intervient sur différents matériaux, notamment acier carbone, acier inoxydable, cuivre et alliages techniques, afin d’émettre des conclusions argumentées sur l’origine de la dégradation et l’aptitude au maintien en service.

To begin the process, it is recommended to provide the available operating information: material, diameter, fluid, temperature, pressure, maintenance history, previous thickness readings, suspected areas, and photographs.

Depending on the context, FILAB can carry out an on-site diagnosis, define an inspection plan, analyze coupons or removed pipe sections, and examine deposits or corrosion products in the laboratory.

The goal is to provide actionable advice to decide quickly: monitor, repair, replace, modify water treatment, or adjust operating conditions.